src/tools/clippy/clippy_lints/src/ptr.rs - toolchain/rustc - Git at Google

 //! Checks for usage of  `&Vec[_]` and `&String`.

 use crate::utils::ptr::get_spans;
 use crate::utils::{
     is_type_diagnostic_item, match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then,
     walk_ptrs_hir_ty,
 };
 use if_chain::if_chain;
 use rustc::hir::QPath;
 use rustc::hir::*;
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
 use rustc::ty;
 use rustc::{declare_lint_pass, declare_tool_lint};
 use rustc_errors::Applicability;
 use std::borrow::Cow;
 use syntax::source_map::Span;
 use syntax_pos::{MultiSpan, Symbol};

 declare_clippy_lint! {
     /// **What it does:** This lint checks for function arguments of type `&String`
     /// or `&Vec` unless the references are mutable. It will also suggest you
     /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
     /// calls.
     ///
     /// **Why is this bad?** Requiring the argument to be of the specific size
     /// makes the function less useful for no benefit; slices in the form of `&[T]`
     /// or `&str` usually suffice and can be obtained from other types, too.
     ///
     /// **Known problems:** The lint does not follow data. So if you have an
     /// argument `x` and write `let y = x; y.clone()` the lint will not suggest
     /// changing that `.clone()` to `.to_owned()`.
     ///
     /// Other functions called from this function taking a `&String` or `&Vec`
     /// argument may also fail to compile if you change the argument. Applying
     /// this lint on them will fix the problem, but they may be in other crates.
     ///
     /// Also there may be `fn(&Vec)`-typed references pointing to your function.
     /// If you have them, you will get a compiler error after applying this lint's
     /// suggestions. You then have the choice to undo your changes or change the
     /// type of the reference.
     ///
     /// Note that if the function is part of your public interface, there may be
     /// other crates referencing it you may not be aware. Carefully deprecate the
     /// function before applying the lint suggestions in this case.
     ///
     /// **Example:**
     /// ```ignore
     /// fn foo(&Vec<u32>) { .. }
     /// ```
     pub PTR_ARG,
     style,
     "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
 }

 declare_clippy_lint! {
     /// **What it does:** This lint checks for equality comparisons with `ptr::null`
     ///
     /// **Why is this bad?** It's easier and more readable to use the inherent
     /// `.is_null()`
     /// method instead
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     /// ```ignore
     /// if x == ptr::null {
     ///     ..
     /// }
     /// ```
     pub CMP_NULL,
     style,
     "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
 }

 declare_clippy_lint! {
     /// **What it does:** This lint checks for functions that take immutable
     /// references and return
     /// mutable ones.
     ///
     /// **Why is this bad?** This is trivially unsound, as one can create two
     /// mutable references
     /// from the same (immutable!) source. This
     /// [error](https://github.com/rust-lang/rust/issues/39465)
     /// actually lead to an interim Rust release 1.15.1.
     ///
     /// **Known problems:** To be on the conservative side, if there's at least one
     /// mutable reference
     /// with the output lifetime, this lint will not trigger. In practice, this
     /// case is unlikely anyway.
     ///
     /// **Example:**
     /// ```ignore
     /// fn foo(&Foo) -> &mut Bar { .. }
     /// ```
     pub MUT_FROM_REF,
     correctness,
     "fns that create mutable refs from immutable ref args"
 }

 declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);

 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ptr {
     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
         if let ItemKind::Fn(ref decl, _, _, body_id) = item.kind {
             check_fn(cx, decl, item.hir_id, Some(body_id));
         }
     }

     fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
         if let ImplItemKind::Method(ref sig, body_id) = item.kind {
             let parent_item = cx.tcx.hir().get_parent_item(item.hir_id);
             if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
                 if let ItemKind::Impl(_, _, _, _, Some(_), _, _) = it.kind {
                     return; // ignore trait impls
                 }
             }
             check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
         }
     }

     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
         if let TraitItemKind::Method(ref sig, ref trait_method) = item.kind {
             let body_id = if let TraitMethod::Provided(b) = *trait_method {
                 Some(b)
             } else {
                 None
             };
             check_fn(cx, &sig.decl, item.hir_id, body_id);
         }
     }

     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
         if let ExprKind::Binary(ref op, ref l, ref r) = expr.kind {
             if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
                 span_lint(
                     cx,
                     CMP_NULL,
                     expr.span,
                     "Comparing with null is better expressed by the .is_null() method",
                 );
             }
         }
     }
 }

 #[allow(clippy::too_many_lines)]
 fn check_fn(cx: &LateContext<'_, '_>, decl: &FnDecl, fn_id: HirId, opt_body_id: Option<BodyId>) {
     let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
     let sig = cx.tcx.fn_sig(fn_def_id);
     let fn_ty = sig.skip_binder();

     for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
         if let ty::Ref(_, ty, MutImmutable) = ty.kind {
             if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) {
                 let mut ty_snippet = None;
                 if_chain! {
                     if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).kind;
                     if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
                     then {
                         let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
                             GenericArg::Type(ty) => Some(ty),
                             _ => None,
                         }).collect();
                         if types.len() == 1 {
                             ty_snippet = snippet_opt(cx, types[0].span);
                         }
                     }
                 };
                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
                     span_lint_and_then(
                         cx,
                         PTR_ARG,
                         arg.span,
                         "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
                          with non-Vec-based slices.",
                         |db| {
                             if let Some(ref snippet) = ty_snippet {
                                 db.span_suggestion(
                                     arg.span,
                                     "change this to",
                                     format!("&[{}]", snippet),
                                     Applicability::Unspecified,
                                 );
                             }
                             for (clonespan, suggestion) in spans {
                                 db.span_suggestion(
                                     clonespan,
                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
                                         Cow::Owned(format!("change `{}` to", x))
                                     }),
                                     suggestion.into(),
                                     Applicability::Unspecified,
                                 );
                             }
                         },
                     );
                 }
             } else if match_type(cx, ty, &paths::STRING) {
                 if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
                     span_lint_and_then(
                         cx,
                         PTR_ARG,
                         arg.span,
                         "writing `&String` instead of `&str` involves a new object where a slice will do.",
                         |db| {
                             db.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
                             for (clonespan, suggestion) in spans {
                                 db.span_suggestion_short(
                                     clonespan,
                                     &snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
                                         Cow::Owned(format!("change `{}` to", x))
                                     }),
                                     suggestion.into(),
                                     Applicability::Unspecified,
                                 );
                             }
                         },
                     );
                 }
             } else if match_type(cx, ty, &paths::COW) {
                 if_chain! {
                     if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.kind;
                     if let TyKind::Path(ref path) = ty.kind;
                     if let QPath::Resolved(None, ref pp) = *path;
                     if let [ref bx] = *pp.segments;
                     if let Some(ref params) = bx.args;
                     if !params.parenthesized;
                     if let Some(inner) = params.args.iter().find_map(|arg| match arg {
                         GenericArg::Type(ty) => Some(ty),
                         _ => None,
                     });
                     then {
                         let replacement = snippet_opt(cx, inner.span);
                         if let Some(r) = replacement {
                             span_lint_and_then(
                                 cx,
                                 PTR_ARG,
                                 arg.span,
                                 "using a reference to `Cow` is not recommended.",
                                 |db| {
                                     db.span_suggestion(
                                         arg.span,
                                         "change this to",
                                         "&".to_owned() + &r,
                                         Applicability::Unspecified,
                                     );
                                 },
                             );
                         }
                     }
                 }
             }
         }
     }

     if let FunctionRetTy::Return(ref ty) = decl.output {
         if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
             let mut immutables = vec![];
             for (_, ref mutbl, ref argspan) in decl
                 .inputs
                 .iter()
                 .filter_map(|ty| get_rptr_lm(ty))
                 .filter(|&(lt, _, _)| lt.name == out.name)
             {
                 if *mutbl == MutMutable {
                     return;
                 }
                 immutables.push(*argspan);
             }
             if immutables.is_empty() {
                 return;
             }
             span_lint_and_then(
                 cx,
                 MUT_FROM_REF,
                 ty.span,
                 "mutable borrow from immutable input(s)",
                 |db| {
                     let ms = MultiSpan::from_spans(immutables);
                     db.span_note(ms, "immutable borrow here");
                 },
             );
         }
     }
 }

 fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
     if let TyKind::Rptr(ref lt, ref m) = ty.kind {
         Some((lt, m.mutbl, ty.span))
     } else {
         None
     }
 }

 fn is_null_path(expr: &Expr) -> bool {
     if let ExprKind::Call(ref pathexp, ref args) = expr.kind {
         if args.is_empty() {
             if let ExprKind::Path(ref path) = pathexp.kind {
                 return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);
             }
         }
     }
     false
 }
	//! Checks for usage of `&Vec[_]` and `&String`.

	use crate::utils::ptr::get_spans;
	use crate::utils::{
	is_type_diagnostic_item, match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then,
	walk_ptrs_hir_ty,
	};
	use if_chain::if_chain;
	use rustc::hir::QPath;
	use rustc::hir::*;
	use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
	use rustc::ty;
	use rustc::{declare_lint_pass, declare_tool_lint};
	use rustc_errors::Applicability;
	use std::borrow::Cow;
	use syntax::source_map::Span;
	use syntax_pos::{MultiSpan, Symbol};

	declare_clippy_lint! {
	/// What it does: This lint checks for function arguments of type `&String`
	/// or `&Vec` unless the references are mutable. It will also suggest you
	/// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
	/// calls.
	///
	/// Why is this bad? Requiring the argument to be of the specific size
	/// makes the function less useful for no benefit; slices in the form of `&[T]`
	/// or `&str` usually suffice and can be obtained from other types, too.
	///
	/// Known problems: The lint does not follow data. So if you have an
	/// argument `x` and write `let y = x; y.clone()` the lint will not suggest
	/// changing that `.clone()` to `.to_owned()`.
	///
	/// Other functions called from this function taking a `&String` or `&Vec`
	/// argument may also fail to compile if you change the argument. Applying
	/// this lint on them will fix the problem, but they may be in other crates.
	///
	/// Also there may be `fn(&Vec)`-typed references pointing to your function.
	/// If you have them, you will get a compiler error after applying this lint's
	/// suggestions. You then have the choice to undo your changes or change the
	/// type of the reference.
	///
	/// Note that if the function is part of your public interface, there may be
	/// other crates referencing it you may not be aware. Carefully deprecate the
	/// function before applying the lint suggestions in this case.
	///
	/// Example:
	/// ```ignore
	/// fn foo(&Vec<u32>) { .. }
	/// ```
	pub PTR_ARG,
	style,
	"fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
	}

	declare_clippy_lint! {
	/// What it does: This lint checks for equality comparisons with `ptr::null`
	///
	/// Why is this bad? It's easier and more readable to use the inherent
	/// `.is_null()`
	/// method instead
	///
	/// Known problems: None.
	///
	/// Example:
	/// ```ignore
	/// if x == ptr::null {
	/// ..
	/// }
	/// ```
	pub CMP_NULL,
	style,
	"comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
	}

	declare_clippy_lint! {
	/// What it does: This lint checks for functions that take immutable
	/// references and return
	/// mutable ones.
	///
	/// Why is this bad? This is trivially unsound, as one can create two
	/// mutable references
	/// from the same (immutable!) source. This
	/// [error](https://github.com/rust-lang/rust/issues/39465)
	/// actually lead to an interim Rust release 1.15.1.
	///
	/// Known problems: To be on the conservative side, if there's at least one
	/// mutable reference
	/// with the output lifetime, this lint will not trigger. In practice, this
	/// case is unlikely anyway.
	///
	/// Example:
	/// ```ignore
	/// fn foo(&Foo) -> &mut Bar { .. }
	/// ```
	pub MUT_FROM_REF,
	correctness,
	"fns that create mutable refs from immutable ref args"
	}

	declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);

	impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ptr {
	fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
	if let ItemKind::Fn(ref decl, _, _, body_id) = item.kind {
	check_fn(cx, decl, item.hir_id, Some(body_id));
	}
	}

	fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
	if let ImplItemKind::Method(ref sig, body_id) = item.kind {
	let parent_item = cx.tcx.hir().get_parent_item(item.hir_id);
	if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
	if let ItemKind::Impl(_, _, _, _, Some(_), _, _) = it.kind {
	return; // ignore trait impls
	}
	}
	check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
	}
	}

	fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
	if let TraitItemKind::Method(ref sig, ref trait_method) = item.kind {
	let body_id = if let TraitMethod::Provided(b) = *trait_method {
	Some(b)
	} else {
	None
	};
	check_fn(cx, &sig.decl, item.hir_id, body_id);
	}
	}

	fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
	if let ExprKind::Binary(ref op, ref l, ref r) = expr.kind {
	if (op.node == BinOpKind::Eq \|\| op.node == BinOpKind::Ne) && (is_null_path(l) \|\| is_null_path(r)) {
	span_lint(
	cx,
	CMP_NULL,
	expr.span,
	"Comparing with null is better expressed by the .is_null() method",
	);
	}
	}
	}
	}

	#[allow(clippy::too_many_lines)]
	fn check_fn(cx: &LateContext<'_, '_>, decl: &FnDecl, fn_id: HirId, opt_body_id: Option<BodyId>) {
	let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
	let sig = cx.tcx.fn_sig(fn_def_id);
	let fn_ty = sig.skip_binder();

	for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
	if let ty::Ref(_, ty, MutImmutable) = ty.kind {
	if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) {
	let mut ty_snippet = None;
	if_chain! {
	if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).kind;
	if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
	then {
	let types: Vec<_> = parameters.args.iter().filter_map(\|arg\| match arg {
	GenericArg::Type(ty) => Some(ty),
	_ => None,
	}).collect();
	if types.len() == 1 {
	ty_snippet = snippet_opt(cx, types[0].span);
	}
	}
	};
	if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
	span_lint_and_then(
	cx,
	PTR_ARG,
	arg.span,
	"writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
	with non-Vec-based slices.",
	\|db\| {
	if let Some(ref snippet) = ty_snippet {
	db.span_suggestion(
	arg.span,
	"change this to",
	format!("&[{}]", snippet),
	Applicability::Unspecified,
	);
	}
	for (clonespan, suggestion) in spans {
	db.span_suggestion(
	clonespan,
	&snippet_opt(cx, clonespan).map_or("change the call to".into(), \|x\| {
	Cow::Owned(format!("change `{}` to", x))
	}),
	suggestion.into(),
	Applicability::Unspecified,
	);
	}
	},
	);
	}
	} else if match_type(cx, ty, &paths::STRING) {
	if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
	span_lint_and_then(
	cx,
	PTR_ARG,
	arg.span,
	"writing `&String` instead of `&str` involves a new object where a slice will do.",
	\|db\| {
	db.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
	for (clonespan, suggestion) in spans {
	db.span_suggestion_short(
	clonespan,
	&snippet_opt(cx, clonespan).map_or("change the call to".into(), \|x\| {
	Cow::Owned(format!("change `{}` to", x))
	}),
	suggestion.into(),
	Applicability::Unspecified,
	);
	}
	},
	);
	}
	} else if match_type(cx, ty, &paths::COW) {
	if_chain! {
	if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.kind;
	if let TyKind::Path(ref path) = ty.kind;
	if let QPath::Resolved(None, ref pp) = *path;
	if let [ref bx] = *pp.segments;
	if let Some(ref params) = bx.args;
	if !params.parenthesized;
	if let Some(inner) = params.args.iter().find_map(\|arg\| match arg {
	GenericArg::Type(ty) => Some(ty),
	_ => None,
	});
	then {
	let replacement = snippet_opt(cx, inner.span);
	if let Some(r) = replacement {
	span_lint_and_then(
	cx,
	PTR_ARG,
	arg.span,
	"using a reference to `Cow` is not recommended.",
	\|db\| {
	db.span_suggestion(
	arg.span,
	"change this to",
	"&".to_owned() + &r,
	Applicability::Unspecified,
	);
	},
	);
	}
	}
	}
	}
	}
	}

	if let FunctionRetTy::Return(ref ty) = decl.output {
	if let Some((out, MutMutable, _)) = get_rptr_lm(ty) {
	let mut immutables = vec![];
	for (_, ref mutbl, ref argspan) in decl
	.inputs
	.iter()
	.filter_map(\|ty\| get_rptr_lm(ty))
	.filter(\|&(lt, _, _)\| lt.name == out.name)
	{
	if *mutbl == MutMutable {
	return;
	}
	immutables.push(*argspan);
	}
	if immutables.is_empty() {
	return;
	}
	span_lint_and_then(
	cx,
	MUT_FROM_REF,
	ty.span,
	"mutable borrow from immutable input(s)",
	\|db\| {
	let ms = MultiSpan::from_spans(immutables);
	db.span_note(ms, "immutable borrow here");
	},
	);
	}
	}
	}

	fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> {
	if let TyKind::Rptr(ref lt, ref m) = ty.kind {
	Some((lt, m.mutbl, ty.span))
	} else {
	None
	}
	}

	fn is_null_path(expr: &Expr) -> bool {
	if let ExprKind::Call(ref pathexp, ref args) = expr.kind {
	if args.is_empty() {
	if let ExprKind::Path(ref path) = pathexp.kind {
	return match_qpath(path, &paths::PTR_NULL) \|\| match_qpath(path, &paths::PTR_NULL_MUT);
	}
	}
	}
	false
	}