library/core/src/macros/mod.rs

   1 #[doc = include_str!("panic.md")]
   2 #[macro_export]
   3 #[rustc_builtin_macro(core_panic)]
   4 #[allow_internal_unstable(edition_panic)]
   5 #[stable(feature = "core", since = "1.6.0")]
   6 #[rustc_diagnostic_item = "core_panic_macro"]
   7 macro_rules! panic {
   8     // Expands to either `$crate::panic::panic_2015` or `$crate::panic::panic_2021`
   9     // depending on the edition of the caller.
  10     ($($arg:tt)*) => {
  11         /* compiler built-in */
  12     };
  13 }
  14
  15 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
  16 ///
  17 /// On panic, this macro will print the values of the expressions with their
  18 /// debug representations.
  19 ///
  20 /// Like [`assert!`], this macro has a second form, where a custom
  21 /// panic message can be provided.
  22 ///
  23 /// # Examples
  24 ///
  25 /// ```
  26 /// let a = 3;
  27 /// let b = 1 + 2;
  28 /// assert_eq!(a, b);
  29 ///
  30 /// assert_eq!(a, b, "we are testing addition with {} and {}", a, b);
  31 /// ```
  32 #[macro_export]
  33 #[stable(feature = "rust1", since = "1.0.0")]
  34 #[cfg_attr(not(test), rustc_diagnostic_item = "assert_eq_macro")]
  35 #[allow_internal_unstable(core_panic)]
  36 macro_rules! assert_eq {
  37     ($left:expr, $right:expr $(,)?) => {
  38         match (&$left, &$right) {
  39             (left_val, right_val) => {
  40                 if !(*left_val == *right_val) {
  41                     let kind = $crate::panicking::AssertKind::Eq;
  42                     // The reborrows below are intentional. Without them, the stack slot for the
  43                     // borrow is initialized even before the values are compared, leading to a
  44                     // noticeable slow down.
  45                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
  46                 }
  47             }
  48         }
  49     };
  50     ($left:expr, $right:expr, $($arg:tt)+) => {
  51         match (&$left, &$right) {
  52             (left_val, right_val) => {
  53                 if !(*left_val == *right_val) {
  54                     let kind = $crate::panicking::AssertKind::Eq;
  55                     // The reborrows below are intentional. Without them, the stack slot for the
  56                     // borrow is initialized even before the values are compared, leading to a
  57                     // noticeable slow down.
  58                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
  59                 }
  60             }
  61         }
  62     };
  63 }
  64
  65 /// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
  66 ///
  67 /// On panic, this macro will print the values of the expressions with their
  68 /// debug representations.
  69 ///
  70 /// Like [`assert!`], this macro has a second form, where a custom
  71 /// panic message can be provided.
  72 ///
  73 /// # Examples
  74 ///
  75 /// ```
  76 /// let a = 3;
  77 /// let b = 2;
  78 /// assert_ne!(a, b);
  79 ///
  80 /// assert_ne!(a, b, "we are testing that the values are not equal");
  81 /// ```
  82 #[macro_export]
  83 #[stable(feature = "assert_ne", since = "1.13.0")]
  84 #[cfg_attr(not(test), rustc_diagnostic_item = "assert_ne_macro")]
  85 #[allow_internal_unstable(core_panic)]
  86 macro_rules! assert_ne {
  87     ($left:expr, $right:expr $(,)?) => {
  88         match (&$left, &$right) {
  89             (left_val, right_val) => {
  90                 if *left_val == *right_val {
  91                     let kind = $crate::panicking::AssertKind::Ne;
  92                     // The reborrows below are intentional. Without them, the stack slot for the
  93                     // borrow is initialized even before the values are compared, leading to a
  94                     // noticeable slow down.
  95                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
  96                 }
  97             }
  98         }
  99     };
 100     ($left:expr, $right:expr, $($arg:tt)+) => {
 101         match (&($left), &($right)) {
 102             (left_val, right_val) => {
 103                 if *left_val == *right_val {
 104                     let kind = $crate::panicking::AssertKind::Ne;
 105                     // The reborrows below are intentional. Without them, the stack slot for the
 106                     // borrow is initialized even before the values are compared, leading to a
 107                     // noticeable slow down.
 108                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
 109                 }
 110             }
 111         }
 112     };
 113 }
 114
 115 /// Asserts that an expression matches any of the given patterns.
 116 ///
 117 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 118 /// and a guard expression that has access to names bound by the pattern.
 119 ///
 120 /// On panic, this macro will print the value of the expression with its
 121 /// debug representation.
 122 ///
 123 /// Like [`assert!`], this macro has a second form, where a custom
 124 /// panic message can be provided.
 125 ///
 126 /// # Examples
 127 ///
 128 /// ```
 129 /// #![feature(assert_matches)]
 130 ///
 131 /// use std::assert_matches::assert_matches;
 132 ///
 133 /// let a = 1u32.checked_add(2);
 134 /// let b = 1u32.checked_sub(2);
 135 /// assert_matches!(a, Some(_));
 136 /// assert_matches!(b, None);
 137 ///
 138 /// let c = Ok("abc".to_string());
 139 /// assert_matches!(c, Ok(x) | Err(x) if x.len() < 100);
 140 /// ```
 141 #[unstable(feature = "assert_matches", issue = "82775")]
 142 #[allow_internal_unstable(core_panic)]
 143 #[rustc_macro_transparency = "semitransparent"]
 144 pub macro assert_matches {
 145     ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )? $(,)?) => {
 146         match $left {
 147             $( $pattern )|+ $( if $guard )? => {}
 148             ref left_val => {
 149                 $crate::panicking::assert_matches_failed(
 150                     left_val,
 151                     $crate::stringify!($($pattern)|+ $(if $guard)?),
 152                     $crate::option::Option::None
 153                 );
 154             }
 155         }
 156     },
 157     ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )?, $($arg:tt)+) => {
 158         match $left {
 159             $( $pattern )|+ $( if $guard )? => {}
 160             ref left_val => {
 161                 $crate::panicking::assert_matches_failed(
 162                     left_val,
 163                     $crate::stringify!($($pattern)|+ $(if $guard)?),
 164                     $crate::option::Option::Some($crate::format_args!($($arg)+))
 165                 );
 166             }
 167         }
 168     },
 169 }
 170
 171 /// Asserts that a boolean expression is `true` at runtime.
 172 ///
 173 /// This will invoke the [`panic!`] macro if the provided expression cannot be
 174 /// evaluated to `true` at runtime.
 175 ///
 176 /// Like [`assert!`], this macro also has a second version, where a custom panic
 177 /// message can be provided.
 178 ///
 179 /// # Uses
 180 ///
 181 /// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
 182 /// optimized builds by default. An optimized build will not execute
 183 /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
 184 /// compiler. This makes `debug_assert!` useful for checks that are too
 185 /// expensive to be present in a release build but may be helpful during
 186 /// development. The result of expanding `debug_assert!` is always type checked.
 187 ///
 188 /// An unchecked assertion allows a program in an inconsistent state to keep
 189 /// running, which might have unexpected consequences but does not introduce
 190 /// unsafety as long as this only happens in safe code. The performance cost
 191 /// of assertions, however, is not measurable in general. Replacing [`assert!`]
 192 /// with `debug_assert!` is thus only encouraged after thorough profiling, and
 193 /// more importantly, only in safe code!
 194 ///
 195 /// # Examples
 196 ///
 197 /// ```
 198 /// // the panic message for these assertions is the stringified value of the
 199 /// // expression given.
 200 /// debug_assert!(true);
 201 ///
 202 /// fn some_expensive_computation() -> bool { true } // a very simple function
 203 /// debug_assert!(some_expensive_computation());
 204 ///
 205 /// // assert with a custom message
 206 /// let x = true;
 207 /// debug_assert!(x, "x wasn't true!");
 208 ///
 209 /// let a = 3; let b = 27;
 210 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
 211 /// ```
 212 #[macro_export]
 213 #[stable(feature = "rust1", since = "1.0.0")]
 214 #[rustc_diagnostic_item = "debug_assert_macro"]
 215 #[allow_internal_unstable(edition_panic)]
 216 macro_rules! debug_assert {
 217     ($($arg:tt)*) => {
 218         if $crate::cfg!(debug_assertions) {
 219             $crate::assert!($($arg)*);
 220         }
 221     };
 222 }
 223
 224 /// Asserts that two expressions are equal to each other.
 225 ///
 226 /// On panic, this macro will print the values of the expressions with their
 227 /// debug representations.
 228 ///
 229 /// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
 230 /// optimized builds by default. An optimized build will not execute
 231 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
 232 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
 233 /// expensive to be present in a release build but may be helpful during
 234 /// development. The result of expanding `debug_assert_eq!` is always type checked.
 235 ///
 236 /// # Examples
 237 ///
 238 /// ```
 239 /// let a = 3;
 240 /// let b = 1 + 2;
 241 /// debug_assert_eq!(a, b);
 242 /// ```
 243 #[macro_export]
 244 #[stable(feature = "rust1", since = "1.0.0")]
 245 #[cfg_attr(not(test), rustc_diagnostic_item = "debug_assert_eq_macro")]
 246 macro_rules! debug_assert_eq {
 247     ($($arg:tt)*) => {
 248         if $crate::cfg!(debug_assertions) {
 249             $crate::assert_eq!($($arg)*);
 250         }
 251     };
 252 }
 253
 254 /// Asserts that two expressions are not equal to each other.
 255 ///
 256 /// On panic, this macro will print the values of the expressions with their
 257 /// debug representations.
 258 ///
 259 /// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
 260 /// optimized builds by default. An optimized build will not execute
 261 /// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
 262 /// compiler. This makes `debug_assert_ne!` useful for checks that are too
 263 /// expensive to be present in a release build but may be helpful during
 264 /// development. The result of expanding `debug_assert_ne!` is always type checked.
 265 ///
 266 /// # Examples
 267 ///
 268 /// ```
 269 /// let a = 3;
 270 /// let b = 2;
 271 /// debug_assert_ne!(a, b);
 272 /// ```
 273 #[macro_export]
 274 #[stable(feature = "assert_ne", since = "1.13.0")]
 275 #[cfg_attr(not(test), rustc_diagnostic_item = "debug_assert_ne_macro")]
 276 macro_rules! debug_assert_ne {
 277     ($($arg:tt)*) => {
 278         if $crate::cfg!(debug_assertions) {
 279             $crate::assert_ne!($($arg)*);
 280         }
 281     };
 282 }
 283
 284 /// Asserts that an expression matches any of the given patterns.
 285 ///
 286 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 287 /// and a guard expression that has access to names bound by the pattern.
 288 ///
 289 /// On panic, this macro will print the value of the expression with its
 290 /// debug representation.
 291 ///
 292 /// Unlike [`assert_matches!`], `debug_assert_matches!` statements are only
 293 /// enabled in non optimized builds by default. An optimized build will not
 294 /// execute `debug_assert_matches!` statements unless `-C debug-assertions` is
 295 /// passed to the compiler. This makes `debug_assert_matches!` useful for
 296 /// checks that are too expensive to be present in a release build but may be
 297 /// helpful during development. The result of expanding `debug_assert_matches!`
 298 /// is always type checked.
 299 ///
 300 /// # Examples
 301 ///
 302 /// ```
 303 /// #![feature(assert_matches)]
 304 ///
 305 /// use std::assert_matches::debug_assert_matches;
 306 ///
 307 /// let a = 1u32.checked_add(2);
 308 /// let b = 1u32.checked_sub(2);
 309 /// debug_assert_matches!(a, Some(_));
 310 /// debug_assert_matches!(b, None);
 311 ///
 312 /// let c = Ok("abc".to_string());
 313 /// debug_assert_matches!(c, Ok(x) | Err(x) if x.len() < 100);
 314 /// ```
 315 #[macro_export]
 316 #[unstable(feature = "assert_matches", issue = "82775")]
 317 #[allow_internal_unstable(assert_matches)]
 318 #[rustc_macro_transparency = "semitransparent"]
 319 pub macro debug_assert_matches($($arg:tt)*) {
 320     if $crate::cfg!(debug_assertions) {
 321         $crate::assert_matches::assert_matches!($($arg)*);
 322     }
 323 }
 324
 325 /// Returns whether the given expression matches any of the given patterns.
 326 ///
 327 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 328 /// and a guard expression that has access to names bound by the pattern.
 329 ///
 330 /// # Examples
 331 ///
 332 /// ```
 333 /// let foo = 'f';
 334 /// assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
 335 ///
 336 /// let bar = Some(4);
 337 /// assert!(matches!(bar, Some(x) if x > 2));
 338 /// ```
 339 #[macro_export]
 340 #[stable(feature = "matches_macro", since = "1.42.0")]
 341 #[cfg_attr(not(test), rustc_diagnostic_item = "matches_macro")]
 342 macro_rules! matches {
 343     ($expression:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )? $(,)?) => {
 344         match $expression {
 345             $( $pattern )|+ $( if $guard )? => true,
 346             _ => false
 347         }
 348     };
 349 }
 350
 351 /// Unwraps a result or propagates its error.
 352 ///
 353 /// The `?` operator was added to replace `try!` and should be used instead.
 354 /// Furthermore, `try` is a reserved word in Rust 2018, so if you must use
 355 /// it, you will need to use the [raw-identifier syntax][ris]: `r#try`.
 356 ///
 357 /// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
 358 ///
 359 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 360 /// expression has the value of the wrapped value.
 361 ///
 362 /// In case of the `Err` variant, it retrieves the inner error. `try!` then
 363 /// performs conversion using `From`. This provides automatic conversion
 364 /// between specialized errors and more general ones. The resulting
 365 /// error is then immediately returned.
 366 ///
 367 /// Because of the early return, `try!` can only be used in functions that
 368 /// return [`Result`].
 369 ///
 370 /// # Examples
 371 ///
 372 /// ```
 373 /// use std::io;
 374 /// use std::fs::File;
 375 /// use std::io::prelude::*;
 376 ///
 377 /// enum MyError {
 378 ///     FileWriteError
 379 /// }
 380 ///
 381 /// impl From<io::Error> for MyError {
 382 ///     fn from(e: io::Error) -> MyError {
 383 ///         MyError::FileWriteError
 384 ///     }
 385 /// }
 386 ///
 387 /// // The preferred method of quick returning Errors
 388 /// fn write_to_file_question() -> Result<(), MyError> {
 389 ///     let mut file = File::create("my_best_friends.txt")?;
 390 ///     file.write_all(b"This is a list of my best friends.")?;
 391 ///     Ok(())
 392 /// }
 393 ///
 394 /// // The previous method of quick returning Errors
 395 /// fn write_to_file_using_try() -> Result<(), MyError> {
 396 ///     let mut file = r#try!(File::create("my_best_friends.txt"));
 397 ///     r#try!(file.write_all(b"This is a list of my best friends."));
 398 ///     Ok(())
 399 /// }
 400 ///
 401 /// // This is equivalent to:
 402 /// fn write_to_file_using_match() -> Result<(), MyError> {
 403 ///     let mut file = r#try!(File::create("my_best_friends.txt"));
 404 ///     match file.write_all(b"This is a list of my best friends.") {
 405 ///         Ok(v) => v,
 406 ///         Err(e) => return Err(From::from(e)),
 407 ///     }
 408 ///     Ok(())
 409 /// }
 410 /// ```
 411 #[macro_export]
 412 #[stable(feature = "rust1", since = "1.0.0")]
 413 #[deprecated(since = "1.39.0", note = "use the `?` operator instead")]
 414 #[doc(alias = "?")]
 415 macro_rules! r#try {
 416     ($expr:expr $(,)?) => {
 417         match $expr {
 418             $crate::result::Result::Ok(val) => val,
 419             $crate::result::Result::Err(err) => {
 420                 return $crate::result::Result::Err($crate::convert::From::from(err));
 421             }
 422         }
 423     };
 424 }
 425
 426 /// Writes formatted data into a buffer.
 427 ///
 428 /// This macro accepts a 'writer', a format string, and a list of arguments. Arguments will be
 429 /// formatted according to the specified format string and the result will be passed to the writer.
 430 /// The writer may be any value with a `write_fmt` method; generally this comes from an
 431 /// implementation of either the [`fmt::Write`] or the [`io::Write`] trait. The macro
 432 /// returns whatever the `write_fmt` method returns; commonly a [`fmt::Result`], or an
 433 /// [`io::Result`].
 434 ///
 435 /// See [`std::fmt`] for more information on the format string syntax.
 436 ///
 437 /// [`std::fmt`]: ../std/fmt/index.html
 438 /// [`fmt::Write`]: crate::fmt::Write
 439 /// [`io::Write`]: ../std/io/trait.Write.html
 440 /// [`fmt::Result`]: crate::fmt::Result
 441 /// [`io::Result`]: ../std/io/type.Result.html
 442 ///
 443 /// # Examples
 444 ///
 445 /// ```
 446 /// use std::io::Write;
 447 ///
 448 /// fn main() -> std::io::Result<()> {
 449 ///     let mut w = Vec::new();
 450 ///     write!(&mut w, "test")?;
 451 ///     write!(&mut w, "formatted {}", "arguments")?;
 452 ///
 453 ///     assert_eq!(w, b"testformatted arguments");
 454 ///     Ok(())
 455 /// }
 456 /// ```
 457 ///
 458 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
 459 /// implementing either, as objects do not typically implement both. However, the module must
 460 /// import the traits qualified so their names do not conflict:
 461 ///
 462 /// ```
 463 /// use std::fmt::Write as FmtWrite;
 464 /// use std::io::Write as IoWrite;
 465 ///
 466 /// fn main() -> Result<(), Box<dyn std::error::Error>> {
 467 ///     let mut s = String::new();
 468 ///     let mut v = Vec::new();
 469 ///
 470 ///     write!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
 471 ///     write!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
 472 ///     assert_eq!(v, b"s = \"abc 123\"");
 473 ///     Ok(())
 474 /// }
 475 /// ```
 476 ///
 477 /// Note: This macro can be used in `no_std` setups as well.
 478 /// In a `no_std` setup you are responsible for the implementation details of the components.
 479 ///
 480 /// ```no_run
 481 /// # extern crate core;
 482 /// use core::fmt::Write;
 483 ///
 484 /// struct Example;
 485 ///
 486 /// impl Write for Example {
 487 ///     fn write_str(&mut self, _s: &str) -> core::fmt::Result {
 488 ///          unimplemented!();
 489 ///     }
 490 /// }
 491 ///
 492 /// let mut m = Example{};
 493 /// write!(&mut m, "Hello World").expect("Not written");
 494 /// ```
 495 #[macro_export]
 496 #[stable(feature = "rust1", since = "1.0.0")]
 497 #[cfg_attr(not(test), rustc_diagnostic_item = "write_macro")]
 498 macro_rules! write {
 499     ($dst:expr, $($arg:tt)*) => {
 500         $dst.write_fmt($crate::format_args!($($arg)*))
 501     };
 502 }
 503
 504 /// Write formatted data into a buffer, with a newline appended.
 505 ///
 506 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
 507 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
 508 ///
 509 /// For more information, see [`write!`]. For information on the format string syntax, see
 510 /// [`std::fmt`].
 511 ///
 512 /// [`std::fmt`]: ../std/fmt/index.html
 513 ///
 514 /// # Examples
 515 ///
 516 /// ```
 517 /// use std::io::{Write, Result};
 518 ///
 519 /// fn main() -> Result<()> {
 520 ///     let mut w = Vec::new();
 521 ///     writeln!(&mut w)?;
 522 ///     writeln!(&mut w, "test")?;
 523 ///     writeln!(&mut w, "formatted {}", "arguments")?;
 524 ///
 525 ///     assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
 526 ///     Ok(())
 527 /// }
 528 /// ```
 529 ///
 530 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
 531 /// implementing either, as objects do not typically implement both. However, the module must
 532 /// import the traits qualified so their names do not conflict:
 533 ///
 534 /// ```
 535 /// use std::fmt::Write as FmtWrite;
 536 /// use std::io::Write as IoWrite;
 537 ///
 538 /// fn main() -> Result<(), Box<dyn std::error::Error>> {
 539 ///     let mut s = String::new();
 540 ///     let mut v = Vec::new();
 541 ///
 542 ///     writeln!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
 543 ///     writeln!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
 544 ///     assert_eq!(v, b"s = \"abc 123\\n\"\n");
 545 ///     Ok(())
 546 /// }
 547 /// ```
 548 #[macro_export]
 549 #[stable(feature = "rust1", since = "1.0.0")]
 550 #[cfg_attr(not(test), rustc_diagnostic_item = "writeln_macro")]
 551 #[allow_internal_unstable(format_args_nl)]
 552 macro_rules! writeln {
 553     ($dst:expr $(,)?) => {
 554         $crate::write!($dst, "\n")
 555     };
 556     ($dst:expr, $($arg:tt)*) => {
 557         $dst.write_fmt($crate::format_args_nl!($($arg)*))
 558     };
 559 }
 560
 561 /// Indicates unreachable code.
 562 ///
 563 /// This is useful any time that the compiler can't determine that some code is unreachable. For
 564 /// example:
 565 ///
 566 /// * Match arms with guard conditions.
 567 /// * Loops that dynamically terminate.
 568 /// * Iterators that dynamically terminate.
 569 ///
 570 /// If the determination that the code is unreachable proves incorrect, the
 571 /// program immediately terminates with a [`panic!`].
 572 ///
 573 /// The unsafe counterpart of this macro is the [`unreachable_unchecked`] function, which
 574 /// will cause undefined behavior if the code is reached.
 575 ///
 576 /// [`unreachable_unchecked`]: crate::hint::unreachable_unchecked
 577 ///
 578 /// # Panics
 579 ///
 580 /// This will always [`panic!`] because `unreachable!` is just a shorthand for `panic!` with a
 581 /// fixed, specific message.
 582 ///
 583 /// Like `panic!`, this macro has a second form for displaying custom values.
 584 ///
 585 /// # Examples
 586 ///
 587 /// Match arms:
 588 ///
 589 /// ```
 590 /// # #[allow(dead_code)]
 591 /// fn foo(x: Option<i32>) {
 592 ///     match x {
 593 ///         Some(n) if n >= 0 => println!("Some(Non-negative)"),
 594 ///         Some(n) if n <  0 => println!("Some(Negative)"),
 595 ///         Some(_)           => unreachable!(), // compile error if commented out
 596 ///         None              => println!("None")
 597 ///     }
 598 /// }
 599 /// ```
 600 ///
 601 /// Iterators:
 602 ///
 603 /// ```
 604 /// # #[allow(dead_code)]
 605 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
 606 ///     for i in 0.. {
 607 ///         if 3*i < i { panic!("u32 overflow"); }
 608 ///         if x < 3*i { return i-1; }
 609 ///     }
 610 ///     unreachable!("The loop should always return");
 611 /// }
 612 /// ```
 613 #[macro_export]
 614 #[rustc_builtin_macro(unreachable)]
 615 #[allow_internal_unstable(edition_panic)]
 616 #[stable(feature = "rust1", since = "1.0.0")]
 617 #[cfg_attr(not(test), rustc_diagnostic_item = "unreachable_macro")]
 618 macro_rules! unreachable {
 619     // Expands to either `$crate::panic::unreachable_2015` or `$crate::panic::unreachable_2021`
 620     // depending on the edition of the caller.
 621     ($($arg:tt)*) => {
 622         /* compiler built-in */
 623     };
 624 }
 625
 626 /// Indicates unimplemented code by panicking with a message of "not implemented".
 627 ///
 628 /// This allows your code to type-check, which is useful if you are prototyping or
 629 /// implementing a trait that requires multiple methods which you don't plan to use all of.
 630 ///
 631 /// The difference between `unimplemented!` and [`todo!`] is that while `todo!`
 632 /// conveys an intent of implementing the functionality later and the message is "not yet
 633 /// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
 634 /// Also some IDEs will mark `todo!`s.
 635 ///
 636 /// # Panics
 637 ///
 638 /// This will always [`panic!`] because `unimplemented!` is just a shorthand for `panic!` with a
 639 /// fixed, specific message.
 640 ///
 641 /// Like `panic!`, this macro has a second form for displaying custom values.
 642 ///
 643 /// [`todo!`]: crate::todo
 644 ///
 645 /// # Examples
 646 ///
 647 /// Say we have a trait `Foo`:
 648 ///
 649 /// ```
 650 /// trait Foo {
 651 ///     fn bar(&self) -> u8;
 652 ///     fn baz(&self);
 653 ///     fn qux(&self) -> Result<u64, ()>;
 654 /// }
 655 /// ```
 656 ///
 657 /// We want to implement `Foo` for 'MyStruct', but for some reason it only makes sense
 658 /// to implement the `bar()` function. `baz()` and `qux()` will still need to be defined
 659 /// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
 660 /// to allow our code to compile.
 661 ///
 662 /// We still want to have our program stop running if the unimplemented methods are
 663 /// reached.
 664 ///
 665 /// ```
 666 /// # trait Foo {
 667 /// #     fn bar(&self) -> u8;
 668 /// #     fn baz(&self);
 669 /// #     fn qux(&self) -> Result<u64, ()>;
 670 /// # }
 671 /// struct MyStruct;
 672 ///
 673 /// impl Foo for MyStruct {
 674 ///     fn bar(&self) -> u8 {
 675 ///         1 + 1
 676 ///     }
 677 ///
 678 ///     fn baz(&self) {
 679 ///         // It makes no sense to `baz` a `MyStruct`, so we have no logic here
 680 ///         // at all.
 681 ///         // This will display "thread 'main' panicked at 'not implemented'".
 682 ///         unimplemented!();
 683 ///     }
 684 ///
 685 ///     fn qux(&self) -> Result<u64, ()> {
 686 ///         // We have some logic here,
 687 ///         // We can add a message to unimplemented! to display our omission.
 688 ///         // This will display:
 689 ///         // "thread 'main' panicked at 'not implemented: MyStruct isn't quxable'".
 690 ///         unimplemented!("MyStruct isn't quxable");
 691 ///     }
 692 /// }
 693 ///
 694 /// fn main() {
 695 ///     let s = MyStruct;
 696 ///     s.bar();
 697 /// }
 698 /// ```
 699 #[macro_export]
 700 #[stable(feature = "rust1", since = "1.0.0")]
 701 #[cfg_attr(not(test), rustc_diagnostic_item = "unimplemented_macro")]
 702 #[allow_internal_unstable(core_panic)]
 703 macro_rules! unimplemented {
 704     () => {
 705         $crate::panicking::panic("not implemented")
 706     };
 707     ($($arg:tt)+) => {
 708         $crate::panic!("not implemented: {}", $crate::format_args!($($arg)+))
 709     };
 710 }
 711
 712 /// Indicates unfinished code.
 713 ///
 714 /// This can be useful if you are prototyping and are just looking to have your
 715 /// code typecheck.
 716 ///
 717 /// The difference between [`unimplemented!`] and `todo!` is that while `todo!` conveys
 718 /// an intent of implementing the functionality later and the message is "not yet
 719 /// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
 720 /// Also some IDEs will mark `todo!`s.
 721 ///
 722 /// # Panics
 723 ///
 724 /// This will always [`panic!`].
 725 ///
 726 /// # Examples
 727 ///
 728 /// Here's an example of some in-progress code. We have a trait `Foo`:
 729 ///
 730 /// ```
 731 /// trait Foo {
 732 ///     fn bar(&self);
 733 ///     fn baz(&self);
 734 /// }
 735 /// ```
 736 ///
 737 /// We want to implement `Foo` on one of our types, but we also want to work on
 738 /// just `bar()` first. In order for our code to compile, we need to implement
 739 /// `baz()`, so we can use `todo!`:
 740 ///
 741 /// ```
 742 /// # trait Foo {
 743 /// #     fn bar(&self);
 744 /// #     fn baz(&self);
 745 /// # }
 746 /// struct MyStruct;
 747 ///
 748 /// impl Foo for MyStruct {
 749 ///     fn bar(&self) {
 750 ///         // implementation goes here
 751 ///     }
 752 ///
 753 ///     fn baz(&self) {
 754 ///         // let's not worry about implementing baz() for now
 755 ///         todo!();
 756 ///     }
 757 /// }
 758 ///
 759 /// fn main() {
 760 ///     let s = MyStruct;
 761 ///     s.bar();
 762 ///
 763 ///     // we aren't even using baz(), so this is fine.
 764 /// }
 765 /// ```
 766 #[macro_export]
 767 #[stable(feature = "todo_macro", since = "1.40.0")]
 768 #[cfg_attr(not(test), rustc_diagnostic_item = "todo_macro")]
 769 #[allow_internal_unstable(core_panic)]
 770 macro_rules! todo {
 771     () => {
 772         $crate::panicking::panic("not yet implemented")
 773     };
 774     ($($arg:tt)+) => {
 775         $crate::panic!("not yet implemented: {}", $crate::format_args!($($arg)+))
 776     };
 777 }
 778
 779 /// Definitions of built-in macros.
 780 ///
 781 /// Most of the macro properties (stability, visibility, etc.) are taken from the source code here,
 782 /// with exception of expansion functions transforming macro inputs into outputs,
 783 /// those functions are provided by the compiler.
 784 pub(crate) mod builtin {
 785
 786     /// Causes compilation to fail with the given error message when encountered.
 787     ///
 788     /// This macro should be used when a crate uses a conditional compilation strategy to provide
 789     /// better error messages for erroneous conditions. It's the compiler-level form of [`panic!`],
 790     /// but emits an error during *compilation* rather than at *runtime*.
 791     ///
 792     /// # Examples
 793     ///
 794     /// Two such examples are macros and `#[cfg]` environments.
 795     ///
 796     /// Emit a better compiler error if a macro is passed invalid values. Without the final branch,
 797     /// the compiler would still emit an error, but the error's message would not mention the two
 798     /// valid values.
 799     ///
 800     /// ```compile_fail
 801     /// macro_rules! give_me_foo_or_bar {
 802     ///     (foo) => {};
 803     ///     (bar) => {};
 804     ///     ($x:ident) => {
 805     ///         compile_error!("This macro only accepts `foo` or `bar`");
 806     ///     }
 807     /// }
 808     ///
 809     /// give_me_foo_or_bar!(neither);
 810     /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
 811     /// ```
 812     ///
 813     /// Emit a compiler error if one of a number of features isn't available.
 814     ///
 815     /// ```compile_fail
 816     /// #[cfg(not(any(feature = "foo", feature = "bar")))]
 817     /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.");
 818     /// ```
 819     #[stable(feature = "compile_error_macro", since = "1.20.0")]
 820     #[rustc_builtin_macro]
 821     #[macro_export]
 822     #[cfg_attr(not(test), rustc_diagnostic_item = "compile_error_macro")]
 823     macro_rules! compile_error {
 824         ($msg:expr $(,)?) => {{ /* compiler built-in */ }};
 825     }
 826
 827     /// Constructs parameters for the other string-formatting macros.
 828     ///
 829     /// This macro functions by taking a formatting string literal containing
 830     /// `{}` for each additional argument passed. `format_args!` prepares the
 831     /// additional parameters to ensure the output can be interpreted as a string
 832     /// and canonicalizes the arguments into a single type. Any value that implements
 833     /// the [`Display`] trait can be passed to `format_args!`, as can any
 834     /// [`Debug`] implementation be passed to a `{:?}` within the formatting string.
 835     ///
 836     /// This macro produces a value of type [`fmt::Arguments`]. This value can be
 837     /// passed to the macros within [`std::fmt`] for performing useful redirection.
 838     /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
 839     /// proxied through this one. `format_args!`, unlike its derived macros, avoids
 840     /// heap allocations.
 841     ///
 842     /// You can use the [`fmt::Arguments`] value that `format_args!` returns
 843     /// in `Debug` and `Display` contexts as seen below. The example also shows
 844     /// that `Debug` and `Display` format to the same thing: the interpolated
 845     /// format string in `format_args!`.
 846     ///
 847     /// ```rust
 848     /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
 849     /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
 850     /// assert_eq!("1 foo 2", display);
 851     /// assert_eq!(display, debug);
 852     /// ```
 853     ///
 854     /// For more information, see the documentation in [`std::fmt`].
 855     ///
 856     /// [`Display`]: crate::fmt::Display
 857     /// [`Debug`]: crate::fmt::Debug
 858     /// [`fmt::Arguments`]: crate::fmt::Arguments
 859     /// [`std::fmt`]: ../std/fmt/index.html
 860     /// [`format!`]: ../std/macro.format.html
 861     /// [`println!`]: ../std/macro.println.html
 862     ///
 863     /// # Examples
 864     ///
 865     /// ```
 866     /// use std::fmt;
 867     ///
 868     /// let s = fmt::format(format_args!("hello {}", "world"));
 869     /// assert_eq!(s, format!("hello {}", "world"));
 870     /// ```
 871     #[stable(feature = "rust1", since = "1.0.0")]
 872     #[cfg_attr(not(test), rustc_diagnostic_item = "format_args_macro")]
 873     #[allow_internal_unsafe]
 874     #[allow_internal_unstable(fmt_internals)]
 875     #[rustc_builtin_macro]
 876     #[macro_export]
 877     macro_rules! format_args {
 878         ($fmt:expr) => {{ /* compiler built-in */ }};
 879         ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
 880     }
 881
 882     /// Same as [`format_args`], but can be used in some const contexts.
 883     ///
 884     /// This macro is used by the panic macros for the `const_panic` feature.
 885     ///
 886     /// This macro will be removed once `format_args` is allowed in const contexts.
 887     #[unstable(feature = "const_format_args", issue = "none")]
 888     #[allow_internal_unstable(fmt_internals, const_fmt_arguments_new)]
 889     #[rustc_builtin_macro]
 890     #[macro_export]
 891     macro_rules! const_format_args {
 892         ($fmt:expr) => {{ /* compiler built-in */ }};
 893         ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
 894     }
 895
 896     /// Same as [`format_args`], but adds a newline in the end.
 897     #[unstable(
 898         feature = "format_args_nl",
 899         issue = "none",
 900         reason = "`format_args_nl` is only for internal \
 901                   language use and is subject to change"
 902     )]
 903     #[allow_internal_unstable(fmt_internals)]
 904     #[rustc_builtin_macro]
 905     #[macro_export]
 906     macro_rules! format_args_nl {
 907         ($fmt:expr) => {{ /* compiler built-in */ }};
 908         ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
 909     }
 910
 911     /// Inspects an environment variable at compile time.
 912     ///
 913     /// This macro will expand to the value of the named environment variable at
 914     /// compile time, yielding an expression of type `&'static str`. Use
 915     /// [`std::env::var`] instead if you want to read the value at runtime.
 916     ///
 917     /// [`std::env::var`]: ../std/env/fn.var.html
 918     ///
 919     /// If the environment variable is not defined, then a compilation error
 920     /// will be emitted. To not emit a compile error, use the [`option_env!`]
 921     /// macro instead.
 922     ///
 923     /// # Examples
 924     ///
 925     /// ```
 926     /// let path: &'static str = env!("PATH");
 927     /// println!("the $PATH variable at the time of compiling was: {path}");
 928     /// ```
 929     ///
 930     /// You can customize the error message by passing a string as the second
 931     /// parameter:
 932     ///
 933     /// ```compile_fail
 934     /// let doc: &'static str = env!("documentation", "what's that?!");
 935     /// ```
 936     ///
 937     /// If the `documentation` environment variable is not defined, you'll get
 938     /// the following error:
 939     ///
 940     /// ```text
 941     /// error: what's that?!
 942     /// ```
 943     #[stable(feature = "rust1", since = "1.0.0")]
 944     #[rustc_builtin_macro]
 945     #[macro_export]
 946     #[cfg_attr(not(test), rustc_diagnostic_item = "env_macro")]
 947     macro_rules! env {
 948         ($name:expr $(,)?) => {{ /* compiler built-in */ }};
 949         ($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
 950     }
 951
 952     /// Optionally inspects an environment variable at compile time.
 953     ///
 954     /// If the named environment variable is present at compile time, this will
 955     /// expand into an expression of type `Option<&'static str>` whose value is
 956     /// `Some` of the value of the environment variable. If the environment
 957     /// variable is not present, then this will expand to `None`. See
 958     /// [`Option<T>`][Option] for more information on this type.  Use
 959     /// [`std::env::var`] instead if you want to read the value at runtime.
 960     ///
 961     /// [`std::env::var`]: ../std/env/fn.var.html
 962     ///
 963     /// A compile time error is never emitted when using this macro regardless
 964     /// of whether the environment variable is present or not.
 965     ///
 966     /// # Examples
 967     ///
 968     /// ```
 969     /// let key: Option<&'static str> = option_env!("SECRET_KEY");
 970     /// println!("the secret key might be: {key:?}");
 971     /// ```
 972     #[stable(feature = "rust1", since = "1.0.0")]
 973     #[rustc_builtin_macro]
 974     #[macro_export]
 975     #[cfg_attr(not(test), rustc_diagnostic_item = "option_env_macro")]
 976     macro_rules! option_env {
 977         ($name:expr $(,)?) => {{ /* compiler built-in */ }};
 978     }
 979
 980     /// Concatenates identifiers into one identifier.
 981     ///
 982     /// This macro takes any number of comma-separated identifiers, and
 983     /// concatenates them all into one, yielding an expression which is a new
 984     /// identifier. Note that hygiene makes it such that this macro cannot
 985     /// capture local variables. Also, as a general rule, macros are only
 986     /// allowed in item, statement or expression position. That means while
 987     /// you may use this macro for referring to existing variables, functions or
 988     /// modules etc, you cannot define a new one with it.
 989     ///
 990     /// # Examples
 991     ///
 992     /// ```
 993     /// #![feature(concat_idents)]
 994     ///
 995     /// # fn main() {
 996     /// fn foobar() -> u32 { 23 }
 997     ///
 998     /// let f = concat_idents!(foo, bar);
 999     /// println!("{}", f());
1000     ///
1001     /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
1002     /// # }
1003     /// ```
1004     #[unstable(
1005         feature = "concat_idents",
1006         issue = "29599",
1007         reason = "`concat_idents` is not stable enough for use and is subject to change"
1008     )]
1009     #[rustc_builtin_macro]
1010     #[macro_export]
1011     macro_rules! concat_idents {
1012         ($($e:ident),+ $(,)?) => {{ /* compiler built-in */ }};
1013     }
1014
1015     /// Concatenates literals into a byte slice.
1016     ///
1017     /// This macro takes any number of comma-separated literals, and concatenates them all into
1018     /// one, yielding an expression of type `&[u8, _]`, which represents all of the literals
1019     /// concatenated left-to-right. The literals passed can be any combination of:
1020     ///
1021     /// - byte literals (`b'r'`)
1022     /// - byte strings (`b"Rust"`)
1023     /// - arrays of bytes/numbers (`[b'A', 66, b'C']`)
1024     ///
1025     /// # Examples
1026     ///
1027     /// ```
1028     /// #![feature(concat_bytes)]
1029     ///
1030     /// # fn main() {
1031     /// let s: &[u8; 6] = concat_bytes!(b'A', b"BC", [68, b'E', 70]);
1032     /// assert_eq!(s, b"ABCDEF");
1033     /// # }
1034     /// ```
1035     #[unstable(feature = "concat_bytes", issue = "87555")]
1036     #[rustc_builtin_macro]
1037     #[macro_export]
1038     macro_rules! concat_bytes {
1039         ($($e:literal),+ $(,)?) => {{ /* compiler built-in */ }};
1040     }
1041
1042     /// Concatenates literals into a static string slice.
1043     ///
1044     /// This macro takes any number of comma-separated literals, yielding an
1045     /// expression of type `&'static str` which represents all of the literals
1046     /// concatenated left-to-right.
1047     ///
1048     /// Integer and floating point literals are stringified in order to be
1049     /// concatenated.
1050     ///
1051     /// # Examples
1052     ///
1053     /// ```
1054     /// let s = concat!("test", 10, 'b', true);
1055     /// assert_eq!(s, "test10btrue");
1056     /// ```
1057     #[stable(feature = "rust1", since = "1.0.0")]
1058     #[rustc_builtin_macro]
1059     #[macro_export]
1060     #[cfg_attr(not(test), rustc_diagnostic_item = "concat_macro")]
1061     macro_rules! concat {
1062         ($($e:expr),* $(,)?) => {{ /* compiler built-in */ }};
1063     }
1064
1065     /// Expands to the line number on which it was invoked.
1066     ///
1067     /// With [`column!`] and [`file!`], these macros provide debugging information for
1068     /// developers about the location within the source.
1069     ///
1070     /// The expanded expression has type `u32` and is 1-based, so the first line
1071     /// in each file evaluates to 1, the second to 2, etc. This is consistent
1072     /// with error messages by common compilers or popular editors.
1073     /// The returned line is *not necessarily* the line of the `line!` invocation itself,
1074     /// but rather the first macro invocation leading up to the invocation
1075     /// of the `line!` macro.
1076     ///
1077     /// # Examples
1078     ///
1079     /// ```
1080     /// let current_line = line!();
1081     /// println!("defined on line: {current_line}");
1082     /// ```
1083     #[stable(feature = "rust1", since = "1.0.0")]
1084     #[rustc_builtin_macro]
1085     #[macro_export]
1086     #[cfg_attr(not(test), rustc_diagnostic_item = "line_macro")]
1087     macro_rules! line {
1088         () => {
1089             /* compiler built-in */
1090         };
1091     }
1092
1093     /// Expands to the column number at which it was invoked.
1094     ///
1095     /// With [`line!`] and [`file!`], these macros provide debugging information for
1096     /// developers about the location within the source.
1097     ///
1098     /// The expanded expression has type `u32` and is 1-based, so the first column
1099     /// in each line evaluates to 1, the second to 2, etc. This is consistent
1100     /// with error messages by common compilers or popular editors.
1101     /// The returned column is *not necessarily* the line of the `column!` invocation itself,
1102     /// but rather the first macro invocation leading up to the invocation
1103     /// of the `column!` macro.
1104     ///
1105     /// # Examples
1106     ///
1107     /// ```
1108     /// let current_col = column!();
1109     /// println!("defined on column: {current_col}");
1110     /// ```
1111     ///
1112     /// `column!` counts Unicode code points, not bytes or graphemes. As a result, the first two
1113     /// invocations return the same value, but the third does not.
1114     ///
1115     /// ```
1116     /// let a = ("foobar", column!()).1;
1117     /// let b = ("人之初性本善", column!()).1;
1118     /// let c = ("f̅o̅o̅b̅a̅r̅", column!()).1; // Uses combining overline (U+0305)
1119     ///
1120     /// assert_eq!(a, b);
1121     /// assert_ne!(b, c);
1122     /// ```
1123     #[stable(feature = "rust1", since = "1.0.0")]
1124     #[rustc_builtin_macro]
1125     #[macro_export]
1126     #[cfg_attr(not(test), rustc_diagnostic_item = "column_macro")]
1127     macro_rules! column {
1128         () => {
1129             /* compiler built-in */
1130         };
1131     }
1132
1133     /// Expands to the file name in which it was invoked.
1134     ///
1135     /// With [`line!`] and [`column!`], these macros provide debugging information for
1136     /// developers about the location within the source.
1137     ///
1138     /// The expanded expression has type `&'static str`, and the returned file
1139     /// is not the invocation of the `file!` macro itself, but rather the
1140     /// first macro invocation leading up to the invocation of the `file!`
1141     /// macro.
1142     ///
1143     /// # Examples
1144     ///
1145     /// ```
1146     /// let this_file = file!();
1147     /// println!("defined in file: {this_file}");
1148     /// ```
1149     #[stable(feature = "rust1", since = "1.0.0")]
1150     #[rustc_builtin_macro]
1151     #[macro_export]
1152     #[cfg_attr(not(test), rustc_diagnostic_item = "file_macro")]
1153     macro_rules! file {
1154         () => {
1155             /* compiler built-in */
1156         };
1157     }
1158
1159     /// Stringifies its arguments.
1160     ///
1161     /// This macro will yield an expression of type `&'static str` which is the
1162     /// stringification of all the tokens passed to the macro. No restrictions
1163     /// are placed on the syntax of the macro invocation itself.
1164     ///
1165     /// Note that the expanded results of the input tokens may change in the
1166     /// future. You should be careful if you rely on the output.
1167     ///
1168     /// # Examples
1169     ///
1170     /// ```
1171     /// let one_plus_one = stringify!(1 + 1);
1172     /// assert_eq!(one_plus_one, "1 + 1");
1173     /// ```
1174     #[stable(feature = "rust1", since = "1.0.0")]
1175     #[rustc_builtin_macro]
1176     #[macro_export]
1177     #[cfg_attr(not(test), rustc_diagnostic_item = "stringify_macro")]
1178     macro_rules! stringify {
1179         ($($t:tt)*) => {
1180             /* compiler built-in */
1181         };
1182     }
1183
1184     /// Includes a UTF-8 encoded file as a string.
1185     ///
1186     /// The file is located relative to the current file (similarly to how
1187     /// modules are found). The provided path is interpreted in a platform-specific
1188     /// way at compile time. So, for instance, an invocation with a Windows path
1189     /// containing backslashes `\` would not compile correctly on Unix.
1190     ///
1191     /// This macro will yield an expression of type `&'static str` which is the
1192     /// contents of the file.
1193     ///
1194     /// # Examples
1195     ///
1196     /// Assume there are two files in the same directory with the following
1197     /// contents:
1198     ///
1199     /// File 'spanish.in':
1200     ///
1201     /// ```text
1202     /// adiós
1203     /// ```
1204     ///
1205     /// File 'main.rs':
1206     ///
1207     /// ```ignore (cannot-doctest-external-file-dependency)
1208     /// fn main() {
1209     ///     let my_str = include_str!("spanish.in");
1210     ///     assert_eq!(my_str, "adiós\n");
1211     ///     print!("{my_str}");
1212     /// }
1213     /// ```
1214     ///
1215     /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1216     #[stable(feature = "rust1", since = "1.0.0")]
1217     #[rustc_builtin_macro]
1218     #[macro_export]
1219     #[cfg_attr(not(test), rustc_diagnostic_item = "include_str_macro")]
1220     macro_rules! include_str {
1221         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1222     }
1223
1224     /// Includes a file as a reference to a byte array.
1225     ///
1226     /// The file is located relative to the current file (similarly to how
1227     /// modules are found). The provided path is interpreted in a platform-specific
1228     /// way at compile time. So, for instance, an invocation with a Windows path
1229     /// containing backslashes `\` would not compile correctly on Unix.
1230     ///
1231     /// This macro will yield an expression of type `&'static [u8; N]` which is
1232     /// the contents of the file.
1233     ///
1234     /// # Examples
1235     ///
1236     /// Assume there are two files in the same directory with the following
1237     /// contents:
1238     ///
1239     /// File 'spanish.in':
1240     ///
1241     /// ```text
1242     /// adiós
1243     /// ```
1244     ///
1245     /// File 'main.rs':
1246     ///
1247     /// ```ignore (cannot-doctest-external-file-dependency)
1248     /// fn main() {
1249     ///     let bytes = include_bytes!("spanish.in");
1250     ///     assert_eq!(bytes, b"adi\xc3\xb3s\n");
1251     ///     print!("{}", String::from_utf8_lossy(bytes));
1252     /// }
1253     /// ```
1254     ///
1255     /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1256     #[stable(feature = "rust1", since = "1.0.0")]
1257     #[rustc_builtin_macro]
1258     #[macro_export]
1259     #[cfg_attr(not(test), rustc_diagnostic_item = "include_bytes_macro")]
1260     macro_rules! include_bytes {
1261         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1262     }
1263
1264     /// Expands to a string that represents the current module path.
1265     ///
1266     /// The current module path can be thought of as the hierarchy of modules
1267     /// leading back up to the crate root. The first component of the path
1268     /// returned is the name of the crate currently being compiled.
1269     ///
1270     /// # Examples
1271     ///
1272     /// ```
1273     /// mod test {
1274     ///     pub fn foo() {
1275     ///         assert!(module_path!().ends_with("test"));
1276     ///     }
1277     /// }
1278     ///
1279     /// test::foo();
1280     /// ```
1281     #[stable(feature = "rust1", since = "1.0.0")]
1282     #[rustc_builtin_macro]
1283     #[macro_export]
1284     #[cfg_attr(not(test), rustc_diagnostic_item = "module_path_macro")]
1285     macro_rules! module_path {
1286         () => {
1287             /* compiler built-in */
1288         };
1289     }
1290
1291     /// Evaluates boolean combinations of configuration flags at compile-time.
1292     ///
1293     /// In addition to the `#[cfg]` attribute, this macro is provided to allow
1294     /// boolean expression evaluation of configuration flags. This frequently
1295     /// leads to less duplicated code.
1296     ///
1297     /// The syntax given to this macro is the same syntax as the [`cfg`]
1298     /// attribute.
1299     ///
1300     /// `cfg!`, unlike `#[cfg]`, does not remove any code and only evaluates to true or false. For
1301     /// example, all blocks in an if/else expression need to be valid when `cfg!` is used for
1302     /// the condition, regardless of what `cfg!` is evaluating.
1303     ///
1304     /// [`cfg`]: ../reference/conditional-compilation.html#the-cfg-attribute
1305     ///
1306     /// # Examples
1307     ///
1308     /// ```
1309     /// let my_directory = if cfg!(windows) {
1310     ///     "windows-specific-directory"
1311     /// } else {
1312     ///     "unix-directory"
1313     /// };
1314     /// ```
1315     #[stable(feature = "rust1", since = "1.0.0")]
1316     #[rustc_builtin_macro]
1317     #[macro_export]
1318     #[cfg_attr(not(test), rustc_diagnostic_item = "cfg_macro")]
1319     macro_rules! cfg {
1320         ($($cfg:tt)*) => {
1321             /* compiler built-in */
1322         };
1323     }
1324
1325     /// Parses a file as an expression or an item according to the context.
1326     ///
1327     /// The file is located relative to the current file (similarly to how
1328     /// modules are found). The provided path is interpreted in a platform-specific
1329     /// way at compile time. So, for instance, an invocation with a Windows path
1330     /// containing backslashes `\` would not compile correctly on Unix.
1331     ///
1332     /// Using this macro is often a bad idea, because if the file is
1333     /// parsed as an expression, it is going to be placed in the
1334     /// surrounding code unhygienically. This could result in variables
1335     /// or functions being different from what the file expected if
1336     /// there are variables or functions that have the same name in
1337     /// the current file.
1338     ///
1339     /// # Examples
1340     ///
1341     /// Assume there are two files in the same directory with the following
1342     /// contents:
1343     ///
1344     /// File 'monkeys.in':
1345     ///
1346     /// ```ignore (only-for-syntax-highlight)
1347     /// ['🙈', '🙊', '🙉']
1348     ///     .iter()
1349     ///     .cycle()
1350     ///     .take(6)
1351     ///     .collect::<String>()
1352     /// ```
1353     ///
1354     /// File 'main.rs':
1355     ///
1356     /// ```ignore (cannot-doctest-external-file-dependency)
1357     /// fn main() {
1358     ///     let my_string = include!("monkeys.in");
1359     ///     assert_eq!("🙈🙊🙉🙈🙊🙉", my_string);
1360     ///     println!("{my_string}");
1361     /// }
1362     /// ```
1363     ///
1364     /// Compiling 'main.rs' and running the resulting binary will print
1365     /// "🙈🙊🙉🙈🙊🙉".
1366     #[stable(feature = "rust1", since = "1.0.0")]
1367     #[rustc_builtin_macro]
1368     #[macro_export]
1369     #[cfg_attr(not(test), rustc_diagnostic_item = "include_macro")]
1370     macro_rules! include {
1371         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1372     }
1373
1374     /// Asserts that a boolean expression is `true` at runtime.
1375     ///
1376     /// This will invoke the [`panic!`] macro if the provided expression cannot be
1377     /// evaluated to `true` at runtime.
1378     ///
1379     /// # Uses
1380     ///
1381     /// Assertions are always checked in both debug and release builds, and cannot
1382     /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
1383     /// release builds by default.
1384     ///
1385     /// Unsafe code may rely on `assert!` to enforce run-time invariants that, if
1386     /// violated could lead to unsafety.
1387     ///
1388     /// Other use-cases of `assert!` include testing and enforcing run-time
1389     /// invariants in safe code (whose violation cannot result in unsafety).
1390     ///
1391     /// # Custom Messages
1392     ///
1393     /// This macro has a second form, where a custom panic message can
1394     /// be provided with or without arguments for formatting. See [`std::fmt`]
1395     /// for syntax for this form. Expressions used as format arguments will only
1396     /// be evaluated if the assertion fails.
1397     ///
1398     /// [`std::fmt`]: ../std/fmt/index.html
1399     ///
1400     /// # Examples
1401     ///
1402     /// ```
1403     /// // the panic message for these assertions is the stringified value of the
1404     /// // expression given.
1405     /// assert!(true);
1406     ///
1407     /// fn some_computation() -> bool { true } // a very simple function
1408     ///
1409     /// assert!(some_computation());
1410     ///
1411     /// // assert with a custom message
1412     /// let x = true;
1413     /// assert!(x, "x wasn't true!");
1414     ///
1415     /// let a = 3; let b = 27;
1416     /// assert!(a + b == 30, "a = {}, b = {}", a, b);
1417     /// ```
1418     #[stable(feature = "rust1", since = "1.0.0")]
1419     #[rustc_builtin_macro]
1420     #[macro_export]
1421     #[rustc_diagnostic_item = "assert_macro"]
1422     #[allow_internal_unstable(core_panic, edition_panic)]
1423     macro_rules! assert {
1424         ($cond:expr $(,)?) => {{ /* compiler built-in */ }};
1425         ($cond:expr, $($arg:tt)+) => {{ /* compiler built-in */ }};
1426     }
1427
1428     /// Prints passed tokens into the standard output.
1429     #[unstable(
1430         feature = "log_syntax",
1431         issue = "29598",
1432         reason = "`log_syntax!` is not stable enough for use and is subject to change"
1433     )]
1434     #[rustc_builtin_macro]
1435     #[macro_export]
1436     macro_rules! log_syntax {
1437         ($($arg:tt)*) => {
1438             /* compiler built-in */
1439         };
1440     }
1441
1442     /// Enables or disables tracing functionality used for debugging other macros.
1443     #[unstable(
1444         feature = "trace_macros",
1445         issue = "29598",
1446         reason = "`trace_macros` is not stable enough for use and is subject to change"
1447     )]
1448     #[rustc_builtin_macro]
1449     #[macro_export]
1450     macro_rules! trace_macros {
1451         (true) => {{ /* compiler built-in */ }};
1452         (false) => {{ /* compiler built-in */ }};
1453     }
1454
1455     /// Attribute macro used to apply derive macros.
1456     ///
1457     /// See [the reference] for more info.
1458     ///
1459     /// [the reference]: ../../../reference/attributes/derive.html
1460     #[stable(feature = "rust1", since = "1.0.0")]
1461     #[rustc_builtin_macro]
1462     pub macro derive($item:item) {
1463         /* compiler built-in */
1464     }
1465
1466     /// Attribute macro applied to a function to turn it into a unit test.
1467     ///
1468     /// See [the reference] for more info.
1469     ///
1470     /// [the reference]: ../../../reference/attributes/testing.html#the-test-attribute
1471     #[stable(feature = "rust1", since = "1.0.0")]
1472     #[allow_internal_unstable(test, rustc_attrs)]
1473     #[rustc_builtin_macro]
1474     pub macro test($item:item) {
1475         /* compiler built-in */
1476     }
1477
1478     /// Attribute macro applied to a function to turn it into a benchmark test.
1479     #[unstable(
1480         feature = "test",
1481         issue = "50297",
1482         soft,
1483         reason = "`bench` is a part of custom test frameworks which are unstable"
1484     )]
1485     #[allow_internal_unstable(test, rustc_attrs)]
1486     #[rustc_builtin_macro]
1487     pub macro bench($item:item) {
1488         /* compiler built-in */
1489     }
1490
1491     /// An implementation detail of the `#[test]` and `#[bench]` macros.
1492     #[unstable(
1493         feature = "custom_test_frameworks",
1494         issue = "50297",
1495         reason = "custom test frameworks are an unstable feature"
1496     )]
1497     #[allow_internal_unstable(test, rustc_attrs)]
1498     #[rustc_builtin_macro]
1499     pub macro test_case($item:item) {
1500         /* compiler built-in */
1501     }
1502
1503     /// Attribute macro applied to a static to register it as a global allocator.
1504     ///
1505     /// See also [`std::alloc::GlobalAlloc`](../../../std/alloc/trait.GlobalAlloc.html).
1506     #[stable(feature = "global_allocator", since = "1.28.0")]
1507     #[allow_internal_unstable(rustc_attrs)]
1508     #[rustc_builtin_macro]
1509     pub macro global_allocator($item:item) {
1510         /* compiler built-in */
1511     }
1512
1513     /// Keeps the item it's applied to if the passed path is accessible, and removes it otherwise.
1514     #[unstable(
1515         feature = "cfg_accessible",
1516         issue = "64797",
1517         reason = "`cfg_accessible` is not fully implemented"
1518     )]
1519     #[rustc_builtin_macro]
1520     pub macro cfg_accessible($item:item) {
1521         /* compiler built-in */
1522     }
1523
1524     /// Expands all `#[cfg]` and `#[cfg_attr]` attributes in the code fragment it's applied to.
1525     #[unstable(
1526         feature = "cfg_eval",
1527         issue = "82679",
1528         reason = "`cfg_eval` is a recently implemented feature"
1529     )]
1530     #[rustc_builtin_macro]
1531     pub macro cfg_eval($($tt:tt)*) {
1532         /* compiler built-in */
1533     }
1534
1535     /// Unstable implementation detail of the `rustc` compiler, do not use.
1536     #[rustc_builtin_macro]
1537     #[stable(feature = "rust1", since = "1.0.0")]
1538     #[allow_internal_unstable(core_intrinsics, libstd_sys_internals)]
1539     #[deprecated(since = "1.52.0", note = "rustc-serialize is deprecated and no longer supported")]
1540     #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
1541     pub macro RustcDecodable($item:item) {
1542         /* compiler built-in */
1543     }
1544
1545     /// Unstable implementation detail of the `rustc` compiler, do not use.
1546     #[rustc_builtin_macro]
1547     #[stable(feature = "rust1", since = "1.0.0")]
1548     #[allow_internal_unstable(core_intrinsics)]
1549     #[deprecated(since = "1.52.0", note = "rustc-serialize is deprecated and no longer supported")]
1550     #[doc(hidden)] // While technically stable, using it is unstable, and deprecated. Hide it.
1551     pub macro RustcEncodable($item:item) {
1552         /* compiler built-in */
1553     }
1554 }