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