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"]
7macro_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/// Assertions are always checked in both debug and release builds, and cannot
18/// be disabled. See [`debug_assert_eq!`] for assertions that are disabled in
19/// release builds by default.
20///
21/// [`debug_assert_eq!`]: crate::debug_assert_eq
22///
23/// On panic, this macro will print the values of the expressions with their
24/// debug representations.
25///
26/// Like [`assert!`], this macro has a second form, where a custom
27/// panic message can be provided.
28///
29/// # Examples
30///
31/// ```
32/// let a = 3;
33/// let b = 1 + 2;
34/// assert_eq!(a, b);
35///
36/// assert_eq!(a, b, "we are testing addition with {} and {}", a, b);
37/// ```
38#[macro_export]
39#[stable(feature = "rust1", since = "1.0.0")]
40#[rustc_diagnostic_item = "assert_eq_macro"]
41#[allow_internal_unstable(panic_internals)]
42macro_rules! assert_eq {
43 ($left:expr, $right:expr $(,)?) => {
44 match (&$left, &$right) {
45 (left_val, right_val) => {
46 if !(*left_val == *right_val) {
47 let kind = $crate::panicking::AssertKind::Eq;
48 // The reborrows below are intentional. Without them, the stack slot for the
49 // borrow is initialized even before the values are compared, leading to a
50 // noticeable slow down.
51 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
52 }
53 }
54 }
55 };
56 ($left:expr, $right:expr, $($arg:tt)+) => {
57 match (&$left, &$right) {
58 (left_val, right_val) => {
59 if !(*left_val == *right_val) {
60 let kind = $crate::panicking::AssertKind::Eq;
61 // The reborrows below are intentional. Without them, the stack slot for the
62 // borrow is initialized even before the values are compared, leading to a
63 // noticeable slow down.
64 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
65 }
66 }
67 }
68 };
69}
70
71/// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
72///
73/// Assertions are always checked in both debug and release builds, and cannot
74/// be disabled. See [`debug_assert_ne!`] for assertions that are disabled in
75/// release builds by default.
76///
77/// [`debug_assert_ne!`]: crate::debug_assert_ne
78///
79/// On panic, this macro will print the values of the expressions with their
80/// debug representations.
81///
82/// Like [`assert!`], this macro has a second form, where a custom
83/// panic message can be provided.
84///
85/// # Examples
86///
87/// ```
88/// let a = 3;
89/// let b = 2;
90/// assert_ne!(a, b);
91///
92/// assert_ne!(a, b, "we are testing that the values are not equal");
93/// ```
94#[macro_export]
95#[stable(feature = "assert_ne", since = "1.13.0")]
96#[rustc_diagnostic_item = "assert_ne_macro"]
97#[allow_internal_unstable(panic_internals)]
98macro_rules! assert_ne {
99 ($left:expr, $right:expr $(,)?) => {
100 match (&$left, &$right) {
101 (left_val, right_val) => {
102 if *left_val == *right_val {
103 let kind = $crate::panicking::AssertKind::Ne;
104 // The reborrows below are intentional. Without them, the stack slot for the
105 // borrow is initialized even before the values are compared, leading to a
106 // noticeable slow down.
107 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
108 }
109 }
110 }
111 };
112 ($left:expr, $right:expr, $($arg:tt)+) => {
113 match (&($left), &($right)) {
114 (left_val, right_val) => {
115 if *left_val == *right_val {
116 let kind = $crate::panicking::AssertKind::Ne;
117 // The reborrows below are intentional. Without them, the stack slot for the
118 // borrow is initialized even before the values are compared, leading to a
119 // noticeable slow down.
120 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
121 }
122 }
123 }
124 };
125}
126
127/// Asserts that an expression matches the provided pattern.
128///
129/// This macro is generally preferable to `assert!(matches!(value, pattern))`, because it can print
130/// the debug representation of the actual value shape that did not meet expectations. In contrast,
131/// using [`assert!`] will only print that expectations were not met, but not why.
132///
133/// The pattern syntax is exactly the same as found in a match arm and the `matches!` macro. The
134/// optional if guard can be used to add additional checks that must be true for the matched value,
135/// otherwise this macro will panic.
136///
137/// Assertions are always checked in both debug and release builds, and cannot
138/// be disabled. See [`debug_assert_matches!`] for assertions that are disabled in
139/// release builds by default.
140///
141/// [`debug_assert_matches!`]: crate::assert_matches::debug_assert_matches
142///
143/// On panic, this macro will print the value of the expression with its debug representation.
144///
145/// Like [`assert!`], this macro has a second form, where a custom panic message can be provided.
146///
147/// # Examples
148///
149/// ```
150/// #![feature(assert_matches)]
151///
152/// use std::assert_matches::assert_matches;
153///
154/// let a = Some(345);
155/// let b = Some(56);
156/// assert_matches!(a, Some(_));
157/// assert_matches!(b, Some(_));
158///
159/// assert_matches!(a, Some(345));
160/// assert_matches!(a, Some(345) | None);
161///
162/// // assert_matches!(a, None); // panics
163/// // assert_matches!(b, Some(345)); // panics
164/// // assert_matches!(b, Some(345) | None); // panics
165///
166/// assert_matches!(a, Some(x) if x > 100);
167/// // assert_matches!(a, Some(x) if x < 100); // panics
168/// ```
169#[unstable(feature = "assert_matches", issue = "82775")]
170#[allow_internal_unstable(panic_internals)]
171#[rustc_macro_transparency = "semitransparent"]
172pub macro assert_matches {
173 ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )? $(,)?) => {
174 match $left {
175 $( $pattern )|+ $( if $guard )? => {}
176 ref left_val => {
177 $crate::panicking::assert_matches_failed(
178 left_val,
179 $crate::stringify!($($pattern)|+ $(if $guard)?),
180 $crate::option::Option::None
181 );
182 }
183 }
184 },
185 ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )?, $($arg:tt)+) => {
186 match $left {
187 $( $pattern )|+ $( if $guard )? => {}
188 ref left_val => {
189 $crate::panicking::assert_matches_failed(
190 left_val,
191 $crate::stringify!($($pattern)|+ $(if $guard)?),
192 $crate::option::Option::Some($crate::format_args!($($arg)+))
193 );
194 }
195 }
196 },
197}
198
199/// A macro for defining `#[cfg]` match-like statements.
200///
201/// It is similar to the `if/elif` C preprocessor macro by allowing definition of a cascade of
202/// `#[cfg]` cases, emitting the implementation which matches first.
203///
204/// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code
205/// without having to rewrite each clause multiple times.
206///
207/// Trailing `_` wildcard match arms are **optional** and they indicate a fallback branch when
208/// all previous declarations do not evaluate to true.
209///
210/// # Example
211///
212/// ```
213/// #![feature(cfg_match)]
214///
215/// cfg_match! {
216/// unix => {
217/// fn foo() { /* unix specific functionality */ }
218/// }
219/// target_pointer_width = "32" => {
220/// fn foo() { /* non-unix, 32-bit functionality */ }
221/// }
222/// _ => {
223/// fn foo() { /* fallback implementation */ }
224/// }
225/// }
226/// ```
227///
228/// If desired, it is possible to return expressions through the use of surrounding braces:
229///
230/// ```
231/// #![feature(cfg_match)]
232///
233/// let _some_string = cfg_match! {{
234/// unix => { "With great power comes great electricity bills" }
235/// _ => { "Behind every successful diet is an unwatched pizza" }
236/// }};
237/// ```
238#[unstable(feature = "cfg_match", issue = "115585")]
239#[rustc_diagnostic_item = "cfg_match"]
240pub macro cfg_match {
241 ({ $($tt:tt)* }) => {{
242 cfg_match! { $($tt)* }
243 }},
244 (_ => { $($output:tt)* }) => {
245 $($output)*
246 },
247 (
248 $cfg:meta => $output:tt
249 $($( $rest:tt )+)?
250 ) => {
251 #[cfg($cfg)]
252 cfg_match! { _ => $output }
253 $(
254 #[cfg(not($cfg))]
255 cfg_match! { $($rest)+ }
256 )?
257 },
258}
259
260/// Asserts that a boolean expression is `true` at runtime.
261///
262/// This will invoke the [`panic!`] macro if the provided expression cannot be
263/// evaluated to `true` at runtime.
264///
265/// Like [`assert!`], this macro also has a second version, where a custom panic
266/// message can be provided.
267///
268/// # Uses
269///
270/// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
271/// optimized builds by default. An optimized build will not execute
272/// `debug_assert!` statements unless `-C debug-assertions` is passed to the
273/// compiler. This makes `debug_assert!` useful for checks that are too
274/// expensive to be present in a release build but may be helpful during
275/// development. The result of expanding `debug_assert!` is always type checked.
276///
277/// An unchecked assertion allows a program in an inconsistent state to keep
278/// running, which might have unexpected consequences but does not introduce
279/// unsafety as long as this only happens in safe code. The performance cost
280/// of assertions, however, is not measurable in general. Replacing [`assert!`]
281/// with `debug_assert!` is thus only encouraged after thorough profiling, and
282/// more importantly, only in safe code!
283///
284/// # Examples
285///
286/// ```
287/// // the panic message for these assertions is the stringified value of the
288/// // expression given.
289/// debug_assert!(true);
290///
291/// fn some_expensive_computation() -> bool { true } // a very simple function
292/// debug_assert!(some_expensive_computation());
293///
294/// // assert with a custom message
295/// let x = true;
296/// debug_assert!(x, "x wasn't true!");
297///
298/// let a = 3; let b = 27;
299/// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
300/// ```
301#[macro_export]
302#[stable(feature = "rust1", since = "1.0.0")]
303#[rustc_diagnostic_item = "debug_assert_macro"]
304#[allow_internal_unstable(edition_panic)]
305macro_rules! debug_assert {
306 ($($arg:tt)*) => {
307 if $crate::cfg!(debug_assertions) {
308 $crate::assert!($($arg)*);
309 }
310 };
311}
312
313/// Asserts that two expressions are equal to each other.
314///
315/// On panic, this macro will print the values of the expressions with their
316/// debug representations.
317///
318/// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
319/// optimized builds by default. An optimized build will not execute
320/// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
321/// compiler. This makes `debug_assert_eq!` useful for checks that are too
322/// expensive to be present in a release build but may be helpful during
323/// development. The result of expanding `debug_assert_eq!` is always type checked.
324///
325/// # Examples
326///
327/// ```
328/// let a = 3;
329/// let b = 1 + 2;
330/// debug_assert_eq!(a, b);
331/// ```
332#[macro_export]
333#[stable(feature = "rust1", since = "1.0.0")]
334#[rustc_diagnostic_item = "debug_assert_eq_macro"]
335macro_rules! debug_assert_eq {
336 ($($arg:tt)*) => {
337 if $crate::cfg!(debug_assertions) {
338 $crate::assert_eq!($($arg)*);
339 }
340 };
341}
342
343/// Asserts that two expressions are not equal to each other.
344///
345/// On panic, this macro will print the values of the expressions with their
346/// debug representations.
347///
348/// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
349/// optimized builds by default. An optimized build will not execute
350/// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
351/// compiler. This makes `debug_assert_ne!` useful for checks that are too
352/// expensive to be present in a release build but may be helpful during
353/// development. The result of expanding `debug_assert_ne!` is always type checked.
354///
355/// # Examples
356///
357/// ```
358/// let a = 3;
359/// let b = 2;
360/// debug_assert_ne!(a, b);
361/// ```
362#[macro_export]
363#[stable(feature = "assert_ne", since = "1.13.0")]
364#[rustc_diagnostic_item = "debug_assert_ne_macro"]
365macro_rules! debug_assert_ne {
366 ($($arg:tt)*) => {
367 if $crate::cfg!(debug_assertions) {
368 $crate::assert_ne!($($arg)*);
369 }
370 };
371}
372
373/// Asserts that an expression matches the provided pattern.
374///
375/// This macro is generally preferable to `debug_assert!(matches!(value, pattern))`, because it can
376/// print the debug representation of the actual value shape that did not meet expectations. In
377/// contrast, using [`debug_assert!`] will only print that expectations were not met, but not why.
378///
379/// The pattern syntax is exactly the same as found in a match arm and the `matches!` macro. The
380/// optional if guard can be used to add additional checks that must be true for the matched value,
381/// otherwise this macro will panic.
382///
383/// On panic, this macro will print the value of the expression with its debug representation.
384///
385/// Like [`assert!`], this macro has a second form, where a custom panic message can be provided.
386///
387/// Unlike [`assert_matches!`], `debug_assert_matches!` statements are only enabled in non optimized
388/// builds by default. An optimized build will not execute `debug_assert_matches!` statements unless
389/// `-C debug-assertions` is passed to the compiler. This makes `debug_assert_matches!` useful for
390/// checks that are too expensive to be present in a release build but may be helpful during
391/// development. The result of expanding `debug_assert_matches!` is always type checked.
392///
393/// # Examples
394///
395/// ```
396/// #![feature(assert_matches)]
397///
398/// use std::assert_matches::debug_assert_matches;
399///
400/// let a = Some(345);
401/// let b = Some(56);
402/// debug_assert_matches!(a, Some(_));
403/// debug_assert_matches!(b, Some(_));
404///
405/// debug_assert_matches!(a, Some(345));
406/// debug_assert_matches!(a, Some(345) | None);
407///
408/// // debug_assert_matches!(a, None); // panics
409/// // debug_assert_matches!(b, Some(345)); // panics
410/// // debug_assert_matches!(b, Some(345) | None); // panics
411///
412/// debug_assert_matches!(a, Some(x) if x > 100);
413/// // debug_assert_matches!(a, Some(x) if x < 100); // panics
414/// ```
415#[unstable(feature = "assert_matches", issue = "82775")]
416#[allow_internal_unstable(assert_matches)]
417#[rustc_macro_transparency = "semitransparent"]
418pub macro debug_assert_matches($($arg:tt)*) {
419 if $crate::cfg!(debug_assertions) {
420 $crate::assert_matches::assert_matches!($($arg)*);
421 }
422}
423
424/// Returns whether the given expression matches the provided pattern.
425///
426/// The pattern syntax is exactly the same as found in a match arm. The optional if guard can be
427/// used to add additional checks that must be true for the matched value, otherwise this macro will
428/// return `false`.
429///
430/// When testing that a value matches a pattern, it's generally preferable to use
431/// [`assert_matches!`] as it will print the debug representation of the value if the assertion
432/// fails.
433///
434/// # Examples
435///
436/// ```
437/// let foo = 'f';
438/// assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
439///
440/// let bar = Some(4);
441/// assert!(matches!(bar, Some(x) if x > 2));
442/// ```
443#[macro_export]
444#[stable(feature = "matches_macro", since = "1.42.0")]
445#[rustc_diagnostic_item = "matches_macro"]
446macro_rules! matches {
447 ($expression:expr, $pattern:pat $(if $guard:expr)? $(,)?) => {
448 match $expression {
449 $pattern $(if $guard)? => true,
450 _ => false
451 }
452 };
453}
454
455/// Unwraps a result or propagates its error.
456///
457/// The [`?` operator][propagating-errors] was added to replace `try!`
458/// and should be used instead. Furthermore, `try` is a reserved word
459/// in Rust 2018, so if you must use it, you will need to use the
460/// [raw-identifier syntax][ris]: `r#try`.
461///
462/// [propagating-errors]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
463/// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
464///
465/// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
466/// expression has the value of the wrapped value.
467///
468/// In case of the `Err` variant, it retrieves the inner error. `try!` then
469/// performs conversion using `From`. This provides automatic conversion
470/// between specialized errors and more general ones. The resulting
471/// error is then immediately returned.
472///
473/// Because of the early return, `try!` can only be used in functions that
474/// return [`Result`].
475///
476/// # Examples
477///
478/// ```
479/// use std::io;
480/// use std::fs::File;
481/// use std::io::prelude::*;
482///
483/// enum MyError {
484/// FileWriteError
485/// }
486///
487/// impl From<io::Error> for MyError {
488/// fn from(e: io::Error) -> MyError {
489/// MyError::FileWriteError
490/// }
491/// }
492///
493/// // The preferred method of quick returning Errors
494/// fn write_to_file_question() -> Result<(), MyError> {
495/// let mut file = File::create("my_best_friends.txt")?;
496/// file.write_all(b"This is a list of my best friends.")?;
497/// Ok(())
498/// }
499///
500/// // The previous method of quick returning Errors
501/// fn write_to_file_using_try() -> Result<(), MyError> {
502/// let mut file = r#try!(File::create("my_best_friends.txt"));
503/// r#try!(file.write_all(b"This is a list of my best friends."));
504/// Ok(())
505/// }
506///
507/// // This is equivalent to:
508/// fn write_to_file_using_match() -> Result<(), MyError> {
509/// let mut file = r#try!(File::create("my_best_friends.txt"));
510/// match file.write_all(b"This is a list of my best friends.") {
511/// Ok(v) => v,
512/// Err(e) => return Err(From::from(e)),
513/// }
514/// Ok(())
515/// }
516/// ```
517#[macro_export]
518#[stable(feature = "rust1", since = "1.0.0")]
519#[deprecated(since = "1.39.0", note = "use the `?` operator instead")]
520#[doc(alias = "?")]
521macro_rules! r#try {
522 ($expr:expr $(,)?) => {
523 match $expr {
524 $crate::result::Result::Ok(val) => val,
525 $crate::result::Result::Err(err) => {
526 return $crate::result::Result::Err($crate::convert::From::from(err));
527 }
528 }
529 };
530}
531
532/// Writes formatted data into a buffer.
533///
534/// This macro accepts a 'writer', a format string, and a list of arguments. Arguments will be
535/// formatted according to the specified format string and the result will be passed to the writer.
536/// The writer may be any value with a `write_fmt` method; generally this comes from an
537/// implementation of either the [`fmt::Write`] or the [`io::Write`] trait. The macro
538/// returns whatever the `write_fmt` method returns; commonly a [`fmt::Result`], or an
539/// [`io::Result`].
540///
541/// See [`std::fmt`] for more information on the format string syntax.
542///
543/// [`std::fmt`]: ../std/fmt/index.html
544/// [`fmt::Write`]: crate::fmt::Write
545/// [`io::Write`]: ../std/io/trait.Write.html
546/// [`fmt::Result`]: crate::fmt::Result
547/// [`io::Result`]: ../std/io/type.Result.html
548///
549/// # Examples
550///
551/// ```
552/// use std::io::Write;
553///
554/// fn main() -> std::io::Result<()> {
555/// let mut w = Vec::new();
556/// write!(&mut w, "test")?;
557/// write!(&mut w, "formatted {}", "arguments")?;
558///
559/// assert_eq!(w, b"testformatted arguments");
560/// Ok(())
561/// }
562/// ```
563///
564/// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
565/// implementing either, as objects do not typically implement both. However, the module must
566/// avoid conflict between the trait names, such as by importing them as `_` or otherwise renaming
567/// them:
568///
569/// ```
570/// use std::fmt::Write as _;
571/// use std::io::Write as _;
572///
573/// fn main() -> Result<(), Box<dyn std::error::Error>> {
574/// let mut s = String::new();
575/// let mut v = Vec::new();
576///
577/// write!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
578/// write!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
579/// assert_eq!(v, b"s = \"abc 123\"");
580/// Ok(())
581/// }
582/// ```
583///
584/// If you also need the trait names themselves, such as to implement one or both on your types,
585/// import the containing module and then name them with a prefix:
586///
587/// ```
588/// # #![allow(unused_imports)]
589/// use std::fmt::{self, Write as _};
590/// use std::io::{self, Write as _};
591///
592/// struct Example;
593///
594/// impl fmt::Write for Example {
595/// fn write_str(&mut self, _s: &str) -> core::fmt::Result {
596/// unimplemented!();
597/// }
598/// }
599/// ```
600///
601/// Note: This macro can be used in `no_std` setups as well.
602/// In a `no_std` setup you are responsible for the implementation details of the components.
603///
604/// ```no_run
605/// use core::fmt::Write;
606///
607/// struct Example;
608///
609/// impl Write for Example {
610/// fn write_str(&mut self, _s: &str) -> core::fmt::Result {
611/// unimplemented!();
612/// }
613/// }
614///
615/// let mut m = Example{};
616/// write!(&mut m, "Hello World").expect("Not written");
617/// ```
618#[macro_export]
619#[stable(feature = "rust1", since = "1.0.0")]
620#[rustc_diagnostic_item = "write_macro"]
621macro_rules! write {
622 ($dst:expr, $($arg:tt)*) => {
623 $dst.write_fmt($crate::format_args!($($arg)*))
624 };
625}
626
627/// Writes formatted data into a buffer, with a newline appended.
628///
629/// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
630/// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
631///
632/// For more information, see [`write!`]. For information on the format string syntax, see
633/// [`std::fmt`].
634///
635/// [`std::fmt`]: ../std/fmt/index.html
636///
637/// # Examples
638///
639/// ```
640/// use std::io::{Write, Result};
641///
642/// fn main() -> Result<()> {
643/// let mut w = Vec::new();
644/// writeln!(&mut w)?;
645/// writeln!(&mut w, "test")?;
646/// writeln!(&mut w, "formatted {}", "arguments")?;
647///
648/// assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
649/// Ok(())
650/// }
651/// ```
652#[macro_export]
653#[stable(feature = "rust1", since = "1.0.0")]
654#[rustc_diagnostic_item = "writeln_macro"]
655#[allow_internal_unstable(format_args_nl)]
656macro_rules! writeln {
657 ($dst:expr $(,)?) => {
658 $crate::write!($dst, "\n")
659 };
660 ($dst:expr, $($arg:tt)*) => {
661 $dst.write_fmt($crate::format_args_nl!($($arg)*))
662 };
663}
664
665/// Indicates unreachable code.
666///
667/// This is useful any time that the compiler can't determine that some code is unreachable. For
668/// example:
669///
670/// * Match arms with guard conditions.
671/// * Loops that dynamically terminate.
672/// * Iterators that dynamically terminate.
673///
674/// If the determination that the code is unreachable proves incorrect, the
675/// program immediately terminates with a [`panic!`].
676///
677/// The unsafe counterpart of this macro is the [`unreachable_unchecked`] function, which
678/// will cause undefined behavior if the code is reached.
679///
680/// [`unreachable_unchecked`]: crate::hint::unreachable_unchecked
681///
682/// # Panics
683///
684/// This will always [`panic!`] because `unreachable!` is just a shorthand for `panic!` with a
685/// fixed, specific message.
686///
687/// Like `panic!`, this macro has a second form for displaying custom values.
688///
689/// # Examples
690///
691/// Match arms:
692///
693/// ```
694/// # #[allow(dead_code)]
695/// fn foo(x: Option<i32>) {
696/// match x {
697/// Some(n) if n >= 0 => println!("Some(Non-negative)"),
698/// Some(n) if n < 0 => println!("Some(Negative)"),
699/// Some(_) => unreachable!(), // compile error if commented out
700/// None => println!("None")
701/// }
702/// }
703/// ```
704///
705/// Iterators:
706///
707/// ```
708/// # #[allow(dead_code)]
709/// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
710/// for i in 0.. {
711/// if 3*i < i { panic!("u32 overflow"); }
712/// if x < 3*i { return i-1; }
713/// }
714/// unreachable!("The loop should always return");
715/// }
716/// ```
717#[macro_export]
718#[rustc_builtin_macro(unreachable)]
719#[allow_internal_unstable(edition_panic)]
720#[stable(feature = "rust1", since = "1.0.0")]
721#[rustc_diagnostic_item = "unreachable_macro"]
722macro_rules! unreachable {
723 // Expands to either `$crate::panic::unreachable_2015` or `$crate::panic::unreachable_2021`
724 // depending on the edition of the caller.
725 ($($arg:tt)*) => {
726 /* compiler built-in */
727 };
728}
729
730/// Indicates unimplemented code by panicking with a message of "not implemented".
731///
732/// This allows your code to type-check, which is useful if you are prototyping or
733/// implementing a trait that requires multiple methods which you don't plan to use all of.
734///
735/// The difference between `unimplemented!` and [`todo!`] is that while `todo!`
736/// conveys an intent of implementing the functionality later and the message is "not yet
737/// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
738///
739/// Also, some IDEs will mark `todo!`s.
740///
741/// # Panics
742///
743/// This will always [`panic!`] because `unimplemented!` is just a shorthand for `panic!` with a
744/// fixed, specific message.
745///
746/// Like `panic!`, this macro has a second form for displaying custom values.
747///
748/// [`todo!`]: crate::todo
749///
750/// # Examples
751///
752/// Say we have a trait `Foo`:
753///
754/// ```
755/// trait Foo {
756/// fn bar(&self) -> u8;
757/// fn baz(&self);
758/// fn qux(&self) -> Result<u64, ()>;
759/// }
760/// ```
761///
762/// We want to implement `Foo` for 'MyStruct', but for some reason it only makes sense
763/// to implement the `bar()` function. `baz()` and `qux()` will still need to be defined
764/// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
765/// to allow our code to compile.
766///
767/// We still want to have our program stop running if the unimplemented methods are
768/// reached.
769///
770/// ```
771/// # trait Foo {
772/// # fn bar(&self) -> u8;
773/// # fn baz(&self);
774/// # fn qux(&self) -> Result<u64, ()>;
775/// # }
776/// struct MyStruct;
777///
778/// impl Foo for MyStruct {
779/// fn bar(&self) -> u8 {
780/// 1 + 1
781/// }
782///
783/// fn baz(&self) {
784/// // It makes no sense to `baz` a `MyStruct`, so we have no logic here
785/// // at all.
786/// // This will display "thread 'main' panicked at 'not implemented'".
787/// unimplemented!();
788/// }
789///
790/// fn qux(&self) -> Result<u64, ()> {
791/// // We have some logic here,
792/// // We can add a message to unimplemented! to display our omission.
793/// // This will display:
794/// // "thread 'main' panicked at 'not implemented: MyStruct isn't quxable'".
795/// unimplemented!("MyStruct isn't quxable");
796/// }
797/// }
798///
799/// fn main() {
800/// let s = MyStruct;
801/// s.bar();
802/// }
803/// ```
804#[macro_export]
805#[stable(feature = "rust1", since = "1.0.0")]
806#[rustc_diagnostic_item = "unimplemented_macro"]
807#[allow_internal_unstable(panic_internals)]
808macro_rules! unimplemented {
809 () => {
810 $crate::panicking::panic("not implemented")
811 };
812 ($($arg:tt)+) => {
813 $crate::panic!("not implemented: {}", $crate::format_args!($($arg)+))
814 };
815}
816
817/// Indicates unfinished code.
818///
819/// This can be useful if you are prototyping and just
820/// want a placeholder to let your code pass type analysis.
821///
822/// The difference between [`unimplemented!`] and `todo!` is that while `todo!` conveys
823/// an intent of implementing the functionality later and the message is "not yet
824/// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
825///
826/// Also, some IDEs will mark `todo!`s.
827///
828/// # Panics
829///
830/// This will always [`panic!`] because `todo!` is just a shorthand for `panic!` with a
831/// fixed, specific message.
832///
833/// Like `panic!`, this macro has a second form for displaying custom values.
834///
835/// # Examples
836///
837/// Here's an example of some in-progress code. We have a trait `Foo`:
838///
839/// ```
840/// trait Foo {
841/// fn bar(&self) -> u8;
842/// fn baz(&self);
843/// fn qux(&self) -> Result<u64, ()>;
844/// }
845/// ```
846///
847/// We want to implement `Foo` on one of our types, but we also want to work on
848/// just `bar()` first. In order for our code to compile, we need to implement
849/// `baz()` and `qux()`, so we can use `todo!`:
850///
851/// ```
852/// # trait Foo {
853/// # fn bar(&self) -> u8;
854/// # fn baz(&self);
855/// # fn qux(&self) -> Result<u64, ()>;
856/// # }
857/// struct MyStruct;
858///
859/// impl Foo for MyStruct {
860/// fn bar(&self) -> u8 {
861/// 1 + 1
862/// }
863///
864/// fn baz(&self) {
865/// // Let's not worry about implementing baz() for now
866/// todo!();
867/// }
868///
869/// fn qux(&self) -> Result<u64, ()> {
870/// // We can add a message to todo! to display our omission.
871/// // This will display:
872/// // "thread 'main' panicked at 'not yet implemented: MyStruct is not yet quxable'".
873/// todo!("MyStruct is not yet quxable");
874/// }
875/// }
876///
877/// fn main() {
878/// let s = MyStruct;
879/// s.bar();
880///
881/// // We aren't even using baz() or qux(), so this is fine.
882/// }
883/// ```
884#[macro_export]
885#[stable(feature = "todo_macro", since = "1.40.0")]
886#[rustc_diagnostic_item = "todo_macro"]
887#[allow_internal_unstable(panic_internals)]
888macro_rules! todo {
889 () => {
890 $crate::panicking::panic("not yet implemented")
891 };
892 ($($arg:tt)+) => {
893 $crate::panic!("not yet implemented: {}", $crate::format_args!($($arg)+))
894 };
895}
896
897/// Definitions of built-in macros.
898///
899/// Most of the macro properties (stability, visibility, etc.) are taken from the source code here,
900/// with exception of expansion functions transforming macro inputs into outputs,
901/// those functions are provided by the compiler.
902pub(crate) mod builtin {
903
904 /// Causes compilation to fail with the given error message when encountered.
905 ///
906 /// This macro should be used when a crate uses a conditional compilation strategy to provide
907 /// better error messages for erroneous conditions. It's the compiler-level form of [`panic!`],
908 /// but emits an error during *compilation* rather than at *runtime*.
909 ///
910 /// # Examples
911 ///
912 /// Two such examples are macros and `#[cfg]` environments.
913 ///
914 /// Emit a better compiler error if a macro is passed invalid values. Without the final branch,
915 /// the compiler would still emit an error, but the error's message would not mention the two
916 /// valid values.
917 ///
918 /// ```compile_fail
919 /// macro_rules! give_me_foo_or_bar {
920 /// (foo) => {};
921 /// (bar) => {};
922 /// ($x:ident) => {
923 /// compile_error!("This macro only accepts `foo` or `bar`");
924 /// }
925 /// }
926 ///
927 /// give_me_foo_or_bar!(neither);
928 /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
929 /// ```
930 ///
931 /// Emit a compiler error if one of a number of features isn't available.
932 ///
933 /// ```compile_fail
934 /// #[cfg(not(any(feature = "foo", feature = "bar")))]
935 /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.");
936 /// ```
937 #[stable(feature = "compile_error_macro", since = "1.20.0")]
938 #[rustc_builtin_macro]
939 #[macro_export]
940 macro_rules! compile_error {
941 ($msg:expr $(,)?) => {{ /* compiler built-in */ }};
942 }
943
944 /// Constructs parameters for the other string-formatting macros.
945 ///
946 /// This macro functions by taking a formatting string literal containing
947 /// `{}` for each additional argument passed. `format_args!` prepares the
948 /// additional parameters to ensure the output can be interpreted as a string
949 /// and canonicalizes the arguments into a single type. Any value that implements
950 /// the [`Display`] trait can be passed to `format_args!`, as can any
951 /// [`Debug`] implementation be passed to a `{:?}` within the formatting string.
952 ///
953 /// This macro produces a value of type [`fmt::Arguments`]. This value can be
954 /// passed to the macros within [`std::fmt`] for performing useful redirection.
955 /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
956 /// proxied through this one. `format_args!`, unlike its derived macros, avoids
957 /// heap allocations.
958 ///
959 /// You can use the [`fmt::Arguments`] value that `format_args!` returns
960 /// in `Debug` and `Display` contexts as seen below. The example also shows
961 /// that `Debug` and `Display` format to the same thing: the interpolated
962 /// format string in `format_args!`.
963 ///
964 /// ```rust
965 /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
966 /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
967 /// assert_eq!("1 foo 2", display);
968 /// assert_eq!(display, debug);
969 /// ```
970 ///
971 /// See [the formatting documentation in `std::fmt`](../std/fmt/index.html)
972 /// for details of the macro argument syntax, and further information.
973 ///
974 /// [`Display`]: crate::fmt::Display
975 /// [`Debug`]: crate::fmt::Debug
976 /// [`fmt::Arguments`]: crate::fmt::Arguments
977 /// [`std::fmt`]: ../std/fmt/index.html
978 /// [`format!`]: ../std/macro.format.html
979 /// [`println!`]: ../std/macro.println.html
980 ///
981 /// # Examples
982 ///
983 /// ```
984 /// use std::fmt;
985 ///
986 /// let s = fmt::format(format_args!("hello {}", "world"));
987 /// assert_eq!(s, format!("hello {}", "world"));
988 /// ```
989 ///
990 /// # Lifetime limitation
991 ///
992 /// Except when no formatting arguments are used,
993 /// the produced `fmt::Arguments` value borrows temporary values,
994 /// which means it can only be used within the same expression
995 /// and cannot be stored for later use.
996 /// This is a known limitation, see [#92698](https://github.com/rust-lang/rust/issues/92698).
997 #[stable(feature = "rust1", since = "1.0.0")]
998 #[rustc_diagnostic_item = "format_args_macro"]
999 #[allow_internal_unsafe]
1000 #[allow_internal_unstable(fmt_internals)]
1001 #[rustc_builtin_macro]
1002 #[macro_export]
1003 macro_rules! format_args {
1004 ($fmt:expr) => {{ /* compiler built-in */ }};
1005 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1006 }
1007
1008 /// Same as [`format_args`], but can be used in some const contexts.
1009 ///
1010 /// This macro is used by the panic macros for the `const_panic` feature.
1011 ///
1012 /// This macro will be removed once `format_args` is allowed in const contexts.
1013 #[unstable(feature = "const_format_args", issue = "none")]
1014 #[allow_internal_unstable(fmt_internals, const_fmt_arguments_new)]
1015 #[rustc_builtin_macro]
1016 #[macro_export]
1017 macro_rules! const_format_args {
1018 ($fmt:expr) => {{ /* compiler built-in */ }};
1019 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1020 }
1021
1022 /// Same as [`format_args`], but adds a newline in the end.
1023 #[unstable(
1024 feature = "format_args_nl",
1025 issue = "none",
1026 reason = "`format_args_nl` is only for internal \
1027 language use and is subject to change"
1028 )]
1029 #[allow_internal_unstable(fmt_internals)]
1030 #[rustc_builtin_macro]
1031 #[macro_export]
1032 macro_rules! format_args_nl {
1033 ($fmt:expr) => {{ /* compiler built-in */ }};
1034 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1035 }
1036
1037 /// Inspects an environment variable at compile time.
1038 ///
1039 /// This macro will expand to the value of the named environment variable at
1040 /// compile time, yielding an expression of type `&'static str`. Use
1041 /// [`std::env::var`] instead if you want to read the value at runtime.
1042 ///
1043 /// [`std::env::var`]: ../std/env/fn.var.html
1044 ///
1045 /// If the environment variable is not defined, then a compilation error
1046 /// will be emitted. To not emit a compile error, use the [`option_env!`]
1047 /// macro instead. A compilation error will also be emitted if the
1048 /// environment variable is not a valid Unicode string.
1049 ///
1050 /// # Examples
1051 ///
1052 /// ```
1053 /// let path: &'static str = env!("PATH");
1054 /// println!("the $PATH variable at the time of compiling was: {path}");
1055 /// ```
1056 ///
1057 /// You can customize the error message by passing a string as the second
1058 /// parameter:
1059 ///
1060 /// ```compile_fail
1061 /// let doc: &'static str = env!("documentation", "what's that?!");
1062 /// ```
1063 ///
1064 /// If the `documentation` environment variable is not defined, you'll get
1065 /// the following error:
1066 ///
1067 /// ```text
1068 /// error: what's that?!
1069 /// ```
1070 #[stable(feature = "rust1", since = "1.0.0")]
1071 #[rustc_builtin_macro]
1072 #[macro_export]
1073 #[rustc_diagnostic_item = "env_macro"] // useful for external lints
1074 macro_rules! env {
1075 ($name:expr $(,)?) => {{ /* compiler built-in */ }};
1076 ($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
1077 }
1078
1079 /// Optionally inspects an environment variable at compile time.
1080 ///
1081 /// If the named environment variable is present at compile time, this will
1082 /// expand into an expression of type `Option<&'static str>` whose value is
1083 /// `Some` of the value of the environment variable (a compilation error
1084 /// will be emitted if the environment variable is not a valid Unicode
1085 /// string). If the environment variable is not present, then this will
1086 /// expand to `None`. See [`Option<T>`][Option] for more information on this
1087 /// type. Use [`std::env::var`] instead if you want to read the value at
1088 /// runtime.
1089 ///
1090 /// [`std::env::var`]: ../std/env/fn.var.html
1091 ///
1092 /// A compile time error is only emitted when using this macro if the
1093 /// environment variable exists and is not a valid Unicode string. To also
1094 /// emit a compile error if the environment variable is not present, use the
1095 /// [`env!`] macro instead.
1096 ///
1097 /// # Examples
1098 ///
1099 /// ```
1100 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
1101 /// println!("the secret key might be: {key:?}");
1102 /// ```
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 #[rustc_builtin_macro]
1105 #[macro_export]
1106 #[rustc_diagnostic_item = "option_env_macro"] // useful for external lints
1107 macro_rules! option_env {
1108 ($name:expr $(,)?) => {{ /* compiler built-in */ }};
1109 }
1110
1111 /// Concatenates identifiers into one identifier.
1112 ///
1113 /// This macro takes any number of comma-separated identifiers, and
1114 /// concatenates them all into one, yielding an expression which is a new
1115 /// identifier. Note that hygiene makes it such that this macro cannot
1116 /// capture local variables. Also, as a general rule, macros are only
1117 /// allowed in item, statement or expression position. That means while
1118 /// you may use this macro for referring to existing variables, functions or
1119 /// modules etc, you cannot define a new one with it.
1120 ///
1121 /// # Examples
1122 ///
1123 /// ```
1124 /// #![feature(concat_idents)]
1125 ///
1126 /// # fn main() {
1127 /// fn foobar() -> u32 { 23 }
1128 ///
1129 /// let f = concat_idents!(foo, bar);
1130 /// println!("{}", f());
1131 ///
1132 /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
1133 /// # }
1134 /// ```
1135 #[unstable(
1136 feature = "concat_idents",
1137 issue = "29599",
1138 reason = "`concat_idents` is not stable enough for use and is subject to change"
1139 )]
1140 #[rustc_builtin_macro]
1141 #[macro_export]
1142 macro_rules! concat_idents {
1143 ($($e:ident),+ $(,)?) => {{ /* compiler built-in */ }};
1144 }
1145
1146 /// Concatenates literals into a byte slice.
1147 ///
1148 /// This macro takes any number of comma-separated literals, and concatenates them all into
1149 /// one, yielding an expression of type `&[u8; _]`, which represents all of the literals
1150 /// concatenated left-to-right. The literals passed can be any combination of:
1151 ///
1152 /// - byte literals (`b'r'`)
1153 /// - byte strings (`b"Rust"`)
1154 /// - arrays of bytes/numbers (`[b'A', 66, b'C']`)
1155 ///
1156 /// # Examples
1157 ///
1158 /// ```
1159 /// #![feature(concat_bytes)]
1160 ///
1161 /// # fn main() {
1162 /// let s: &[u8; 6] = concat_bytes!(b'A', b"BC", [68, b'E', 70]);
1163 /// assert_eq!(s, b"ABCDEF");
1164 /// # }
1165 /// ```
1166 #[unstable(feature = "concat_bytes", issue = "87555")]
1167 #[rustc_builtin_macro]
1168 #[macro_export]
1169 macro_rules! concat_bytes {
1170 ($($e:literal),+ $(,)?) => {{ /* compiler built-in */ }};
1171 }
1172
1173 /// Concatenates literals into a static string slice.
1174 ///
1175 /// This macro takes any number of comma-separated literals, yielding an
1176 /// expression of type `&'static str` which represents all of the literals
1177 /// concatenated left-to-right.
1178 ///
1179 /// Integer and floating point literals are [stringified](core::stringify) in order to be
1180 /// concatenated.
1181 ///
1182 /// # Examples
1183 ///
1184 /// ```
1185 /// let s = concat!("test", 10, 'b', true);
1186 /// assert_eq!(s, "test10btrue");
1187 /// ```
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 #[rustc_builtin_macro]
1190 #[macro_export]
1191 macro_rules! concat {
1192 ($($e:expr),* $(,)?) => {{ /* compiler built-in */ }};
1193 }
1194
1195 /// Expands to the line number on which it was invoked.
1196 ///
1197 /// With [`column!`] and [`file!`], these macros provide debugging information for
1198 /// developers about the location within the source.
1199 ///
1200 /// The expanded expression has type `u32` and is 1-based, so the first line
1201 /// in each file evaluates to 1, the second to 2, etc. This is consistent
1202 /// with error messages by common compilers or popular editors.
1203 /// The returned line is *not necessarily* the line of the `line!` invocation itself,
1204 /// but rather the first macro invocation leading up to the invocation
1205 /// of the `line!` macro.
1206 ///
1207 /// # Examples
1208 ///
1209 /// ```
1210 /// let current_line = line!();
1211 /// println!("defined on line: {current_line}");
1212 /// ```
1213 #[stable(feature = "rust1", since = "1.0.0")]
1214 #[rustc_builtin_macro]
1215 #[macro_export]
1216 macro_rules! line {
1217 () => {
1218 /* compiler built-in */
1219 };
1220 }
1221
1222 /// Expands to the column number at which it was invoked.
1223 ///
1224 /// With [`line!`] and [`file!`], these macros provide debugging information for
1225 /// developers about the location within the source.
1226 ///
1227 /// The expanded expression has type `u32` and is 1-based, so the first column
1228 /// in each line evaluates to 1, the second to 2, etc. This is consistent
1229 /// with error messages by common compilers or popular editors.
1230 /// The returned column is *not necessarily* the line of the `column!` invocation itself,
1231 /// but rather the first macro invocation leading up to the invocation
1232 /// of the `column!` macro.
1233 ///
1234 /// # Examples
1235 ///
1236 /// ```
1237 /// let current_col = column!();
1238 /// println!("defined on column: {current_col}");
1239 /// ```
1240 ///
1241 /// `column!` counts Unicode code points, not bytes or graphemes. As a result, the first two
1242 /// invocations return the same value, but the third does not.
1243 ///
1244 /// ```
1245 /// let a = ("foobar", column!()).1;
1246 /// let b = ("人之初性本善", column!()).1;
1247 /// let c = ("f̅o̅o̅b̅a̅r̅", column!()).1; // Uses combining overline (U+0305)
1248 ///
1249 /// assert_eq!(a, b);
1250 /// assert_ne!(b, c);
1251 /// ```
1252 #[stable(feature = "rust1", since = "1.0.0")]
1253 #[rustc_builtin_macro]
1254 #[macro_export]
1255 macro_rules! column {
1256 () => {
1257 /* compiler built-in */
1258 };
1259 }
1260
1261 /// Expands to the file name in which it was invoked.
1262 ///
1263 /// With [`line!`] and [`column!`], these macros provide debugging information for
1264 /// developers about the location within the source.
1265 ///
1266 /// The expanded expression has type `&'static str`, and the returned file
1267 /// is not the invocation of the `file!` macro itself, but rather the
1268 /// first macro invocation leading up to the invocation of the `file!`
1269 /// macro.
1270 ///
1271 /// # Examples
1272 ///
1273 /// ```
1274 /// let this_file = file!();
1275 /// println!("defined in file: {this_file}");
1276 /// ```
1277 #[stable(feature = "rust1", since = "1.0.0")]
1278 #[rustc_builtin_macro]
1279 #[macro_export]
1280 macro_rules! file {
1281 () => {
1282 /* compiler built-in */
1283 };
1284 }
1285
1286 /// Stringifies its arguments.
1287 ///
1288 /// This macro will yield an expression of type `&'static str` which is the
1289 /// stringification of all the tokens passed to the macro. No restrictions
1290 /// are placed on the syntax of the macro invocation itself.
1291 ///
1292 /// Note that the expanded results of the input tokens may change in the
1293 /// future. You should be careful if you rely on the output.
1294 ///
1295 /// # Examples
1296 ///
1297 /// ```
1298 /// let one_plus_one = stringify!(1 + 1);
1299 /// assert_eq!(one_plus_one, "1 + 1");
1300 /// ```
1301 #[stable(feature = "rust1", since = "1.0.0")]
1302 #[rustc_builtin_macro]
1303 #[macro_export]
1304 macro_rules! stringify {
1305 ($($t:tt)*) => {
1306 /* compiler built-in */
1307 };
1308 }
1309
1310 /// Includes a UTF-8 encoded file as a string.
1311 ///
1312 /// The file is located relative to the current file (similarly to how
1313 /// modules are found). The provided path is interpreted in a platform-specific
1314 /// way at compile time. So, for instance, an invocation with a Windows path
1315 /// containing backslashes `\` would not compile correctly on Unix.
1316 ///
1317 /// This macro will yield an expression of type `&'static str` which is the
1318 /// contents of the file.
1319 ///
1320 /// # Examples
1321 ///
1322 /// Assume there are two files in the same directory with the following
1323 /// contents:
1324 ///
1325 /// File 'spanish.in':
1326 ///
1327 /// ```text
1328 /// adiós
1329 /// ```
1330 ///
1331 /// File 'main.rs':
1332 ///
1333 /// ```ignore (cannot-doctest-external-file-dependency)
1334 /// fn main() {
1335 /// let my_str = include_str!("spanish.in");
1336 /// assert_eq!(my_str, "adiós\n");
1337 /// print!("{my_str}");
1338 /// }
1339 /// ```
1340 ///
1341 /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1342 #[stable(feature = "rust1", since = "1.0.0")]
1343 #[rustc_builtin_macro]
1344 #[macro_export]
1345 #[rustc_diagnostic_item = "include_str_macro"]
1346 macro_rules! include_str {
1347 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1348 }
1349
1350 /// Includes a file as a reference to a byte array.
1351 ///
1352 /// The file is located relative to the current file (similarly to how
1353 /// modules are found). The provided path is interpreted in a platform-specific
1354 /// way at compile time. So, for instance, an invocation with a Windows path
1355 /// containing backslashes `\` would not compile correctly on Unix.
1356 ///
1357 /// This macro will yield an expression of type `&'static [u8; N]` which is
1358 /// the contents of the file.
1359 ///
1360 /// # Examples
1361 ///
1362 /// Assume there are two files in the same directory with the following
1363 /// contents:
1364 ///
1365 /// File 'spanish.in':
1366 ///
1367 /// ```text
1368 /// adiós
1369 /// ```
1370 ///
1371 /// File 'main.rs':
1372 ///
1373 /// ```ignore (cannot-doctest-external-file-dependency)
1374 /// fn main() {
1375 /// let bytes = include_bytes!("spanish.in");
1376 /// assert_eq!(bytes, b"adi\xc3\xb3s\n");
1377 /// print!("{}", String::from_utf8_lossy(bytes));
1378 /// }
1379 /// ```
1380 ///
1381 /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1382 #[stable(feature = "rust1", since = "1.0.0")]
1383 #[rustc_builtin_macro]
1384 #[macro_export]
1385 #[rustc_diagnostic_item = "include_bytes_macro"]
1386 macro_rules! include_bytes {
1387 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1388 }
1389
1390 /// Expands to a string that represents the current module path.
1391 ///
1392 /// The current module path can be thought of as the hierarchy of modules
1393 /// leading back up to the crate root. The first component of the path
1394 /// returned is the name of the crate currently being compiled.
1395 ///
1396 /// # Examples
1397 ///
1398 /// ```
1399 /// mod test {
1400 /// pub fn foo() {
1401 /// assert!(module_path!().ends_with("test"));
1402 /// }
1403 /// }
1404 ///
1405 /// test::foo();
1406 /// ```
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 #[rustc_builtin_macro]
1409 #[macro_export]
1410 macro_rules! module_path {
1411 () => {
1412 /* compiler built-in */
1413 };
1414 }
1415
1416 /// Evaluates boolean combinations of configuration flags at compile-time.
1417 ///
1418 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
1419 /// boolean expression evaluation of configuration flags. This frequently
1420 /// leads to less duplicated code.
1421 ///
1422 /// The syntax given to this macro is the same syntax as the [`cfg`]
1423 /// attribute.
1424 ///
1425 /// `cfg!`, unlike `#[cfg]`, does not remove any code and only evaluates to true or false. For
1426 /// example, all blocks in an if/else expression need to be valid when `cfg!` is used for
1427 /// the condition, regardless of what `cfg!` is evaluating.
1428 ///
1429 /// [`cfg`]: ../reference/conditional-compilation.html#the-cfg-attribute
1430 ///
1431 /// # Examples
1432 ///
1433 /// ```
1434 /// let my_directory = if cfg!(windows) {
1435 /// "windows-specific-directory"
1436 /// } else {
1437 /// "unix-directory"
1438 /// };
1439 /// ```
1440 #[stable(feature = "rust1", since = "1.0.0")]
1441 #[rustc_builtin_macro]
1442 #[macro_export]
1443 macro_rules! cfg {
1444 ($($cfg:tt)*) => {
1445 /* compiler built-in */
1446 };
1447 }
1448
1449 /// Parses a file as an expression or an item according to the context.
1450 ///
1451 /// **Warning**: For multi-file Rust projects, the `include!` macro is probably not what you
1452 /// are looking for. Usually, multi-file Rust projects use
1453 /// [modules](https://doc.rust-lang.org/reference/items/modules.html). Multi-file projects and
1454 /// modules are explained in the Rust-by-Example book
1455 /// [here](https://doc.rust-lang.org/rust-by-example/mod/split.html) and the module system is
1456 /// explained in the Rust Book
1457 /// [here](https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html).
1458 ///
1459 /// The included file is placed in the surrounding code
1460 /// [unhygienically](https://doc.rust-lang.org/reference/macros-by-example.html#hygiene). If
1461 /// the included file is parsed as an expression and variables or functions share names across
1462 /// both files, it could result in variables or functions being different from what the
1463 /// included file expected.
1464 ///
1465 /// The included file is located relative to the current file (similarly to how modules are
1466 /// found). The provided path is interpreted in a platform-specific way at compile time. So,
1467 /// for instance, an invocation with a Windows path containing backslashes `\` would not
1468 /// compile correctly on Unix.
1469 ///
1470 /// # Uses
1471 ///
1472 /// The `include!` macro is primarily used for two purposes. It is used to include
1473 /// documentation that is written in a separate file and it is used to include [build artifacts
1474 /// usually as a result from the `build.rs`
1475 /// script](https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script).
1476 ///
1477 /// When using the `include` macro to include stretches of documentation, remember that the
1478 /// included file still needs to be a valid Rust syntax. It is also possible to
1479 /// use the [`include_str`] macro as `#![doc = include_str!("...")]` (at the module level) or
1480 /// `#[doc = include_str!("...")]` (at the item level) to include documentation from a plain
1481 /// text or markdown file.
1482 ///
1483 /// # Examples
1484 ///
1485 /// Assume there are two files in the same directory with the following contents:
1486 ///
1487 /// File 'monkeys.in':
1488 ///
1489 /// ```ignore (only-for-syntax-highlight)
1490 /// ['🙈', '🙊', '🙉']
1491 /// .iter()
1492 /// .cycle()
1493 /// .take(6)
1494 /// .collect::<String>()
1495 /// ```
1496 ///
1497 /// File 'main.rs':
1498 ///
1499 /// ```ignore (cannot-doctest-external-file-dependency)
1500 /// fn main() {
1501 /// let my_string = include!("monkeys.in");
1502 /// assert_eq!("🙈🙊🙉🙈🙊🙉", my_string);
1503 /// println!("{my_string}");
1504 /// }
1505 /// ```
1506 ///
1507 /// Compiling 'main.rs' and running the resulting binary will print
1508 /// "🙈🙊🙉🙈🙊🙉".
1509 #[stable(feature = "rust1", since = "1.0.0")]
1510 #[rustc_builtin_macro]
1511 #[macro_export]
1512 #[rustc_diagnostic_item = "include_macro"] // useful for external lints
1513 macro_rules! include {
1514 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1515 }
1516
1517 /// Automatic Differentiation macro which allows generating a new function to compute
1518 /// the derivative of a given function. It may only be applied to a function.
1519 /// The expected usage syntax is
1520 /// `#[autodiff(NAME, MODE, INPUT_ACTIVITIES, OUTPUT_ACTIVITY)]`
1521 /// where:
1522 /// NAME is a string that represents a valid function name.
1523 /// MODE is any of Forward, Reverse, ForwardFirst, ReverseFirst.
1524 /// INPUT_ACTIVITIES consists of one valid activity for each input parameter.
1525 /// OUTPUT_ACTIVITY must not be set if we implicitly return nothing (or explicitly return
1526 /// `-> ()`). Otherwise it must be set to one of the allowed activities.
1527 #[unstable(feature = "autodiff", issue = "124509")]
1528 #[allow_internal_unstable(rustc_attrs)]
1529 #[rustc_builtin_macro]
1530 pub macro autodiff($item:item) {
1531 /* compiler built-in */
1532 }
1533
1534 /// Asserts that a boolean expression is `true` at runtime.
1535 ///
1536 /// This will invoke the [`panic!`] macro if the provided expression cannot be
1537 /// evaluated to `true` at runtime.
1538 ///
1539 /// # Uses
1540 ///
1541 /// Assertions are always checked in both debug and release builds, and cannot
1542 /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
1543 /// release builds by default.
1544 ///
1545 /// Unsafe code may rely on `assert!` to enforce run-time invariants that, if
1546 /// violated could lead to unsafety.
1547 ///
1548 /// Other use-cases of `assert!` include testing and enforcing run-time
1549 /// invariants in safe code (whose violation cannot result in unsafety).
1550 ///
1551 /// # Custom Messages
1552 ///
1553 /// This macro has a second form, where a custom panic message can
1554 /// be provided with or without arguments for formatting. See [`std::fmt`]
1555 /// for syntax for this form. Expressions used as format arguments will only
1556 /// be evaluated if the assertion fails.
1557 ///
1558 /// [`std::fmt`]: ../std/fmt/index.html
1559 ///
1560 /// # Examples
1561 ///
1562 /// ```
1563 /// // the panic message for these assertions is the stringified value of the
1564 /// // expression given.
1565 /// assert!(true);
1566 ///
1567 /// fn some_computation() -> bool { true } // a very simple function
1568 ///
1569 /// assert!(some_computation());
1570 ///
1571 /// // assert with a custom message
1572 /// let x = true;
1573 /// assert!(x, "x wasn't true!");
1574 ///
1575 /// let a = 3; let b = 27;
1576 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
1577 /// ```
1578 #[stable(feature = "rust1", since = "1.0.0")]
1579 #[rustc_builtin_macro]
1580 #[macro_export]
1581 #[rustc_diagnostic_item = "assert_macro"]
1582 #[allow_internal_unstable(
1583 core_intrinsics,
1584 panic_internals,
1585 edition_panic,
1586 generic_assert_internals
1587 )]
1588 macro_rules! assert {
1589 ($cond:expr $(,)?) => {{ /* compiler built-in */ }};
1590 ($cond:expr, $($arg:tt)+) => {{ /* compiler built-in */ }};
1591 }
1592
1593 /// Prints passed tokens into the standard output.
1594 #[unstable(
1595 feature = "log_syntax",
1596 issue = "29598",
1597 reason = "`log_syntax!` is not stable enough for use and is subject to change"
1598 )]
1599 #[rustc_builtin_macro]
1600 #[macro_export]
1601 macro_rules! log_syntax {
1602 ($($arg:tt)*) => {
1603 /* compiler built-in */
1604 };
1605 }
1606
1607 /// Enables or disables tracing functionality used for debugging other macros.
1608 #[unstable(
1609 feature = "trace_macros",
1610 issue = "29598",
1611 reason = "`trace_macros` is not stable enough for use and is subject to change"
1612 )]
1613 #[rustc_builtin_macro]
1614 #[macro_export]
1615 macro_rules! trace_macros {
1616 (true) => {{ /* compiler built-in */ }};
1617 (false) => {{ /* compiler built-in */ }};
1618 }
1619
1620 /// Attribute macro used to apply derive macros.
1621 ///
1622 /// See [the reference] for more info.
1623 ///
1624 /// [the reference]: ../../../reference/attributes/derive.html
1625 #[stable(feature = "rust1", since = "1.0.0")]
1626 #[rustc_builtin_macro]
1627 pub macro derive($item:item) {
1628 /* compiler built-in */
1629 }
1630
1631 /// Attribute macro used to apply derive macros for implementing traits
1632 /// in a const context.
1633 ///
1634 /// See [the reference] for more info.
1635 ///
1636 /// [the reference]: ../../../reference/attributes/derive.html
1637 #[unstable(feature = "derive_const", issue = "none")]
1638 #[rustc_builtin_macro]
1639 pub macro derive_const($item:item) {
1640 /* compiler built-in */
1641 }
1642
1643 /// Attribute macro applied to a function to turn it into a unit test.
1644 ///
1645 /// See [the reference] for more info.
1646 ///
1647 /// [the reference]: ../../../reference/attributes/testing.html#the-test-attribute
1648 #[stable(feature = "rust1", since = "1.0.0")]
1649 #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
1650 #[rustc_builtin_macro]
1651 pub macro test($item:item) {
1652 /* compiler built-in */
1653 }
1654
1655 /// Attribute macro applied to a function to turn it into a benchmark test.
1656 #[unstable(
1657 feature = "test",
1658 issue = "50297",
1659 soft,
1660 reason = "`bench` is a part of custom test frameworks which are unstable"
1661 )]
1662 #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
1663 #[rustc_builtin_macro]
1664 pub macro bench($item:item) {
1665 /* compiler built-in */
1666 }
1667
1668 /// An implementation detail of the `#[test]` and `#[bench]` macros.
1669 #[unstable(
1670 feature = "custom_test_frameworks",
1671 issue = "50297",
1672 reason = "custom test frameworks are an unstable feature"
1673 )]
1674 #[allow_internal_unstable(test, rustc_attrs)]
1675 #[rustc_builtin_macro]
1676 pub macro test_case($item:item) {
1677 /* compiler built-in */
1678 }
1679
1680 /// Attribute macro applied to a static to register it as a global allocator.
1681 ///
1682 /// See also [`std::alloc::GlobalAlloc`](../../../std/alloc/trait.GlobalAlloc.html).
1683 #[stable(feature = "global_allocator", since = "1.28.0")]
1684 #[allow_internal_unstable(rustc_attrs)]
1685 #[rustc_builtin_macro]
1686 pub macro global_allocator($item:item) {
1687 /* compiler built-in */
1688 }
1689
1690 /// Attribute macro applied to a function to give it a post-condition.
1691 ///
1692 /// The attribute carries an argument token-tree which is
1693 /// eventually parsed as a unary closure expression that is
1694 /// invoked on a reference to the return value.
1695 #[unstable(feature = "contracts", issue = "128044")]
1696 #[allow_internal_unstable(contracts_internals)]
1697 #[rustc_builtin_macro]
1698 pub macro contracts_ensures($item:item) {
1699 /* compiler built-in */
1700 }
1701
1702 /// Attribute macro applied to a function to give it a precondition.
1703 ///
1704 /// The attribute carries an argument token-tree which is
1705 /// eventually parsed as an boolean expression with access to the
1706 /// function's formal parameters
1707 #[unstable(feature = "contracts", issue = "128044")]
1708 #[allow_internal_unstable(contracts_internals)]
1709 #[rustc_builtin_macro]
1710 pub macro contracts_requires($item:item) {
1711 /* compiler built-in */
1712 }
1713
1714 /// Attribute macro applied to a function to register it as a handler for allocation failure.
1715 ///
1716 /// See also [`std::alloc::handle_alloc_error`](../../../std/alloc/fn.handle_alloc_error.html).
1717 #[unstable(feature = "alloc_error_handler", issue = "51540")]
1718 #[allow_internal_unstable(rustc_attrs)]
1719 #[rustc_builtin_macro]
1720 pub macro alloc_error_handler($item:item) {
1721 /* compiler built-in */
1722 }
1723
1724 /// Keeps the item it's applied to if the passed path is accessible, and removes it otherwise.
1725 #[unstable(
1726 feature = "cfg_accessible",
1727 issue = "64797",
1728 reason = "`cfg_accessible` is not fully implemented"
1729 )]
1730 #[rustc_builtin_macro]
1731 pub macro cfg_accessible($item:item) {
1732 /* compiler built-in */
1733 }
1734
1735 /// Expands all `#[cfg]` and `#[cfg_attr]` attributes in the code fragment it's applied to.
1736 #[unstable(
1737 feature = "cfg_eval",
1738 issue = "82679",
1739 reason = "`cfg_eval` is a recently implemented feature"
1740 )]
1741 #[rustc_builtin_macro]
1742 pub macro cfg_eval($($tt:tt)*) {
1743 /* compiler built-in */
1744 }
1745
1746 /// Provide a list of type aliases and other opaque-type-containing type definitions.
1747 /// This list will be used in the body of the item it is applied to define opaque
1748 /// types' hidden types.
1749 /// Can only be applied to things that have bodies.
1750 #[unstable(
1751 feature = "type_alias_impl_trait",
1752 issue = "63063",
1753 reason = "`type_alias_impl_trait` has open design concerns"
1754 )]
1755 #[rustc_builtin_macro]
1756 #[cfg(not(bootstrap))]
1757 pub macro define_opaque($($tt:tt)*) {
1758 /* compiler built-in */
1759 }
1760
1761 /// Unstable placeholder for type ascription.
1762 #[allow_internal_unstable(builtin_syntax)]
1763 #[unstable(
1764 feature = "type_ascription",
1765 issue = "23416",
1766 reason = "placeholder syntax for type ascription"
1767 )]
1768 #[rustfmt::skip]
1769 pub macro type_ascribe($expr:expr, $ty:ty) {
1770 builtin # type_ascribe($expr, $ty)
1771 }
1772
1773 /// Unstable placeholder for deref patterns.
1774 #[allow_internal_unstable(builtin_syntax)]
1775 #[unstable(
1776 feature = "deref_patterns",
1777 issue = "87121",
1778 reason = "placeholder syntax for deref patterns"
1779 )]
1780 pub macro deref($pat:pat) {
1781 builtin # deref($pat)
1782 }
1783}
1784