library/std/src/macros.rs - rust-lang/rust - Git at Google

 //! Standard library macros
 //!
 //! This module contains a set of macros which are exported from the standard
 //! library. Each macro is available for use when linking against the standard
 //! library.
 // ignore-tidy-dbg

 #[doc = include_str!("../../core/src/macros/panic.md")]
 #[macro_export]
 #[rustc_builtin_macro(std_panic)]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[allow_internal_unstable(edition_panic)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "std_panic_macro")]
 macro_rules! panic {
     // Expands to either `$crate::panic::panic_2015` or `$crate::panic::panic_2021`
     // depending on the edition of the caller.
     ($($arg:tt)*) => {
         /* compiler built-in */
     };
 }

 /// Prints to the standard output.
 ///
 /// Equivalent to the [`println!`] macro except that a newline is not printed at
 /// the end of the message.
 ///
 /// Note that stdout is frequently line-buffered by default so it may be
 /// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted
 /// immediately.
 ///
 /// The `print!` macro will lock the standard output on each call. If you call
 /// `print!` within a hot loop, this behavior may be the bottleneck of the loop.
 /// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
 /// ```
 /// use std::io::{stdout, Write};
 ///
 /// let mut lock = stdout().lock();
 /// write!(lock, "hello world").unwrap();
 /// ```
 ///
 /// Use `print!` only for the primary output of your program. Use
 /// [`eprint!`] instead to print error and progress messages.
 ///
 /// See the formatting documentation in [`std::fmt`](crate::fmt)
 /// for details of the macro argument syntax.
 ///
 /// [flush]: crate::io::Write::flush
 /// [`println!`]: crate::println
 /// [`eprint!`]: crate::eprint
 /// [lock]: crate::io::Stdout
 ///
 /// # Panics
 ///
 /// Panics if writing to `io::stdout()` fails.
 ///
 /// Writing to non-blocking stdout can cause an error, which will lead
 /// this macro to panic.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::io::{self, Write};
 ///
 /// print!("this ");
 /// print!("will ");
 /// print!("be ");
 /// print!("on ");
 /// print!("the ");
 /// print!("same ");
 /// print!("line ");
 ///
 /// io::stdout().flush().unwrap();
 ///
 /// print!("this string has a newline, why not choose println! instead?\n");
 ///
 /// io::stdout().flush().unwrap();
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "print_macro")]
 #[allow_internal_unstable(print_internals)]
 macro_rules! print {
     ($($arg:tt)*) => {{
         $crate::io::_print($crate::format_args!($($arg)*));
     }};
 }

 /// Prints to the standard output, with a newline.
 ///
 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`)).
 ///
 /// This macro uses the same syntax as [`format!`], but writes to the standard output instead.
 /// See [`std::fmt`] for more information.
 ///
 /// The `println!` macro will lock the standard output on each call. If you call
 /// `println!` within a hot loop, this behavior may be the bottleneck of the loop.
 /// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
 /// ```
 /// use std::io::{stdout, Write};
 ///
 /// let mut lock = stdout().lock();
 /// writeln!(lock, "hello world").unwrap();
 /// ```
 ///
 /// Use `println!` only for the primary output of your program. Use
 /// [`eprintln!`] instead to print error and progress messages.
 ///
 /// See the formatting documentation in [`std::fmt`](crate::fmt)
 /// for details of the macro argument syntax.
 ///
 /// [`std::fmt`]: crate::fmt
 /// [`eprintln!`]: crate::eprintln
 /// [lock]: crate::io::Stdout
 ///
 /// # Panics
 ///
 /// Panics if writing to [`io::stdout`] fails.
 ///
 /// Writing to non-blocking stdout can cause an error, which will lead
 /// this macro to panic.
 ///
 /// [`io::stdout`]: crate::io::stdout
 ///
 /// # Examples
 ///
 /// ```
 /// println!(); // prints just a newline
 /// println!("hello there!");
 /// println!("format {} arguments", "some");
 /// let local_variable = "some";
 /// println!("format {local_variable} arguments");
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "println_macro")]
 #[allow_internal_unstable(print_internals, format_args_nl)]
 macro_rules! println {
     () => {
         $crate::print!("\n")
     };
     ($($arg:tt)*) => {{
         $crate::io::_print($crate::format_args_nl!($($arg)*));
     }};
 }

 /// Prints to the standard error.
 ///
 /// Equivalent to the [`print!`] macro, except that output goes to
 /// [`io::stderr`] instead of [`io::stdout`]. See [`print!`] for
 /// example usage.
 ///
 /// Use `eprint!` only for error and progress messages. Use `print!`
 /// instead for the primary output of your program.
 ///
 /// [`io::stderr`]: crate::io::stderr
 /// [`io::stdout`]: crate::io::stdout
 ///
 /// See the formatting documentation in [`std::fmt`](crate::fmt)
 /// for details of the macro argument syntax.
 ///
 /// # Panics
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
 /// Writing to non-blocking stderr can cause an error, which will lead
 /// this macro to panic.
 ///
 /// # Examples
 ///
 /// ```
 /// eprint!("Error: Could not complete task");
 /// ```
 #[macro_export]
 #[stable(feature = "eprint", since = "1.19.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "eprint_macro")]
 #[allow_internal_unstable(print_internals)]
 macro_rules! eprint {
     ($($arg:tt)*) => {{
         $crate::io::_eprint($crate::format_args!($($arg)*));
     }};
 }

 /// Prints to the standard error, with a newline.
 ///
 /// Equivalent to the [`println!`] macro, except that output goes to
 /// [`io::stderr`] instead of [`io::stdout`]. See [`println!`] for
 /// example usage.
 ///
 /// Use `eprintln!` only for error and progress messages. Use `println!`
 /// instead for the primary output of your program.
 ///
 /// See the formatting documentation in [`std::fmt`](crate::fmt)
 /// for details of the macro argument syntax.
 ///
 /// [`io::stderr`]: crate::io::stderr
 /// [`io::stdout`]: crate::io::stdout
 /// [`println!`]: crate::println
 ///
 /// # Panics
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
 /// Writing to non-blocking stderr can cause an error, which will lead
 /// this macro to panic.
 ///
 /// # Examples
 ///
 /// ```
 /// eprintln!("Error: Could not complete task");
 /// ```
 #[macro_export]
 #[stable(feature = "eprint", since = "1.19.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "eprintln_macro")]
 #[allow_internal_unstable(print_internals, format_args_nl)]
 macro_rules! eprintln {
     () => {
         $crate::eprint!("\n")
     };
     ($($arg:tt)*) => {{
         $crate::io::_eprint($crate::format_args_nl!($($arg)*));
     }};
 }

 /// Prints and returns the value of a given expression for quick and dirty
 /// debugging.
 ///
 /// An example:
 ///
 /// ```rust
 /// let a = 2;
 /// let b = dbg!(a * 2) + 1;
 /// //      ^-- prints: [src/main.rs:2:9] a * 2 = 4
 /// assert_eq!(b, 5);
 /// ```
 ///
 /// The macro works by using the `Debug` implementation of the type of
 /// the given expression to print the value to [stderr] along with the
 /// source location of the macro invocation as well as the source code
 /// of the expression.
 ///
 /// Invoking the macro on an expression moves and takes ownership of it
 /// before returning the evaluated expression unchanged. If the type
 /// of the expression does not implement `Copy` and you don't want
 /// to give up ownership, you can instead borrow with `dbg!(&expr)`
 /// for some expression `expr`.
 ///
 /// The `dbg!` macro works exactly the same in release builds.
 /// This is useful when debugging issues that only occur in release
 /// builds or when debugging in release mode is significantly faster.
 ///
 /// Note that the macro is intended as a debugging tool and therefore you
 /// should avoid having uses of it in version control for long periods
 /// (other than in tests and similar).
 /// Debug output from production code is better done with other facilities
 /// such as the [`debug!`] macro from the [`log`] crate.
 ///
 /// # Stability
 ///
 /// The exact output printed by this macro should not be relied upon
 /// and is subject to future changes.
 ///
 /// # Panics
 ///
 /// Panics if writing to `io::stderr` fails.
 ///
 /// # Further examples
 ///
 /// With a method call:
 ///
 /// ```rust
 /// fn foo(n: usize) {
 ///     if let Some(_) = dbg!(n.checked_sub(4)) {
 ///         // ...
 ///     }
 /// }
 ///
 /// foo(3)
 /// ```
 ///
 /// This prints to [stderr]:
 ///
 /// ```text,ignore
 /// [src/main.rs:2:22] n.checked_sub(4) = None
 /// ```
 ///
 /// Naive factorial implementation:
 ///
 /// ```rust
 /// fn factorial(n: u32) -> u32 {
 ///     if dbg!(n <= 1) {
 ///         dbg!(1)
 ///     } else {
 ///         dbg!(n * factorial(n - 1))
 ///     }
 /// }
 ///
 /// dbg!(factorial(4));
 /// ```
 ///
 /// This prints to [stderr]:
 ///
 /// ```text,ignore
 /// [src/main.rs:2:8] n <= 1 = false
 /// [src/main.rs:2:8] n <= 1 = false
 /// [src/main.rs:2:8] n <= 1 = false
 /// [src/main.rs:2:8] n <= 1 = true
 /// [src/main.rs:3:9] 1 = 1
 /// [src/main.rs:7:9] n * factorial(n - 1) = 2
 /// [src/main.rs:7:9] n * factorial(n - 1) = 6
 /// [src/main.rs:7:9] n * factorial(n - 1) = 24
 /// [src/main.rs:9:1] factorial(4) = 24
 /// ```
 ///
 /// The `dbg!(..)` macro moves the input:
 ///
 /// ```compile_fail
 /// /// A wrapper around `usize` which importantly is not Copyable.
 /// #[derive(Debug)]
 /// struct NoCopy(usize);
 ///
 /// let a = NoCopy(42);
 /// let _ = dbg!(a); // <-- `a` is moved here.
 /// let _ = dbg!(a); // <-- `a` is moved again; error!
 /// ```
 ///
 /// You can also use `dbg!()` without a value to just print the
 /// file and line whenever it's reached.
 ///
 /// Finally, if you want to `dbg!(..)` multiple values, it will treat them as
 /// a tuple (and return it, too):
 ///
 /// ```
 /// assert_eq!(dbg!(1usize, 2u32), (1, 2));
 /// ```
 ///
 /// However, a single argument with a trailing comma will still not be treated
 /// as a tuple, following the convention of ignoring trailing commas in macro
 /// invocations. You can use a 1-tuple directly if you need one:
 ///
 /// ```
 /// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored
 /// assert_eq!((1,), dbg!((1u32,))); // 1-tuple
 /// ```
 ///
 /// [stderr]: https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr)
 /// [`debug!`]: https://docs.rs/log/*/log/macro.debug.html
 /// [`log`]: https://crates.io/crates/log
 #[macro_export]
 #[cfg_attr(not(test), rustc_diagnostic_item = "dbg_macro")]
 #[stable(feature = "dbg_macro", since = "1.32.0")]
 macro_rules! dbg {
     // NOTE: We cannot use `concat!` to make a static string as a format argument
     // of `eprintln!` because `file!` could contain a `{` or
     // `$val` expression could be a block (`{ .. }`), in which case the `eprintln!`
     // will be malformed.
     () => {
         $crate::eprintln!("[{}:{}:{}]", $crate::file!(), $crate::line!(), $crate::column!())
     };
     ($val:expr $(,)?) => {
         // Use of `match` here is intentional because it affects the lifetimes
         // of temporaries - https://stackoverflow.com/a/48732525/1063961
         match $val {
             tmp => {
                 $crate::eprintln!("[{}:{}:{}] {} = {:#?}",
                     $crate::file!(),
                     $crate::line!(),
                     $crate::column!(),
                     $crate::stringify!($val),
                     // The `&T: Debug` check happens here (not in the format literal desugaring)
                     // to avoid format literal related messages and suggestions.
                     &&tmp as &dyn $crate::fmt::Debug,
                 );
                 tmp
             }
         }
     };
     ($($val:expr),+ $(,)?) => {
         ($($crate::dbg!($val)),+,)
     };
 }
	//! Standard library macros
	//!
	//! This module contains a set of macros which are exported from the standard
	//! library. Each macro is available for use when linking against the standard
	//! library.
	// ignore-tidy-dbg

	#[doc = include_str!("../../core/src/macros/panic.md")]
	#[macro_export]
	#[rustc_builtin_macro(std_panic)]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[allow_internal_unstable(edition_panic)]
	#[cfg_attr(not(test), rustc_diagnostic_item = "std_panic_macro")]
	macro_rules! panic {
	// Expands to either `$crate::panic::panic_2015` or `$crate::panic::panic_2021`
	// depending on the edition of the caller.
	($($arg:tt)*) => {
	/* compiler built-in */
	};
	}

	/// Prints to the standard output.
	///
	/// Equivalent to the [`println!`] macro except that a newline is not printed at
	/// the end of the message.
	///
	/// Note that stdout is frequently line-buffered by default so it may be
	/// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted
	/// immediately.
	///
	/// The `print!` macro will lock the standard output on each call. If you call
	/// `print!` within a hot loop, this behavior may be the bottleneck of the loop.
	/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
	/// ```
	/// use std::io::{stdout, Write};
	///
	/// let mut lock = stdout().lock();
	/// write!(lock, "hello world").unwrap();
	/// ```
	///
	/// Use `print!` only for the primary output of your program. Use
	/// [`eprint!`] instead to print error and progress messages.
	///
	/// See the formatting documentation in [`std::fmt`](crate::fmt)
	/// for details of the macro argument syntax.
	///
	/// [flush]: crate::io::Write::flush
	/// [`println!`]: crate::println
	/// [`eprint!`]: crate::eprint
	/// [lock]: crate::io::Stdout
	///
	/// # Panics
	///
	/// Panics if writing to `io::stdout()` fails.
	///
	/// Writing to non-blocking stdout can cause an error, which will lead
	/// this macro to panic.
	///
	/// # Examples
	///
	/// ```
	/// use std::io::{self, Write};
	///
	/// print!("this ");
	/// print!("will ");
	/// print!("be ");
	/// print!("on ");
	/// print!("the ");
	/// print!("same ");
	/// print!("line ");
	///
	/// io::stdout().flush().unwrap();
	///
	/// print!("this string has a newline, why not choose println! instead?\n");
	///
	/// io::stdout().flush().unwrap();
	/// ```
	#[macro_export]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[cfg_attr(not(test), rustc_diagnostic_item = "print_macro")]
	#[allow_internal_unstable(print_internals)]
	macro_rules! print {
	($($arg:tt)*) => {{
	$crate::io::_print($crate::format_args!($($arg)*));
	}};
	}

	/// Prints to the standard output, with a newline.
	///
	/// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
	/// (no additional CARRIAGE RETURN (`\r`/`U+000D`)).
	///
	/// This macro uses the same syntax as [`format!`], but writes to the standard output instead.
	/// See [`std::fmt`] for more information.
	///
	/// The `println!` macro will lock the standard output on each call. If you call
	/// `println!` within a hot loop, this behavior may be the bottleneck of the loop.
	/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
	/// ```
	/// use std::io::{stdout, Write};
	///
	/// let mut lock = stdout().lock();
	/// writeln!(lock, "hello world").unwrap();
	/// ```
	///
	/// Use `println!` only for the primary output of your program. Use
	/// [`eprintln!`] instead to print error and progress messages.
	///
	/// See the formatting documentation in [`std::fmt`](crate::fmt)
	/// for details of the macro argument syntax.
	///
	/// [`std::fmt`]: crate::fmt
	/// [`eprintln!`]: crate::eprintln
	/// [lock]: crate::io::Stdout
	///
	/// # Panics
	///
	/// Panics if writing to [`io::stdout`] fails.
	///
	/// Writing to non-blocking stdout can cause an error, which will lead
	/// this macro to panic.
	///
	/// [`io::stdout`]: crate::io::stdout
	///
	/// # Examples
	///
	/// ```
	/// println!(); // prints just a newline
	/// println!("hello there!");
	/// println!("format {} arguments", "some");
	/// let local_variable = "some";
	/// println!("format {local_variable} arguments");
	/// ```
	#[macro_export]
	#[stable(feature = "rust1", since = "1.0.0")]
	#[cfg_attr(not(test), rustc_diagnostic_item = "println_macro")]
	#[allow_internal_unstable(print_internals, format_args_nl)]
	macro_rules! println {
	() => {
	$crate::print!("\n")
	};
	($($arg:tt)*) => {{
	$crate::io::_print($crate::format_args_nl!($($arg)*));
	}};
	}

	/// Prints to the standard error.
	///
	/// Equivalent to the [`print!`] macro, except that output goes to
	/// [`io::stderr`] instead of [`io::stdout`]. See [`print!`] for
	/// example usage.
	///
	/// Use `eprint!` only for error and progress messages. Use `print!`
	/// instead for the primary output of your program.
	///
	/// [`io::stderr`]: crate::io::stderr
	/// [`io::stdout`]: crate::io::stdout
	///
	/// See the formatting documentation in [`std::fmt`](crate::fmt)
	/// for details of the macro argument syntax.
	///
	/// # Panics
	///
	/// Panics if writing to `io::stderr` fails.
	///
	/// Writing to non-blocking stderr can cause an error, which will lead
	/// this macro to panic.
	///
	/// # Examples
	///
	/// ```
	/// eprint!("Error: Could not complete task");
	/// ```
	#[macro_export]
	#[stable(feature = "eprint", since = "1.19.0")]
	#[cfg_attr(not(test), rustc_diagnostic_item = "eprint_macro")]
	#[allow_internal_unstable(print_internals)]
	macro_rules! eprint {
	($($arg:tt)*) => {{
	$crate::io::_eprint($crate::format_args!($($arg)*));
	}};
	}

	/// Prints to the standard error, with a newline.
	///
	/// Equivalent to the [`println!`] macro, except that output goes to
	/// [`io::stderr`] instead of [`io::stdout`]. See [`println!`] for
	/// example usage.
	///
	/// Use `eprintln!` only for error and progress messages. Use `println!`
	/// instead for the primary output of your program.
	///
	/// See the formatting documentation in [`std::fmt`](crate::fmt)
	/// for details of the macro argument syntax.
	///
	/// [`io::stderr`]: crate::io::stderr
	/// [`io::stdout`]: crate::io::stdout
	/// [`println!`]: crate::println
	///
	/// # Panics
	///
	/// Panics if writing to `io::stderr` fails.
	///
	/// Writing to non-blocking stderr can cause an error, which will lead
	/// this macro to panic.
	///
	/// # Examples
	///
	/// ```
	/// eprintln!("Error: Could not complete task");
	/// ```
	#[macro_export]
	#[stable(feature = "eprint", since = "1.19.0")]
	#[cfg_attr(not(test), rustc_diagnostic_item = "eprintln_macro")]
	#[allow_internal_unstable(print_internals, format_args_nl)]
	macro_rules! eprintln {
	() => {
	$crate::eprint!("\n")
	};
	($($arg:tt)*) => {{
	$crate::io::_eprint($crate::format_args_nl!($($arg)*));
	}};
	}

	/// Prints and returns the value of a given expression for quick and dirty
	/// debugging.
	///
	/// An example:
	///
	/// ```rust
	/// let a = 2;
	/// let b = dbg!(a * 2) + 1;
	/// // ^-- prints: [src/main.rs:2:9] a * 2 = 4
	/// assert_eq!(b, 5);
	/// ```
	///
	/// The macro works by using the `Debug` implementation of the type of
	/// the given expression to print the value to [stderr] along with the
	/// source location of the macro invocation as well as the source code
	/// of the expression.
	///
	/// Invoking the macro on an expression moves and takes ownership of it
	/// before returning the evaluated expression unchanged. If the type
	/// of the expression does not implement `Copy` and you don't want
	/// to give up ownership, you can instead borrow with `dbg!(&expr)`
	/// for some expression `expr`.
	///
	/// The `dbg!` macro works exactly the same in release builds.
	/// This is useful when debugging issues that only occur in release
	/// builds or when debugging in release mode is significantly faster.
	///
	/// Note that the macro is intended as a debugging tool and therefore you
	/// should avoid having uses of it in version control for long periods
	/// (other than in tests and similar).
	/// Debug output from production code is better done with other facilities
	/// such as the [`debug!`] macro from the [`log`] crate.
	///
	/// # Stability
	///
	/// The exact output printed by this macro should not be relied upon
	/// and is subject to future changes.
	///
	/// # Panics
	///
	/// Panics if writing to `io::stderr` fails.
	///
	/// # Further examples
	///
	/// With a method call:
	///
	/// ```rust
	/// fn foo(n: usize) {
	/// if let Some(_) = dbg!(n.checked_sub(4)) {
	/// // ...
	/// }
	/// }
	///
	/// foo(3)
	/// ```
	///
	/// This prints to [stderr]:
	///
	/// ```text,ignore
	/// [src/main.rs:2:22] n.checked_sub(4) = None
	/// ```
	///
	/// Naive factorial implementation:
	///
	/// ```rust
	/// fn factorial(n: u32) -> u32 {
	/// if dbg!(n <= 1) {
	/// dbg!(1)
	/// } else {
	/// dbg!(n * factorial(n - 1))
	/// }
	/// }
	///
	/// dbg!(factorial(4));
	/// ```
	///
	/// This prints to [stderr]:
	///
	/// ```text,ignore
	/// [src/main.rs:2:8] n <= 1 = false
	/// [src/main.rs:2:8] n <= 1 = false
	/// [src/main.rs:2:8] n <= 1 = false
	/// [src/main.rs:2:8] n <= 1 = true
	/// [src/main.rs:3:9] 1 = 1
	/// [src/main.rs:7:9] n * factorial(n - 1) = 2
	/// [src/main.rs:7:9] n * factorial(n - 1) = 6
	/// [src/main.rs:7:9] n * factorial(n - 1) = 24
	/// [src/main.rs:9:1] factorial(4) = 24
	/// ```
	///
	/// The `dbg!(..)` macro moves the input:
	///
	/// ```compile_fail
	/// /// A wrapper around `usize` which importantly is not Copyable.
	/// #[derive(Debug)]
	/// struct NoCopy(usize);
	///
	/// let a = NoCopy(42);
	/// let _ = dbg!(a); // <-- `a` is moved here.
	/// let _ = dbg!(a); // <-- `a` is moved again; error!
	/// ```
	///
	/// You can also use `dbg!()` without a value to just print the
	/// file and line whenever it's reached.
	///
	/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as
	/// a tuple (and return it, too):
	///
	/// ```
	/// assert_eq!(dbg!(1usize, 2u32), (1, 2));
	/// ```
	///
	/// However, a single argument with a trailing comma will still not be treated
	/// as a tuple, following the convention of ignoring trailing commas in macro
	/// invocations. You can use a 1-tuple directly if you need one:
	///
	/// ```
	/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored
	/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple
	/// ```
	///
	/// [stderr]: https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr)
	/// [`debug!`]: https://docs.rs/log/*/log/macro.debug.html
	/// [`log`]: https://crates.io/crates/log
	#[macro_export]
	#[cfg_attr(not(test), rustc_diagnostic_item = "dbg_macro")]
	#[stable(feature = "dbg_macro", since = "1.32.0")]
	macro_rules! dbg {
	// NOTE: We cannot use `concat!` to make a static string as a format argument
	// of `eprintln!` because `file!` could contain a `{` or
	// `$val` expression could be a block (`{ .. }`), in which case the `eprintln!`
	// will be malformed.
	() => {
	$crate::eprintln!("[{}:{}:{}]", $crate::file!(), $crate::line!(), $crate::column!())
	};
	($val:expr $(,)?) => {
	// Use of `match` here is intentional because it affects the lifetimes
	// of temporaries - https://stackoverflow.com/a/48732525/1063961
	match $val {
	tmp => {
	$crate::eprintln!("[{}:{}:{}] {} = {:#?}",
	$crate::file!(),
	$crate::line!(),
	$crate::column!(),
	$crate::stringify!($val),
	// The `&T: Debug` check happens here (not in the format literal desugaring)
	// to avoid format literal related messages and suggestions.
	&&tmp as &dyn $crate::fmt::Debug,
	);
	tmp
	}
	}
	};
	($($val:expr),+ $(,)?) => {
	($($crate::dbg!($val)),+,)
	};
	}