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 #[allow_internal_unstable(core_panic)]
  35 macro_rules! assert_eq {
  36     ($left:expr, $right:expr $(,)?) => ({
  37         match (&$left, &$right) {
  38             (left_val, right_val) => {
  39                 if !(*left_val == *right_val) {
  40                     let kind = $crate::panicking::AssertKind::Eq;
  41                     // The reborrows below are intentional. Without them, the stack slot for the
  42                     // borrow is initialized even before the values are compared, leading to a
  43                     // noticeable slow down.
  44                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
  45                 }
  46             }
  47         }
  48     });
  49     ($left:expr, $right:expr, $($arg:tt)+) => ({
  50         match (&$left, &$right) {
  51             (left_val, right_val) => {
  52                 if !(*left_val == *right_val) {
  53                     let kind = $crate::panicking::AssertKind::Eq;
  54                     // The reborrows below are intentional. Without them, the stack slot for the
  55                     // borrow is initialized even before the values are compared, leading to a
  56                     // noticeable slow down.
  57                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
  58                 }
  59             }
  60         }
  61     });
  62 }
  63
  64 /// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
  65 ///
  66 /// On panic, this macro will print the values of the expressions with their
  67 /// debug representations.
  68 ///
  69 /// Like [`assert!`], this macro has a second form, where a custom
  70 /// panic message can be provided.
  71 ///
  72 /// # Examples
  73 ///
  74 /// ```
  75 /// let a = 3;
  76 /// let b = 2;
  77 /// assert_ne!(a, b);
  78 ///
  79 /// assert_ne!(a, b, "we are testing that the values are not equal");
  80 /// ```
  81 #[macro_export]
  82 #[stable(feature = "assert_ne", since = "1.13.0")]
  83 #[allow_internal_unstable(core_panic)]
  84 macro_rules! assert_ne {
  85     ($left:expr, $right:expr $(,)?) => ({
  86         match (&$left, &$right) {
  87             (left_val, right_val) => {
  88                 if *left_val == *right_val {
  89                     let kind = $crate::panicking::AssertKind::Ne;
  90                     // The reborrows below are intentional. Without them, the stack slot for the
  91                     // borrow is initialized even before the values are compared, leading to a
  92                     // noticeable slow down.
  93                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
  94                 }
  95             }
  96         }
  97     });
  98     ($left:expr, $right:expr, $($arg:tt)+) => ({
  99         match (&($left), &($right)) {
 100             (left_val, right_val) => {
 101                 if *left_val == *right_val {
 102                     let kind = $crate::panicking::AssertKind::Ne;
 103                     // The reborrows below are intentional. Without them, the stack slot for the
 104                     // borrow is initialized even before the values are compared, leading to a
 105                     // noticeable slow down.
 106                     $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
 107                 }
 108             }
 109         }
 110     });
 111 }
 112
 113 /// Asserts that an expression matches any of the given patterns.
 114 ///
 115 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 116 /// and a guard expression that has access to names bound by the pattern.
 117 ///
 118 /// On panic, this macro will print the value of the expression with its
 119 /// debug representation.
 120 ///
 121 /// Like [`assert!`], this macro has a second form, where a custom
 122 /// panic message can be provided.
 123 ///
 124 /// # Examples
 125 ///
 126 /// ```
 127 /// #![feature(assert_matches)]
 128 ///
 129 /// let a = 1u32.checked_add(2);
 130 /// let b = 1u32.checked_sub(2);
 131 /// assert_matches!(a, Some(_));
 132 /// assert_matches!(b, None);
 133 ///
 134 /// let c = Ok("abc".to_string());
 135 /// assert_matches!(c, Ok(x) | Err(x) if x.len() < 100);
 136 /// ```
 137 #[macro_export]
 138 #[unstable(feature = "assert_matches", issue = "82775")]
 139 #[allow_internal_unstable(core_panic)]
 140 macro_rules! assert_matches {
 141     ($left:expr, $( $pattern:pat )|+ $( if $guard: expr )? $(,)?) => ({
 142         match $left {
 143             $( $pattern )|+ $( if $guard )? => {}
 144             ref left_val => {
 145                 $crate::panicking::assert_matches_failed(
 146                     left_val,
 147                     $crate::stringify!($($pattern)|+ $(if $guard)?),
 148                     $crate::option::Option::None
 149                 );
 150             }
 151         }
 152     });
 153     ($left:expr, $( $pattern:pat )|+ $( if $guard: expr )?, $($arg:tt)+) => ({
 154         match $left {
 155             $( $pattern )|+ $( if $guard )? => {}
 156             ref left_val => {
 157                 $crate::panicking::assert_matches_failed(
 158                     left_val,
 159                     $crate::stringify!($($pattern)|+ $(if $guard)?),
 160                     $crate::option::Option::Some($crate::format_args!($($arg)+))
 161                 );
 162             }
 163         }
 164     });
 165 }
 166
 167 /// Asserts that a boolean expression is `true` at runtime.
 168 ///
 169 /// This will invoke the [`panic!`] macro if the provided expression cannot be
 170 /// evaluated to `true` at runtime.
 171 ///
 172 /// Like [`assert!`], this macro also has a second version, where a custom panic
 173 /// message can be provided.
 174 ///
 175 /// # Uses
 176 ///
 177 /// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
 178 /// optimized builds by default. An optimized build will not execute
 179 /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
 180 /// compiler. This makes `debug_assert!` useful for checks that are too
 181 /// expensive to be present in a release build but may be helpful during
 182 /// development. The result of expanding `debug_assert!` is always type checked.
 183 ///
 184 /// An unchecked assertion allows a program in an inconsistent state to keep
 185 /// running, which might have unexpected consequences but does not introduce
 186 /// unsafety as long as this only happens in safe code. The performance cost
 187 /// of assertions, however, is not measurable in general. Replacing [`assert!`]
 188 /// with `debug_assert!` is thus only encouraged after thorough profiling, and
 189 /// more importantly, only in safe code!
 190 ///
 191 /// # Examples
 192 ///
 193 /// ```
 194 /// // the panic message for these assertions is the stringified value of the
 195 /// // expression given.
 196 /// debug_assert!(true);
 197 ///
 198 /// fn some_expensive_computation() -> bool { true } // a very simple function
 199 /// debug_assert!(some_expensive_computation());
 200 ///
 201 /// // assert with a custom message
 202 /// let x = true;
 203 /// debug_assert!(x, "x wasn't true!");
 204 ///
 205 /// let a = 3; let b = 27;
 206 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
 207 /// ```
 208 #[macro_export]
 209 #[stable(feature = "rust1", since = "1.0.0")]
 210 #[rustc_diagnostic_item = "debug_assert_macro"]
 211 macro_rules! debug_assert {
 212     ($($arg:tt)*) => (if $crate::cfg!(debug_assertions) { $crate::assert!($($arg)*); })
 213 }
 214
 215 /// Asserts that two expressions are equal to each other.
 216 ///
 217 /// On panic, this macro will print the values of the expressions with their
 218 /// debug representations.
 219 ///
 220 /// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
 221 /// optimized builds by default. An optimized build will not execute
 222 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
 223 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
 224 /// expensive to be present in a release build but may be helpful during
 225 /// development. The result of expanding `debug_assert_eq!` is always type checked.
 226 ///
 227 /// # Examples
 228 ///
 229 /// ```
 230 /// let a = 3;
 231 /// let b = 1 + 2;
 232 /// debug_assert_eq!(a, b);
 233 /// ```
 234 #[macro_export]
 235 #[stable(feature = "rust1", since = "1.0.0")]
 236 macro_rules! debug_assert_eq {
 237     ($($arg:tt)*) => (if $crate::cfg!(debug_assertions) { $crate::assert_eq!($($arg)*); })
 238 }
 239
 240 /// Asserts that two expressions are not equal to each other.
 241 ///
 242 /// On panic, this macro will print the values of the expressions with their
 243 /// debug representations.
 244 ///
 245 /// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
 246 /// optimized builds by default. An optimized build will not execute
 247 /// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
 248 /// compiler. This makes `debug_assert_ne!` useful for checks that are too
 249 /// expensive to be present in a release build but may be helpful during
 250 /// development. The result of expanding `debug_assert_ne!` is always type checked.
 251 ///
 252 /// # Examples
 253 ///
 254 /// ```
 255 /// let a = 3;
 256 /// let b = 2;
 257 /// debug_assert_ne!(a, b);
 258 /// ```
 259 #[macro_export]
 260 #[stable(feature = "assert_ne", since = "1.13.0")]
 261 macro_rules! debug_assert_ne {
 262     ($($arg:tt)*) => (if $crate::cfg!(debug_assertions) { $crate::assert_ne!($($arg)*); })
 263 }
 264
 265 /// Asserts that an expression matches any of the given patterns.
 266 ///
 267 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 268 /// and a guard expression that has access to names bound by the pattern.
 269 ///
 270 /// On panic, this macro will print the value of the expression with its
 271 /// debug representation.
 272 ///
 273 /// Unlike [`assert_matches!`], `debug_assert_matches!` statements are only
 274 /// enabled in non optimized builds by default. An optimized build will not
 275 /// execute `debug_assert_matches!` statements unless `-C debug-assertions` is
 276 /// passed to the compiler. This makes `debug_assert_matches!` useful for
 277 /// checks that are too expensive to be present in a release build but may be
 278 /// helpful during development. The result of expanding `debug_assert_matches!`
 279 /// is always type checked.
 280 ///
 281 /// # Examples
 282 ///
 283 /// ```
 284 /// #![feature(assert_matches)]
 285 ///
 286 /// let a = 1u32.checked_add(2);
 287 /// let b = 1u32.checked_sub(2);
 288 /// debug_assert_matches!(a, Some(_));
 289 /// debug_assert_matches!(b, None);
 290 ///
 291 /// let c = Ok("abc".to_string());
 292 /// debug_assert_matches!(c, Ok(x) | Err(x) if x.len() < 100);
 293 /// ```
 294 #[macro_export]
 295 #[unstable(feature = "assert_matches", issue = "82775")]
 296 #[allow_internal_unstable(assert_matches)]
 297 macro_rules! debug_assert_matches {
 298     ($($arg:tt)*) => (if $crate::cfg!(debug_assertions) { $crate::assert_matches!($($arg)*); })
 299 }
 300
 301 /// Returns whether the given expression matches any of the given patterns.
 302 ///
 303 /// Like in a `match` expression, the pattern can be optionally followed by `if`
 304 /// and a guard expression that has access to names bound by the pattern.
 305 ///
 306 /// # Examples
 307 ///
 308 /// ```
 309 /// let foo = 'f';
 310 /// assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
 311 ///
 312 /// let bar = Some(4);
 313 /// assert!(matches!(bar, Some(x) if x > 2));
 314 /// ```
 315 #[macro_export]
 316 #[stable(feature = "matches_macro", since = "1.42.0")]
 317 macro_rules! matches {
 318     ($expression:expr, $( $pattern:pat )|+ $( if $guard: expr )? $(,)?) => {
 319         match $expression {
 320             $( $pattern )|+ $( if $guard )? => true,
 321             _ => false
 322         }
 323     }
 324 }
 325
 326 /// Unwraps a result or propagates its error.
 327 ///
 328 /// The `?` operator was added to replace `try!` and should be used instead.
 329 /// Furthermore, `try` is a reserved word in Rust 2018, so if you must use
 330 /// it, you will need to use the [raw-identifier syntax][ris]: `r#try`.
 331 ///
 332 /// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
 333 ///
 334 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 335 /// expression has the value of the wrapped value.
 336 ///
 337 /// In case of the `Err` variant, it retrieves the inner error. `try!` then
 338 /// performs conversion using `From`. This provides automatic conversion
 339 /// between specialized errors and more general ones. The resulting
 340 /// error is then immediately returned.
 341 ///
 342 /// Because of the early return, `try!` can only be used in functions that
 343 /// return [`Result`].
 344 ///
 345 /// # Examples
 346 ///
 347 /// ```
 348 /// use std::io;
 349 /// use std::fs::File;
 350 /// use std::io::prelude::*;
 351 ///
 352 /// enum MyError {
 353 ///     FileWriteError
 354 /// }
 355 ///
 356 /// impl From<io::Error> for MyError {
 357 ///     fn from(e: io::Error) -> MyError {
 358 ///         MyError::FileWriteError
 359 ///     }
 360 /// }
 361 ///
 362 /// // The preferred method of quick returning Errors
 363 /// fn write_to_file_question() -> Result<(), MyError> {
 364 ///     let mut file = File::create("my_best_friends.txt")?;
 365 ///     file.write_all(b"This is a list of my best friends.")?;
 366 ///     Ok(())
 367 /// }
 368 ///
 369 /// // The previous method of quick returning Errors
 370 /// fn write_to_file_using_try() -> Result<(), MyError> {
 371 ///     let mut file = r#try!(File::create("my_best_friends.txt"));
 372 ///     r#try!(file.write_all(b"This is a list of my best friends."));
 373 ///     Ok(())
 374 /// }
 375 ///
 376 /// // This is equivalent to:
 377 /// fn write_to_file_using_match() -> Result<(), MyError> {
 378 ///     let mut file = r#try!(File::create("my_best_friends.txt"));
 379 ///     match file.write_all(b"This is a list of my best friends.") {
 380 ///         Ok(v) => v,
 381 ///         Err(e) => return Err(From::from(e)),
 382 ///     }
 383 ///     Ok(())
 384 /// }
 385 /// ```
 386 #[macro_export]
 387 #[stable(feature = "rust1", since = "1.0.0")]
 388 #[rustc_deprecated(since = "1.39.0", reason = "use the `?` operator instead")]
 389 #[doc(alias = "?")]
 390 macro_rules! r#try {
 391     ($expr:expr $(,)?) => {
 392         match $expr {
 393             $crate::result::Result::Ok(val) => val,
 394             $crate::result::Result::Err(err) => {
 395                 return $crate::result::Result::Err($crate::convert::From::from(err));
 396             }
 397         }
 398     };
 399 }
 400
 401 /// Writes formatted data into a buffer.
 402 ///
 403 /// This macro accepts a 'writer', a format string, and a list of arguments. Arguments will be
 404 /// formatted according to the specified format string and the result will be passed to the writer.
 405 /// The writer may be any value with a `write_fmt` method; generally this comes from an
 406 /// implementation of either the [`fmt::Write`] or the [`io::Write`] trait. The macro
 407 /// returns whatever the `write_fmt` method returns; commonly a [`fmt::Result`], or an
 408 /// [`io::Result`].
 409 ///
 410 /// See [`std::fmt`] for more information on the format string syntax.
 411 ///
 412 /// [`std::fmt`]: ../std/fmt/index.html
 413 /// [`fmt::Write`]: crate::fmt::Write
 414 /// [`io::Write`]: ../std/io/trait.Write.html
 415 /// [`fmt::Result`]: crate::fmt::Result
 416 /// [`io::Result`]: ../std/io/type.Result.html
 417 ///
 418 /// # Examples
 419 ///
 420 /// ```
 421 /// use std::io::Write;
 422 ///
 423 /// fn main() -> std::io::Result<()> {
 424 ///     let mut w = Vec::new();
 425 ///     write!(&mut w, "test")?;
 426 ///     write!(&mut w, "formatted {}", "arguments")?;
 427 ///
 428 ///     assert_eq!(w, b"testformatted arguments");
 429 ///     Ok(())
 430 /// }
 431 /// ```
 432 ///
 433 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
 434 /// implementing either, as objects do not typically implement both. However, the module must
 435 /// import the traits qualified so their names do not conflict:
 436 ///
 437 /// ```
 438 /// use std::fmt::Write as FmtWrite;
 439 /// use std::io::Write as IoWrite;
 440 ///
 441 /// fn main() -> Result<(), Box<dyn std::error::Error>> {
 442 ///     let mut s = String::new();
 443 ///     let mut v = Vec::new();
 444 ///
 445 ///     write!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
 446 ///     write!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
 447 ///     assert_eq!(v, b"s = \"abc 123\"");
 448 ///     Ok(())
 449 /// }
 450 /// ```
 451 ///
 452 /// Note: This macro can be used in `no_std` setups as well.
 453 /// In a `no_std` setup you are responsible for the implementation details of the components.
 454 ///
 455 /// ```no_run
 456 /// # extern crate core;
 457 /// use core::fmt::Write;
 458 ///
 459 /// struct Example;
 460 ///
 461 /// impl Write for Example {
 462 ///     fn write_str(&mut self, _s: &str) -> core::fmt::Result {
 463 ///          unimplemented!();
 464 ///     }
 465 /// }
 466 ///
 467 /// let mut m = Example{};
 468 /// write!(&mut m, "Hello World").expect("Not written");
 469 /// ```
 470 #[macro_export]
 471 #[stable(feature = "rust1", since = "1.0.0")]
 472 macro_rules! write {
 473     ($dst:expr, $($arg:tt)*) => ($dst.write_fmt($crate::format_args!($($arg)*)))
 474 }
 475
 476 /// Write formatted data into a buffer, with a newline appended.
 477 ///
 478 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
 479 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
 480 ///
 481 /// For more information, see [`write!`]. For information on the format string syntax, see
 482 /// [`std::fmt`].
 483 ///
 484 /// [`std::fmt`]: ../std/fmt/index.html
 485 ///
 486 /// # Examples
 487 ///
 488 /// ```
 489 /// use std::io::{Write, Result};
 490 ///
 491 /// fn main() -> Result<()> {
 492 ///     let mut w = Vec::new();
 493 ///     writeln!(&mut w)?;
 494 ///     writeln!(&mut w, "test")?;
 495 ///     writeln!(&mut w, "formatted {}", "arguments")?;
 496 ///
 497 ///     assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
 498 ///     Ok(())
 499 /// }
 500 /// ```
 501 ///
 502 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
 503 /// implementing either, as objects do not typically implement both. However, the module must
 504 /// import the traits qualified so their names do not conflict:
 505 ///
 506 /// ```
 507 /// use std::fmt::Write as FmtWrite;
 508 /// use std::io::Write as IoWrite;
 509 ///
 510 /// fn main() -> Result<(), Box<dyn std::error::Error>> {
 511 ///     let mut s = String::new();
 512 ///     let mut v = Vec::new();
 513 ///
 514 ///     writeln!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
 515 ///     writeln!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
 516 ///     assert_eq!(v, b"s = \"abc 123\\n\"\n");
 517 ///     Ok(())
 518 /// }
 519 /// ```
 520 #[macro_export]
 521 #[stable(feature = "rust1", since = "1.0.0")]
 522 #[allow_internal_unstable(format_args_nl)]
 523 macro_rules! writeln {
 524     ($dst:expr $(,)?) => (
 525         $crate::write!($dst, "\n")
 526     );
 527     ($dst:expr, $($arg:tt)*) => (
 528         $dst.write_fmt($crate::format_args_nl!($($arg)*))
 529     );
 530 }
 531
 532 /// Indicates unreachable code.
 533 ///
 534 /// This is useful any time that the compiler can't determine that some code is unreachable. For
 535 /// example:
 536 ///
 537 /// * Match arms with guard conditions.
 538 /// * Loops that dynamically terminate.
 539 /// * Iterators that dynamically terminate.
 540 ///
 541 /// If the determination that the code is unreachable proves incorrect, the
 542 /// program immediately terminates with a [`panic!`].
 543 ///
 544 /// The unsafe counterpart of this macro is the [`unreachable_unchecked`] function, which
 545 /// will cause undefined behavior if the code is reached.
 546 ///
 547 /// [`unreachable_unchecked`]: crate::hint::unreachable_unchecked
 548 ///
 549 /// # Panics
 550 ///
 551 /// This will always [`panic!`].
 552 ///
 553 /// # Examples
 554 ///
 555 /// Match arms:
 556 ///
 557 /// ```
 558 /// # #[allow(dead_code)]
 559 /// fn foo(x: Option<i32>) {
 560 ///     match x {
 561 ///         Some(n) if n >= 0 => println!("Some(Non-negative)"),
 562 ///         Some(n) if n <  0 => println!("Some(Negative)"),
 563 ///         Some(_)           => unreachable!(), // compile error if commented out
 564 ///         None              => println!("None")
 565 ///     }
 566 /// }
 567 /// ```
 568 ///
 569 /// Iterators:
 570 ///
 571 /// ```
 572 /// # #[allow(dead_code)]
 573 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
 574 ///     for i in 0.. {
 575 ///         if 3*i < i { panic!("u32 overflow"); }
 576 ///         if x < 3*i { return i-1; }
 577 ///     }
 578 ///     unreachable!();
 579 /// }
 580 /// ```
 581 #[macro_export]
 582 #[stable(feature = "rust1", since = "1.0.0")]
 583 macro_rules! unreachable {
 584     () => ({
 585         $crate::panic!("internal error: entered unreachable code")
 586     });
 587     ($msg:expr $(,)?) => ({
 588         $crate::unreachable!("{}", $msg)
 589     });
 590     ($fmt:expr, $($arg:tt)*) => ({
 591         $crate::panic!($crate::concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
 592     });
 593 }
 594
 595 /// Indicates unimplemented code by panicking with a message of "not implemented".
 596 ///
 597 /// This allows your code to type-check, which is useful if you are prototyping or
 598 /// implementing a trait that requires multiple methods which you don't plan of using all of.
 599 ///
 600 /// The difference between `unimplemented!` and [`todo!`] is that while `todo!`
 601 /// conveys an intent of implementing the functionality later and the message is "not yet
 602 /// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
 603 /// Also some IDEs will mark `todo!`s.
 604 ///
 605 /// # Panics
 606 ///
 607 /// This will always [`panic!`] because `unimplemented!` is just a shorthand for `panic!` with a
 608 /// fixed, specific message.
 609 ///
 610 /// Like `panic!`, this macro has a second form for displaying custom values.
 611 ///
 612 /// # Examples
 613 ///
 614 /// Say we have a trait `Foo`:
 615 ///
 616 /// ```
 617 /// trait Foo {
 618 ///     fn bar(&self) -> u8;
 619 ///     fn baz(&self);
 620 ///     fn qux(&self) -> Result<u64, ()>;
 621 /// }
 622 /// ```
 623 ///
 624 /// We want to implement `Foo` for 'MyStruct', but for some reason it only makes sense
 625 /// to implement the `bar()` function. `baz()` and `qux()` will still need to be defined
 626 /// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
 627 /// to allow our code to compile.
 628 ///
 629 /// We still want to have our program stop running if the unimplemented methods are
 630 /// reached.
 631 ///
 632 /// ```
 633 /// # trait Foo {
 634 /// #     fn bar(&self) -> u8;
 635 /// #     fn baz(&self);
 636 /// #     fn qux(&self) -> Result<u64, ()>;
 637 /// # }
 638 /// struct MyStruct;
 639 ///
 640 /// impl Foo for MyStruct {
 641 ///     fn bar(&self) -> u8 {
 642 ///         1 + 1
 643 ///     }
 644 ///
 645 ///     fn baz(&self) {
 646 ///         // It makes no sense to `baz` a `MyStruct`, so we have no logic here
 647 ///         // at all.
 648 ///         // This will display "thread 'main' panicked at 'not implemented'".
 649 ///         unimplemented!();
 650 ///     }
 651 ///
 652 ///     fn qux(&self) -> Result<u64, ()> {
 653 ///         // We have some logic here,
 654 ///         // We can add a message to unimplemented! to display our omission.
 655 ///         // This will display:
 656 ///         // "thread 'main' panicked at 'not implemented: MyStruct isn't quxable'".
 657 ///         unimplemented!("MyStruct isn't quxable");
 658 ///     }
 659 /// }
 660 ///
 661 /// fn main() {
 662 ///     let s = MyStruct;
 663 ///     s.bar();
 664 /// }
 665 /// ```
 666 #[macro_export]
 667 #[stable(feature = "rust1", since = "1.0.0")]
 668 macro_rules! unimplemented {
 669     () => ($crate::panic!("not implemented"));
 670     ($($arg:tt)+) => ($crate::panic!("not implemented: {}", $crate::format_args!($($arg)+)));
 671 }
 672
 673 /// Indicates unfinished code.
 674 ///
 675 /// This can be useful if you are prototyping and are just looking to have your
 676 /// code typecheck.
 677 ///
 678 /// The difference between [`unimplemented!`] and `todo!` is that while `todo!` conveys
 679 /// an intent of implementing the functionality later and the message is "not yet
 680 /// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
 681 /// Also some IDEs will mark `todo!`s.
 682 ///
 683 /// # Panics
 684 ///
 685 /// This will always [`panic!`].
 686 ///
 687 /// # Examples
 688 ///
 689 /// Here's an example of some in-progress code. We have a trait `Foo`:
 690 ///
 691 /// ```
 692 /// trait Foo {
 693 ///     fn bar(&self);
 694 ///     fn baz(&self);
 695 /// }
 696 /// ```
 697 ///
 698 /// We want to implement `Foo` on one of our types, but we also want to work on
 699 /// just `bar()` first. In order for our code to compile, we need to implement
 700 /// `baz()`, so we can use `todo!`:
 701 ///
 702 /// ```
 703 /// # trait Foo {
 704 /// #     fn bar(&self);
 705 /// #     fn baz(&self);
 706 /// # }
 707 /// struct MyStruct;
 708 ///
 709 /// impl Foo for MyStruct {
 710 ///     fn bar(&self) {
 711 ///         // implementation goes here
 712 ///     }
 713 ///
 714 ///     fn baz(&self) {
 715 ///         // let's not worry about implementing baz() for now
 716 ///         todo!();
 717 ///     }
 718 /// }
 719 ///
 720 /// fn main() {
 721 ///     let s = MyStruct;
 722 ///     s.bar();
 723 ///
 724 ///     // we aren't even using baz(), so this is fine.
 725 /// }
 726 /// ```
 727 #[macro_export]
 728 #[stable(feature = "todo_macro", since = "1.40.0")]
 729 macro_rules! todo {
 730     () => ($crate::panic!("not yet implemented"));
 731     ($($arg:tt)+) => ($crate::panic!("not yet implemented: {}", $crate::format_args!($($arg)+)));
 732 }
 733
 734 /// Definitions of built-in macros.
 735 ///
 736 /// Most of the macro properties (stability, visibility, etc.) are taken from the source code here,
 737 /// with exception of expansion functions transforming macro inputs into outputs,
 738 /// those functions are provided by the compiler.
 739 pub(crate) mod builtin {
 740
 741     /// Causes compilation to fail with the given error message when encountered.
 742     ///
 743     /// This macro should be used when a crate uses a conditional compilation strategy to provide
 744     /// better error messages for erroneous conditions. It's the compiler-level form of [`panic!`],
 745     /// but emits an error during *compilation* rather than at *runtime*.
 746     ///
 747     /// # Examples
 748     ///
 749     /// Two such examples are macros and `#[cfg]` environments.
 750     ///
 751     /// Emit better compiler error if a macro is passed invalid values. Without the final branch,
 752     /// the compiler would still emit an error, but the error's message would not mention the two
 753     /// valid values.
 754     ///
 755     /// ```compile_fail
 756     /// macro_rules! give_me_foo_or_bar {
 757     ///     (foo) => {};
 758     ///     (bar) => {};
 759     ///     ($x:ident) => {
 760     ///         compile_error!("This macro only accepts `foo` or `bar`");
 761     ///     }
 762     /// }
 763     ///
 764     /// give_me_foo_or_bar!(neither);
 765     /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
 766     /// ```
 767     ///
 768     /// Emit compiler error if one of a number of features isn't available.
 769     ///
 770     /// ```compile_fail
 771     /// #[cfg(not(any(feature = "foo", feature = "bar")))]
 772     /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.");
 773     /// ```
 774     #[stable(feature = "compile_error_macro", since = "1.20.0")]
 775     #[rustc_builtin_macro]
 776     #[macro_export]
 777     macro_rules! compile_error {
 778         ($msg:expr $(,)?) => {{ /* compiler built-in */ }};
 779     }
 780
 781     /// Constructs parameters for the other string-formatting macros.
 782     ///
 783     /// This macro functions by taking a formatting string literal containing
 784     /// `{}` for each additional argument passed. `format_args!` prepares the
 785     /// additional parameters to ensure the output can be interpreted as a string
 786     /// and canonicalizes the arguments into a single type. Any value that implements
 787     /// the [`Display`] trait can be passed to `format_args!`, as can any
 788     /// [`Debug`] implementation be passed to a `{:?}` within the formatting string.
 789     ///
 790     /// This macro produces a value of type [`fmt::Arguments`]. This value can be
 791     /// passed to the macros within [`std::fmt`] for performing useful redirection.
 792     /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
 793     /// proxied through this one. `format_args!`, unlike its derived macros, avoids
 794     /// heap allocations.
 795     ///
 796     /// You can use the [`fmt::Arguments`] value that `format_args!` returns
 797     /// in `Debug` and `Display` contexts as seen below. The example also shows
 798     /// that `Debug` and `Display` format to the same thing: the interpolated
 799     /// format string in `format_args!`.
 800     ///
 801     /// ```rust
 802     /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
 803     /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
 804     /// assert_eq!("1 foo 2", display);
 805     /// assert_eq!(display, debug);
 806     /// ```
 807     ///
 808     /// For more information, see the documentation in [`std::fmt`].
 809     ///
 810     /// [`Display`]: crate::fmt::Display
 811     /// [`Debug`]: crate::fmt::Debug
 812     /// [`fmt::Arguments`]: crate::fmt::Arguments
 813     /// [`std::fmt`]: ../std/fmt/index.html
 814     /// [`format!`]: ../std/macro.format.html
 815     /// [`println!`]: ../std/macro.println.html
 816     ///
 817     /// # Examples
 818     ///
 819     /// ```
 820     /// use std::fmt;
 821     ///
 822     /// let s = fmt::format(format_args!("hello {}", "world"));
 823     /// assert_eq!(s, format!("hello {}", "world"));
 824     /// ```
 825     #[stable(feature = "rust1", since = "1.0.0")]
 826     #[allow_internal_unstable(fmt_internals)]
 827     #[rustc_builtin_macro]
 828     #[macro_export]
 829     macro_rules! format_args {
 830         ($fmt:expr) => {{ /* compiler built-in */ }};
 831         ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
 832     }
 833
 834     /// Same as `format_args`, but adds a newline in the end.
 835     #[unstable(
 836         feature = "format_args_nl",
 837         issue = "none",
 838         reason = "`format_args_nl` is only for internal \
 839                   language use and is subject to change"
 840     )]
 841     #[allow_internal_unstable(fmt_internals)]
 842     #[rustc_builtin_macro]
 843     #[macro_export]
 844     macro_rules! format_args_nl {
 845         ($fmt:expr) => {{ /* compiler built-in */ }};
 846         ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
 847     }
 848
 849     /// Inspects an environment variable at compile time.
 850     ///
 851     /// This macro will expand to the value of the named environment variable at
 852     /// compile time, yielding an expression of type `&'static str`.
 853     ///
 854     /// If the environment variable is not defined, then a compilation error
 855     /// will be emitted. To not emit a compile error, use the [`option_env!`]
 856     /// macro instead.
 857     ///
 858     /// # Examples
 859     ///
 860     /// ```
 861     /// let path: &'static str = env!("PATH");
 862     /// println!("the $PATH variable at the time of compiling was: {}", path);
 863     /// ```
 864     ///
 865     /// You can customize the error message by passing a string as the second
 866     /// parameter:
 867     ///
 868     /// ```compile_fail
 869     /// let doc: &'static str = env!("documentation", "what's that?!");
 870     /// ```
 871     ///
 872     /// If the `documentation` environment variable is not defined, you'll get
 873     /// the following error:
 874     ///
 875     /// ```text
 876     /// error: what's that?!
 877     /// ```
 878     #[stable(feature = "rust1", since = "1.0.0")]
 879     #[rustc_builtin_macro]
 880     #[macro_export]
 881     macro_rules! env {
 882         ($name:expr $(,)?) => {{ /* compiler built-in */ }};
 883         ($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
 884     }
 885
 886     /// Optionally inspects an environment variable at compile time.
 887     ///
 888     /// If the named environment variable is present at compile time, this will
 889     /// expand into an expression of type `Option<&'static str>` whose value is
 890     /// `Some` of the value of the environment variable. If the environment
 891     /// variable is not present, then this will expand to `None`. See
 892     /// [`Option<T>`][Option] for more information on this type.
 893     ///
 894     /// A compile time error is never emitted when using this macro regardless
 895     /// of whether the environment variable is present or not.
 896     ///
 897     /// # Examples
 898     ///
 899     /// ```
 900     /// let key: Option<&'static str> = option_env!("SECRET_KEY");
 901     /// println!("the secret key might be: {:?}", key);
 902     /// ```
 903     #[stable(feature = "rust1", since = "1.0.0")]
 904     #[rustc_builtin_macro]
 905     #[macro_export]
 906     macro_rules! option_env {
 907         ($name:expr $(,)?) => {{ /* compiler built-in */ }};
 908     }
 909
 910     /// Concatenates identifiers into one identifier.
 911     ///
 912     /// This macro takes any number of comma-separated identifiers, and
 913     /// concatenates them all into one, yielding an expression which is a new
 914     /// identifier. Note that hygiene makes it such that this macro cannot
 915     /// capture local variables. Also, as a general rule, macros are only
 916     /// allowed in item, statement or expression position. That means while
 917     /// you may use this macro for referring to existing variables, functions or
 918     /// modules etc, you cannot define a new one with it.
 919     ///
 920     /// # Examples
 921     ///
 922     /// ```
 923     /// #![feature(concat_idents)]
 924     ///
 925     /// # fn main() {
 926     /// fn foobar() -> u32 { 23 }
 927     ///
 928     /// let f = concat_idents!(foo, bar);
 929     /// println!("{}", f());
 930     ///
 931     /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
 932     /// # }
 933     /// ```
 934     #[unstable(
 935         feature = "concat_idents",
 936         issue = "29599",
 937         reason = "`concat_idents` is not stable enough for use and is subject to change"
 938     )]
 939     #[rustc_builtin_macro]
 940     #[macro_export]
 941     macro_rules! concat_idents {
 942         ($($e:ident),+ $(,)?) => {{ /* compiler built-in */ }};
 943     }
 944
 945     /// Concatenates literals into a static string slice.
 946     ///
 947     /// This macro takes any number of comma-separated literals, yielding an
 948     /// expression of type `&'static str` which represents all of the literals
 949     /// concatenated left-to-right.
 950     ///
 951     /// Integer and floating point literals are stringified in order to be
 952     /// concatenated.
 953     ///
 954     /// # Examples
 955     ///
 956     /// ```
 957     /// let s = concat!("test", 10, 'b', true);
 958     /// assert_eq!(s, "test10btrue");
 959     /// ```
 960     #[stable(feature = "rust1", since = "1.0.0")]
 961     #[rustc_builtin_macro]
 962     #[macro_export]
 963     macro_rules! concat {
 964         ($($e:expr),* $(,)?) => {{ /* compiler built-in */ }};
 965     }
 966
 967     /// Expands to the line number on which it was invoked.
 968     ///
 969     /// With [`column!`] and [`file!`], these macros provide debugging information for
 970     /// developers about the location within the source.
 971     ///
 972     /// The expanded expression has type `u32` and is 1-based, so the first line
 973     /// in each file evaluates to 1, the second to 2, etc. This is consistent
 974     /// with error messages by common compilers or popular editors.
 975     /// The returned line is *not necessarily* the line of the `line!` invocation itself,
 976     /// but rather the first macro invocation leading up to the invocation
 977     /// of the `line!` macro.
 978     ///
 979     /// # Examples
 980     ///
 981     /// ```
 982     /// let current_line = line!();
 983     /// println!("defined on line: {}", current_line);
 984     /// ```
 985     #[stable(feature = "rust1", since = "1.0.0")]
 986     #[rustc_builtin_macro]
 987     #[macro_export]
 988     macro_rules! line {
 989         () => {
 990             /* compiler built-in */
 991         };
 992     }
 993
 994     /// Expands to the column number at which it was invoked.
 995     ///
 996     /// With [`line!`] and [`file!`], these macros provide debugging information for
 997     /// developers about the location within the source.
 998     ///
 999     /// The expanded expression has type `u32` and is 1-based, so the first column
1000     /// in each line evaluates to 1, the second to 2, etc. This is consistent
1001     /// with error messages by common compilers or popular editors.
1002     /// The returned column is *not necessarily* the line of the `column!` invocation itself,
1003     /// but rather the first macro invocation leading up to the invocation
1004     /// of the `column!` macro.
1005     ///
1006     /// # Examples
1007     ///
1008     /// ```
1009     /// let current_col = column!();
1010     /// println!("defined on column: {}", current_col);
1011     /// ```
1012     #[stable(feature = "rust1", since = "1.0.0")]
1013     #[rustc_builtin_macro]
1014     #[macro_export]
1015     macro_rules! column {
1016         () => {
1017             /* compiler built-in */
1018         };
1019     }
1020
1021     /// Expands to the file name in which it was invoked.
1022     ///
1023     /// With [`line!`] and [`column!`], these macros provide debugging information for
1024     /// developers about the location within the source.
1025     ///
1026     /// The expanded expression has type `&'static str`, and the returned file
1027     /// is not the invocation of the `file!` macro itself, but rather the
1028     /// first macro invocation leading up to the invocation of the `file!`
1029     /// macro.
1030     ///
1031     /// # Examples
1032     ///
1033     /// ```
1034     /// let this_file = file!();
1035     /// println!("defined in file: {}", this_file);
1036     /// ```
1037     #[stable(feature = "rust1", since = "1.0.0")]
1038     #[rustc_builtin_macro]
1039     #[macro_export]
1040     macro_rules! file {
1041         () => {
1042             /* compiler built-in */
1043         };
1044     }
1045
1046     /// Stringifies its arguments.
1047     ///
1048     /// This macro will yield an expression of type `&'static str` which is the
1049     /// stringification of all the tokens passed to the macro. No restrictions
1050     /// are placed on the syntax of the macro invocation itself.
1051     ///
1052     /// Note that the expanded results of the input tokens may change in the
1053     /// future. You should be careful if you rely on the output.
1054     ///
1055     /// # Examples
1056     ///
1057     /// ```
1058     /// let one_plus_one = stringify!(1 + 1);
1059     /// assert_eq!(one_plus_one, "1 + 1");
1060     /// ```
1061     #[stable(feature = "rust1", since = "1.0.0")]
1062     #[rustc_builtin_macro]
1063     #[macro_export]
1064     macro_rules! stringify {
1065         ($($t:tt)*) => {
1066             /* compiler built-in */
1067         };
1068     }
1069
1070     /// Includes a UTF-8 encoded file as a string.
1071     ///
1072     /// The file is located relative to the current file (similarly to how
1073     /// modules are found). The provided path is interpreted in a platform-specific
1074     /// way at compile time. So, for instance, an invocation with a Windows path
1075     /// containing backslashes `\` would not compile correctly on Unix.
1076     ///
1077     /// This macro will yield an expression of type `&'static str` which is the
1078     /// contents of the file.
1079     ///
1080     /// # Examples
1081     ///
1082     /// Assume there are two files in the same directory with the following
1083     /// contents:
1084     ///
1085     /// File 'spanish.in':
1086     ///
1087     /// ```text
1088     /// adiós
1089     /// ```
1090     ///
1091     /// File 'main.rs':
1092     ///
1093     /// ```ignore (cannot-doctest-external-file-dependency)
1094     /// fn main() {
1095     ///     let my_str = include_str!("spanish.in");
1096     ///     assert_eq!(my_str, "adiós\n");
1097     ///     print!("{}", my_str);
1098     /// }
1099     /// ```
1100     ///
1101     /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1102     #[stable(feature = "rust1", since = "1.0.0")]
1103     #[rustc_builtin_macro]
1104     #[macro_export]
1105     macro_rules! include_str {
1106         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1107     }
1108
1109     /// Includes a file as a reference to a byte array.
1110     ///
1111     /// The file is located relative to the current file (similarly to how
1112     /// modules are found). The provided path is interpreted in a platform-specific
1113     /// way at compile time. So, for instance, an invocation with a Windows path
1114     /// containing backslashes `\` would not compile correctly on Unix.
1115     ///
1116     /// This macro will yield an expression of type `&'static [u8; N]` which is
1117     /// the contents of the file.
1118     ///
1119     /// # Examples
1120     ///
1121     /// Assume there are two files in the same directory with the following
1122     /// contents:
1123     ///
1124     /// File 'spanish.in':
1125     ///
1126     /// ```text
1127     /// adiós
1128     /// ```
1129     ///
1130     /// File 'main.rs':
1131     ///
1132     /// ```ignore (cannot-doctest-external-file-dependency)
1133     /// fn main() {
1134     ///     let bytes = include_bytes!("spanish.in");
1135     ///     assert_eq!(bytes, b"adi\xc3\xb3s\n");
1136     ///     print!("{}", String::from_utf8_lossy(bytes));
1137     /// }
1138     /// ```
1139     ///
1140     /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1141     #[stable(feature = "rust1", since = "1.0.0")]
1142     #[rustc_builtin_macro]
1143     #[macro_export]
1144     macro_rules! include_bytes {
1145         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1146     }
1147
1148     /// Expands to a string that represents the current module path.
1149     ///
1150     /// The current module path can be thought of as the hierarchy of modules
1151     /// leading back up to the crate root. The first component of the path
1152     /// returned is the name of the crate currently being compiled.
1153     ///
1154     /// # Examples
1155     ///
1156     /// ```
1157     /// mod test {
1158     ///     pub fn foo() {
1159     ///         assert!(module_path!().ends_with("test"));
1160     ///     }
1161     /// }
1162     ///
1163     /// test::foo();
1164     /// ```
1165     #[stable(feature = "rust1", since = "1.0.0")]
1166     #[rustc_builtin_macro]
1167     #[macro_export]
1168     macro_rules! module_path {
1169         () => {
1170             /* compiler built-in */
1171         };
1172     }
1173
1174     /// Evaluates boolean combinations of configuration flags at compile-time.
1175     ///
1176     /// In addition to the `#[cfg]` attribute, this macro is provided to allow
1177     /// boolean expression evaluation of configuration flags. This frequently
1178     /// leads to less duplicated code.
1179     ///
1180     /// The syntax given to this macro is the same syntax as the [`cfg`]
1181     /// attribute.
1182     ///
1183     /// `cfg!`, unlike `#[cfg]`, does not remove any code and only evaluates to true or false. For
1184     /// example, all blocks in an if/else expression need to be valid when `cfg!` is used for
1185     /// the condition, regardless of what `cfg!` is evaluating.
1186     ///
1187     /// [`cfg`]: ../reference/conditional-compilation.html#the-cfg-attribute
1188     ///
1189     /// # Examples
1190     ///
1191     /// ```
1192     /// let my_directory = if cfg!(windows) {
1193     ///     "windows-specific-directory"
1194     /// } else {
1195     ///     "unix-directory"
1196     /// };
1197     /// ```
1198     #[stable(feature = "rust1", since = "1.0.0")]
1199     #[rustc_builtin_macro]
1200     #[macro_export]
1201     macro_rules! cfg {
1202         ($($cfg:tt)*) => {
1203             /* compiler built-in */
1204         };
1205     }
1206
1207     /// Parses a file as an expression or an item according to the context.
1208     ///
1209     /// The file is located relative to the current file (similarly to how
1210     /// modules are found). The provided path is interpreted in a platform-specific
1211     /// way at compile time. So, for instance, an invocation with a Windows path
1212     /// containing backslashes `\` would not compile correctly on Unix.
1213     ///
1214     /// Using this macro is often a bad idea, because if the file is
1215     /// parsed as an expression, it is going to be placed in the
1216     /// surrounding code unhygienically. This could result in variables
1217     /// or functions being different from what the file expected if
1218     /// there are variables or functions that have the same name in
1219     /// the current file.
1220     ///
1221     /// # Examples
1222     ///
1223     /// Assume there are two files in the same directory with the following
1224     /// contents:
1225     ///
1226     /// File 'monkeys.in':
1227     ///
1228     /// ```ignore (only-for-syntax-highlight)
1229     /// ['🙈', '🙊', '🙉']
1230     ///     .iter()
1231     ///     .cycle()
1232     ///     .take(6)
1233     ///     .collect::<String>()
1234     /// ```
1235     ///
1236     /// File 'main.rs':
1237     ///
1238     /// ```ignore (cannot-doctest-external-file-dependency)
1239     /// fn main() {
1240     ///     let my_string = include!("monkeys.in");
1241     ///     assert_eq!("🙈🙊🙉🙈🙊🙉", my_string);
1242     ///     println!("{}", my_string);
1243     /// }
1244     /// ```
1245     ///
1246     /// Compiling 'main.rs' and running the resulting binary will print
1247     /// "🙈🙊🙉🙈🙊🙉".
1248     #[stable(feature = "rust1", since = "1.0.0")]
1249     #[rustc_builtin_macro]
1250     #[macro_export]
1251     macro_rules! include {
1252         ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1253     }
1254
1255     /// Asserts that a boolean expression is `true` at runtime.
1256     ///
1257     /// This will invoke the [`panic!`] macro if the provided expression cannot be
1258     /// evaluated to `true` at runtime.
1259     ///
1260     /// # Uses
1261     ///
1262     /// Assertions are always checked in both debug and release builds, and cannot
1263     /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
1264     /// release builds by default.
1265     ///
1266     /// Unsafe code may rely on `assert!` to enforce run-time invariants that, if
1267     /// violated could lead to unsafety.
1268     ///
1269     /// Other use-cases of `assert!` include testing and enforcing run-time
1270     /// invariants in safe code (whose violation cannot result in unsafety).
1271     ///
1272     /// # Custom Messages
1273     ///
1274     /// This macro has a second form, where a custom panic message can
1275     /// be provided with or without arguments for formatting. See [`std::fmt`]
1276     /// for syntax for this form. Expressions used as format arguments will only
1277     /// be evaluated if the assertion fails.
1278     ///
1279     /// [`std::fmt`]: ../std/fmt/index.html
1280     ///
1281     /// # Examples
1282     ///
1283     /// ```
1284     /// // the panic message for these assertions is the stringified value of the
1285     /// // expression given.
1286     /// assert!(true);
1287     ///
1288     /// fn some_computation() -> bool { true } // a very simple function
1289     ///
1290     /// assert!(some_computation());
1291     ///
1292     /// // assert with a custom message
1293     /// let x = true;
1294     /// assert!(x, "x wasn't true!");
1295     ///
1296     /// let a = 3; let b = 27;
1297     /// assert!(a + b == 30, "a = {}, b = {}", a, b);
1298     /// ```
1299     #[stable(feature = "rust1", since = "1.0.0")]
1300     #[rustc_builtin_macro]
1301     #[macro_export]
1302     #[rustc_diagnostic_item = "assert_macro"]
1303     #[allow_internal_unstable(core_panic, edition_panic)]
1304     macro_rules! assert {
1305         ($cond:expr $(,)?) => {{ /* compiler built-in */ }};
1306         ($cond:expr, $($arg:tt)+) => {{ /* compiler built-in */ }};
1307     }
1308
1309     /// Inline assembly.
1310     ///
1311     /// Read the [unstable book] for the usage.
1312     ///
1313     /// [unstable book]: ../unstable-book/library-features/asm.html
1314     #[unstable(
1315         feature = "asm",
1316         issue = "72016",
1317         reason = "inline assembly is not stable enough for use and is subject to change"
1318     )]
1319     #[rustc_builtin_macro]
1320     #[macro_export]
1321     macro_rules! asm {
1322         ("assembly template",
1323             $(operands,)*
1324             $(options($(option),*))?
1325         ) => {
1326             /* compiler built-in */
1327         };
1328     }
1329
1330     /// LLVM-style inline assembly.
1331     ///
1332     /// Read the [unstable book] for the usage.
1333     ///
1334     /// [unstable book]: ../unstable-book/library-features/llvm-asm.html
1335     #[unstable(
1336         feature = "llvm_asm",
1337         issue = "70173",
1338         reason = "prefer using the new asm! syntax instead"
1339     )]
1340     #[rustc_builtin_macro]
1341     #[macro_export]
1342     macro_rules! llvm_asm {
1343         ("assembly template"
1344                         : $("output"(operand),)*
1345                         : $("input"(operand),)*
1346                         : $("clobbers",)*
1347                         : $("options",)*) => {
1348             /* compiler built-in */
1349         };
1350     }
1351
1352     /// Module-level inline assembly.
1353     #[unstable(
1354         feature = "global_asm",
1355         issue = "35119",
1356         reason = "`global_asm!` is not stable enough for use and is subject to change"
1357     )]
1358     #[rustc_builtin_macro]
1359     #[macro_export]
1360     macro_rules! global_asm {
1361         ("assembly") => {
1362             /* compiler built-in */
1363         };
1364     }
1365
1366     /// Prints passed tokens into the standard output.
1367     #[unstable(
1368         feature = "log_syntax",
1369         issue = "29598",
1370         reason = "`log_syntax!` is not stable enough for use and is subject to change"
1371     )]
1372     #[rustc_builtin_macro]
1373     #[macro_export]
1374     macro_rules! log_syntax {
1375         ($($arg:tt)*) => {
1376             /* compiler built-in */
1377         };
1378     }
1379
1380     /// Enables or disables tracing functionality used for debugging other macros.
1381     #[unstable(
1382         feature = "trace_macros",
1383         issue = "29598",
1384         reason = "`trace_macros` is not stable enough for use and is subject to change"
1385     )]
1386     #[rustc_builtin_macro]
1387     #[macro_export]
1388     macro_rules! trace_macros {
1389         (true) => {{ /* compiler built-in */ }};
1390         (false) => {{ /* compiler built-in */ }};
1391     }
1392
1393     /// Attribute macro used to apply derive macros.
1394     #[cfg(not(bootstrap))]
1395     #[stable(feature = "rust1", since = "1.0.0")]
1396     #[rustc_builtin_macro]
1397     pub macro derive($item:item) {
1398         /* compiler built-in */
1399     }
1400
1401     /// Attribute macro applied to a function to turn it into a unit test.
1402     #[stable(feature = "rust1", since = "1.0.0")]
1403     #[allow_internal_unstable(test, rustc_attrs)]
1404     #[rustc_builtin_macro]
1405     pub macro test($item:item) {
1406         /* compiler built-in */
1407     }
1408
1409     /// Attribute macro applied to a function to turn it into a benchmark test.
1410     #[unstable(
1411         feature = "test",
1412         issue = "50297",
1413         soft,
1414         reason = "`bench` is a part of custom test frameworks which are unstable"
1415     )]
1416     #[allow_internal_unstable(test, rustc_attrs)]
1417     #[rustc_builtin_macro]
1418     pub macro bench($item:item) {
1419         /* compiler built-in */
1420     }
1421
1422     /// An implementation detail of the `#[test]` and `#[bench]` macros.
1423     #[unstable(
1424         feature = "custom_test_frameworks",
1425         issue = "50297",
1426         reason = "custom test frameworks are an unstable feature"
1427     )]
1428     #[allow_internal_unstable(test, rustc_attrs)]
1429     #[rustc_builtin_macro]
1430     pub macro test_case($item:item) {
1431         /* compiler built-in */
1432     }
1433
1434     /// Attribute macro applied to a static to register it as a global allocator.
1435     ///
1436     /// See also [`std::alloc::GlobalAlloc`](../std/alloc/trait.GlobalAlloc.html).
1437     #[stable(feature = "global_allocator", since = "1.28.0")]
1438     #[allow_internal_unstable(rustc_attrs)]
1439     #[rustc_builtin_macro]
1440     pub macro global_allocator($item:item) {
1441         /* compiler built-in */
1442     }
1443
1444     /// Keeps the item it's applied to if the passed path is accessible, and removes it otherwise.
1445     #[unstable(
1446         feature = "cfg_accessible",
1447         issue = "64797",
1448         reason = "`cfg_accessible` is not fully implemented"
1449     )]
1450     #[rustc_builtin_macro]
1451     pub macro cfg_accessible($item:item) {
1452         /* compiler built-in */
1453     }
1454
1455     /// Expands all `#[cfg]` and `#[cfg_attr]` attributes in the code fragment it's applied to.
1456     #[cfg(not(bootstrap))]
1457     #[unstable(
1458         feature = "cfg_eval",
1459         issue = "82679",
1460         reason = "`cfg_eval` is a recently implemented feature"
1461     )]
1462     #[rustc_builtin_macro]
1463     pub macro cfg_eval($($tt:tt)*) {
1464         /* compiler built-in */
1465     }
1466
1467     /// Unstable implementation detail of the `rustc` compiler, do not use.
1468     #[rustc_builtin_macro]
1469     #[stable(feature = "rust1", since = "1.0.0")]
1470     #[allow_internal_unstable(core_intrinsics, libstd_sys_internals)]
1471     #[rustc_deprecated(
1472         since = "1.52.0",
1473         reason = "rustc-serialize is deprecated and no longer supported"
1474     )]
1475     pub macro RustcDecodable($item:item) {
1476         /* compiler built-in */
1477     }
1478
1479     /// Unstable implementation detail of the `rustc` compiler, do not use.
1480     #[rustc_builtin_macro]
1481     #[stable(feature = "rust1", since = "1.0.0")]
1482     #[allow_internal_unstable(core_intrinsics)]
1483     #[rustc_deprecated(
1484         since = "1.52.0",
1485         reason = "rustc-serialize is deprecated and no longer supported"
1486     )]
1487     pub macro RustcEncodable($item:item) {
1488         /* compiler built-in */
1489     }
1490 }