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

 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::macros::{find_format_args, format_arg_removal_span, root_macro_call_first_node, MacroCall};
 use clippy_utils::source::{expand_past_previous_comma, snippet_opt};
 use clippy_utils::{is_in_cfg_test, is_in_test_function};
 use rustc_ast::token::LitKind;
 use rustc_ast::{FormatArgPosition, FormatArgs, FormatArgsPiece, FormatOptions, FormatPlaceholder, FormatTrait};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, Impl, Item, ItemKind};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{sym, BytePos};

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns when you use `println!("")` to
     /// print a newline.
     ///
     /// ### Why is this bad?
     /// You should use `println!()`, which is simpler.
     ///
     /// ### Example
     /// ```rust
     /// println!("");
     /// ```
     ///
     /// Use instead:
     /// ```rust
     /// println!();
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub PRINTLN_EMPTY_STRING,
     style,
     "using `println!(\"\")` with an empty string"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns when you use `print!()` with a format
     /// string that ends in a newline.
     ///
     /// ### Why is this bad?
     /// You should use `println!()` instead, which appends the
     /// newline.
     ///
     /// ### Example
     /// ```rust
     /// # let name = "World";
     /// print!("Hello {}!\n", name);
     /// ```
     /// use println!() instead
     /// ```rust
     /// # let name = "World";
     /// println!("Hello {}!", name);
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub PRINT_WITH_NEWLINE,
     style,
     "using `print!()` with a format string that ends in a single newline"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for printing on *stdout*. The purpose of this lint
     /// is to catch debugging remnants.
     ///
     /// ### Why is this bad?
     /// People often print on *stdout* while debugging an
     /// application and might forget to remove those prints afterward.
     ///
     /// ### Known problems
     /// Only catches `print!` and `println!` calls.
     ///
     /// ### Example
     /// ```rust
     /// println!("Hello world!");
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub PRINT_STDOUT,
     restriction,
     "printing on stdout"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for printing on *stderr*. The purpose of this lint
     /// is to catch debugging remnants.
     ///
     /// ### Why is this bad?
     /// People often print on *stderr* while debugging an
     /// application and might forget to remove those prints afterward.
     ///
     /// ### Known problems
     /// Only catches `eprint!` and `eprintln!` calls.
     ///
     /// ### Example
     /// ```rust
     /// eprintln!("Hello world!");
     /// ```
     #[clippy::version = "1.50.0"]
     pub PRINT_STDERR,
     restriction,
     "printing on stderr"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for usage of `Debug` formatting. The purpose of this
     /// lint is to catch debugging remnants.
     ///
     /// ### Why is this bad?
     /// The purpose of the `Debug` trait is to facilitate
     /// debugging Rust code. It should not be used in user-facing output.
     ///
     /// ### Example
     /// ```rust
     /// # let foo = "bar";
     /// println!("{:?}", foo);
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub USE_DEBUG,
     restriction,
     "use of `Debug`-based formatting"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns about the use of literals as `print!`/`println!` args.
     ///
     /// ### Why is this bad?
     /// Using literals as `println!` args is inefficient
     /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
     /// (i.e., just put the literal in the format string)
     ///
     /// ### Example
     /// ```rust
     /// println!("{}", "foo");
     /// ```
     /// use the literal without formatting:
     /// ```rust
     /// println!("foo");
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub PRINT_LITERAL,
     style,
     "printing a literal with a format string"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns when you use `writeln!(buf, "")` to
     /// print a newline.
     ///
     /// ### Why is this bad?
     /// You should use `writeln!(buf)`, which is simpler.
     ///
     /// ### Example
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// writeln!(buf, "");
     /// ```
     ///
     /// Use instead:
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// writeln!(buf);
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub WRITELN_EMPTY_STRING,
     style,
     "using `writeln!(buf, \"\")` with an empty string"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns when you use `write!()` with a format
     /// string that
     /// ends in a newline.
     ///
     /// ### Why is this bad?
     /// You should use `writeln!()` instead, which appends the
     /// newline.
     ///
     /// ### Example
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// # let name = "World";
     /// write!(buf, "Hello {}!\n", name);
     /// ```
     ///
     /// Use instead:
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// # let name = "World";
     /// writeln!(buf, "Hello {}!", name);
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub WRITE_WITH_NEWLINE,
     style,
     "using `write!()` with a format string that ends in a single newline"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// This lint warns about the use of literals as `write!`/`writeln!` args.
     ///
     /// ### Why is this bad?
     /// Using literals as `writeln!` args is inefficient
     /// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
     /// (i.e., just put the literal in the format string)
     ///
     /// ### Example
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// writeln!(buf, "{}", "foo");
     /// ```
     ///
     /// Use instead:
     /// ```rust
     /// # use std::fmt::Write;
     /// # let mut buf = String::new();
     /// writeln!(buf, "foo");
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub WRITE_LITERAL,
     style,
     "writing a literal with a format string"
 }

 #[derive(Default)]
 pub struct Write {
     in_debug_impl: bool,
     allow_print_in_tests: bool,
 }

 impl Write {
     pub fn new(allow_print_in_tests: bool) -> Self {
         Self {
             allow_print_in_tests,
             ..Default::default()
         }
     }
 }

 impl_lint_pass!(Write => [
     PRINT_WITH_NEWLINE,
     PRINTLN_EMPTY_STRING,
     PRINT_STDOUT,
     PRINT_STDERR,
     USE_DEBUG,
     PRINT_LITERAL,
     WRITE_WITH_NEWLINE,
     WRITELN_EMPTY_STRING,
     WRITE_LITERAL,
 ]);

 impl<'tcx> LateLintPass<'tcx> for Write {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
         if is_debug_impl(cx, item) {
             self.in_debug_impl = true;
         }
     }

     fn check_item_post(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
         if is_debug_impl(cx, item) {
             self.in_debug_impl = false;
         }
     }

     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         let Some(macro_call) = root_macro_call_first_node(cx, expr) else {
             return;
         };
         let Some(diag_name) = cx.tcx.get_diagnostic_name(macro_call.def_id) else {
             return;
         };
         let Some(name) = diag_name.as_str().strip_suffix("_macro") else {
             return;
         };

         let is_build_script = cx
             .sess()
             .opts
             .crate_name
             .as_ref()
             .map_or(false, |crate_name| crate_name == "build_script_build");

         let allowed_in_tests = self.allow_print_in_tests
             && (is_in_test_function(cx.tcx, expr.hir_id) || is_in_cfg_test(cx.tcx, expr.hir_id));
         match diag_name {
             sym::print_macro | sym::println_macro if !allowed_in_tests => {
                 if !is_build_script {
                     span_lint(cx, PRINT_STDOUT, macro_call.span, &format!("use of `{name}!`"));
                 }
             },
             sym::eprint_macro | sym::eprintln_macro if !allowed_in_tests => {
                 span_lint(cx, PRINT_STDERR, macro_call.span, &format!("use of `{name}!`"));
             },
             sym::write_macro | sym::writeln_macro => {},
             _ => return,
         }

         find_format_args(cx, expr, macro_call.expn, |format_args| {
             // ignore `writeln!(w)` and `write!(v, some_macro!())`
             if format_args.span.from_expansion() {
                 return;
             }

             match diag_name {
                 sym::print_macro | sym::eprint_macro | sym::write_macro => {
                     check_newline(cx, format_args, &macro_call, name);
                 },
                 sym::println_macro | sym::eprintln_macro | sym::writeln_macro => {
                     check_empty_string(cx, format_args, &macro_call, name);
                 },
                 _ => {},
             }

             check_literal(cx, format_args, name);

             if !self.in_debug_impl {
                 for piece in &format_args.template {
                     if let &FormatArgsPiece::Placeholder(FormatPlaceholder {
                         span: Some(span),
                         format_trait: FormatTrait::Debug,
                         ..
                     }) = piece
                     {
                         span_lint(cx, USE_DEBUG, span, "use of `Debug`-based formatting");
                     }
                 }
             }
         });
     }
 }

 fn is_debug_impl(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
     if let ItemKind::Impl(Impl { of_trait: Some(trait_ref), .. }) = &item.kind
         && let Some(trait_id) = trait_ref.trait_def_id()
     {
         cx.tcx.is_diagnostic_item(sym::Debug, trait_id)
     } else {
         false
     }
 }

 fn check_newline(cx: &LateContext<'_>, format_args: &FormatArgs, macro_call: &MacroCall, name: &str) {
     let Some(FormatArgsPiece::Literal(last)) = format_args.template.last() else {
         return;
     };

     let count_vertical_whitespace = || {
         format_args
             .template
             .iter()
             .filter_map(|piece| match piece {
                 FormatArgsPiece::Literal(literal) => Some(literal),
                 FormatArgsPiece::Placeholder(_) => None,
             })
             .flat_map(|literal| literal.as_str().chars())
             .filter(|ch| matches!(ch, '\r' | '\n'))
             .count()
     };

     if last.as_str().ends_with('\n')
         // ignore format strings with other internal vertical whitespace
         && count_vertical_whitespace() == 1
     {
         let mut format_string_span = format_args.span;

         let lint = if name == "write" {
             format_string_span = expand_past_previous_comma(cx, format_string_span);

             WRITE_WITH_NEWLINE
         } else {
             PRINT_WITH_NEWLINE
         };

         span_lint_and_then(
             cx,
             lint,
             macro_call.span,
             &format!("using `{name}!()` with a format string that ends in a single newline"),
             |diag| {
                 let name_span = cx.sess().source_map().span_until_char(macro_call.span, '!');
                 let Some(format_snippet) = snippet_opt(cx, format_string_span) else {
                     return;
                 };

                 if format_args.template.len() == 1 && last.as_str() == "\n" {
                     // print!("\n"), write!(f, "\n")

                     diag.multipart_suggestion(
                         format!("use `{name}ln!` instead"),
                         vec![(name_span, format!("{name}ln")), (format_string_span, String::new())],
                         Applicability::MachineApplicable,
                     );
                 } else if format_snippet.ends_with("\\n\"") {
                     // print!("...\n"), write!(f, "...\n")

                     let hi = format_string_span.hi();
                     let newline_span = format_string_span.with_lo(hi - BytePos(3)).with_hi(hi - BytePos(1));

                     diag.multipart_suggestion(
                         format!("use `{name}ln!` instead"),
                         vec![(name_span, format!("{name}ln")), (newline_span, String::new())],
                         Applicability::MachineApplicable,
                     );
                 }
             },
         );
     }
 }

 fn check_empty_string(cx: &LateContext<'_>, format_args: &FormatArgs, macro_call: &MacroCall, name: &str) {
     if let [FormatArgsPiece::Literal(literal)] = &format_args.template[..]
         && literal.as_str() == "\n"
     {
         let mut span = format_args.span;

         let lint = if name == "writeln" {
             span = expand_past_previous_comma(cx, span);

             WRITELN_EMPTY_STRING
         } else {
             PRINTLN_EMPTY_STRING
         };

         span_lint_and_then(
             cx,
             lint,
             macro_call.span,
             &format!("empty string literal in `{name}!`"),
             |diag| {
                 diag.span_suggestion(
                     span,
                     "remove the empty string",
                     String::new(),
                     Applicability::MachineApplicable,
                 );
             },
         );
     }
 }

 fn check_literal(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
     let arg_index = |argument: &FormatArgPosition| argument.index.unwrap_or_else(|pos| pos);

     let mut counts = vec![0u32; format_args.arguments.all_args().len()];
     for piece in &format_args.template {
         if let FormatArgsPiece::Placeholder(placeholder) = piece {
             counts[arg_index(&placeholder.argument)] += 1;
         }
     }

     for piece in &format_args.template {
         if let FormatArgsPiece::Placeholder(FormatPlaceholder {
             argument,
             span: Some(placeholder_span),
             format_trait: FormatTrait::Display,
             format_options,
         }) = piece
             && *format_options == FormatOptions::default()
             && let index = arg_index(argument)
             && counts[index] == 1
             && let Some(arg) = format_args.arguments.by_index(index)
             && let rustc_ast::ExprKind::Lit(lit) = &arg.expr.kind
             && !arg.expr.span.from_expansion()
             && let Some(value_string) = snippet_opt(cx, arg.expr.span)
     {
             let (replacement, replace_raw) = match lit.kind {
                 LitKind::Str | LitKind::StrRaw(_)  => match extract_str_literal(&value_string) {
                     Some(extracted) => extracted,
                     None => return,
                 },
                 LitKind::Char => (
                     match lit.symbol.as_str() {
                         "\"" => "\\\"",
                         "\\'" => "'",
                         _ => match value_string.strip_prefix('\'').and_then(|s| s.strip_suffix('\'')) {
                             Some(stripped) => stripped,
                             None => return,
                         },
                     }
                     .to_string(),
                     false,
                 ),
                 LitKind::Bool => (lit.symbol.to_string(), false),
                 _ => continue,
             };

             let lint = if name.starts_with("write") {
                 WRITE_LITERAL
             } else {
                 PRINT_LITERAL
             };

             let Some(format_string_snippet) = snippet_opt(cx, format_args.span) else { continue };
             let format_string_is_raw = format_string_snippet.starts_with('r');

             let replacement = match (format_string_is_raw, replace_raw) {
                 (false, false) => Some(replacement),
                 (false, true) => Some(replacement.replace('"', "\\\"").replace('\\', "\\\\")),
                 (true, false) => match conservative_unescape(&replacement) {
                     Ok(unescaped) => Some(unescaped),
                     Err(UnescapeErr::Lint) => None,
                     Err(UnescapeErr::Ignore) => continue,
                 },
                 (true, true) => {
                     if replacement.contains(['#', '"']) {
                         None
                     } else {
                         Some(replacement)
                     }
                 },
             };

             span_lint_and_then(
                 cx,
                 lint,
                 arg.expr.span,
                 "literal with an empty format string",
                 |diag| {
                     if let Some(replacement) = replacement
                         // `format!("{}", "a")`, `format!("{named}", named = "b")
                         //              ~~~~~                      ~~~~~~~~~~~~~
                         && let Some(removal_span) = format_arg_removal_span(format_args, index)
                     {
                         let replacement = replacement.replace('{', "{{").replace('}', "}}");
                         diag.multipart_suggestion(
                             "try",
                             vec![(*placeholder_span, replacement), (removal_span, String::new())],
                             Applicability::MachineApplicable,
                         );
                     }
                 },
             );

         }
     }
 }

 /// Removes the raw marker, `#`s and quotes from a str, and returns if the literal is raw
 ///
 /// `r#"a"#` -> (`a`, true)
 ///
 /// `"b"` -> (`b`, false)
 fn extract_str_literal(literal: &str) -> Option<(String, bool)> {
     let (literal, raw) = match literal.strip_prefix('r') {
         Some(stripped) => (stripped.trim_matches('#'), true),
         None => (literal, false),
     };

     Some((literal.strip_prefix('"')?.strip_suffix('"')?.to_string(), raw))
 }

 enum UnescapeErr {
     /// Should still be linted, can be manually resolved by author, e.g.
     ///
     /// ```ignore
     /// print!(r"{}", '"');
     /// ```
     Lint,
     /// Should not be linted, e.g.
     ///
     /// ```ignore
     /// print!(r"{}", '\r');
     /// ```
     Ignore,
 }

 /// Unescape a normal string into a raw string
 fn conservative_unescape(literal: &str) -> Result<String, UnescapeErr> {
     let mut unescaped = String::with_capacity(literal.len());
     let mut chars = literal.chars();
     let mut err = false;

     while let Some(ch) = chars.next() {
         match ch {
             '#' => err = true,
             '\\' => match chars.next() {
                 Some('\\') => unescaped.push('\\'),
                 Some('"') => err = true,
                 _ => return Err(UnescapeErr::Ignore),
             },
             _ => unescaped.push(ch),
         }
     }

     if err { Err(UnescapeErr::Lint) } else { Ok(unescaped) }
 }
	use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
	use clippy_utils::macros::{find_format_args, format_arg_removal_span, root_macro_call_first_node, MacroCall};
	use clippy_utils::source::{expand_past_previous_comma, snippet_opt};
	use clippy_utils::{is_in_cfg_test, is_in_test_function};
	use rustc_ast::token::LitKind;
	use rustc_ast::{FormatArgPosition, FormatArgs, FormatArgsPiece, FormatOptions, FormatPlaceholder, FormatTrait};
	use rustc_errors::Applicability;
	use rustc_hir::{Expr, Impl, Item, ItemKind};
	use rustc_lint::{LateContext, LateLintPass, LintContext};
	use rustc_session::{declare_tool_lint, impl_lint_pass};
	use rustc_span::{sym, BytePos};

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns when you use `println!("")` to
	/// print a newline.
	///
	/// ### Why is this bad?
	/// You should use `println!()`, which is simpler.
	///
	/// ### Example
	/// ```rust
	/// println!("");
	/// ```
	///
	/// Use instead:
	/// ```rust
	/// println!();
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub PRINTLN_EMPTY_STRING,
	style,
	"using `println!(\"\")` with an empty string"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns when you use `print!()` with a format
	/// string that ends in a newline.
	///
	/// ### Why is this bad?
	/// You should use `println!()` instead, which appends the
	/// newline.
	///
	/// ### Example
	/// ```rust
	/// # let name = "World";
	/// print!("Hello {}!\n", name);
	/// ```
	/// use println!() instead
	/// ```rust
	/// # let name = "World";
	/// println!("Hello {}!", name);
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub PRINT_WITH_NEWLINE,
	style,
	"using `print!()` with a format string that ends in a single newline"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for printing on stdout. The purpose of this lint
	/// is to catch debugging remnants.
	///
	/// ### Why is this bad?
	/// People often print on stdout while debugging an
	/// application and might forget to remove those prints afterward.
	///
	/// ### Known problems
	/// Only catches `print!` and `println!` calls.
	///
	/// ### Example
	/// ```rust
	/// println!("Hello world!");
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub PRINT_STDOUT,
	restriction,
	"printing on stdout"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for printing on stderr. The purpose of this lint
	/// is to catch debugging remnants.
	///
	/// ### Why is this bad?
	/// People often print on stderr while debugging an
	/// application and might forget to remove those prints afterward.
	///
	/// ### Known problems
	/// Only catches `eprint!` and `eprintln!` calls.
	///
	/// ### Example
	/// ```rust
	/// eprintln!("Hello world!");
	/// ```
	#[clippy::version = "1.50.0"]
	pub PRINT_STDERR,
	restriction,
	"printing on stderr"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for usage of `Debug` formatting. The purpose of this
	/// lint is to catch debugging remnants.
	///
	/// ### Why is this bad?
	/// The purpose of the `Debug` trait is to facilitate
	/// debugging Rust code. It should not be used in user-facing output.
	///
	/// ### Example
	/// ```rust
	/// # let foo = "bar";
	/// println!("{:?}", foo);
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub USE_DEBUG,
	restriction,
	"use of `Debug`-based formatting"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns about the use of literals as `print!`/`println!` args.
	///
	/// ### Why is this bad?
	/// Using literals as `println!` args is inefficient
	/// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
	/// (i.e., just put the literal in the format string)
	///
	/// ### Example
	/// ```rust
	/// println!("{}", "foo");
	/// ```
	/// use the literal without formatting:
	/// ```rust
	/// println!("foo");
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub PRINT_LITERAL,
	style,
	"printing a literal with a format string"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns when you use `writeln!(buf, "")` to
	/// print a newline.
	///
	/// ### Why is this bad?
	/// You should use `writeln!(buf)`, which is simpler.
	///
	/// ### Example
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// writeln!(buf, "");
	/// ```
	///
	/// Use instead:
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// writeln!(buf);
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub WRITELN_EMPTY_STRING,
	style,
	"using `writeln!(buf, \"\")` with an empty string"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns when you use `write!()` with a format
	/// string that
	/// ends in a newline.
	///
	/// ### Why is this bad?
	/// You should use `writeln!()` instead, which appends the
	/// newline.
	///
	/// ### Example
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// # let name = "World";
	/// write!(buf, "Hello {}!\n", name);
	/// ```
	///
	/// Use instead:
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// # let name = "World";
	/// writeln!(buf, "Hello {}!", name);
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub WRITE_WITH_NEWLINE,
	style,
	"using `write!()` with a format string that ends in a single newline"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// This lint warns about the use of literals as `write!`/`writeln!` args.
	///
	/// ### Why is this bad?
	/// Using literals as `writeln!` args is inefficient
	/// (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
	/// (i.e., just put the literal in the format string)
	///
	/// ### Example
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// writeln!(buf, "{}", "foo");
	/// ```
	///
	/// Use instead:
	/// ```rust
	/// # use std::fmt::Write;
	/// # let mut buf = String::new();
	/// writeln!(buf, "foo");
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub WRITE_LITERAL,
	style,
	"writing a literal with a format string"
	}

	#[derive(Default)]
	pub struct Write {
	in_debug_impl: bool,
	allow_print_in_tests: bool,
	}

	impl Write {
	pub fn new(allow_print_in_tests: bool) -> Self {
	Self {
	allow_print_in_tests,
	..Default::default()
	}
	}
	}

	impl_lint_pass!(Write => [
	PRINT_WITH_NEWLINE,
	PRINTLN_EMPTY_STRING,
	PRINT_STDOUT,
	PRINT_STDERR,
	USE_DEBUG,
	PRINT_LITERAL,
	WRITE_WITH_NEWLINE,
	WRITELN_EMPTY_STRING,
	WRITE_LITERAL,
	]);

	impl<'tcx> LateLintPass<'tcx> for Write {
	fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
	if is_debug_impl(cx, item) {
	self.in_debug_impl = true;
	}
	}

	fn check_item_post(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
	if is_debug_impl(cx, item) {
	self.in_debug_impl = false;
	}
	}

	fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
	let Some(macro_call) = root_macro_call_first_node(cx, expr) else {
	return;
	};
	let Some(diag_name) = cx.tcx.get_diagnostic_name(macro_call.def_id) else {
	return;
	};
	let Some(name) = diag_name.as_str().strip_suffix("_macro") else {
	return;
	};

	let is_build_script = cx
	.sess()
	.opts
	.crate_name
	.as_ref()
	.map_or(false, \|crate_name\| crate_name == "build_script_build");

	let allowed_in_tests = self.allow_print_in_tests
	&& (is_in_test_function(cx.tcx, expr.hir_id) \|\| is_in_cfg_test(cx.tcx, expr.hir_id));
	match diag_name {
	sym::print_macro \| sym::println_macro if !allowed_in_tests => {
	if !is_build_script {
	span_lint(cx, PRINT_STDOUT, macro_call.span, &format!("use of `{name}!`"));
	}
	},
	sym::eprint_macro \| sym::eprintln_macro if !allowed_in_tests => {
	span_lint(cx, PRINT_STDERR, macro_call.span, &format!("use of `{name}!`"));
	},
	sym::write_macro \| sym::writeln_macro => {},
	_ => return,
	}

	find_format_args(cx, expr, macro_call.expn, \|format_args\| {
	// ignore `writeln!(w)` and `write!(v, some_macro!())`
	if format_args.span.from_expansion() {
	return;
	}

	match diag_name {
	sym::print_macro \| sym::eprint_macro \| sym::write_macro => {
	check_newline(cx, format_args, &macro_call, name);
	},
	sym::println_macro \| sym::eprintln_macro \| sym::writeln_macro => {
	check_empty_string(cx, format_args, &macro_call, name);
	},
	_ => {},
	}

	check_literal(cx, format_args, name);

	if !self.in_debug_impl {
	for piece in &format_args.template {
	if let &FormatArgsPiece::Placeholder(FormatPlaceholder {
	span: Some(span),
	format_trait: FormatTrait::Debug,
	..
	}) = piece
	{
	span_lint(cx, USE_DEBUG, span, "use of `Debug`-based formatting");
	}
	}
	}
	});
	}
	}

	fn is_debug_impl(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
	if let ItemKind::Impl(Impl { of_trait: Some(trait_ref), .. }) = &item.kind
	&& let Some(trait_id) = trait_ref.trait_def_id()
	{
	cx.tcx.is_diagnostic_item(sym::Debug, trait_id)
	} else {
	false
	}
	}

	fn check_newline(cx: &LateContext<'_>, format_args: &FormatArgs, macro_call: &MacroCall, name: &str) {
	let Some(FormatArgsPiece::Literal(last)) = format_args.template.last() else {
	return;
	};

	let count_vertical_whitespace = \|\| {
	format_args
	.template
	.iter()
	.filter_map(\|piece\| match piece {
	FormatArgsPiece::Literal(literal) => Some(literal),
	FormatArgsPiece::Placeholder(_) => None,
	})
	.flat_map(\|literal\| literal.as_str().chars())
	.filter(\|ch\| matches!(ch, '\r' \| '\n'))
	.count()
	};

	if last.as_str().ends_with('\n')
	// ignore format strings with other internal vertical whitespace
	&& count_vertical_whitespace() == 1
	{
	let mut format_string_span = format_args.span;

	let lint = if name == "write" {
	format_string_span = expand_past_previous_comma(cx, format_string_span);

	WRITE_WITH_NEWLINE
	} else {
	PRINT_WITH_NEWLINE
	};

	span_lint_and_then(
	cx,
	lint,
	macro_call.span,
	&format!("using `{name}!()` with a format string that ends in a single newline"),
	\|diag\| {
	let name_span = cx.sess().source_map().span_until_char(macro_call.span, '!');
	let Some(format_snippet) = snippet_opt(cx, format_string_span) else {
	return;
	};

	if format_args.template.len() == 1 && last.as_str() == "\n" {
	// print!("\n"), write!(f, "\n")

	diag.multipart_suggestion(
	format!("use `{name}ln!` instead"),
	vec![(name_span, format!("{name}ln")), (format_string_span, String::new())],
	Applicability::MachineApplicable,
	);
	} else if format_snippet.ends_with("\\n\"") {
	// print!("...\n"), write!(f, "...\n")

	let hi = format_string_span.hi();
	let newline_span = format_string_span.with_lo(hi - BytePos(3)).with_hi(hi - BytePos(1));

	diag.multipart_suggestion(
	format!("use `{name}ln!` instead"),
	vec![(name_span, format!("{name}ln")), (newline_span, String::new())],
	Applicability::MachineApplicable,
	);
	}
	},
	);
	}
	}

	fn check_empty_string(cx: &LateContext<'_>, format_args: &FormatArgs, macro_call: &MacroCall, name: &str) {
	if let [FormatArgsPiece::Literal(literal)] = &format_args.template[..]
	&& literal.as_str() == "\n"
	{
	let mut span = format_args.span;

	let lint = if name == "writeln" {
	span = expand_past_previous_comma(cx, span);

	WRITELN_EMPTY_STRING
	} else {
	PRINTLN_EMPTY_STRING
	};

	span_lint_and_then(
	cx,
	lint,
	macro_call.span,
	&format!("empty string literal in `{name}!`"),
	\|diag\| {
	diag.span_suggestion(
	span,
	"remove the empty string",
	String::new(),
	Applicability::MachineApplicable,
	);
	},
	);
	}
	}

	fn check_literal(cx: &LateContext<'_>, format_args: &FormatArgs, name: &str) {
	let arg_index = \|argument: &FormatArgPosition\| argument.index.unwrap_or_else(\|pos\| pos);

	let mut counts = vec![0u32; format_args.arguments.all_args().len()];
	for piece in &format_args.template {
	if let FormatArgsPiece::Placeholder(placeholder) = piece {
	counts[arg_index(&placeholder.argument)] += 1;
	}
	}

	for piece in &format_args.template {
	if let FormatArgsPiece::Placeholder(FormatPlaceholder {
	argument,
	span: Some(placeholder_span),
	format_trait: FormatTrait::Display,
	format_options,
	}) = piece
	&& *format_options == FormatOptions::default()
	&& let index = arg_index(argument)
	&& counts[index] == 1
	&& let Some(arg) = format_args.arguments.by_index(index)
	&& let rustc_ast::ExprKind::Lit(lit) = &arg.expr.kind
	&& !arg.expr.span.from_expansion()
	&& let Some(value_string) = snippet_opt(cx, arg.expr.span)
	{
	let (replacement, replace_raw) = match lit.kind {
	LitKind::Str \| LitKind::StrRaw(_) => match extract_str_literal(&value_string) {
	Some(extracted) => extracted,
	None => return,
	},
	LitKind::Char => (
	match lit.symbol.as_str() {
	"\"" => "\\\"",
	"\\'" => "'",
	_ => match value_string.strip_prefix('\'').and_then(\|s\| s.strip_suffix('\'')) {
	Some(stripped) => stripped,
	None => return,
	},
	}
	.to_string(),
	false,
	),
	LitKind::Bool => (lit.symbol.to_string(), false),
	_ => continue,
	};

	let lint = if name.starts_with("write") {
	WRITE_LITERAL
	} else {
	PRINT_LITERAL
	};

	let Some(format_string_snippet) = snippet_opt(cx, format_args.span) else { continue };
	let format_string_is_raw = format_string_snippet.starts_with('r');

	let replacement = match (format_string_is_raw, replace_raw) {
	(false, false) => Some(replacement),
	(false, true) => Some(replacement.replace('"', "\\\"").replace('\\', "\\\\")),
	(true, false) => match conservative_unescape(&replacement) {
	Ok(unescaped) => Some(unescaped),
	Err(UnescapeErr::Lint) => None,
	Err(UnescapeErr::Ignore) => continue,
	},
	(true, true) => {
	if replacement.contains(['#', '"']) {
	None
	} else {
	Some(replacement)
	}
	},
	};

	span_lint_and_then(
	cx,
	lint,
	arg.expr.span,
	"literal with an empty format string",
	\|diag\| {
	if let Some(replacement) = replacement
	// `format!("{}", "a")`, `format!("{named}", named = "b")
	// ~~~~~ ~~~~~~~~~~~~~
	&& let Some(removal_span) = format_arg_removal_span(format_args, index)
	{
	let replacement = replacement.replace('{', "{{").replace('}', "}}");
	diag.multipart_suggestion(
	"try",
	vec![(*placeholder_span, replacement), (removal_span, String::new())],
	Applicability::MachineApplicable,
	);
	}
	},
	);

	}
	}
	}

	/// Removes the raw marker, `#`s and quotes from a str, and returns if the literal is raw
	///
	/// `r#"a"#` -> (`a`, true)
	///
	/// `"b"` -> (`b`, false)
	fn extract_str_literal(literal: &str) -> Option<(String, bool)> {
	let (literal, raw) = match literal.strip_prefix('r') {
	Some(stripped) => (stripped.trim_matches('#'), true),
	None => (literal, false),
	};

	Some((literal.strip_prefix('"')?.strip_suffix('"')?.to_string(), raw))
	}

	enum UnescapeErr {
	/// Should still be linted, can be manually resolved by author, e.g.
	///
	/// ```ignore
	/// print!(r"{}", '"');
	/// ```
	Lint,
	/// Should not be linted, e.g.
	///
	/// ```ignore
	/// print!(r"{}", '\r');
	/// ```
	Ignore,
	}

	/// Unescape a normal string into a raw string
	fn conservative_unescape(literal: &str) -> Result<String, UnescapeErr> {
	let mut unescaped = String::with_capacity(literal.len());
	let mut chars = literal.chars();
	let mut err = false;

	while let Some(ch) = chars.next() {
	match ch {
	'#' => err = true,
	'\\' => match chars.next() {
	Some('\\') => unescaped.push('\\'),
	Some('"') => err = true,
	_ => return Err(UnescapeErr::Ignore),
	},
	_ => unescaped.push(ch),
	}
	}

	if err { Err(UnescapeErr::Lint) } else { Ok(unescaped) }
	}