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//! Some lints that are built in to the compiler.
//!
//! These are the built-in lints that are emitted direct in the main
//! compiler code, rather than using their own custom pass. Those
//! lints are all available in `rustc_lint::builtin`.
use crate::{declare_lint, declare_lint_pass, FutureIncompatibilityReason};
use rustc_span::edition::Edition;
use rustc_span::symbol::sym;
declare_lint! {
/// The `forbidden_lint_groups` lint detects violations of
/// `forbid` applied to a lint group. Due to a bug in the compiler,
/// these used to be overlooked entirely. They now generate a warning.
///
/// ### Example
///
/// ```rust
/// #![forbid(warnings)]
/// #![deny(bad_style)]
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Recommended fix
///
/// If your crate is using `#![forbid(warnings)]`,
/// we recommend that you change to `#![deny(warnings)]`.
///
/// ### Explanation
///
/// Due to a compiler bug, applying `forbid` to lint groups
/// previously had no effect. The bug is now fixed but instead of
/// enforcing `forbid` we issue this future-compatibility warning
/// to avoid breaking existing crates.
pub FORBIDDEN_LINT_GROUPS,
Warn,
"applying forbid to lint-groups",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
};
}
declare_lint! {
/// The `ill_formed_attribute_input` lint detects ill-formed attribute
/// inputs that were previously accepted and used in practice.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[inline = "this is not valid"]
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previously, inputs for many built-in attributes weren't validated and
/// nonsensical attribute inputs were accepted. After validation was
/// added, it was determined that some existing projects made use of these
/// invalid forms. This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #57571] for more details.
///
/// Check the [attribute reference] for details on the valid inputs for
/// attributes.
///
/// [issue #57571]: https://github.com/rust-lang/rust/issues/57571
/// [attribute reference]: https://doc.rust-lang.org/nightly/reference/attributes.html
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ILL_FORMED_ATTRIBUTE_INPUT,
Deny,
"ill-formed attribute inputs that were previously accepted and used in practice",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
};
crate_level_only
}
declare_lint! {
/// The `conflicting_repr_hints` lint detects [`repr` attributes] with
/// conflicting hints.
///
/// [`repr` attributes]: https://doc.rust-lang.org/reference/type-layout.html#representations
///
/// ### Example
///
/// ```rust,compile_fail
/// #[repr(u32, u64)]
/// enum Foo {
/// Variant1,
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The compiler incorrectly accepted these conflicting representations in
/// the past. This is a [future-incompatible] lint to transition this to a
/// hard error in the future. See [issue #68585] for more details.
///
/// To correct the issue, remove one of the conflicting hints.
///
/// [issue #68585]: https://github.com/rust-lang/rust/issues/68585
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub CONFLICTING_REPR_HINTS,
Deny,
"conflicts between `#[repr(..)]` hints that were previously accepted and used in practice",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #68585 <https://github.com/rust-lang/rust/issues/68585>",
};
}
declare_lint! {
/// The `meta_variable_misuse` lint detects possible meta-variable misuse
/// in macro definitions.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(meta_variable_misuse)]
///
/// macro_rules! foo {
/// () => {};
/// ($( $i:ident = $($j:ident),+ );*) => { $( $( $i = $k; )+ )* };
/// }
///
/// fn main() {
/// foo!();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// There are quite a few different ways a [`macro_rules`] macro can be
/// improperly defined. Many of these errors were previously only detected
/// when the macro was expanded or not at all. This lint is an attempt to
/// catch some of these problems when the macro is *defined*.
///
/// This lint is "allow" by default because it may have false positives
/// and other issues. See [issue #61053] for more details.
///
/// [`macro_rules`]: https://doc.rust-lang.org/reference/macros-by-example.html
/// [issue #61053]: https://github.com/rust-lang/rust/issues/61053
pub META_VARIABLE_MISUSE,
Allow,
"possible meta-variable misuse at macro definition"
}
declare_lint! {
/// The `incomplete_include` lint detects the use of the [`include!`]
/// macro with a file that contains more than one expression.
///
/// [`include!`]: https://doc.rust-lang.org/std/macro.include.html
///
/// ### Example
///
/// ```rust,ignore (needs separate file)
/// fn main() {
/// include!("foo.txt");
/// }
/// ```
///
/// where the file `foo.txt` contains:
///
/// ```text
/// println!("hi!");
/// ```
///
/// produces:
///
/// ```text
/// error: include macro expected single expression in source
/// --> foo.txt:1:14
/// |
/// 1 | println!("1");
/// | ^
/// |
/// = note: `#[deny(incomplete_include)]` on by default
/// ```
///
/// ### Explanation
///
/// The [`include!`] macro is currently only intended to be used to
/// include a single [expression] or multiple [items]. Historically it
/// would ignore any contents after the first expression, but that can be
/// confusing. In the example above, the `println!` expression ends just
/// before the semicolon, making the semicolon "extra" information that is
/// ignored. Perhaps even more surprising, if the included file had
/// multiple print statements, the subsequent ones would be ignored!
///
/// One workaround is to place the contents in braces to create a [block
/// expression]. Also consider alternatives, like using functions to
/// encapsulate the expressions, or use [proc-macros].
///
/// This is a lint instead of a hard error because existing projects were
/// found to hit this error. To be cautious, it is a lint for now. The
/// future semantics of the `include!` macro are also uncertain, see
/// [issue #35560].
///
/// [items]: https://doc.rust-lang.org/reference/items.html
/// [expression]: https://doc.rust-lang.org/reference/expressions.html
/// [block expression]: https://doc.rust-lang.org/reference/expressions/block-expr.html
/// [proc-macros]: https://doc.rust-lang.org/reference/procedural-macros.html
/// [issue #35560]: https://github.com/rust-lang/rust/issues/35560
pub INCOMPLETE_INCLUDE,
Deny,
"trailing content in included file"
}
declare_lint! {
/// The `arithmetic_overflow` lint detects that an arithmetic operation
/// will [overflow].
///
/// [overflow]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#overflow
///
/// ### Example
///
/// ```rust,compile_fail
/// 1_i32 << 32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is very likely a mistake to perform an arithmetic operation that
/// overflows its value. If the compiler is able to detect these kinds of
/// overflows at compile-time, it will trigger this lint. Consider
/// adjusting the expression to avoid overflow, or use a data type that
/// will not overflow.
pub ARITHMETIC_OVERFLOW,
Deny,
"arithmetic operation overflows"
}
declare_lint! {
/// The `unconditional_panic` lint detects an operation that will cause a
/// panic at runtime.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// let x = 1 / 0;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint detects code that is very likely incorrect because it will
/// always panic, such as division by zero and out-of-bounds array
/// accesses. Consider adjusting your code if this is a bug, or using the
/// `panic!` or `unreachable!` macro instead in case the panic is intended.
pub UNCONDITIONAL_PANIC,
Deny,
"operation will cause a panic at runtime"
}
declare_lint! {
/// The `unused_imports` lint detects imports that are never used.
///
/// ### Example
///
/// ```rust
/// use std::collections::HashMap;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused imports may signal a mistake or unfinished code, and clutter
/// the code, and should be removed. If you intended to re-export the item
/// to make it available outside of the module, add a visibility modifier
/// like `pub`.
pub UNUSED_IMPORTS,
Warn,
"imports that are never used"
}
declare_lint! {
/// The `must_not_suspend` lint guards against values that shouldn't be held across suspend points
/// (`.await`)
///
/// ### Example
///
/// ```rust
/// #![feature(must_not_suspend)]
/// #![warn(must_not_suspend)]
///
/// #[must_not_suspend]
/// struct SyncThing {}
///
/// async fn yield_now() {}
///
/// pub async fn uhoh() {
/// let guard = SyncThing {};
/// yield_now().await;
/// let _guard = guard;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `must_not_suspend` lint detects values that are marked with the `#[must_not_suspend]`
/// attribute being held across suspend points. A "suspend" point is usually a `.await` in an async
/// function.
///
/// This attribute can be used to mark values that are semantically incorrect across suspends
/// (like certain types of timers), values that have async alternatives, and values that
/// regularly cause problems with the `Send`-ness of async fn's returned futures (like
/// `MutexGuard`'s)
///
pub MUST_NOT_SUSPEND,
Allow,
"use of a `#[must_not_suspend]` value across a yield point",
@feature_gate = rustc_span::symbol::sym::must_not_suspend;
}
declare_lint! {
/// The `unused_extern_crates` lint guards against `extern crate` items
/// that are never used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_extern_crates)]
/// #![deny(warnings)]
/// extern crate proc_macro;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `extern crate` items that are unused have no effect and should be
/// removed. Note that there are some cases where specifying an `extern
/// crate` is desired for the side effect of ensuring the given crate is
/// linked, even though it is not otherwise directly referenced. The lint
/// can be silenced by aliasing the crate to an underscore, such as
/// `extern crate foo as _`. Also note that it is no longer idiomatic to
/// use `extern crate` in the [2018 edition], as extern crates are now
/// automatically added in scope.
///
/// This lint is "allow" by default because it can be noisy, and produce
/// false-positives. If a dependency is being removed from a project, it
/// is recommended to remove it from the build configuration (such as
/// `Cargo.toml`) to ensure stale build entries aren't left behind.
///
/// [2018 edition]: https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html#no-more-extern-crate
pub UNUSED_EXTERN_CRATES,
Allow,
"extern crates that are never used"
}
declare_lint! {
/// The `unused_crate_dependencies` lint detects crate dependencies that
/// are never used.
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #![deny(unused_crate_dependencies)]
/// ```
///
/// This will produce:
///
/// ```text
/// error: external crate `regex` unused in `lint_example`: remove the dependency or add `use regex as _;`
/// |
/// note: the lint level is defined here
/// --> src/lib.rs:1:9
/// |
/// 1 | #![deny(unused_crate_dependencies)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^
/// ```
///
/// ### Explanation
///
/// After removing the code that uses a dependency, this usually also
/// requires removing the dependency from the build configuration.
/// However, sometimes that step can be missed, which leads to time wasted
/// building dependencies that are no longer used. This lint can be
/// enabled to detect dependencies that are never used (more specifically,
/// any dependency passed with the `--extern` command-line flag that is
/// never referenced via [`use`], [`extern crate`], or in any [path]).
///
/// This lint is "allow" by default because it can provide false positives
/// depending on how the build system is configured. For example, when
/// using Cargo, a "package" consists of multiple crates (such as a
/// library and a binary), but the dependencies are defined for the
/// package as a whole. If there is a dependency that is only used in the
/// binary, but not the library, then the lint will be incorrectly issued
/// in the library.
///
/// [path]: https://doc.rust-lang.org/reference/paths.html
/// [`use`]: https://doc.rust-lang.org/reference/items/use-declarations.html
/// [`extern crate`]: https://doc.rust-lang.org/reference/items/extern-crates.html
pub UNUSED_CRATE_DEPENDENCIES,
Allow,
"crate dependencies that are never used",
crate_level_only
}
declare_lint! {
/// The `unused_qualifications` lint detects unnecessarily qualified
/// names.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unused_qualifications)]
/// mod foo {
/// pub fn bar() {}
/// }
///
/// fn main() {
/// use foo::bar;
/// foo::bar();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If an item from another module is already brought into scope, then
/// there is no need to qualify it in this case. You can call `bar()`
/// directly, without the `foo::`.
///
/// This lint is "allow" by default because it is somewhat pedantic, and
/// doesn't indicate an actual problem, but rather a stylistic choice, and
/// can be noisy when refactoring or moving around code.
pub UNUSED_QUALIFICATIONS,
Allow,
"detects unnecessarily qualified names"
}
declare_lint! {
/// The `unknown_lints` lint detects unrecognized lint attributes.
///
/// ### Example
///
/// ```rust
/// #![allow(not_a_real_lint)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify a lint that does not exist. Check
/// the spelling, and check the lint listing for the correct name. Also
/// consider if you are using an old version of the compiler, and the lint
/// is only available in a newer version.
pub UNKNOWN_LINTS,
Warn,
"unrecognized lint attribute"
}
declare_lint! {
/// The `unfulfilled_lint_expectations` lint detects lint trigger expectations
/// that have not been fulfilled.
///
/// ### Example
///
/// ```rust
/// #![feature(lint_reasons)]
///
/// #[expect(unused_variables)]
/// let x = 10;
/// println!("{}", x);
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It was expected that the marked code would emit a lint. This expectation
/// has not been fulfilled.
///
/// The `expect` attribute can be removed if this is intended behavior otherwise
/// it should be investigated why the expected lint is no longer issued.
///
/// In rare cases, the expectation might be emitted at a different location than
/// shown in the shown code snippet. In most cases, the `#[expect]` attribute
/// works when added to the outer scope. A few lints can only be expected
/// on a crate level.
///
/// Part of RFC 2383. The progress is being tracked in [#54503]
///
/// [#54503]: https://github.com/rust-lang/rust/issues/54503
pub UNFULFILLED_LINT_EXPECTATIONS,
Warn,
"unfulfilled lint expectation",
@feature_gate = rustc_span::sym::lint_reasons;
}
declare_lint! {
/// The `unused_variables` lint detects variables which are not used in
/// any way.
///
/// ### Example
///
/// ```rust
/// let x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused variables may signal a mistake or unfinished code. To silence
/// the warning for the individual variable, prefix it with an underscore
/// such as `_x`.
pub UNUSED_VARIABLES,
Warn,
"detect variables which are not used in any way"
}
declare_lint! {
/// The `unused_assignments` lint detects assignments that will never be read.
///
/// ### Example
///
/// ```rust
/// let mut x = 5;
/// x = 6;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused assignments may signal a mistake or unfinished code. If the
/// variable is never used after being assigned, then the assignment can
/// be removed. Variables with an underscore prefix such as `_x` will not
/// trigger this lint.
pub UNUSED_ASSIGNMENTS,
Warn,
"detect assignments that will never be read"
}
declare_lint! {
/// The `dead_code` lint detects unused, unexported items.
///
/// ### Example
///
/// ```rust
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Dead code may signal a mistake or unfinished code. To silence the
/// warning for individual items, prefix the name with an underscore such
/// as `_foo`. If it was intended to expose the item outside of the crate,
/// consider adding a visibility modifier like `pub`. Otherwise consider
/// removing the unused code.
pub DEAD_CODE,
Warn,
"detect unused, unexported items"
}
declare_lint! {
/// The `unused_attributes` lint detects attributes that were not used by
/// the compiler.
///
/// ### Example
///
/// ```rust
/// #![ignore]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused [attributes] may indicate the attribute is placed in the wrong
/// position. Consider removing it, or placing it in the correct position.
/// Also consider if you intended to use an _inner attribute_ (with a `!`
/// such as `#![allow(unused)]`) which applies to the item the attribute
/// is within, or an _outer attribute_ (without a `!` such as
/// `#[allow(unused)]`) which applies to the item *following* the
/// attribute.
///
/// [attributes]: https://doc.rust-lang.org/reference/attributes.html
pub UNUSED_ATTRIBUTES,
Warn,
"detects attributes that were not used by the compiler"
}
declare_lint! {
/// The `unused_tuple_struct_fields` lint detects fields of tuple structs
/// that are never read.
///
/// ### Example
///
/// ```rust
/// #[warn(unused_tuple_struct_fields)]
/// struct S(i32, i32, i32);
/// let s = S(1, 2, 3);
/// let _ = (s.0, s.2);
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Tuple struct fields that are never read anywhere may indicate a
/// mistake or unfinished code. To silence this warning, consider
/// removing the unused field(s) or, to preserve the numbering of the
/// remaining fields, change the unused field(s) to have unit type.
pub UNUSED_TUPLE_STRUCT_FIELDS,
Allow,
"detects tuple struct fields that are never read"
}
declare_lint! {
/// The `unreachable_code` lint detects unreachable code paths.
///
/// ### Example
///
/// ```rust,no_run
/// panic!("we never go past here!");
///
/// let x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unreachable code may signal a mistake or unfinished code. If the code
/// is no longer in use, consider removing it.
pub UNREACHABLE_CODE,
Warn,
"detects unreachable code paths",
report_in_external_macro
}
declare_lint! {
/// The `unreachable_patterns` lint detects unreachable patterns.
///
/// ### Example
///
/// ```rust
/// let x = 5;
/// match x {
/// y => (),
/// 5 => (),
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This usually indicates a mistake in how the patterns are specified or
/// ordered. In this example, the `y` pattern will always match, so the
/// five is impossible to reach. Remember, match arms match in order, you
/// probably wanted to put the `5` case above the `y` case.
pub UNREACHABLE_PATTERNS,
Warn,
"detects unreachable patterns"
}
declare_lint! {
/// The `overlapping_range_endpoints` lint detects `match` arms that have [range patterns] that
/// overlap on their endpoints.
///
/// [range patterns]: https://doc.rust-lang.org/nightly/reference/patterns.html#range-patterns
///
/// ### Example
///
/// ```rust
/// let x = 123u8;
/// match x {
/// 0..=100 => { println!("small"); }
/// 100..=255 => { println!("large"); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is likely a mistake to have range patterns in a match expression that overlap in this
/// way. Check that the beginning and end values are what you expect, and keep in mind that
/// with `..=` the left and right bounds are inclusive.
pub OVERLAPPING_RANGE_ENDPOINTS,
Warn,
"detects range patterns with overlapping endpoints"
}
declare_lint! {
/// The `bindings_with_variant_name` lint detects pattern bindings with
/// the same name as one of the matched variants.
///
/// ### Example
///
/// ```rust,compile_fail
/// pub enum Enum {
/// Foo,
/// Bar,
/// }
///
/// pub fn foo(x: Enum) {
/// match x {
/// Foo => {}
/// Bar => {}
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to specify an enum variant name as an
/// [identifier pattern]. In the example above, the `match` arms are
/// specifying a variable name to bind the value of `x` to. The second arm
/// is ignored because the first one matches *all* values. The likely
/// intent is that the arm was intended to match on the enum variant.
///
/// Two possible solutions are:
///
/// * Specify the enum variant using a [path pattern], such as
/// `Enum::Foo`.
/// * Bring the enum variants into local scope, such as adding `use
/// Enum::*;` to the beginning of the `foo` function in the example
/// above.
///
/// [identifier pattern]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
/// [path pattern]: https://doc.rust-lang.org/reference/patterns.html#path-patterns
pub BINDINGS_WITH_VARIANT_NAME,
Deny,
"detects pattern bindings with the same name as one of the matched variants"
}
declare_lint! {
/// The `unused_macros` lint detects macros that were not used.
///
/// Note that this lint is distinct from the `unused_macro_rules` lint,
/// which checks for single rules that never match of an otherwise used
/// macro, and thus never expand.
///
/// ### Example
///
/// ```rust
/// macro_rules! unused {
/// () => {};
/// }
///
/// fn main() {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused macros may signal a mistake or unfinished code. To silence the
/// warning for the individual macro, prefix the name with an underscore
/// such as `_my_macro`. If you intended to export the macro to make it
/// available outside of the crate, use the [`macro_export` attribute].
///
/// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
pub UNUSED_MACROS,
Warn,
"detects macros that were not used"
}
declare_lint! {
/// The `unused_macro_rules` lint detects macro rules that were not used.
///
/// Note that the lint is distinct from the `unused_macros` lint, which
/// fires if the entire macro is never called, while this lint fires for
/// single unused rules of the macro that is otherwise used.
/// `unused_macro_rules` fires only if `unused_macros` wouldn't fire.
///
/// ### Example
///
/// ```rust
/// #[warn(unused_macro_rules)]
/// macro_rules! unused_empty {
/// (hello) => { println!("Hello, world!") }; // This rule is unused
/// () => { println!("empty") }; // This rule is used
/// }
///
/// fn main() {
/// unused_empty!(hello);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused macro rules may signal a mistake or unfinished code. Furthermore,
/// they slow down compilation. Right now, silencing the warning is not
/// supported on a single rule level, so you have to add an allow to the
/// entire macro definition.
///
/// If you intended to export the macro to make it
/// available outside of the crate, use the [`macro_export` attribute].
///
/// [`macro_export` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
pub UNUSED_MACRO_RULES,
Allow,
"detects macro rules that were not used"
}
declare_lint! {
/// The `warnings` lint allows you to change the level of other
/// lints which produce warnings.
///
/// ### Example
///
/// ```rust
/// #![deny(warnings)]
/// fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `warnings` lint is a bit special; by changing its level, you
/// change every other warning that would produce a warning to whatever
/// value you'd like. As such, you won't ever trigger this lint in your
/// code directly.
pub WARNINGS,
Warn,
"mass-change the level for lints which produce warnings"
}
declare_lint! {
/// The `unused_features` lint detects unused or unknown features found in
/// crate-level [`feature` attributes].
///
/// [`feature` attributes]: https://doc.rust-lang.org/nightly/unstable-book/
///
/// Note: This lint is currently not functional, see [issue #44232] for
/// more details.
///
/// [issue #44232]: https://github.com/rust-lang/rust/issues/44232
pub UNUSED_FEATURES,
Warn,
"unused features found in crate-level `#[feature]` directives"
}
declare_lint! {
/// The `stable_features` lint detects a [`feature` attribute] that
/// has since been made stable.
///
/// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
///
/// ### Example
///
/// ```rust
/// #![feature(test_accepted_feature)]
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// When a feature is stabilized, it is no longer necessary to include a
/// `#![feature]` attribute for it. To fix, simply remove the
/// `#![feature]` attribute.
pub STABLE_FEATURES,
Warn,
"stable features found in `#[feature]` directive"
}
declare_lint! {
/// The `unknown_crate_types` lint detects an unknown crate type found in
/// a [`crate_type` attribute].
///
/// ### Example
///
/// ```rust,compile_fail
/// #![crate_type="lol"]
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// An unknown value give to the `crate_type` attribute is almost
/// certainly a mistake.
///
/// [`crate_type` attribute]: https://doc.rust-lang.org/reference/linkage.html
pub UNKNOWN_CRATE_TYPES,
Deny,
"unknown crate type found in `#[crate_type]` directive",
crate_level_only
}
declare_lint! {
/// The `trivial_casts` lint detects trivial casts which could be replaced
/// with coercion, which may require a temporary variable.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(trivial_casts)]
/// let x: &u32 = &42;
/// let y = x as *const u32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A trivial cast is a cast `e as T` where `e` has type `U` and `U` is a
/// subtype of `T`. This type of cast is usually unnecessary, as it can be
/// usually be inferred.
///
/// This lint is "allow" by default because there are situations, such as
/// with FFI interfaces or complex type aliases, where it triggers
/// incorrectly, or in situations where it will be more difficult to
/// clearly express the intent. It may be possible that this will become a
/// warning in the future, possibly with an explicit syntax for coercions
/// providing a convenient way to work around the current issues.
/// See [RFC 401 (coercions)][rfc-401], [RFC 803 (type ascription)][rfc-803] and
/// [RFC 3307 (remove type ascription)][rfc-3307] for historical context.
///
/// [rfc-401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
/// [rfc-803]: https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md
/// [rfc-3307]: https://github.com/rust-lang/rfcs/blob/master/text/3307-de-rfc-type-ascription.md
pub TRIVIAL_CASTS,
Allow,
"detects trivial casts which could be removed"
}
declare_lint! {
/// The `trivial_numeric_casts` lint detects trivial numeric casts of types
/// which could be removed.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(trivial_numeric_casts)]
/// let x = 42_i32 as i32;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A trivial numeric cast is a cast of a numeric type to the same numeric
/// type. This type of cast is usually unnecessary.
///
/// This lint is "allow" by default because there are situations, such as
/// with FFI interfaces or complex type aliases, where it triggers
/// incorrectly, or in situations where it will be more difficult to
/// clearly express the intent. It may be possible that this will become a
/// warning in the future, possibly with an explicit syntax for coercions
/// providing a convenient way to work around the current issues.
/// See [RFC 401 (coercions)][rfc-401], [RFC 803 (type ascription)][rfc-803] and
/// [RFC 3307 (remove type ascription)][rfc-3307] for historical context.
///
/// [rfc-401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
/// [rfc-803]: https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md
/// [rfc-3307]: https://github.com/rust-lang/rfcs/blob/master/text/3307-de-rfc-type-ascription.md
pub TRIVIAL_NUMERIC_CASTS,
Allow,
"detects trivial casts of numeric types which could be removed"
}
declare_lint! {
/// The `exported_private_dependencies` lint detects private dependencies
/// that are exposed in a public interface.
///
/// ### Example
///
/// ```rust,ignore (needs-dependency)
/// pub fn foo() -> Option<some_private_dependency::Thing> {
/// None
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: type `bar::Thing` from private dependency 'bar' in public interface
/// --> src/lib.rs:3:1
/// |
/// 3 | pub fn foo() -> Option<bar::Thing> {
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = note: `#[warn(exported_private_dependencies)]` on by default
/// ```
///
/// ### Explanation
///
/// Dependencies can be marked as "private" to indicate that they are not
/// exposed in the public interface of a crate. This can be used by Cargo
/// to independently resolve those dependencies because it can assume it
/// does not need to unify them with other packages using that same
/// dependency. This lint is an indication of a violation of that
/// contract.
///
/// To fix this, avoid exposing the dependency in your public interface.
/// Or, switch the dependency to a public dependency.
///
/// Note that support for this is only available on the nightly channel.
/// See [RFC 1977] for more details, as well as the [Cargo documentation].
///
/// [RFC 1977]: https://github.com/rust-lang/rfcs/blob/master/text/1977-public-private-dependencies.md
/// [Cargo documentation]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#public-dependency
pub EXPORTED_PRIVATE_DEPENDENCIES,
Warn,
"public interface leaks type from a private dependency"
}
declare_lint! {
/// The `pub_use_of_private_extern_crate` lint detects a specific
/// situation of re-exporting a private `extern crate`.
///
/// ### Example
///
/// ```rust,compile_fail
/// extern crate core;
/// pub use core as reexported_core;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A public `use` declaration should not be used to publicly re-export a
/// private `extern crate`. `pub extern crate` should be used instead.
///
/// This was historically allowed, but is not the intended behavior
/// according to the visibility rules. This is a [future-incompatible]
/// lint to transition this to a hard error in the future. See [issue
/// #34537] for more details.
///
/// [issue #34537]: https://github.com/rust-lang/rust/issues/34537
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PUB_USE_OF_PRIVATE_EXTERN_CRATE,
Deny,
"detect public re-exports of private extern crates",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #34537 <https://github.com/rust-lang/rust/issues/34537>",
};
}
declare_lint! {
/// The `invalid_type_param_default` lint detects type parameter defaults
/// erroneously allowed in an invalid location.
///
/// ### Example
///
/// ```rust,compile_fail
/// fn foo<T=i32>(t: T) {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Default type parameters were only intended to be allowed in certain
/// situations, but historically the compiler allowed them everywhere.
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #36887] for more details.
///
/// [issue #36887]: https://github.com/rust-lang/rust/issues/36887
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub INVALID_TYPE_PARAM_DEFAULT,
Deny,
"type parameter default erroneously allowed in invalid location",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #36887 <https://github.com/rust-lang/rust/issues/36887>",
};
}
declare_lint! {
/// The `renamed_and_removed_lints` lint detects lints that have been
/// renamed or removed.
///
/// ### Example
///
/// ```rust
/// #![deny(raw_pointer_derive)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To fix this, either remove the lint or use the new name. This can help
/// avoid confusion about lints that are no longer valid, and help
/// maintain consistency for renamed lints.
pub RENAMED_AND_REMOVED_LINTS,
Warn,
"lints that have been renamed or removed"
}
declare_lint! {
/// The `const_item_mutation` lint detects attempts to mutate a `const`
/// item.
///
/// ### Example
///
/// ```rust
/// const FOO: [i32; 1] = [0];
///
/// fn main() {
/// FOO[0] = 1;
/// // This will print "[0]".
/// println!("{:?}", FOO);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Trying to directly mutate a `const` item is almost always a mistake.
/// What is happening in the example above is that a temporary copy of the
/// `const` is mutated, but the original `const` is not. Each time you
/// refer to the `const` by name (such as `FOO` in the example above), a
/// separate copy of the value is inlined at that location.
///
/// This lint checks for writing directly to a field (`FOO.field =
/// some_value`) or array entry (`FOO[0] = val`), or taking a mutable
/// reference to the const item (`&mut FOO`), including through an
/// autoderef (`FOO.some_mut_self_method()`).
///
/// There are various alternatives depending on what you are trying to
/// accomplish:
///
/// * First, always reconsider using mutable globals, as they can be
/// difficult to use correctly, and can make the code more difficult to
/// use or understand.
/// * If you are trying to perform a one-time initialization of a global:
/// * If the value can be computed at compile-time, consider using
/// const-compatible values (see [Constant Evaluation]).
/// * For more complex single-initialization cases, consider using a
/// third-party crate, such as [`lazy_static`] or [`once_cell`].
/// * If you are using the [nightly channel], consider the new
/// [`lazy`] module in the standard library.
/// * If you truly need a mutable global, consider using a [`static`],
/// which has a variety of options:
/// * Simple data types can be directly defined and mutated with an
/// [`atomic`] type.
/// * More complex types can be placed in a synchronization primitive
/// like a [`Mutex`], which can be initialized with one of the options
/// listed above.
/// * A [mutable `static`] is a low-level primitive, requiring unsafe.
/// Typically This should be avoided in preference of something
/// higher-level like one of the above.
///
/// [Constant Evaluation]: https://doc.rust-lang.org/reference/const_eval.html
/// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
/// [mutable `static`]: https://doc.rust-lang.org/reference/items/static-items.html#mutable-statics
/// [`lazy`]: https://doc.rust-lang.org/nightly/std/lazy/index.html
/// [`lazy_static`]: https://crates.io/crates/lazy_static
/// [`once_cell`]: https://crates.io/crates/once_cell
/// [`atomic`]: https://doc.rust-lang.org/std/sync/atomic/index.html
/// [`Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
pub CONST_ITEM_MUTATION,
Warn,
"detects attempts to mutate a `const` item",
}
declare_lint! {
/// The `patterns_in_fns_without_body` lint detects `mut` identifier
/// patterns as a parameter in functions without a body.
///
/// ### Example
///
/// ```rust,compile_fail
/// trait Trait {
/// fn foo(mut arg: u8);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To fix this, remove `mut` from the parameter in the trait definition;
/// it can be used in the implementation. That is, the following is OK:
///
/// ```rust
/// trait Trait {
/// fn foo(arg: u8); // Removed `mut` here
/// }
///
/// impl Trait for i32 {
/// fn foo(mut arg: u8) { // `mut` here is OK
///
/// }
/// }
/// ```
///
/// Trait definitions can define functions without a body to specify a
/// function that implementors must define. The parameter names in the
/// body-less functions are only allowed to be `_` or an [identifier] for
/// documentation purposes (only the type is relevant). Previous versions
/// of the compiler erroneously allowed [identifier patterns] with the
/// `mut` keyword, but this was not intended to be allowed. This is a
/// [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #35203] for more details.
///
/// [identifier]: https://doc.rust-lang.org/reference/identifiers.html
/// [identifier patterns]: https://doc.rust-lang.org/reference/patterns.html#identifier-patterns
/// [issue #35203]: https://github.com/rust-lang/rust/issues/35203
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PATTERNS_IN_FNS_WITHOUT_BODY,
Deny,
"patterns in functions without body were erroneously allowed",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #35203 <https://github.com/rust-lang/rust/issues/35203>",
};
}
declare_lint! {
/// The `missing_fragment_specifier` lint is issued when an unused pattern in a
/// `macro_rules!` macro definition has a meta-variable (e.g. `$e`) that is not
/// followed by a fragment specifier (e.g. `:expr`).
///
/// This warning can always be fixed by removing the unused pattern in the
/// `macro_rules!` macro definition.
///
/// ### Example
///
/// ```rust,compile_fail
/// macro_rules! foo {
/// () => {};
/// ($name) => { };
/// }
///
/// fn main() {
/// foo!();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// To fix this, remove the unused pattern from the `macro_rules!` macro definition:
///
/// ```rust
/// macro_rules! foo {
/// () => {};
/// }
/// fn main() {
/// foo!();
/// }
/// ```
pub MISSING_FRAGMENT_SPECIFIER,
Deny,
"detects missing fragment specifiers in unused `macro_rules!` patterns",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #40107 <https://github.com/rust-lang/rust/issues/40107>",
};
}
declare_lint! {
/// The `late_bound_lifetime_arguments` lint detects generic lifetime
/// arguments in path segments with late bound lifetime parameters.
///
/// ### Example
///
/// ```rust
/// struct S;
///
/// impl S {
/// fn late(self, _: &u8, _: &u8) {}
/// }
///
/// fn main() {
/// S.late::<'static>(&0, &0);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is not clear how to provide arguments for early-bound lifetime
/// parameters if they are intermixed with late-bound parameters in the
/// same list. For now, providing any explicit arguments will trigger this
/// lint if late-bound parameters are present, so in the future a solution
/// can be adopted without hitting backward compatibility issues. This is
/// a [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #42868] for more details, along with a description
/// of the difference between early and late-bound parameters.
///
/// [issue #42868]: https://github.com/rust-lang/rust/issues/42868
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub LATE_BOUND_LIFETIME_ARGUMENTS,
Warn,
"detects generic lifetime arguments in path segments with late bound lifetime parameters",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #42868 <https://github.com/rust-lang/rust/issues/42868>",
};
}
declare_lint! {
/// The `order_dependent_trait_objects` lint detects a trait coherency
/// violation that would allow creating two trait impls for the same
/// dynamic trait object involving marker traits.
///
/// ### Example
///
/// ```rust,compile_fail
/// pub trait Trait {}
///
/// impl Trait for dyn Send + Sync { }
/// impl Trait for dyn Sync + Send { }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A previous bug caused the compiler to interpret traits with different
/// orders (such as `Send + Sync` and `Sync + Send`) as distinct types
/// when they were intended to be treated the same. This allowed code to
/// define separate trait implementations when there should be a coherence
/// error. This is a [future-incompatible] lint to transition this to a
/// hard error in the future. See [issue #56484] for more details.
///
/// [issue #56484]: https://github.com/rust-lang/rust/issues/56484
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ORDER_DEPENDENT_TRAIT_OBJECTS,
Deny,
"trait-object types were treated as different depending on marker-trait order",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #56484 <https://github.com/rust-lang/rust/issues/56484>",
};
}
declare_lint! {
/// The `coherence_leak_check` lint detects conflicting implementations of
/// a trait that are only distinguished by the old leak-check code.
///
/// ### Example
///
/// ```rust
/// trait SomeTrait { }
/// impl SomeTrait for for<'a> fn(&'a u8) { }
/// impl<'a> SomeTrait for fn(&'a u8) { }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the past, the compiler would accept trait implementations for
/// identical functions that differed only in where the lifetime binder
/// appeared. Due to a change in the borrow checker implementation to fix
/// several bugs, this is no longer allowed. However, since this affects
/// existing code, this is a [future-incompatible] lint to transition this
/// to a hard error in the future.
///
/// Code relying on this pattern should introduce "[newtypes]",
/// like `struct Foo(for<'a> fn(&'a u8))`.
///
/// See [issue #56105] for more details.
///
/// [issue #56105]: https://github.com/rust-lang/rust/issues/56105
/// [newtypes]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub COHERENCE_LEAK_CHECK,
Warn,
"distinct impls distinguished only by the leak-check code",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #56105 <https://github.com/rust-lang/rust/issues/56105>",
};
}
declare_lint! {
/// The `deprecated` lint detects use of deprecated items.
///
/// ### Example
///
/// ```rust
/// #[deprecated]
/// fn foo() {}
///
/// fn bar() {
/// foo();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Items may be marked "deprecated" with the [`deprecated` attribute] to
/// indicate that they should no longer be used. Usually the attribute
/// should include a note on what to use instead, or check the
/// documentation.
///
/// [`deprecated` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
pub DEPRECATED,
Warn,
"detects use of deprecated items",
report_in_external_macro
}
declare_lint! {
/// The `unused_unsafe` lint detects unnecessary use of an `unsafe` block.
///
/// ### Example
///
/// ```rust
/// unsafe {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If nothing within the block requires `unsafe`, then remove the
/// `unsafe` marker because it is not required and may cause confusion.
pub UNUSED_UNSAFE,
Warn,
"unnecessary use of an `unsafe` block"
}
declare_lint! {
/// The `unused_mut` lint detects mut variables which don't need to be
/// mutable.
///
/// ### Example
///
/// ```rust
/// let mut x = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The preferred style is to only mark variables as `mut` if it is
/// required.
pub UNUSED_MUT,
Warn,
"detect mut variables which don't need to be mutable"
}
declare_lint! {
/// The `unconditional_recursion` lint detects functions that cannot
/// return without calling themselves.
///
/// ### Example
///
/// ```rust
/// fn foo() {
/// foo();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is usually a mistake to have a recursive call that does not have
/// some condition to cause it to terminate. If you really intend to have
/// an infinite loop, using a `loop` expression is recommended.
pub UNCONDITIONAL_RECURSION,
Warn,
"functions that cannot return without calling themselves"
}
declare_lint! {
/// The `single_use_lifetimes` lint detects lifetimes that are only used
/// once.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(single_use_lifetimes)]
///
/// fn foo<'a>(x: &'a u32) {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Specifying an explicit lifetime like `'a` in a function or `impl`
/// should only be used to link together two things. Otherwise, you should
/// just use `'_` to indicate that the lifetime is not linked to anything,
/// or elide the lifetime altogether if possible.
///
/// This lint is "allow" by default because it was introduced at a time
/// when `'_` and elided lifetimes were first being introduced, and this
/// lint would be too noisy. Also, there are some known false positives
/// that it produces. See [RFC 2115] for historical context, and [issue
/// #44752] for more details.
///
/// [RFC 2115]: https://github.com/rust-lang/rfcs/blob/master/text/2115-argument-lifetimes.md
/// [issue #44752]: https://github.com/rust-lang/rust/issues/44752
pub SINGLE_USE_LIFETIMES,
Allow,
"detects lifetime parameters that are only used once"
}
declare_lint! {
/// The `unused_lifetimes` lint detects lifetime parameters that are never
/// used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[deny(unused_lifetimes)]
///
/// pub fn foo<'a>() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused lifetime parameters may signal a mistake or unfinished code.
/// Consider removing the parameter.
pub UNUSED_LIFETIMES,
Allow,
"detects lifetime parameters that are never used"
}
declare_lint! {
/// The `tyvar_behind_raw_pointer` lint detects raw pointer to an
/// inference variable.
///
/// ### Example
///
/// ```rust,edition2015
/// // edition 2015
/// let data = std::ptr::null();
/// let _ = &data as *const *const ();
///
/// if data.is_null() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This kind of inference was previously allowed, but with the future
/// arrival of [arbitrary self types], this can introduce ambiguity. To
/// resolve this, use an explicit type instead of relying on type
/// inference.
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the 2018 edition. See [issue #46906] for more details. This
/// is currently a hard-error on the 2018 edition, and is "warn" by
/// default in the 2015 edition.
///
/// [arbitrary self types]: https://github.com/rust-lang/rust/issues/44874
/// [issue #46906]: https://github.com/rust-lang/rust/issues/46906
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub TYVAR_BEHIND_RAW_POINTER,
Warn,
"raw pointer to an inference variable",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
reference: "issue #46906 <https://github.com/rust-lang/rust/issues/46906>",
};
}
declare_lint! {
/// The `elided_lifetimes_in_paths` lint detects the use of hidden
/// lifetime parameters.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(elided_lifetimes_in_paths)]
/// #![deny(warnings)]
/// struct Foo<'a> {
/// x: &'a u32
/// }
///
/// fn foo(x: &Foo) {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Elided lifetime parameters can make it difficult to see at a glance
/// that borrowing is occurring. This lint ensures that lifetime
/// parameters are always explicitly stated, even if it is the `'_`
/// [placeholder lifetime].
///
/// This lint is "allow" by default because it has some known issues, and
/// may require a significant transition for old code.
///
/// [placeholder lifetime]: https://doc.rust-lang.org/reference/lifetime-elision.html#lifetime-elision-in-functions
pub ELIDED_LIFETIMES_IN_PATHS,
Allow,
"hidden lifetime parameters in types are deprecated",
crate_level_only
}
declare_lint! {
/// The `bare_trait_objects` lint suggests using `dyn Trait` for trait
/// objects.
///
/// ### Example
///
/// ```rust,edition2018
/// trait Trait { }
///
/// fn takes_trait_object(_: Box<Trait>) {
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Without the `dyn` indicator, it can be ambiguous or confusing when
/// reading code as to whether or not you are looking at a trait object.
/// The `dyn` keyword makes it explicit, and adds a symmetry to contrast
/// with [`impl Trait`].
///
/// [`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
pub BARE_TRAIT_OBJECTS,
Warn,
"suggest using `dyn Trait` for trait objects",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>",
};
}
declare_lint! {
/// The `absolute_paths_not_starting_with_crate` lint detects fully
/// qualified paths that start with a module name instead of `crate`,
/// `self`, or an extern crate name
///
/// ### Example
///
/// ```rust,edition2015,compile_fail
/// #![deny(absolute_paths_not_starting_with_crate)]
///
/// mod foo {
/// pub fn bar() {}
/// }
///
/// fn main() {
/// ::foo::bar();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust [editions] allow the language to evolve without breaking
/// backwards compatibility. This lint catches code that uses absolute
/// paths in the style of the 2015 edition. In the 2015 edition, absolute
/// paths (those starting with `::`) refer to either the crate root or an
/// external crate. In the 2018 edition it was changed so that they only
/// refer to external crates. The path prefix `crate::` should be used
/// instead to reference items from the crate root.
///
/// If you switch the compiler from the 2015 to 2018 edition without
/// updating the code, then it will fail to compile if the old style paths
/// are used. You can manually change the paths to use the `crate::`
/// prefix to transition to the 2018 edition.
///
/// This lint solves the problem automatically. It is "allow" by default
/// because the code is perfectly valid in the 2015 edition. The [`cargo
/// fix`] tool with the `--edition` flag will switch this lint to "warn"
/// and automatically apply the suggested fix from the compiler. This
/// provides a completely automated way to update old code to the 2018
/// edition.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
/// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
pub ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
Allow,
"fully qualified paths that start with a module name \
instead of `crate`, `self`, or an extern crate name",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2018),
reference: "issue #53130 <https://github.com/rust-lang/rust/issues/53130>",
};
}
declare_lint! {
/// The `illegal_floating_point_literal_pattern` lint detects
/// floating-point literals used in patterns.
///
/// ### Example
///
/// ```rust
/// let x = 42.0;
///
/// match x {
/// 5.0 => {}
/// _ => {}
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of the compiler accepted floating-point literals in
/// patterns, but it was later determined this was a mistake. The
/// semantics of comparing floating-point values may not be clear in a
/// pattern when contrasted with "structural equality". Typically you can
/// work around this by using a [match guard], such as:
///
/// ```rust
/// # let x = 42.0;
///
/// match x {
/// y if y == 5.0 => {}
/// _ => {}
/// }
/// ```
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #41620] for more details.
///
/// [issue #41620]: https://github.com/rust-lang/rust/issues/41620
/// [match guard]: https://doc.rust-lang.org/reference/expressions/match-expr.html#match-guards
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
Warn,
"floating-point literals cannot be used in patterns",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #41620 <https://github.com/rust-lang/rust/issues/41620>",
};
}
declare_lint! {
/// The `unstable_name_collisions` lint detects that you have used a name
/// that the standard library plans to add in the future.
///
/// ### Example
///
/// ```rust
/// trait MyIterator : Iterator {
/// // is_sorted is an unstable method that already exists on the Iterator trait
/// fn is_sorted(self) -> bool where Self: Sized {true}
/// }
///
/// impl<T: ?Sized> MyIterator for T where T: Iterator { }
///
/// let x = vec![1, 2, 3];
/// let _ = x.iter().is_sorted();
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// When new methods are added to traits in the standard library, they are
/// usually added in an "unstable" form which is only available on the
/// [nightly channel] with a [`feature` attribute]. If there is any
/// preexisting code which extends a trait to have a method with the same
/// name, then the names will collide. In the future, when the method is
/// stabilized, this will cause an error due to the ambiguity. This lint
/// is an early-warning to let you know that there may be a collision in
/// the future. This can be avoided by adding type annotations to
/// disambiguate which trait method you intend to call, such as
/// `MyIterator::is_sorted(my_iter)` or renaming or removing the method.
///
/// [nightly channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
/// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
pub UNSTABLE_NAME_COLLISIONS,
Warn,
"detects name collision with an existing but unstable method",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::Custom(
"once this associated item is added to the standard library, \
the ambiguity may cause an error or change in behavior!"
),
reference: "issue #48919 <https://github.com/rust-lang/rust/issues/48919>",
// Note: this item represents future incompatibility of all unstable functions in the
// standard library, and thus should never be removed or changed to an error.
};
}
declare_lint! {
/// The `irrefutable_let_patterns` lint detects [irrefutable patterns]
/// in [`if let`]s, [`while let`]s, and `if let` guards.
///
/// ### Example
///
/// ```rust
/// if let _ = 123 {
/// println!("always runs!");
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// There usually isn't a reason to have an irrefutable pattern in an
/// `if let` or `while let` statement, because the pattern will always match
/// successfully. A [`let`] or [`loop`] statement will suffice. However,
/// when generating code with a macro, forbidding irrefutable patterns
/// would require awkward workarounds in situations where the macro
/// doesn't know if the pattern is refutable or not. This lint allows
/// macros to accept this form, while alerting for a possibly incorrect
/// use in normal code.
///
/// See [RFC 2086] for more details.
///
/// [irrefutable patterns]: https://doc.rust-lang.org/reference/patterns.html#refutability
/// [`if let`]: https://doc.rust-lang.org/reference/expressions/if-expr.html#if-let-expressions
/// [`while let`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#predicate-pattern-loops
/// [`let`]: https://doc.rust-lang.org/reference/statements.html#let-statements
/// [`loop`]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#infinite-loops
/// [RFC 2086]: https://github.com/rust-lang/rfcs/blob/master/text/2086-allow-if-let-irrefutables.md
pub IRREFUTABLE_LET_PATTERNS,
Warn,
"detects irrefutable patterns in `if let` and `while let` statements"
}
declare_lint! {
/// The `unused_labels` lint detects [labels] that are never used.
///
/// [labels]: https://doc.rust-lang.org/reference/expressions/loop-expr.html#loop-labels
///
/// ### Example
///
/// ```rust,no_run
/// 'unused_label: loop {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unused labels may signal a mistake or unfinished code. To silence the
/// warning for the individual label, prefix it with an underscore such as
/// `'_my_label:`.
pub UNUSED_LABELS,
Warn,
"detects labels that are never used"
}
declare_lint! {
/// The `where_clauses_object_safety` lint detects for [object safety] of
/// [where clauses].
///
/// [object safety]: https://doc.rust-lang.org/reference/items/traits.html#object-safety
/// [where clauses]: https://doc.rust-lang.org/reference/items/generics.html#where-clauses
///
/// ### Example
///
/// ```rust,no_run
/// trait Trait {}
///
/// trait X { fn foo(&self) where Self: Trait; }
///
/// impl X for () { fn foo(&self) {} }
///
/// impl Trait for dyn X {}
///
/// // Segfault at opt-level 0, SIGILL otherwise.
/// pub fn main() { <dyn X as X>::foo(&()); }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The compiler previously allowed these object-unsafe bounds, which was
/// incorrect. This is a [future-incompatible] lint to transition this to
/// a hard error in the future. See [issue #51443] for more details.
///
/// [issue #51443]: https://github.com/rust-lang/rust/issues/51443
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub WHERE_CLAUSES_OBJECT_SAFETY,
Warn,
"checks the object safety of where clauses",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #51443 <https://github.com/rust-lang/rust/issues/51443>",
};
}
declare_lint! {
/// The `proc_macro_derive_resolution_fallback` lint detects proc macro
/// derives using inaccessible names from parent modules.
///
/// ### Example
///
/// ```rust,ignore (proc-macro)
/// // foo.rs
/// #![crate_type = "proc-macro"]
///
/// extern crate proc_macro;
///
/// use proc_macro::*;
///
/// #[proc_macro_derive(Foo)]
/// pub fn foo1(a: TokenStream) -> TokenStream {
/// drop(a);
/// "mod __bar { static mut BAR: Option<Something> = None; }".parse().unwrap()
/// }
/// ```
///
/// ```rust,ignore (needs-dependency)
/// // bar.rs
/// #[macro_use]
/// extern crate foo;
///
/// struct Something;
///
/// #[derive(Foo)]
/// struct Another;
///
/// fn main() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: cannot find type `Something` in this scope
/// --> src/main.rs:8:10
/// |
/// 8 | #[derive(Foo)]
/// | ^^^ names from parent modules are not accessible without an explicit import
/// |
/// = note: `#[warn(proc_macro_derive_resolution_fallback)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #50504 <https://github.com/rust-lang/rust/issues/50504>
/// ```
///
/// ### Explanation
///
/// If a proc-macro generates a module, the compiler unintentionally
/// allowed items in that module to refer to items in the crate root
/// without importing them. This is a [future-incompatible] lint to
/// transition this to a hard error in the future. See [issue #50504] for
/// more details.
///
/// [issue #50504]: https://github.com/rust-lang/rust/issues/50504
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
Deny,
"detects proc macro derives using inaccessible names from parent modules",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #83583 <https://github.com/rust-lang/rust/issues/83583>",
};
}
declare_lint! {
/// The `macro_use_extern_crate` lint detects the use of the
/// [`macro_use` attribute].
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #![deny(macro_use_extern_crate)]
///
/// #[macro_use]
/// extern crate serde_json;
///
/// fn main() {
/// let _ = json!{{}};
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// error: deprecated `#[macro_use]` attribute used to import macros should be replaced at use sites with a `use` item to import the macro instead
/// --> src/main.rs:3:1
/// |
/// 3 | #[macro_use]
/// | ^^^^^^^^^^^^
/// |
/// note: the lint level is defined here
/// --> src/main.rs:1:9
/// |
/// 1 | #![deny(macro_use_extern_crate)]
/// | ^^^^^^^^^^^^^^^^^^^^^^
/// ```
///
/// ### Explanation
///
/// The [`macro_use` attribute] on an [`extern crate`] item causes
/// macros in that external crate to be brought into the prelude of the
/// crate, making the macros in scope everywhere. As part of the efforts
/// to simplify handling of dependencies in the [2018 edition], the use of
/// `extern crate` is being phased out. To bring macros from extern crates
/// into scope, it is recommended to use a [`use` import].
///
/// This lint is "allow" by default because this is a stylistic choice
/// that has not been settled, see [issue #52043] for more information.
///
/// [`macro_use` attribute]: https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute
/// [`use` import]: https://doc.rust-lang.org/reference/items/use-declarations.html
/// [issue #52043]: https://github.com/rust-lang/rust/issues/52043
pub MACRO_USE_EXTERN_CRATE,
Allow,
"the `#[macro_use]` attribute is now deprecated in favor of using macros \
via the module system"
}
declare_lint! {
/// The `macro_expanded_macro_exports_accessed_by_absolute_paths` lint
/// detects macro-expanded [`macro_export`] macros from the current crate
/// that cannot be referred to by absolute paths.
///
/// [`macro_export`]: https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope
///
/// ### Example
///
/// ```rust,compile_fail
/// macro_rules! define_exported {
/// () => {
/// #[macro_export]
/// macro_rules! exported {
/// () => {};
/// }
/// };
/// }
///
/// define_exported!();
///
/// fn main() {
/// crate::exported!();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The intent is that all macros marked with the `#[macro_export]`
/// attribute are made available in the root of the crate. However, when a
/// `macro_rules!` definition is generated by another macro, the macro
/// expansion is unable to uphold this rule. This is a
/// [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #53495] for more details.
///
/// [issue #53495]: https://github.com/rust-lang/rust/issues/53495
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
Deny,
"macro-expanded `macro_export` macros from the current crate \
cannot be referred to by absolute paths",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
};
crate_level_only
}
declare_lint! {
/// The `explicit_outlives_requirements` lint detects unnecessary
/// lifetime bounds that can be inferred.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(explicit_outlives_requirements)]
/// #![deny(warnings)]
///
/// struct SharedRef<'a, T>
/// where
/// T: 'a,
/// {
/// data: &'a T,
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// If a `struct` contains a reference, such as `&'a T`, the compiler
/// requires that `T` outlives the lifetime `'a`. This historically
/// required writing an explicit lifetime bound to indicate this
/// requirement. However, this can be overly explicit, causing clutter and
/// unnecessary complexity. The language was changed to automatically
/// infer the bound if it is not specified. Specifically, if the struct
/// contains a reference, directly or indirectly, to `T` with lifetime
/// `'x`, then it will infer that `T: 'x` is a requirement.
///
/// This lint is "allow" by default because it can be noisy for existing
/// code that already had these requirements. This is a stylistic choice,
/// as it is still valid to explicitly state the bound. It also has some
/// false positives that can cause confusion.
///
/// See [RFC 2093] for more details.
///
/// [RFC 2093]: https://github.com/rust-lang/rfcs/blob/master/text/2093-infer-outlives.md
pub EXPLICIT_OUTLIVES_REQUIREMENTS,
Allow,
"outlives requirements can be inferred"
}
declare_lint! {
/// The `indirect_structural_match` lint detects a `const` in a pattern
/// that manually implements [`PartialEq`] and [`Eq`].
///
/// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(indirect_structural_match)]
///
/// struct NoDerive(i32);
/// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
/// impl Eq for NoDerive { }
/// #[derive(PartialEq, Eq)]
/// struct WrapParam<T>(T);
/// const WRAP_INDIRECT_PARAM: & &WrapParam<NoDerive> = & &WrapParam(NoDerive(0));
/// fn main() {
/// match WRAP_INDIRECT_PARAM {
/// WRAP_INDIRECT_PARAM => { }
/// _ => { }
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The compiler unintentionally accepted this form in the past. This is a
/// [future-incompatible] lint to transition this to a hard error in the
/// future. See [issue #62411] for a complete description of the problem,
/// and some possible solutions.
///
/// [issue #62411]: https://github.com/rust-lang/rust/issues/62411
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub INDIRECT_STRUCTURAL_MATCH,
Warn,
"constant used in pattern contains value of non-structural-match type in a field or a variant",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #62411 <https://github.com/rust-lang/rust/issues/62411>",
};
}
declare_lint! {
/// The `deprecated_in_future` lint is internal to rustc and should not be
/// used by user code.
///
/// This lint is only enabled in the standard library. It works with the
/// use of `#[deprecated]` with a `since` field of a version in the future.
/// This allows something to be marked as deprecated in a future version,
/// and then this lint will ensure that the item is no longer used in the
/// standard library. See the [stability documentation] for more details.
///
/// [stability documentation]: https://rustc-dev-guide.rust-lang.org/stability.html#deprecated
pub DEPRECATED_IN_FUTURE,
Allow,
"detects use of items that will be deprecated in a future version",
report_in_external_macro
}
declare_lint! {
/// The `pointer_structural_match` lint detects pointers used in patterns whose behaviour
/// cannot be relied upon across compiler versions and optimization levels.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(pointer_structural_match)]
/// fn foo(a: usize, b: usize) -> usize { a + b }
/// const FOO: fn(usize, usize) -> usize = foo;
/// fn main() {
/// match FOO {
/// FOO => {},
/// _ => {},
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust allowed function pointers and all raw pointers in patterns.
/// While these work in many cases as expected by users, it is possible that due to
/// optimizations pointers are "not equal to themselves" or pointers to different functions
/// compare as equal during runtime. This is because LLVM optimizations can deduplicate
/// functions if their bodies are the same, thus also making pointers to these functions point
/// to the same location. Additionally functions may get duplicated if they are instantiated
/// in different crates and not deduplicated again via LTO. Pointer identity for memory
/// created by `const` is similarly unreliable.
pub POINTER_STRUCTURAL_MATCH,
Warn,
"pointers are not structural-match",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #62411 <https://github.com/rust-lang/rust/issues/70861>",
};
}
declare_lint! {
/// The `nontrivial_structural_match` lint detects constants that are used in patterns,
/// whose type is not structural-match and whose initializer body actually uses values
/// that are not structural-match. So `Option<NotStructuralMatch>` is ok if the constant
/// is just `None`.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(nontrivial_structural_match)]
///
/// #[derive(Copy, Clone, Debug)]
/// struct NoDerive(u32);
/// impl PartialEq for NoDerive { fn eq(&self, _: &Self) -> bool { false } }
/// impl Eq for NoDerive { }
/// fn main() {
/// const INDEX: Option<NoDerive> = [None, Some(NoDerive(10))][0];
/// match None { Some(_) => panic!("whoops"), INDEX => dbg!(INDEX), };
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust accepted constants in patterns, even if those constants' types
/// did not have `PartialEq` derived. Thus the compiler falls back to runtime execution of
/// `PartialEq`, which can report that two constants are not equal even if they are
/// bit-equivalent.
pub NONTRIVIAL_STRUCTURAL_MATCH,
Warn,
"constant used in pattern of non-structural-match type and the constant's initializer \
expression contains values of non-structural-match types",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #73448 <https://github.com/rust-lang/rust/issues/73448>",
};
}
declare_lint! {
/// The `const_patterns_without_partial_eq` lint detects constants that are used in patterns,
/// whose type does not implement `PartialEq`.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(const_patterns_without_partial_eq)]
///
/// trait EnumSetType {
/// type Repr;
/// }
///
/// enum Enum8 { }
/// impl EnumSetType for Enum8 {
/// type Repr = u8;
/// }
///
/// #[derive(PartialEq, Eq)]
/// struct EnumSet<T: EnumSetType> {
/// __enumset_underlying: T::Repr,
/// }
///
/// const CONST_SET: EnumSet<Enum8> = EnumSet { __enumset_underlying: 3 };
///
/// fn main() {
/// match CONST_SET {
/// CONST_SET => { /* ok */ }
/// _ => panic!("match fell through?"),
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust accepted constants in patterns, even if those constants' types
/// did not have `PartialEq` implemented. The compiler falls back to comparing the value
/// field-by-field. In the future we'd like to ensure that pattern matching always
/// follows `PartialEq` semantics, so that trait bound will become a requirement for
/// matching on constants.
pub CONST_PATTERNS_WITHOUT_PARTIAL_EQ,
Warn,
"constant in pattern does not implement `PartialEq`",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #116122 <https://github.com/rust-lang/rust/issues/116122>",
};
}
declare_lint! {
/// The `ambiguous_associated_items` lint detects ambiguity between
/// [associated items] and [enum variants].
///
/// [associated items]: https://doc.rust-lang.org/reference/items/associated-items.html
/// [enum variants]: https://doc.rust-lang.org/reference/items/enumerations.html
///
/// ### Example
///
/// ```rust,compile_fail
/// enum E {
/// V
/// }
///
/// trait Tr {
/// type V;
/// fn foo() -> Self::V;
/// }
///
/// impl Tr for E {
/// type V = u8;
/// // `Self::V` is ambiguous because it may refer to the associated type or
/// // the enum variant.
/// fn foo() -> Self::V { 0 }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust did not allow accessing enum variants
/// through [type aliases]. When this ability was added (see [RFC 2338]), this
/// introduced some situations where it can be ambiguous what a type
/// was referring to.
///
/// To fix this ambiguity, you should use a [qualified path] to explicitly
/// state which type to use. For example, in the above example the
/// function can be written as `fn f() -> <Self as Tr>::V { 0 }` to
/// specifically refer to the associated type.
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #57644] for more details.
///
/// [issue #57644]: https://github.com/rust-lang/rust/issues/57644
/// [type aliases]: https://doc.rust-lang.org/reference/items/type-aliases.html#type-aliases
/// [RFC 2338]: https://github.com/rust-lang/rfcs/blob/master/text/2338-type-alias-enum-variants.md
/// [qualified path]: https://doc.rust-lang.org/reference/paths.html#qualified-paths
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub AMBIGUOUS_ASSOCIATED_ITEMS,
Deny,
"ambiguous associated items",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #57644 <https://github.com/rust-lang/rust/issues/57644>",
};
}
declare_lint! {
/// The `soft_unstable` lint detects unstable features that were
/// unintentionally allowed on stable.
///
/// ### Example
///
/// ```rust,compile_fail
/// #[cfg(test)]
/// extern crate test;
///
/// #[bench]
/// fn name(b: &mut test::Bencher) {
/// b.iter(|| 123)
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The [`bench` attribute] was accidentally allowed to be specified on
/// the [stable release channel]. Turning this to a hard error would have
/// broken some projects. This lint allows those projects to continue to
/// build correctly when [`--cap-lints`] is used, but otherwise signal an
/// error that `#[bench]` should not be used on the stable channel. This
/// is a [future-incompatible] lint to transition this to a hard error in
/// the future. See [issue #64266] for more details.
///
/// [issue #64266]: https://github.com/rust-lang/rust/issues/64266
/// [`bench` attribute]: https://doc.rust-lang.org/nightly/unstable-book/library-features/test.html
/// [stable release channel]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
/// [`--cap-lints`]: https://doc.rust-lang.org/rustc/lints/levels.html#capping-lints
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub SOFT_UNSTABLE,
Deny,
"a feature gate that doesn't break dependent crates",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #64266 <https://github.com/rust-lang/rust/issues/64266>",
};
}
declare_lint! {
/// The `inline_no_sanitize` lint detects incompatible use of
/// [`#[inline(always)]`][inline] and [`#[no_sanitize(...)]`][no_sanitize].
///
/// [inline]: https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute
/// [no_sanitize]: https://doc.rust-lang.org/nightly/unstable-book/language-features/no-sanitize.html
///
/// ### Example
///
/// ```rust
/// #![feature(no_sanitize)]
///
/// #[inline(always)]
/// #[no_sanitize(address)]
/// fn x() {}
///
/// fn main() {
/// x()
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The use of the [`#[inline(always)]`][inline] attribute prevents the
/// the [`#[no_sanitize(...)]`][no_sanitize] attribute from working.
/// Consider temporarily removing `inline` attribute.
pub INLINE_NO_SANITIZE,
Warn,
"detects incompatible use of `#[inline(always)]` and `#[no_sanitize(...)]`",
}
declare_lint! {
/// The `asm_sub_register` lint detects using only a subset of a register
/// for inline asm inputs.
///
/// ### Example
///
/// ```rust,ignore (fails on non-x86_64)
/// #[cfg(target_arch="x86_64")]
/// use std::arch::asm;
///
/// fn main() {
/// #[cfg(target_arch="x86_64")]
/// unsafe {
/// asm!("mov {0}, {0}", in(reg) 0i16);
/// }
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: formatting may not be suitable for sub-register argument
/// --> src/main.rs:7:19
/// |
/// 7 | asm!("mov {0}, {0}", in(reg) 0i16);
/// | ^^^ ^^^ ---- for this argument
/// |
/// = note: `#[warn(asm_sub_register)]` on by default
/// = help: use the `x` modifier to have the register formatted as `ax`
/// = help: or use the `r` modifier to keep the default formatting of `rax`
/// ```
///
/// ### Explanation
///
/// Registers on some architectures can use different names to refer to a
/// subset of the register. By default, the compiler will use the name for
/// the full register size. To explicitly use a subset of the register,
/// you can override the default by using a modifier on the template
/// string operand to specify when subregister to use. This lint is issued
/// if you pass in a value with a smaller data type than the default
/// register size, to alert you of possibly using the incorrect width. To
/// fix this, add the suggested modifier to the template, or cast the
/// value to the correct size.
///
/// See [register template modifiers] in the reference for more details.
///
/// [register template modifiers]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html#template-modifiers
pub ASM_SUB_REGISTER,
Warn,
"using only a subset of a register for inline asm inputs",
}
declare_lint! {
/// The `bad_asm_style` lint detects the use of the `.intel_syntax` and
/// `.att_syntax` directives.
///
/// ### Example
///
/// ```rust,ignore (fails on non-x86_64)
/// #[cfg(target_arch="x86_64")]
/// use std::arch::asm;
///
/// fn main() {
/// #[cfg(target_arch="x86_64")]
/// unsafe {
/// asm!(
/// ".att_syntax",
/// "movq %{0}, %{0}", in(reg) 0usize
/// );
/// }
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: avoid using `.att_syntax`, prefer using `options(att_syntax)` instead
/// --> src/main.rs:8:14
/// |
/// 8 | ".att_syntax",
/// | ^^^^^^^^^^^
/// |
/// = note: `#[warn(bad_asm_style)]` on by default
/// ```
///
/// ### Explanation
///
/// On x86, `asm!` uses the intel assembly syntax by default. While this
/// can be switched using assembler directives like `.att_syntax`, using the
/// `att_syntax` option is recommended instead because it will also properly
/// prefix register placeholders with `%` as required by AT&T syntax.
pub BAD_ASM_STYLE,
Warn,
"incorrect use of inline assembly",
}
declare_lint! {
/// The `unsafe_op_in_unsafe_fn` lint detects unsafe operations in unsafe
/// functions without an explicit unsafe block.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unsafe_op_in_unsafe_fn)]
///
/// unsafe fn foo() {}
///
/// unsafe fn bar() {
/// foo();
/// }
///
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Currently, an [`unsafe fn`] allows any [unsafe] operation within its
/// body. However, this can increase the surface area of code that needs
/// to be scrutinized for proper behavior. The [`unsafe` block] provides a
/// convenient way to make it clear exactly which parts of the code are
/// performing unsafe operations. In the future, it is desired to change
/// it so that unsafe operations cannot be performed in an `unsafe fn`
/// without an `unsafe` block.
///
/// The fix to this is to wrap the unsafe code in an `unsafe` block.
///
/// This lint is "allow" by default on editions up to 2021, from 2024 it is
/// "warn" by default; the plan for increasing severity further is
/// still being considered. See [RFC #2585] and [issue #71668] for more
/// details.
///
/// [`unsafe fn`]: https://doc.rust-lang.org/reference/unsafe-functions.html
/// [`unsafe` block]: https://doc.rust-lang.org/reference/expressions/block-expr.html#unsafe-blocks
/// [unsafe]: https://doc.rust-lang.org/reference/unsafety.html
/// [RFC #2585]: https://github.com/rust-lang/rfcs/blob/master/text/2585-unsafe-block-in-unsafe-fn.md
/// [issue #71668]: https://github.com/rust-lang/rust/issues/71668
pub UNSAFE_OP_IN_UNSAFE_FN,
Allow,
"unsafe operations in unsafe functions without an explicit unsafe block are deprecated",
@edition Edition2024 => Warn;
}
declare_lint! {
/// The `cenum_impl_drop_cast` lint detects an `as` cast of a field-less
/// `enum` that implements [`Drop`].
///
/// [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// enum E {
/// A,
/// }
///
/// impl Drop for E {
/// fn drop(&mut self) {
/// println!("Drop");
/// }
/// }
///
/// fn main() {
/// let e = E::A;
/// let i = e as u32;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Casting a field-less `enum` that does not implement [`Copy`] to an
/// integer moves the value without calling `drop`. This can result in
/// surprising behavior if it was expected that `drop` should be called.
/// Calling `drop` automatically would be inconsistent with other move
/// operations. Since neither behavior is clear or consistent, it was
/// decided that a cast of this nature will no longer be allowed.
///
/// This is a [future-incompatible] lint to transition this to a hard error
/// in the future. See [issue #73333] for more details.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
/// [issue #73333]: https://github.com/rust-lang/rust/issues/73333
/// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
pub CENUM_IMPL_DROP_CAST,
Deny,
"a C-like enum implementing Drop is cast",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #73333 <https://github.com/rust-lang/rust/issues/73333>",
};
}
declare_lint! {
/// The `fuzzy_provenance_casts` lint detects an `as` cast between an integer
/// and a pointer.
///
/// ### Example
///
/// ```rust
/// #![feature(strict_provenance)]
/// #![warn(fuzzy_provenance_casts)]
///
/// fn main() {
/// let _dangling = 16_usize as *const u8;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is part of the strict provenance effort, see [issue #95228].
/// Casting an integer to a pointer is considered bad style, as a pointer
/// contains, besides the *address* also a *provenance*, indicating what
/// memory the pointer is allowed to read/write. Casting an integer, which
/// doesn't have provenance, to a pointer requires the compiler to assign
/// (guess) provenance. The compiler assigns "all exposed valid" (see the
/// docs of [`ptr::from_exposed_addr`] for more information about this
/// "exposing"). This penalizes the optimiser and is not well suited for
/// dynamic analysis/dynamic program verification (e.g. Miri or CHERI
/// platforms).
///
/// It is much better to use [`ptr::with_addr`] instead to specify the
/// provenance you want. If using this function is not possible because the
/// code relies on exposed provenance then there is as an escape hatch
/// [`ptr::from_exposed_addr`].
///
/// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
/// [`ptr::with_addr`]: https://doc.rust-lang.org/core/ptr/fn.with_addr
/// [`ptr::from_exposed_addr`]: https://doc.rust-lang.org/core/ptr/fn.from_exposed_addr
pub FUZZY_PROVENANCE_CASTS,
Allow,
"a fuzzy integer to pointer cast is used",
@feature_gate = sym::strict_provenance;
}
declare_lint! {
/// The `lossy_provenance_casts` lint detects an `as` cast between a pointer
/// and an integer.
///
/// ### Example
///
/// ```rust
/// #![feature(strict_provenance)]
/// #![warn(lossy_provenance_casts)]
///
/// fn main() {
/// let x: u8 = 37;
/// let _addr: usize = &x as *const u8 as usize;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is part of the strict provenance effort, see [issue #95228].
/// Casting a pointer to an integer is a lossy operation, because beyond
/// just an *address* a pointer may be associated with a particular
/// *provenance*. This information is used by the optimiser and for dynamic
/// analysis/dynamic program verification (e.g. Miri or CHERI platforms).
///
/// Since this cast is lossy, it is considered good style to use the
/// [`ptr::addr`] method instead, which has a similar effect, but doesn't
/// "expose" the pointer provenance. This improves optimisation potential.
/// See the docs of [`ptr::addr`] and [`ptr::expose_addr`] for more information
/// about exposing pointer provenance.
///
/// If your code can't comply with strict provenance and needs to expose
/// the provenance, then there is [`ptr::expose_addr`] as an escape hatch,
/// which preserves the behaviour of `as usize` casts while being explicit
/// about the semantics.
///
/// [issue #95228]: https://github.com/rust-lang/rust/issues/95228
/// [`ptr::addr`]: https://doc.rust-lang.org/core/ptr/fn.addr
/// [`ptr::expose_addr`]: https://doc.rust-lang.org/core/ptr/fn.expose_addr
pub LOSSY_PROVENANCE_CASTS,
Allow,
"a lossy pointer to integer cast is used",
@feature_gate = sym::strict_provenance;
}
declare_lint! {
/// The `const_evaluatable_unchecked` lint detects a generic constant used
/// in a type.
///
/// ### Example
///
/// ```rust
/// const fn foo<T>() -> usize {
/// if std::mem::size_of::<*mut T>() < 8 { // size of *mut T does not depend on T
/// 4
/// } else {
/// 8
/// }
/// }
///
/// fn test<T>() {
/// let _ = [0; foo::<T>()];
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the 1.43 release, some uses of generic parameters in array repeat
/// expressions were accidentally allowed. This is a [future-incompatible]
/// lint to transition this to a hard error in the future. See [issue
/// #76200] for a more detailed description and possible fixes.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
/// [issue #76200]: https://github.com/rust-lang/rust/issues/76200
pub CONST_EVALUATABLE_UNCHECKED,
Warn,
"detects a generic constant is used in a type without a emitting a warning",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #76200 <https://github.com/rust-lang/rust/issues/76200>",
};
}
declare_lint! {
/// The `function_item_references` lint detects function references that are
/// formatted with [`fmt::Pointer`] or transmuted.
///
/// [`fmt::Pointer`]: https://doc.rust-lang.org/std/fmt/trait.Pointer.html
///
/// ### Example
///
/// ```rust
/// fn foo() { }
///
/// fn main() {
/// println!("{:p}", &foo);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Taking a reference to a function may be mistaken as a way to obtain a
/// pointer to that function. This can give unexpected results when
/// formatting the reference as a pointer or transmuting it. This lint is
/// issued when function references are formatted as pointers, passed as
/// arguments bound by [`fmt::Pointer`] or transmuted.
pub FUNCTION_ITEM_REFERENCES,
Warn,
"suggest casting to a function pointer when attempting to take references to function items",
}
declare_lint! {
/// The `uninhabited_static` lint detects uninhabited statics.
///
/// ### Example
///
/// ```rust
/// enum Void {}
/// extern {
/// static EXTERN: Void;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Statics with an uninhabited type can never be initialized, so they are impossible to define.
/// However, this can be side-stepped with an `extern static`, leading to problems later in the
/// compiler which assumes that there are no initialized uninhabited places (such as locals or
/// statics). This was accidentally allowed, but is being phased out.
pub UNINHABITED_STATIC,
Warn,
"uninhabited static",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #74840 <https://github.com/rust-lang/rust/issues/74840>",
};
}
declare_lint! {
/// The `unnameable_test_items` lint detects [`#[test]`][test] functions
/// that are not able to be run by the test harness because they are in a
/// position where they are not nameable.
///
/// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
///
/// ### Example
///
/// ```rust,test
/// fn main() {
/// #[test]
/// fn foo() {
/// // This test will not fail because it does not run.
/// assert_eq!(1, 2);
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In order for the test harness to run a test, the test function must be
/// located in a position where it can be accessed from the crate root.
/// This generally means it must be defined in a module, and not anywhere
/// else such as inside another function. The compiler previously allowed
/// this without an error, so a lint was added as an alert that a test is
/// not being used. Whether or not this should be allowed has not yet been
/// decided, see [RFC 2471] and [issue #36629].
///
/// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
/// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
pub UNNAMEABLE_TEST_ITEMS,
Warn,
"detects an item that cannot be named being marked as `#[test_case]`",
report_in_external_macro
}
declare_lint! {
/// The `useless_deprecated` lint detects deprecation attributes with no effect.
///
/// ### Example
///
/// ```rust,compile_fail
/// struct X;
///
/// #[deprecated = "message"]
/// impl Default for X {
/// fn default() -> Self {
/// X
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Deprecation attributes have no effect on trait implementations.
pub USELESS_DEPRECATED,
Deny,
"detects deprecation attributes with no effect",
}
declare_lint! {
/// The `undefined_naked_function_abi` lint detects naked function definitions that
/// either do not specify an ABI or specify the Rust ABI.
///
/// ### Example
///
/// ```rust
/// #![feature(asm_experimental_arch, naked_functions)]
///
/// use std::arch::asm;
///
/// #[naked]
/// pub fn default_abi() -> u32 {
/// unsafe { asm!("", options(noreturn)); }
/// }
///
/// #[naked]
/// pub extern "Rust" fn rust_abi() -> u32 {
/// unsafe { asm!("", options(noreturn)); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The Rust ABI is currently undefined. Therefore, naked functions should
/// specify a non-Rust ABI.
pub UNDEFINED_NAKED_FUNCTION_ABI,
Warn,
"undefined naked function ABI"
}
declare_lint! {
/// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![feature(staged_api)]
///
/// #[derive(Clone)]
/// #[stable(feature = "x", since = "1")]
/// struct S {}
///
/// #[unstable(feature = "y", issue = "none")]
/// impl Copy for S {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `staged_api` does not currently support using a stability attribute on `impl` blocks.
/// `impl`s are always stable if both the type and trait are stable, and always unstable otherwise.
pub INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
Deny,
"detects `#[unstable]` on stable trait implementations for stable types"
}
declare_lint! {
/// The `semicolon_in_expressions_from_macros` lint detects trailing semicolons
/// in macro bodies when the macro is invoked in expression position.
/// This was previous accepted, but is being phased out.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(semicolon_in_expressions_from_macros)]
/// macro_rules! foo {
/// () => { true; }
/// }
///
/// fn main() {
/// let val = match true {
/// true => false,
/// _ => foo!()
/// };
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous, Rust ignored trailing semicolon in a macro
/// body when a macro was invoked in expression position.
/// However, this makes the treatment of semicolons in the language
/// inconsistent, and could lead to unexpected runtime behavior
/// in some circumstances (e.g. if the macro author expects
/// a value to be dropped).
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #79813] for more details.
///
/// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
Warn,
"trailing semicolon in macro body used as expression",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #79813 <https://github.com/rust-lang/rust/issues/79813>",
};
}
declare_lint! {
/// The `legacy_derive_helpers` lint detects derive helper attributes
/// that are used before they are introduced.
///
/// ### Example
///
/// ```rust,ignore (needs extern crate)
/// #[serde(rename_all = "camelCase")]
/// #[derive(Deserialize)]
/// struct S { /* fields */ }
/// ```
///
/// produces:
///
/// ```text
/// warning: derive helper attribute is used before it is introduced
/// --> $DIR/legacy-derive-helpers.rs:1:3
/// |
/// 1 | #[serde(rename_all = "camelCase")]
/// | ^^^^^
/// ...
/// 2 | #[derive(Deserialize)]
/// | ----------- the attribute is introduced here
/// ```
///
/// ### Explanation
///
/// Attributes like this work for historical reasons, but attribute expansion works in
/// left-to-right order in general, so, to resolve `#[serde]`, compiler has to try to "look
/// into the future" at not yet expanded part of the item , but such attempts are not always
/// reliable.
///
/// To fix the warning place the helper attribute after its corresponding derive.
/// ```rust,ignore (needs extern crate)
/// #[derive(Deserialize)]
/// #[serde(rename_all = "camelCase")]
/// struct S { /* fields */ }
/// ```
pub LEGACY_DERIVE_HELPERS,
Warn,
"detects derive helper attributes that are used before they are introduced",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #79202 <https://github.com/rust-lang/rust/issues/79202>",
};
}
declare_lint! {
/// The `large_assignments` lint detects when objects of large
/// types are being moved around.
///
/// ### Example
///
/// ```rust,ignore (can crash on some platforms)
/// let x = [0; 50000];
/// let y = x;
/// ```
///
/// produces:
///
/// ```text
/// warning: moving a large value
/// --> $DIR/move-large.rs:1:3
/// let y = x;
/// - Copied large value here
/// ```
///
/// ### Explanation
///
/// When using a large type in a plain assignment or in a function
/// argument, idiomatic code can be inefficient.
/// Ideally appropriate optimizations would resolve this, but such
/// optimizations are only done in a best-effort manner.
/// This lint will trigger on all sites of large moves and thus allow the
/// user to resolve them in code.
pub LARGE_ASSIGNMENTS,
Warn,
"detects large moves or copies",
}
declare_lint! {
/// The `deprecated_cfg_attr_crate_type_name` lint detects uses of the
/// `#![cfg_attr(..., crate_type = "...")]` and
/// `#![cfg_attr(..., crate_name = "...")]` attributes to conditionally
/// specify the crate type and name in the source code.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![cfg_attr(debug_assertions, crate_type = "lib")]
/// ```
///
/// {{produces}}
///
///
/// ### Explanation
///
/// The `#![crate_type]` and `#![crate_name]` attributes require a hack in
/// the compiler to be able to change the used crate type and crate name
/// after macros have been expanded. Neither attribute works in combination
/// with Cargo as it explicitly passes `--crate-type` and `--crate-name` on
/// the commandline. These values must match the value used in the source
/// code to prevent an error.
///
/// To fix the warning use `--crate-type` on the commandline when running
/// rustc instead of `#![cfg_attr(..., crate_type = "...")]` and
/// `--crate-name` instead of `#![cfg_attr(..., crate_name = "...")]`.
pub DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
Deny,
"detects usage of `#![cfg_attr(..., crate_type/crate_name = \"...\")]`",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #91632 <https://github.com/rust-lang/rust/issues/91632>",
};
}
declare_lint! {
/// The `unexpected_cfgs` lint detects unexpected conditional compilation conditions.
///
/// ### Example
///
/// ```text
/// rustc --check-cfg 'names()'
/// ```
///
/// ```rust,ignore (needs command line option)
/// #[cfg(widnows)]
/// fn foo() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: unknown condition name used
/// --> lint_example.rs:1:7
/// |
/// 1 | #[cfg(widnows)]
/// | ^^^^^^^
/// |
/// = note: `#[warn(unexpected_cfgs)]` on by default
/// ```
///
/// ### Explanation
///
/// This lint is only active when a `--check-cfg='names(...)'` option has been passed
/// to the compiler and triggers whenever an unknown condition name or value is used.
/// The known condition include names or values passed in `--check-cfg`, `--cfg`, and some
/// well-knows names and values built into the compiler.
pub UNEXPECTED_CFGS,
Warn,
"detects unexpected names and values in `#[cfg]` conditions",
}
declare_lint! {
/// The `repr_transparent_external_private_fields` lint
/// detects types marked `#[repr(transparent)]` that (transitively)
/// contain an external ZST type marked `#[non_exhaustive]` or containing
/// private fields
///
/// ### Example
///
/// ```rust,ignore (needs external crate)
/// #![deny(repr_transparent_external_private_fields)]
/// use foo::NonExhaustiveZst;
///
/// #[repr(transparent)]
/// struct Bar(u32, ([u32; 0], NonExhaustiveZst));
/// ```
///
/// This will produce:
///
/// ```text
/// error: zero-sized fields in repr(transparent) cannot contain external non-exhaustive types
/// --> src/main.rs:5:28
/// |
/// 5 | struct Bar(u32, ([u32; 0], NonExhaustiveZst));
/// | ^^^^^^^^^^^^^^^^
/// |
/// note: the lint level is defined here
/// --> src/main.rs:1:9
/// |
/// 1 | #![deny(repr_transparent_external_private_fields)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #78586 <https://github.com/rust-lang/rust/issues/78586>
/// = note: this struct contains `NonExhaustiveZst`, which is marked with `#[non_exhaustive]`, and makes it not a breaking change to become non-zero-sized in the future.
/// ```
///
/// ### Explanation
///
/// Previous, Rust accepted fields that contain external private zero-sized types,
/// even though it should not be a breaking change to add a non-zero-sized field to
/// that private type.
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #78586] for more details.
///
/// [issue #78586]: https://github.com/rust-lang/rust/issues/78586
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
Warn,
"transparent type contains an external ZST that is marked #[non_exhaustive] or contains private fields",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #78586 <https://github.com/rust-lang/rust/issues/78586>",
};
}
declare_lint! {
/// The `unstable_syntax_pre_expansion` lint detects the use of unstable
/// syntax that is discarded during attribute expansion.
///
/// ### Example
///
/// ```rust
/// #[cfg(FALSE)]
/// macro foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The input to active attributes such as `#[cfg]` or procedural macro
/// attributes is required to be valid syntax. Previously, the compiler only
/// gated the use of unstable syntax features after resolving `#[cfg]` gates
/// and expanding procedural macros.
///
/// To avoid relying on unstable syntax, move the use of unstable syntax
/// into a position where the compiler does not parse the syntax, such as a
/// functionlike macro.
///
/// ```rust
/// # #![deny(unstable_syntax_pre_expansion)]
///
/// macro_rules! identity {
/// ( $($tokens:tt)* ) => { $($tokens)* }
/// }
///
/// #[cfg(FALSE)]
/// identity! {
/// macro foo() {}
/// }
/// ```
///
/// This is a [future-incompatible] lint to transition this
/// to a hard error in the future. See [issue #65860] for more details.
///
/// [issue #65860]: https://github.com/rust-lang/rust/issues/65860
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub UNSTABLE_SYNTAX_PRE_EXPANSION,
Warn,
"unstable syntax can change at any point in the future, causing a hard error!",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #65860 <https://github.com/rust-lang/rust/issues/65860>",
};
}
declare_lint! {
/// The `ambiguous_glob_reexports` lint detects cases where names re-exported via globs
/// collide. Downstream users trying to use the same name re-exported from multiple globs
/// will receive a warning pointing out redefinition of the same name.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(ambiguous_glob_reexports)]
/// pub mod foo {
/// pub type X = u8;
/// }
///
/// pub mod bar {
/// pub type Y = u8;
/// pub type X = u8;
/// }
///
/// pub use foo::*;
/// pub use bar::*;
///
///
/// pub fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This was previously accepted but it could silently break a crate's downstream users code.
/// For example, if `foo::*` and `bar::*` were re-exported before `bar::X` was added to the
/// re-exports, down stream users could use `this_crate::X` without problems. However, adding
/// `bar::X` would cause compilation errors in downstream crates because `X` is defined
/// multiple times in the same namespace of `this_crate`.
pub AMBIGUOUS_GLOB_REEXPORTS,
Warn,
"ambiguous glob re-exports",
}
declare_lint! {
/// The `hidden_glob_reexports` lint detects cases where glob re-export items are shadowed by
/// private items.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(hidden_glob_reexports)]
///
/// pub mod upstream {
/// mod inner { pub struct Foo {}; pub struct Bar {}; }
/// pub use self::inner::*;
/// struct Foo {} // private item shadows `inner::Foo`
/// }
///
/// // mod downstream {
/// // fn test() {
/// // let _ = crate::upstream::Foo; // inaccessible
/// // }
/// // }
///
/// pub fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This was previously accepted without any errors or warnings but it could silently break a
/// crate's downstream user code. If the `struct Foo` was added, `dep::inner::Foo` would
/// silently become inaccessible and trigger a "`struct `Foo` is private`" visibility error at
/// the downstream use site.
pub HIDDEN_GLOB_REEXPORTS,
Warn,
"name introduced by a private item shadows a name introduced by a public glob re-export",
}
declare_lint_pass! {
/// Does nothing as a lint pass, but registers some `Lint`s
/// that are used by other parts of the compiler.
HardwiredLints => [
// tidy-alphabetical-start
ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
AMBIGUOUS_ASSOCIATED_ITEMS,
AMBIGUOUS_GLOB_IMPORTS,
AMBIGUOUS_GLOB_REEXPORTS,
ARITHMETIC_OVERFLOW,
ASM_SUB_REGISTER,
BAD_ASM_STYLE,
BARE_TRAIT_OBJECTS,
BINDINGS_WITH_VARIANT_NAME,
BREAK_WITH_LABEL_AND_LOOP,
BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
CENUM_IMPL_DROP_CAST,
COHERENCE_LEAK_CHECK,
COINDUCTIVE_OVERLAP_IN_COHERENCE,
CONFLICTING_REPR_HINTS,
CONST_EVALUATABLE_UNCHECKED,
CONST_ITEM_MUTATION,
CONST_PATTERNS_WITHOUT_PARTIAL_EQ,
DEAD_CODE,
DEPRECATED,
DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
DEPRECATED_IN_FUTURE,
DEPRECATED_WHERE_CLAUSE_LOCATION,
DUPLICATE_MACRO_ATTRIBUTES,
ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
ELIDED_LIFETIMES_IN_PATHS,
EXPORTED_PRIVATE_DEPENDENCIES,
FFI_UNWIND_CALLS,
FORBIDDEN_LINT_GROUPS,
FUNCTION_ITEM_REFERENCES,
FUZZY_PROVENANCE_CASTS,
HIDDEN_GLOB_REEXPORTS,
ILL_FORMED_ATTRIBUTE_INPUT,
ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
IMPLIED_BOUNDS_ENTAILMENT,
INCOMPLETE_INCLUDE,
INDIRECT_STRUCTURAL_MATCH,
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
INLINE_NO_SANITIZE,
INVALID_DOC_ATTRIBUTES,
INVALID_MACRO_EXPORT_ARGUMENTS,
INVALID_TYPE_PARAM_DEFAULT,
IRREFUTABLE_LET_PATTERNS,
LARGE_ASSIGNMENTS,
LATE_BOUND_LIFETIME_ARGUMENTS,
LEGACY_DERIVE_HELPERS,
LONG_RUNNING_CONST_EVAL,
LOSSY_PROVENANCE_CASTS,
MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
MACRO_USE_EXTERN_CRATE,
META_VARIABLE_MISUSE,
MISSING_ABI,
MISSING_FRAGMENT_SPECIFIER,
MUST_NOT_SUSPEND,
NAMED_ARGUMENTS_USED_POSITIONALLY,
NON_EXHAUSTIVE_OMITTED_PATTERNS,
NONTRIVIAL_STRUCTURAL_MATCH,
ORDER_DEPENDENT_TRAIT_OBJECTS,
OVERLAPPING_RANGE_ENDPOINTS,
PATTERNS_IN_FNS_WITHOUT_BODY,
POINTER_STRUCTURAL_MATCH,
PRIVATE_BOUNDS,
PRIVATE_INTERFACES,
PROC_MACRO_BACK_COMPAT,
PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
PUB_USE_OF_PRIVATE_EXTERN_CRATE,
REFINING_IMPL_TRAIT,
RENAMED_AND_REMOVED_LINTS,
REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
RUST_2021_INCOMPATIBLE_OR_PATTERNS,
RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
RUST_2021_PRELUDE_COLLISIONS,
SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
SINGLE_USE_LIFETIMES,
SOFT_UNSTABLE,
STABLE_FEATURES,
SUSPICIOUS_AUTO_TRAIT_IMPLS,
TEST_UNSTABLE_LINT,
TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
TRIVIAL_CASTS,
TRIVIAL_NUMERIC_CASTS,
TYVAR_BEHIND_RAW_POINTER,
UNCONDITIONAL_PANIC,
UNCONDITIONAL_RECURSION,
UNDEFINED_NAKED_FUNCTION_ABI,
UNFULFILLED_LINT_EXPECTATIONS,
UNINHABITED_STATIC,
UNKNOWN_CRATE_TYPES,
UNKNOWN_LINTS,
UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,
UNNAMEABLE_TEST_ITEMS,
UNNAMEABLE_TYPES,
UNREACHABLE_CODE,
UNREACHABLE_PATTERNS,
UNSAFE_OP_IN_UNSAFE_FN,
UNSTABLE_NAME_COLLISIONS,
UNSTABLE_SYNTAX_PRE_EXPANSION,
UNSUPPORTED_CALLING_CONVENTIONS,
UNUSED_ASSIGNMENTS,
UNUSED_ASSOCIATED_TYPE_BOUNDS,
UNUSED_ATTRIBUTES,
UNUSED_CRATE_DEPENDENCIES,
UNUSED_EXTERN_CRATES,
UNUSED_FEATURES,
UNUSED_IMPORTS,
UNUSED_LABELS,
UNUSED_LIFETIMES,
UNUSED_MACRO_RULES,
UNUSED_MACROS,
UNUSED_MUT,
UNUSED_QUALIFICATIONS,
UNUSED_TUPLE_STRUCT_FIELDS,
UNUSED_UNSAFE,
UNUSED_VARIABLES,
USELESS_DEPRECATED,
WARNINGS,
WHERE_CLAUSES_OBJECT_SAFETY,
// tidy-alphabetical-end
]
}
declare_lint! {
/// The `long_running_const_eval` lint is emitted when const
/// eval is running for a long time to ensure rustc terminates
/// even if you accidentally wrote an infinite loop.
///
/// ### Example
///
/// ```rust,compile_fail
/// const FOO: () = loop {};
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Loops allow const evaluation to compute arbitrary code, but may also
/// cause infinite loops or just very long running computations.
/// Users can enable long running computations by allowing the lint
/// on individual constants or for entire crates.
///
/// ### Unconditional warnings
///
/// Note that regardless of whether the lint is allowed or set to warn,
/// the compiler will issue warnings if constant evaluation runs significantly
/// longer than this lint's limit. These warnings are also shown to downstream
/// users from crates.io or similar registries. If you are above the lint's limit,
/// both you and downstream users might be exposed to these warnings.
/// They might also appear on compiler updates, as the compiler makes minor changes
/// about how complexity is measured: staying below the limit ensures that there
/// is enough room, and given that the lint is disabled for people who use your
/// dependency it means you will be the only one to get the warning and can put
/// out an update in your own time.
pub LONG_RUNNING_CONST_EVAL,
Deny,
"detects long const eval operations",
report_in_external_macro
}
declare_lint! {
/// The `unused_associated_type_bounds` lint is emitted when an
/// associated type bound is added to a trait object, but the associated
/// type has a `where Self: Sized` bound, and is thus unavailable on the
/// trait object anyway.
///
/// ### Example
///
/// ```rust
/// trait Foo {
/// type Bar where Self: Sized;
/// }
/// type Mop = dyn Foo<Bar = ()>;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Just like methods with `Self: Sized` bounds are unavailable on trait
/// objects, associated types can be removed from the trait object.
pub UNUSED_ASSOCIATED_TYPE_BOUNDS,
Warn,
"detects unused `Foo = Bar` bounds in `dyn Trait<Foo = Bar>`"
}
declare_lint! {
/// The `unused_doc_comments` lint detects doc comments that aren't used
/// by `rustdoc`.
///
/// ### Example
///
/// ```rust
/// /// docs for x
/// let x = 12;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `rustdoc` does not use doc comments in all positions, and so the doc
/// comment will be ignored. Try changing it to a normal comment with `//`
/// to avoid the warning.
pub UNUSED_DOC_COMMENTS,
Warn,
"detects doc comments that aren't used by rustdoc"
}
declare_lint! {
/// The `rust_2021_incompatible_closure_captures` lint detects variables that aren't completely
/// captured in Rust 2021, such that the `Drop` order of their fields may differ between
/// Rust 2018 and 2021.
///
/// It can also detect when a variable implements a trait like `Send`, but one of its fields does not,
/// and the field is captured by a closure and used with the assumption that said field implements
/// the same trait as the root variable.
///
/// ### Example of drop reorder
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_incompatible_closure_captures)]
/// # #![allow(unused)]
///
/// struct FancyInteger(i32);
///
/// impl Drop for FancyInteger {
/// fn drop(&mut self) {
/// println!("Just dropped {}", self.0);
/// }
/// }
///
/// struct Point { x: FancyInteger, y: FancyInteger }
///
/// fn main() {
/// let p = Point { x: FancyInteger(10), y: FancyInteger(20) };
///
/// let c = || {
/// let x = p.x;
/// };
///
/// c();
///
/// // ... More code ...
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the above example, `p.y` will be dropped at the end of `f` instead of
/// with `c` in Rust 2021.
///
/// ### Example of auto-trait
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_incompatible_closure_captures)]
/// use std::thread;
///
/// struct Pointer(*mut i32);
/// unsafe impl Send for Pointer {}
///
/// fn main() {
/// let mut f = 10;
/// let fptr = Pointer(&mut f as *mut i32);
/// thread::spawn(move || unsafe {
/// *fptr.0 = 20;
/// });
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In the above example, only `fptr.0` is captured in Rust 2021.
/// The field is of type `*mut i32`, which doesn't implement `Send`,
/// making the code invalid as the field cannot be sent between threads safely.
pub RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
Allow,
"detects closures affected by Rust 2021 changes",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
explain_reason: false,
};
}
declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
declare_lint! {
/// The `missing_abi` lint detects cases where the ABI is omitted from
/// extern declarations.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(missing_abi)]
///
/// extern fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Historically, Rust implicitly selected C as the ABI for extern
/// declarations. We expect to add new ABIs, like `C-unwind`, in the future,
/// though this has not yet happened, and especially with their addition
/// seeing the ABI easily will make code review easier.
pub MISSING_ABI,
Allow,
"No declared ABI for extern declaration"
}
declare_lint! {
/// The `invalid_doc_attributes` lint detects when the `#[doc(...)]` is
/// misused.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(warnings)]
///
/// pub mod submodule {
/// #![doc(test(no_crate_inject))]
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previously, incorrect usage of the `#[doc(..)]` attribute was not
/// being validated. Usually these should be rejected as a hard error,
/// but this lint was introduced to avoid breaking any existing
/// crates which included them.
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #82730] for more details.
///
/// [issue #82730]: https://github.com/rust-lang/rust/issues/82730
pub INVALID_DOC_ATTRIBUTES,
Warn,
"detects invalid `#[doc(...)]` attributes",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #82730 <https://github.com/rust-lang/rust/issues/82730>",
};
}
declare_lint! {
/// The `proc_macro_back_compat` lint detects uses of old versions of certain
/// proc-macro crates, which have hardcoded workarounds in the compiler.
///
/// ### Example
///
/// ```rust,ignore (needs-dependency)
///
/// use time_macros_impl::impl_macros;
/// struct Foo;
/// impl_macros!(Foo);
/// ```
///
/// This will produce:
///
/// ```text
/// warning: using an old version of `time-macros-impl`
/// ::: $DIR/group-compat-hack.rs:27:5
/// |
/// LL | impl_macros!(Foo);
/// | ------------------ in this macro invocation
/// |
/// = note: `#[warn(proc_macro_back_compat)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
/// = note: the `time-macros-impl` crate will stop compiling in futures version of Rust. Please update to the latest version of the `time` crate to avoid breakage
/// = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
/// ```
///
/// ### Explanation
///
/// Eventually, the backwards-compatibility hacks present in the compiler will be removed,
/// causing older versions of certain crates to stop compiling.
/// This is a [future-incompatible] lint to ease the transition to an error.
/// See [issue #83125] for more details.
///
/// [issue #83125]: https://github.com/rust-lang/rust/issues/83125
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PROC_MACRO_BACK_COMPAT,
Deny,
"detects usage of old versions of certain proc-macro crates",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #83125 <https://github.com/rust-lang/rust/issues/83125>",
};
}
declare_lint! {
/// The `rust_2021_incompatible_or_patterns` lint detects usage of old versions of or-patterns.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(rust_2021_incompatible_or_patterns)]
///
/// macro_rules! match_any {
/// ( $expr:expr , $( $( $pat:pat )|+ => $expr_arm:expr ),+ ) => {
/// match $expr {
/// $(
/// $( $pat => $expr_arm, )+
/// )+
/// }
/// };
/// }
///
/// fn main() {
/// let result: Result<i64, i32> = Err(42);
/// let int: i64 = match_any!(result, Ok(i) | Err(i) => i.into());
/// assert_eq!(int, 42);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2021, the `pat` matcher will match additional patterns, which include the `|` character.
pub RUST_2021_INCOMPATIBLE_OR_PATTERNS,
Allow,
"detects usage of old versions of or-patterns",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/or-patterns-macro-rules.html>",
};
}
declare_lint! {
/// The `rust_2021_prelude_collisions` lint detects the usage of trait methods which are ambiguous
/// with traits added to the prelude in future editions.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(rust_2021_prelude_collisions)]
///
/// trait Foo {
/// fn try_into(self) -> Result<String, !>;
/// }
///
/// impl Foo for &str {
/// fn try_into(self) -> Result<String, !> {
/// Ok(String::from(self))
/// }
/// }
///
/// fn main() {
/// let x: String = "3".try_into().unwrap();
/// // ^^^^^^^^
/// // This call to try_into matches both Foo::try_into and TryInto::try_into as
/// // `TryInto` has been added to the Rust prelude in 2021 edition.
/// println!("{x}");
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2021, one of the important introductions is the [prelude changes], which add
/// `TryFrom`, `TryInto`, and `FromIterator` into the standard library's prelude. Since this
/// results in an ambiguity as to which method/function to call when an existing `try_into`
/// method is called via dot-call syntax or a `try_from`/`from_iter` associated function
/// is called directly on a type.
///
/// [prelude changes]: https://blog.rust-lang.org/inside-rust/2021/03/04/planning-rust-2021.html#prelude-changes
pub RUST_2021_PRELUDE_COLLISIONS,
Allow,
"detects the usage of trait methods which are ambiguous with traits added to the \
prelude in future editions",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/prelude.html>",
};
}
declare_lint! {
/// The `rust_2021_prefixes_incompatible_syntax` lint detects identifiers that will be parsed as a
/// prefix instead in Rust 2021.
///
/// ### Example
///
/// ```rust,edition2018,compile_fail
/// #![deny(rust_2021_prefixes_incompatible_syntax)]
///
/// macro_rules! m {
/// (z $x:expr) => ();
/// }
///
/// m!(z"hey");
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust 2015 and 2018, `z"hey"` is two tokens: the identifier `z`
/// followed by the string literal `"hey"`. In Rust 2021, the `z` is
/// considered a prefix for `"hey"`.
///
/// This lint suggests to add whitespace between the `z` and `"hey"` tokens
/// to keep them separated in Rust 2021.
// Allow this lint -- rustdoc doesn't yet support threading edition into this lint's parser.
#[allow(rustdoc::invalid_rust_codeblocks)]
pub RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
Allow,
"identifiers that will be parsed as a prefix in Rust 2021",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionError(Edition::Edition2021),
reference: "<https://doc.rust-lang.org/nightly/edition-guide/rust-2021/reserving-syntax.html>",
};
crate_level_only
}
declare_lint! {
/// The `unsupported_calling_conventions` lint is output whenever there is a use of the
/// `stdcall`, `fastcall`, `thiscall`, `vectorcall` calling conventions (or their unwind
/// variants) on targets that cannot meaningfully be supported for the requested target.
///
/// For example `stdcall` does not make much sense for a x86_64 or, more apparently, powerpc
/// code, because this calling convention was never specified for those targets.
///
/// Historically MSVC toolchains have fallen back to the regular C calling convention for
/// targets other than x86, but Rust doesn't really see a similar need to introduce a similar
/// hack across many more targets.
///
/// ### Example
///
/// ```rust,ignore (needs specific targets)
/// extern "stdcall" fn stdcall() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: use of calling convention not supported on this target
/// --> $DIR/unsupported.rs:39:1
/// |
/// LL | extern "stdcall" fn stdcall() {}
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// |
/// = note: `#[warn(unsupported_calling_conventions)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out;
/// it will become a hard error in a future release!
/// = note: for more information, see issue ...
/// ```
///
/// ### Explanation
///
/// On most of the targets the behaviour of `stdcall` and similar calling conventions is not
/// defined at all, but was previously accepted due to a bug in the implementation of the
/// compiler.
pub UNSUPPORTED_CALLING_CONVENTIONS,
Warn,
"use of unsupported calling convention",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #87678 <https://github.com/rust-lang/rust/issues/87678>",
};
}
declare_lint! {
/// The `break_with_label_and_loop` lint detects labeled `break` expressions with
/// an unlabeled loop as their value expression.
///
/// ### Example
///
/// ```rust
/// 'label: loop {
/// break 'label loop { break 42; };
/// };
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In Rust, loops can have a label, and `break` expressions can refer to that label to
/// break out of specific loops (and not necessarily the innermost one). `break` expressions
/// can also carry a value expression, which can be another loop. A labeled `break` with an
/// unlabeled loop as its value expression is easy to confuse with an unlabeled break with
/// a labeled loop and is thus discouraged (but allowed for compatibility); use parentheses
/// around the loop expression to silence this warning. Unlabeled `break` expressions with
/// labeled loops yield a hard error, which can also be silenced by wrapping the expression
/// in parentheses.
pub BREAK_WITH_LABEL_AND_LOOP,
Warn,
"`break` expression with label and unlabeled loop as value expression"
}
declare_lint! {
/// The `non_exhaustive_omitted_patterns` lint aims to help consumers of a `#[non_exhaustive]`
/// struct or enum who want to match all of its fields/variants explicitly.
///
/// The `#[non_exhaustive]` annotation forces matches to use wildcards, so exhaustiveness
/// checking cannot be used to ensure that all fields/variants are matched explicitly. To remedy
/// this, this allow-by-default lint warns the user when a match mentions some but not all of
/// the fields/variants of a `#[non_exhaustive]` struct or enum.
///
/// ### Example
///
/// ```rust,ignore (needs separate crate)
/// // crate A
/// #[non_exhaustive]
/// pub enum Bar {
/// A,
/// B, // added variant in non breaking change
/// }
///
/// // in crate B
/// #![feature(non_exhaustive_omitted_patterns_lint)]
/// #[warn(non_exhaustive_omitted_patterns)]
/// match Bar::A {
/// Bar::A => {},
/// _ => {},
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: some variants are not matched explicitly
/// --> $DIR/reachable-patterns.rs:70:9
/// |
/// LL | match Bar::A {
/// | ^ pattern `Bar::B` not covered
/// |
/// note: the lint level is defined here
/// --> $DIR/reachable-patterns.rs:69:16
/// |
/// LL | #[warn(non_exhaustive_omitted_patterns)]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// = help: ensure that all variants are matched explicitly by adding the suggested match arms
/// = note: the matched value is of type `Bar` and the `non_exhaustive_omitted_patterns` attribute was found
/// ```
///
/// Warning: setting this to `deny` will make upstream non-breaking changes (adding fields or
/// variants to a `#[non_exhaustive]` struct or enum) break your crate. This goes against
/// expected semver behavior.
///
/// ### Explanation
///
/// Structs and enums tagged with `#[non_exhaustive]` force the user to add a (potentially
/// redundant) wildcard when pattern-matching, to allow for future addition of fields or
/// variants. The `non_exhaustive_omitted_patterns` lint detects when such a wildcard happens to
/// actually catch some fields/variants. In other words, when the match without the wildcard
/// would not be exhaustive. This lets the user be informed if new fields/variants were added.
pub NON_EXHAUSTIVE_OMITTED_PATTERNS,
Allow,
"detect when patterns of types marked `non_exhaustive` are missed",
@feature_gate = sym::non_exhaustive_omitted_patterns_lint;
}
declare_lint! {
/// The `text_direction_codepoint_in_comment` lint detects Unicode codepoints in comments that
/// change the visual representation of text on screen in a way that does not correspond to
/// their on memory representation.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(text_direction_codepoint_in_comment)]
/// fn main() {
/// println!("{:?}"); // '‮');
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Unicode allows changing the visual flow of text on screen in order to support scripts that
/// are written right-to-left, but a specially crafted comment can make code that will be
/// compiled appear to be part of a comment, depending on the software used to read the code.
/// To avoid potential problems or confusion, such as in CVE-2021-42574, by default we deny
/// their use.
pub TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
Deny,
"invisible directionality-changing codepoints in comment"
}
declare_lint! {
/// The `duplicate_macro_attributes` lint detects when a `#[test]`-like built-in macro
/// attribute is duplicated on an item. This lint may trigger on `bench`, `cfg_eval`, `test`
/// and `test_case`.
///
/// ### Example
///
/// ```rust,ignore (needs --test)
/// #[test]
/// #[test]
/// fn foo() {}
/// ```
///
/// This will produce:
///
/// ```text
/// warning: duplicated attribute
/// --> src/lib.rs:2:1
/// |
/// 2 | #[test]
/// | ^^^^^^^
/// |
/// = note: `#[warn(duplicate_macro_attributes)]` on by default
/// ```
///
/// ### Explanation
///
/// A duplicated attribute may erroneously originate from a copy-paste and the effect of it
/// being duplicated may not be obvious or desirable.
///
/// For instance, doubling the `#[test]` attributes registers the test to be run twice with no
/// change to its environment.
///
/// [issue #90979]: https://github.com/rust-lang/rust/issues/90979
pub DUPLICATE_MACRO_ATTRIBUTES,
Warn,
"duplicated attribute"
}
declare_lint! {
/// The `suspicious_auto_trait_impls` lint checks for potentially incorrect
/// implementations of auto traits.
///
/// ### Example
///
/// ```rust
/// struct Foo<T>(T);
///
/// unsafe impl<T> Send for Foo<*const T> {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A type can implement auto traits, e.g. `Send`, `Sync` and `Unpin`,
/// in two different ways: either by writing an explicit impl or if
/// all fields of the type implement that auto trait.
///
/// The compiler disables the automatic implementation if an explicit one
/// exists for given type constructor. The exact rules governing this
/// were previously unsound, quite subtle, and have been recently modified.
/// This change caused the automatic implementation to be disabled in more
/// cases, potentially breaking some code.
pub SUSPICIOUS_AUTO_TRAIT_IMPLS,
Warn,
"the rules governing auto traits have recently changed resulting in potential breakage",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
reference: "issue #93367 <https://github.com/rust-lang/rust/issues/93367>",
};
}
declare_lint! {
/// The `deprecated_where_clause_location` lint detects when a where clause in front of the equals
/// in an associated type.
///
/// ### Example
///
/// ```rust
/// trait Trait {
/// type Assoc<'a> where Self: 'a;
/// }
///
/// impl Trait for () {
/// type Assoc<'a> where Self: 'a = ();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The preferred location for where clauses on associated types
/// is after the type. However, for most of generic associated types development,
/// it was only accepted before the equals. To provide a transition period and
/// further evaluate this change, both are currently accepted. At some point in
/// the future, this may be disallowed at an edition boundary; but, that is
/// undecided currently.
pub DEPRECATED_WHERE_CLAUSE_LOCATION,
Warn,
"deprecated where clause location"
}
declare_lint! {
/// The `test_unstable_lint` lint tests unstable lints and is perma-unstable.
///
/// ### Example
///
/// ```rust
/// #![allow(test_unstable_lint)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In order to test the behavior of unstable lints, a permanently-unstable
/// lint is required. This lint can be used to trigger warnings and errors
/// from the compiler related to unstable lints.
pub TEST_UNSTABLE_LINT,
Deny,
"this unstable lint is only for testing",
@feature_gate = sym::test_unstable_lint;
}
declare_lint! {
/// The `ffi_unwind_calls` lint detects calls to foreign functions or function pointers with
/// `C-unwind` or other FFI-unwind ABIs.
///
/// ### Example
///
/// ```rust
/// #![warn(ffi_unwind_calls)]
///
/// extern "C-unwind" {
/// fn foo();
/// }
///
/// fn bar() {
/// unsafe { foo(); }
/// let ptr: unsafe extern "C-unwind" fn() = foo;
/// unsafe { ptr(); }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// For crates containing such calls, if they are compiled with `-C panic=unwind` then the
/// produced library cannot be linked with crates compiled with `-C panic=abort`. For crates
/// that desire this ability it is therefore necessary to avoid such calls.
pub FFI_UNWIND_CALLS,
Allow,
"call to foreign functions or function pointers with FFI-unwind ABI"
}
declare_lint! {
/// The `named_arguments_used_positionally` lint detects cases where named arguments are only
/// used positionally in format strings. This usage is valid but potentially very confusing.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(named_arguments_used_positionally)]
/// fn main() {
/// let _x = 5;
/// println!("{}", _x = 1); // Prints 1, will trigger lint
///
/// println!("{}", _x); // Prints 5, no lint emitted
/// println!("{_x}", _x = _x); // Prints 5, no lint emitted
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust formatting strings can refer to named arguments by their position, but this usage is
/// potentially confusing. In particular, readers can incorrectly assume that the declaration
/// of named arguments is an assignment (which would produce the unit type).
/// For backwards compatibility, this is not a hard error.
pub NAMED_ARGUMENTS_USED_POSITIONALLY,
Warn,
"named arguments in format used positionally"
}
declare_lint! {
/// The `implied_bounds_entailment` lint detects cases where the arguments of an impl method
/// have stronger implied bounds than those from the trait method it's implementing.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(implied_bounds_entailment)]
///
/// trait Trait {
/// fn get<'s>(s: &'s str, _: &'static &'static ()) -> &'static str;
/// }
///
/// impl Trait for () {
/// fn get<'s>(s: &'s str, _: &'static &'s ()) -> &'static str {
/// s
/// }
/// }
///
/// let val = <() as Trait>::get(&String::from("blah blah blah"), &&());
/// println!("{}", val);
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Neither the trait method, which provides no implied bounds about `'s`, nor the impl,
/// requires the main function to prove that 's: 'static, but the impl method is allowed
/// to assume that `'s: 'static` within its own body.
///
/// This can be used to implement an unsound API if used incorrectly.
pub IMPLIED_BOUNDS_ENTAILMENT,
Deny,
"impl method assumes more implied bounds than its corresponding trait method",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #105572 <https://github.com/rust-lang/rust/issues/105572>",
};
}
declare_lint! {
/// The `byte_slice_in_packed_struct_with_derive` lint detects cases where a byte slice field
/// (`[u8]`) or string slice field (`str`) is used in a `packed` struct that derives one or
/// more built-in traits.
///
/// ### Example
///
/// ```rust
/// #[repr(packed)]
/// #[derive(Hash)]
/// struct FlexZeroSlice {
/// width: u8,
/// data: [u8],
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This was previously accepted but is being phased out, because fields in packed structs are
/// now required to implement `Copy` for `derive` to work. Byte slices and string slices are a
/// temporary exception because certain crates depended on them.
pub BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
Warn,
"`[u8]` or `str` used in a packed struct with `derive`",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #107457 <https://github.com/rust-lang/rust/issues/107457>",
};
report_in_external_macro
}
declare_lint! {
/// The `invalid_macro_export_arguments` lint detects cases where `#[macro_export]` is being used with invalid arguments.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(invalid_macro_export_arguments)]
///
/// #[macro_export(invalid_parameter)]
/// macro_rules! myMacro {
/// () => {
/// // [...]
/// }
/// }
///
/// #[macro_export(too, many, items)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The only valid argument is `#[macro_export(local_inner_macros)]` or no argument (`#[macro_export]`).
/// You can't have multiple arguments in a `#[macro_export(..)]`, or mention arguments other than `local_inner_macros`.
///
pub INVALID_MACRO_EXPORT_ARGUMENTS,
Warn,
"\"invalid_parameter\" isn't a valid argument for `#[macro_export]`",
}
declare_lint! {
/// The `private_interfaces` lint detects types in a primary interface of an item,
/// that are more private than the item itself. Primary interface of an item is all
/// its interface except for bounds on generic parameters and where clauses.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(private_interfaces)]
/// struct SemiPriv;
///
/// mod m1 {
/// struct Priv;
/// impl crate::SemiPriv {
/// pub fn f(_: Priv) {}
/// }
/// }
///
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Having something private in primary interface guarantees that
/// the item will be unusable from outer modules due to type privacy.
pub PRIVATE_INTERFACES,
Warn,
"private type in primary interface of an item",
}
declare_lint! {
/// The `private_bounds` lint detects types in a secondary interface of an item,
/// that are more private than the item itself. Secondary interface of an item consists of
/// bounds on generic parameters and where clauses, including supertraits for trait items.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![allow(unused)]
/// #![deny(private_bounds)]
///
/// struct PrivTy;
/// pub struct S
/// where PrivTy:
/// {}
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Having private types or traits in item bounds makes it less clear what interface
/// the item actually provides.
pub PRIVATE_BOUNDS,
Warn,
"private type in secondary interface of an item",
}
declare_lint! {
/// The `unnameable_types` lint detects types for which you can get objects of that type,
/// but cannot name the type itself.
///
/// ### Example
///
/// ```rust,compile_fail
/// # #![feature(type_privacy_lints)]
/// # #![allow(unused)]
/// #![deny(unnameable_types)]
/// mod m {
/// pub struct S;
/// }
///
/// pub fn get_unnameable() -> m::S { m::S }
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// It is often expected that if you can obtain an object of type `T`, then
/// you can name the type `T` as well, this lint attempts to enforce this rule.
pub UNNAMEABLE_TYPES,
Allow,
"effective visibility of a type is larger than the area in which it can be named",
@feature_gate = sym::type_privacy_lints;
}
declare_lint! {
/// The `coinductive_overlap_in_coherence` lint detects impls which are currently
/// considered not overlapping, but may be considered to overlap if support for
/// coinduction is added to the trait solver.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(coinductive_overlap_in_coherence)]
///
/// trait CyclicTrait {}
/// impl<T: CyclicTrait> CyclicTrait for T {}
///
/// trait Trait {}
/// impl<T: CyclicTrait> Trait for T {}
/// // conflicting impl with the above
/// impl Trait for u8 {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// We have two choices for impl which satisfy `u8: Trait`: the blanket impl
/// for generic `T`, and the direct impl for `u8`. These two impls nominally
/// overlap, since we can infer `T = u8` in the former impl, but since the where
/// clause `u8: CyclicTrait` would end up resulting in a cycle (since it depends
/// on itself), the blanket impl is not considered to hold for `u8`. This will
/// change in a future release.
pub COINDUCTIVE_OVERLAP_IN_COHERENCE,
Deny,
"impls that are not considered to overlap may be considered to \
overlap in the future",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
reference: "issue #114040 <https://github.com/rust-lang/rust/issues/114040>",
};
}
declare_lint! {
/// The `unknown_or_malformed_diagnostic_attributes` lint detects unrecognized or otherwise malformed
/// diagnostic attributes.
///
/// ### Example
///
/// ```rust
/// #![feature(diagnostic_namespace)]
/// #[diagnostic::does_not_exist]
/// struct Foo;
/// ```
///
/// {{produces}}
///
///
/// ### Explanation
///
/// It is usually a mistake to specify a diagnostic attribute that does not exist. Check
/// the spelling, and check the diagnostic attribute listing for the correct name. Also
/// consider if you are using an old version of the compiler, and the attribute
/// is only available in a newer version.
pub UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,
Warn,
"unrecognized or malformed diagnostic attribute",
@feature_gate = sym::diagnostic_namespace;
}
declare_lint! {
/// The `ambiguous_glob_imports` lint detects glob imports that should report ambiguity
/// errors, but previously didn't do that due to rustc bugs.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(ambiguous_glob_imports)]
/// pub fn foo() -> u32 {
/// use sub::*;
/// C
/// }
///
/// mod sub {
/// mod mod1 { pub const C: u32 = 1; }
/// mod mod2 { pub const C: u32 = 2; }
///
/// pub use mod1::*;
/// pub use mod2::*;
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous versions of Rust compile it successfully because it
/// had lost the ambiguity error when resolve `use sub::mod2::*`.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub AMBIGUOUS_GLOB_IMPORTS,
Warn,
"detects certain glob imports that require reporting an ambiguity error",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #114095 <https://github.com/rust-lang/rust/issues/114095>",
};
}
declare_lint! {
/// The `refining_impl_trait` lint detects usages of return-position impl
/// traits in trait signatures which are refined by implementations.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(refining_impl_trait)]
///
/// use std::fmt::Display;
///
/// pub trait AsDisplay {
/// fn as_display(&self) -> impl Display;
/// }
///
/// impl<'s> AsDisplay for &'s str {
/// fn as_display(&self) -> Self {
/// *self
/// }
/// }
///
/// fn main() {
/// // users can observe that the return type of
/// // `<&str as AsDisplay>::as_display()` is `&str`.
/// let x: &str = "".as_display();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Return-position impl trait in traits (RPITITs) desugar to associated types,
/// and callers of methods for types where the implementation is known are
/// able to observe the types written in the impl signature. This may be
/// intended behavior, but may also pose a semver hazard for authors of libraries
/// who do not wish to make stronger guarantees about the types than what is
/// written in the trait signature.
pub REFINING_IMPL_TRAIT,
Warn,
"impl trait in impl method signature does not match trait method signature",
}
declare_lint! {
/// The `elided_lifetimes_in_associated_constant` lint detects elided lifetimes
/// that were erroneously allowed in associated constants.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(elided_lifetimes_in_associated_constant)]
///
/// struct Foo;
///
/// impl Foo {
/// const STR: &str = "hello, world";
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous version of Rust
///
/// Implicit static-in-const behavior was decided [against] for associated
/// constants because of ambiguity. This, however, regressed and the compiler
/// erroneously treats elided lifetimes in associated constants as lifetime
/// parameters on the impl.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [against]: https://github.com/rust-lang/rust/issues/38831
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
Warn,
"elided lifetimes cannot be used in associated constants in impls",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
reference: "issue #115010 <https://github.com/rust-lang/rust/issues/115010>",
};
}