core/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"]
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)]
42#[cfg(not(feature = "ferrocene_certified"))]
43macro_rules! assert_eq {
44 ($left:expr, $right:expr $(,)?) => {
45 match (&$left, &$right) {
46 (left_val, right_val) => {
47 if !(*left_val == *right_val) {
48 let kind = $crate::panicking::AssertKind::Eq;
49 // The reborrows below are intentional. Without them, the stack slot for the
50 // borrow is initialized even before the values are compared, leading to a
51 // noticeable slow down.
52 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
53 }
54 }
55 }
56 };
57 ($left:expr, $right:expr, $($arg:tt)+) => {
58 match (&$left, &$right) {
59 (left_val, right_val) => {
60 if !(*left_val == *right_val) {
61 let kind = $crate::panicking::AssertKind::Eq;
62 // The reborrows below are intentional. Without them, the stack slot for the
63 // borrow is initialized even before the values are compared, leading to a
64 // noticeable slow down.
65 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
66 }
67 }
68 }
69 };
70}
71
72/// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
73///
74/// Assertions are always checked in both debug and release builds, and cannot
75/// be disabled. See [`debug_assert_ne!`] for assertions that are disabled in
76/// release builds by default.
77///
78/// [`debug_assert_ne!`]: crate::debug_assert_ne
79///
80/// On panic, this macro will print the values of the expressions with their
81/// debug representations.
82///
83/// Like [`assert!`], this macro has a second form, where a custom
84/// panic message can be provided.
85///
86/// # Examples
87///
88/// ```
89/// let a = 3;
90/// let b = 2;
91/// assert_ne!(a, b);
92///
93/// assert_ne!(a, b, "we are testing that the values are not equal");
94/// ```
95#[macro_export]
96#[stable(feature = "assert_ne", since = "1.13.0")]
97#[rustc_diagnostic_item = "assert_ne_macro"]
98#[allow_internal_unstable(panic_internals)]
99#[cfg(not(feature = "ferrocene_certified"))]
100macro_rules! assert_ne {
101 ($left:expr, $right:expr $(,)?) => {
102 match (&$left, &$right) {
103 (left_val, right_val) => {
104 if *left_val == *right_val {
105 let kind = $crate::panicking::AssertKind::Ne;
106 // The reborrows below are intentional. Without them, the stack slot for the
107 // borrow is initialized even before the values are compared, leading to a
108 // noticeable slow down.
109 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::None);
110 }
111 }
112 }
113 };
114 ($left:expr, $right:expr, $($arg:tt)+) => {
115 match (&($left), &($right)) {
116 (left_val, right_val) => {
117 if *left_val == *right_val {
118 let kind = $crate::panicking::AssertKind::Ne;
119 // The reborrows below are intentional. Without them, the stack slot for the
120 // borrow is initialized even before the values are compared, leading to a
121 // noticeable slow down.
122 $crate::panicking::assert_failed(kind, &*left_val, &*right_val, $crate::option::Option::Some($crate::format_args!($($arg)+)));
123 }
124 }
125 }
126 };
127}
128
129/// Asserts that an expression matches the provided pattern.
130///
131/// This macro is generally preferable to `assert!(matches!(value, pattern))`, because it can print
132/// the debug representation of the actual value shape that did not meet expectations. In contrast,
133/// using [`assert!`] will only print that expectations were not met, but not why.
134///
135/// The pattern syntax is exactly the same as found in a match arm and the `matches!` macro. The
136/// optional if guard can be used to add additional checks that must be true for the matched value,
137/// otherwise this macro will panic.
138///
139/// Assertions are always checked in both debug and release builds, and cannot
140/// be disabled. See [`debug_assert_matches!`] for assertions that are disabled in
141/// release builds by default.
142///
143/// [`debug_assert_matches!`]: crate::assert_matches::debug_assert_matches
144///
145/// On panic, this macro will print the value of the expression with its debug representation.
146///
147/// Like [`assert!`], this macro has a second form, where a custom panic message can be provided.
148///
149/// # Examples
150///
151/// ```
152/// #![feature(assert_matches)]
153///
154/// use std::assert_matches::assert_matches;
155///
156/// let a = Some(345);
157/// let b = Some(56);
158/// assert_matches!(a, Some(_));
159/// assert_matches!(b, Some(_));
160///
161/// assert_matches!(a, Some(345));
162/// assert_matches!(a, Some(345) | None);
163///
164/// // assert_matches!(a, None); // panics
165/// // assert_matches!(b, Some(345)); // panics
166/// // assert_matches!(b, Some(345) | None); // panics
167///
168/// assert_matches!(a, Some(x) if x > 100);
169/// // assert_matches!(a, Some(x) if x < 100); // panics
170/// ```
171#[unstable(feature = "assert_matches", issue = "82775")]
172#[allow_internal_unstable(panic_internals)]
173#[rustc_macro_transparency = "semitransparent"]
174#[cfg(not(feature = "ferrocene_certified"))]
175pub macro assert_matches {
176 ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )? $(,)?) => {
177 match $left {
178 $( $pattern )|+ $( if $guard )? => {}
179 ref left_val => {
180 $crate::panicking::assert_matches_failed(
181 left_val,
182 $crate::stringify!($($pattern)|+ $(if $guard)?),
183 $crate::option::Option::None
184 );
185 }
186 }
187 },
188 ($left:expr, $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )?, $($arg:tt)+) => {
189 match $left {
190 $( $pattern )|+ $( if $guard )? => {}
191 ref left_val => {
192 $crate::panicking::assert_matches_failed(
193 left_val,
194 $crate::stringify!($($pattern)|+ $(if $guard)?),
195 $crate::option::Option::Some($crate::format_args!($($arg)+))
196 );
197 }
198 }
199 },
200}
201
202/// Selects code at compile-time based on `cfg` predicates.
203///
204/// This macro evaluates, at compile-time, a series of `cfg` predicates,
205/// selects the first that is true, and emits the code guarded by that
206/// predicate. The code guarded by other predicates is not emitted.
207///
208/// An optional trailing `_` wildcard can be used to specify a fallback. If
209/// none of the predicates are true, a [`compile_error`] is emitted.
210///
211/// # Example
212///
213/// ```
214/// #![feature(cfg_select)]
215///
216/// cfg_select! {
217/// unix => {
218/// fn foo() { /* unix specific functionality */ }
219/// }
220/// target_pointer_width = "32" => {
221/// fn foo() { /* non-unix, 32-bit functionality */ }
222/// }
223/// _ => {
224/// fn foo() { /* fallback implementation */ }
225/// }
226/// }
227/// ```
228///
229/// The `cfg_select!` macro can also be used in expression position, with or without braces on the
230/// right-hand side:
231///
232/// ```
233/// #![feature(cfg_select)]
234///
235/// let _some_string = cfg_select! {
236/// unix => "With great power comes great electricity bills",
237/// _ => { "Behind every successful diet is an unwatched pizza" }
238/// };
239/// ```
240#[unstable(feature = "cfg_select", issue = "115585")]
241#[rustc_diagnostic_item = "cfg_select"]
242#[rustc_builtin_macro]
243#[cfg(not(feature = "ferrocene_certified"))]
244pub macro cfg_select($($tt:tt)*) {
245 /* compiler built-in */
246}
247
248/// Asserts that a boolean expression is `true` at runtime.
249///
250/// This will invoke the [`panic!`] macro if the provided expression cannot be
251/// evaluated to `true` at runtime.
252///
253/// Like [`assert!`], this macro also has a second version, where a custom panic
254/// message can be provided.
255///
256/// # Uses
257///
258/// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
259/// optimized builds by default. An optimized build will not execute
260/// `debug_assert!` statements unless `-C debug-assertions` is passed to the
261/// compiler. This makes `debug_assert!` useful for checks that are too
262/// expensive to be present in a release build but may be helpful during
263/// development. The result of expanding `debug_assert!` is always type checked.
264///
265/// An unchecked assertion allows a program in an inconsistent state to keep
266/// running, which might have unexpected consequences but does not introduce
267/// unsafety as long as this only happens in safe code. The performance cost
268/// of assertions, however, is not measurable in general. Replacing [`assert!`]
269/// with `debug_assert!` is thus only encouraged after thorough profiling, and
270/// more importantly, only in safe code!
271///
272/// # Examples
273///
274/// ```
275/// // the panic message for these assertions is the stringified value of the
276/// // expression given.
277/// debug_assert!(true);
278///
279/// fn some_expensive_computation() -> bool {
280/// // Some expensive computation here
281/// true
282/// }
283/// debug_assert!(some_expensive_computation());
284///
285/// // assert with a custom message
286/// let x = true;
287/// debug_assert!(x, "x wasn't true!");
288///
289/// let a = 3; let b = 27;
290/// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
291/// ```
292#[macro_export]
293#[stable(feature = "rust1", since = "1.0.0")]
294#[rustc_diagnostic_item = "debug_assert_macro"]
295#[allow_internal_unstable(edition_panic)]
296#[cfg(not(feature = "ferrocene_certified"))]
297macro_rules! debug_assert {
298 ($($arg:tt)*) => {
299 if $crate::cfg!(debug_assertions) {
300 $crate::assert!($($arg)*);
301 }
302 };
303}
304
305/// Asserts that two expressions are equal to each other.
306///
307/// On panic, this macro will print the values of the expressions with their
308/// debug representations.
309///
310/// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
311/// optimized builds by default. An optimized build will not execute
312/// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
313/// compiler. This makes `debug_assert_eq!` useful for checks that are too
314/// expensive to be present in a release build but may be helpful during
315/// development. The result of expanding `debug_assert_eq!` is always type checked.
316///
317/// # Examples
318///
319/// ```
320/// let a = 3;
321/// let b = 1 + 2;
322/// debug_assert_eq!(a, b);
323/// ```
324#[macro_export]
325#[stable(feature = "rust1", since = "1.0.0")]
326#[rustc_diagnostic_item = "debug_assert_eq_macro"]
327#[cfg(not(feature = "ferrocene_certified"))]
328macro_rules! debug_assert_eq {
329 ($($arg:tt)*) => {
330 if $crate::cfg!(debug_assertions) {
331 $crate::assert_eq!($($arg)*);
332 }
333 };
334}
335
336/// Asserts that two expressions are not equal to each other.
337///
338/// On panic, this macro will print the values of the expressions with their
339/// debug representations.
340///
341/// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
342/// optimized builds by default. An optimized build will not execute
343/// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
344/// compiler. This makes `debug_assert_ne!` useful for checks that are too
345/// expensive to be present in a release build but may be helpful during
346/// development. The result of expanding `debug_assert_ne!` is always type checked.
347///
348/// # Examples
349///
350/// ```
351/// let a = 3;
352/// let b = 2;
353/// debug_assert_ne!(a, b);
354/// ```
355#[macro_export]
356#[stable(feature = "assert_ne", since = "1.13.0")]
357#[rustc_diagnostic_item = "debug_assert_ne_macro"]
358#[cfg(not(feature = "ferrocene_certified"))]
359macro_rules! debug_assert_ne {
360 ($($arg:tt)*) => {
361 if $crate::cfg!(debug_assertions) {
362 $crate::assert_ne!($($arg)*);
363 }
364 };
365}
366
367/// Asserts that an expression matches the provided pattern.
368///
369/// This macro is generally preferable to `debug_assert!(matches!(value, pattern))`, because it can
370/// print the debug representation of the actual value shape that did not meet expectations. In
371/// contrast, using [`debug_assert!`] will only print that expectations were not met, but not why.
372///
373/// The pattern syntax is exactly the same as found in a match arm and the `matches!` macro. The
374/// optional if guard can be used to add additional checks that must be true for the matched value,
375/// otherwise this macro will panic.
376///
377/// On panic, this macro will print the value of the expression with its debug representation.
378///
379/// Like [`assert!`], this macro has a second form, where a custom panic message can be provided.
380///
381/// Unlike [`assert_matches!`], `debug_assert_matches!` statements are only enabled in non optimized
382/// builds by default. An optimized build will not execute `debug_assert_matches!` statements unless
383/// `-C debug-assertions` is passed to the compiler. This makes `debug_assert_matches!` useful for
384/// checks that are too expensive to be present in a release build but may be helpful during
385/// development. The result of expanding `debug_assert_matches!` is always type checked.
386///
387/// # Examples
388///
389/// ```
390/// #![feature(assert_matches)]
391///
392/// use std::assert_matches::debug_assert_matches;
393///
394/// let a = Some(345);
395/// let b = Some(56);
396/// debug_assert_matches!(a, Some(_));
397/// debug_assert_matches!(b, Some(_));
398///
399/// debug_assert_matches!(a, Some(345));
400/// debug_assert_matches!(a, Some(345) | None);
401///
402/// // debug_assert_matches!(a, None); // panics
403/// // debug_assert_matches!(b, Some(345)); // panics
404/// // debug_assert_matches!(b, Some(345) | None); // panics
405///
406/// debug_assert_matches!(a, Some(x) if x > 100);
407/// // debug_assert_matches!(a, Some(x) if x < 100); // panics
408/// ```
409#[unstable(feature = "assert_matches", issue = "82775")]
410#[allow_internal_unstable(assert_matches)]
411#[rustc_macro_transparency = "semitransparent"]
412#[cfg(not(feature = "ferrocene_certified"))]
413pub macro debug_assert_matches($($arg:tt)*) {
414 if $crate::cfg!(debug_assertions) {
415 $crate::assert_matches::assert_matches!($($arg)*);
416 }
417}
418
419/// Returns whether the given expression matches the provided pattern.
420///
421/// The pattern syntax is exactly the same as found in a match arm. The optional if guard can be
422/// used to add additional checks that must be true for the matched value, otherwise this macro will
423/// return `false`.
424///
425/// When testing that a value matches a pattern, it's generally preferable to use
426/// [`assert_matches!`] as it will print the debug representation of the value if the assertion
427/// fails.
428///
429/// # Examples
430///
431/// ```
432/// let foo = 'f';
433/// assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));
434///
435/// let bar = Some(4);
436/// assert!(matches!(bar, Some(x) if x > 2));
437/// ```
438#[macro_export]
439#[stable(feature = "matches_macro", since = "1.42.0")]
440#[rustc_diagnostic_item = "matches_macro"]
441#[allow_internal_unstable(non_exhaustive_omitted_patterns_lint, stmt_expr_attributes)]
442macro_rules! matches {
443 ($expression:expr, $pattern:pat $(if $guard:expr)? $(,)?) => {
444 #[allow(non_exhaustive_omitted_patterns)]
445 match $expression {
446 $pattern $(if $guard)? => true,
447 _ => false
448 }
449 };
450}
451
452/// Unwraps a result or propagates its error.
453///
454/// The [`?` operator][propagating-errors] was added to replace `try!`
455/// and should be used instead. Furthermore, `try` is a reserved word
456/// in Rust 2018, so if you must use it, you will need to use the
457/// [raw-identifier syntax][ris]: `r#try`.
458///
459/// [propagating-errors]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
460/// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
461///
462/// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
463/// expression has the value of the wrapped value.
464///
465/// In case of the `Err` variant, it retrieves the inner error. `try!` then
466/// performs conversion using `From`. This provides automatic conversion
467/// between specialized errors and more general ones. The resulting
468/// error is then immediately returned.
469///
470/// Because of the early return, `try!` can only be used in functions that
471/// return [`Result`].
472///
473/// # Examples
474///
475/// ```
476/// use std::io;
477/// use std::fs::File;
478/// use std::io::prelude::*;
479///
480/// enum MyError {
481/// FileWriteError
482/// }
483///
484/// impl From<io::Error> for MyError {
485/// fn from(e: io::Error) -> MyError {
486/// MyError::FileWriteError
487/// }
488/// }
489///
490/// // The preferred method of quick returning Errors
491/// fn write_to_file_question() -> Result<(), MyError> {
492/// let mut file = File::create("my_best_friends.txt")?;
493/// file.write_all(b"This is a list of my best friends.")?;
494/// Ok(())
495/// }
496///
497/// // The previous method of quick returning Errors
498/// fn write_to_file_using_try() -> Result<(), MyError> {
499/// let mut file = r#try!(File::create("my_best_friends.txt"));
500/// r#try!(file.write_all(b"This is a list of my best friends."));
501/// Ok(())
502/// }
503///
504/// // This is equivalent to:
505/// fn write_to_file_using_match() -> Result<(), MyError> {
506/// let mut file = r#try!(File::create("my_best_friends.txt"));
507/// match file.write_all(b"This is a list of my best friends.") {
508/// Ok(v) => v,
509/// Err(e) => return Err(From::from(e)),
510/// }
511/// Ok(())
512/// }
513/// ```
514#[macro_export]
515#[stable(feature = "rust1", since = "1.0.0")]
516#[deprecated(since = "1.39.0", note = "use the `?` operator instead")]
517#[doc(alias = "?")]
518#[cfg(not(feature = "ferrocene_certified"))]
519macro_rules! r#try {
520 ($expr:expr $(,)?) => {
521 match $expr {
522 $crate::result::Result::Ok(val) => val,
523 $crate::result::Result::Err(err) => {
524 return $crate::result::Result::Err($crate::convert::From::from(err));
525 }
526 }
527 };
528}
529
530/// Writes formatted data into a buffer.
531///
532/// This macro accepts a 'writer', a format string, and a list of arguments. Arguments will be
533/// formatted according to the specified format string and the result will be passed to the writer.
534/// The writer may be any value with a `write_fmt` method; generally this comes from an
535/// implementation of either the [`fmt::Write`] or the [`io::Write`] trait. The macro
536/// returns whatever the `write_fmt` method returns; commonly a [`fmt::Result`], or an
537/// [`io::Result`].
538///
539/// See [`std::fmt`] for more information on the format string syntax.
540///
541/// [`std::fmt`]: ../std/fmt/index.html
542/// [`fmt::Write`]: crate::fmt::Write
543/// [`io::Write`]: ../std/io/trait.Write.html
544/// [`fmt::Result`]: crate::fmt::Result
545/// [`io::Result`]: ../std/io/type.Result.html
546///
547/// # Examples
548///
549/// ```
550/// use std::io::Write;
551///
552/// fn main() -> std::io::Result<()> {
553/// let mut w = Vec::new();
554/// write!(&mut w, "test")?;
555/// write!(&mut w, "formatted {}", "arguments")?;
556///
557/// assert_eq!(w, b"testformatted arguments");
558/// Ok(())
559/// }
560/// ```
561///
562/// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
563/// implementing either, as objects do not typically implement both. However, the module must
564/// avoid conflict between the trait names, such as by importing them as `_` or otherwise renaming
565/// them:
566///
567/// ```
568/// use std::fmt::Write as _;
569/// use std::io::Write as _;
570///
571/// fn main() -> Result<(), Box<dyn std::error::Error>> {
572/// let mut s = String::new();
573/// let mut v = Vec::new();
574///
575/// write!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
576/// write!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
577/// assert_eq!(v, b"s = \"abc 123\"");
578/// Ok(())
579/// }
580/// ```
581///
582/// If you also need the trait names themselves, such as to implement one or both on your types,
583/// import the containing module and then name them with a prefix:
584///
585/// ```
586/// # #![allow(unused_imports)]
587/// use std::fmt::{self, Write as _};
588/// use std::io::{self, Write as _};
589///
590/// struct Example;
591///
592/// impl fmt::Write for Example {
593/// fn write_str(&mut self, _s: &str) -> core::fmt::Result {
594/// unimplemented!();
595/// }
596/// }
597/// ```
598///
599/// Note: This macro can be used in `no_std` setups as well.
600/// In a `no_std` setup you are responsible for the implementation details of the components.
601///
602/// ```no_run
603/// use core::fmt::Write;
604///
605/// struct Example;
606///
607/// impl Write for Example {
608/// fn write_str(&mut self, _s: &str) -> core::fmt::Result {
609/// unimplemented!();
610/// }
611/// }
612///
613/// let mut m = Example{};
614/// write!(&mut m, "Hello World").expect("Not written");
615/// ```
616#[macro_export]
617#[stable(feature = "rust1", since = "1.0.0")]
618#[rustc_diagnostic_item = "write_macro"]
619#[cfg(not(feature = "ferrocene_certified"))]
620macro_rules! write {
621 ($dst:expr, $($arg:tt)*) => {
622 $dst.write_fmt($crate::format_args!($($arg)*))
623 };
624}
625
626/// Writes formatted data into a buffer, with a newline appended.
627///
628/// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
629/// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
630///
631/// For more information, see [`write!`]. For information on the format string syntax, see
632/// [`std::fmt`].
633///
634/// [`std::fmt`]: ../std/fmt/index.html
635///
636/// # Examples
637///
638/// ```
639/// use std::io::{Write, Result};
640///
641/// fn main() -> Result<()> {
642/// let mut w = Vec::new();
643/// writeln!(&mut w)?;
644/// writeln!(&mut w, "test")?;
645/// writeln!(&mut w, "formatted {}", "arguments")?;
646///
647/// assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
648/// Ok(())
649/// }
650/// ```
651#[macro_export]
652#[stable(feature = "rust1", since = "1.0.0")]
653#[rustc_diagnostic_item = "writeln_macro"]
654#[allow_internal_unstable(format_args_nl)]
655#[cfg(not(feature = "ferrocene_certified"))]
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"]
722#[cfg(not(feature = "ferrocene_certified"))]
723macro_rules! unreachable {
724 // Expands to either `$crate::panic::unreachable_2015` or `$crate::panic::unreachable_2021`
725 // depending on the edition of the caller.
726 ($($arg:tt)*) => {
727 /* compiler built-in */
728 };
729}
730
731/// Indicates unimplemented code by panicking with a message of "not implemented".
732///
733/// This allows your code to type-check, which is useful if you are prototyping or
734/// implementing a trait that requires multiple methods which you don't plan to use all of.
735///
736/// The difference between `unimplemented!` and [`todo!`] is that while `todo!`
737/// conveys an intent of implementing the functionality later and the message is "not yet
738/// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
739///
740/// Also, some IDEs will mark `todo!`s.
741///
742/// # Panics
743///
744/// This will always [`panic!`] because `unimplemented!` is just a shorthand for `panic!` with a
745/// fixed, specific message.
746///
747/// Like `panic!`, this macro has a second form for displaying custom values.
748///
749/// [`todo!`]: crate::todo
750///
751/// # Examples
752///
753/// Say we have a trait `Foo`:
754///
755/// ```
756/// trait Foo {
757/// fn bar(&self) -> u8;
758/// fn baz(&self);
759/// fn qux(&self) -> Result<u64, ()>;
760/// }
761/// ```
762///
763/// We want to implement `Foo` for 'MyStruct', but for some reason it only makes sense
764/// to implement the `bar()` function. `baz()` and `qux()` will still need to be defined
765/// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
766/// to allow our code to compile.
767///
768/// We still want to have our program stop running if the unimplemented methods are
769/// reached.
770///
771/// ```
772/// # trait Foo {
773/// # fn bar(&self) -> u8;
774/// # fn baz(&self);
775/// # fn qux(&self) -> Result<u64, ()>;
776/// # }
777/// struct MyStruct;
778///
779/// impl Foo for MyStruct {
780/// fn bar(&self) -> u8 {
781/// 1 + 1
782/// }
783///
784/// fn baz(&self) {
785/// // It makes no sense to `baz` a `MyStruct`, so we have no logic here
786/// // at all.
787/// // This will display "thread 'main' panicked at 'not implemented'".
788/// unimplemented!();
789/// }
790///
791/// fn qux(&self) -> Result<u64, ()> {
792/// // We have some logic here,
793/// // We can add a message to unimplemented! to display our omission.
794/// // This will display:
795/// // "thread 'main' panicked at 'not implemented: MyStruct isn't quxable'".
796/// unimplemented!("MyStruct isn't quxable");
797/// }
798/// }
799///
800/// fn main() {
801/// let s = MyStruct;
802/// s.bar();
803/// }
804/// ```
805#[macro_export]
806#[stable(feature = "rust1", since = "1.0.0")]
807#[rustc_diagnostic_item = "unimplemented_macro"]
808#[allow_internal_unstable(panic_internals)]
809#[cfg(not(feature = "ferrocene_certified"))]
810macro_rules! unimplemented {
811 () => {
812 $crate::panicking::panic("not implemented")
813 };
814 ($($arg:tt)+) => {
815 $crate::panic!("not implemented: {}", $crate::format_args!($($arg)+))
816 };
817}
818
819/// Indicates unfinished code.
820///
821/// This can be useful if you are prototyping and just
822/// want a placeholder to let your code pass type analysis.
823///
824/// The difference between [`unimplemented!`] and `todo!` is that while `todo!` conveys
825/// an intent of implementing the functionality later and the message is "not yet
826/// implemented", `unimplemented!` makes no such claims. Its message is "not implemented".
827///
828/// Also, some IDEs will mark `todo!`s.
829///
830/// # Panics
831///
832/// This will always [`panic!`] because `todo!` is just a shorthand for `panic!` with a
833/// fixed, specific message.
834///
835/// Like `panic!`, this macro has a second form for displaying custom values.
836///
837/// # Examples
838///
839/// Here's an example of some in-progress code. We have a trait `Foo`:
840///
841/// ```
842/// trait Foo {
843/// fn bar(&self) -> u8;
844/// fn baz(&self);
845/// fn qux(&self) -> Result<u64, ()>;
846/// }
847/// ```
848///
849/// We want to implement `Foo` on one of our types, but we also want to work on
850/// just `bar()` first. In order for our code to compile, we need to implement
851/// `baz()` and `qux()`, so we can use `todo!`:
852///
853/// ```
854/// # trait Foo {
855/// # fn bar(&self) -> u8;
856/// # fn baz(&self);
857/// # fn qux(&self) -> Result<u64, ()>;
858/// # }
859/// struct MyStruct;
860///
861/// impl Foo for MyStruct {
862/// fn bar(&self) -> u8 {
863/// 1 + 1
864/// }
865///
866/// fn baz(&self) {
867/// // Let's not worry about implementing baz() for now
868/// todo!();
869/// }
870///
871/// fn qux(&self) -> Result<u64, ()> {
872/// // We can add a message to todo! to display our omission.
873/// // This will display:
874/// // "thread 'main' panicked at 'not yet implemented: MyStruct is not yet quxable'".
875/// todo!("MyStruct is not yet quxable");
876/// }
877/// }
878///
879/// fn main() {
880/// let s = MyStruct;
881/// s.bar();
882///
883/// // We aren't even using baz() or qux(), so this is fine.
884/// }
885/// ```
886#[macro_export]
887#[stable(feature = "todo_macro", since = "1.40.0")]
888#[rustc_diagnostic_item = "todo_macro"]
889#[allow_internal_unstable(panic_internals)]
890#[cfg(not(feature = "ferrocene_certified"))]
891macro_rules! todo {
892 () => {
893 $crate::panicking::panic("not yet implemented")
894 };
895 ($($arg:tt)+) => {
896 $crate::panic!("not yet implemented: {}", $crate::format_args!($($arg)+))
897 };
898}
899
900/// Definitions of built-in macros.
901///
902/// Most of the macro properties (stability, visibility, etc.) are taken from the source code here,
903/// with exception of expansion functions transforming macro inputs into outputs,
904/// those functions are provided by the compiler.
905pub(crate) mod builtin {
906
907 /// Causes compilation to fail with the given error message when encountered.
908 ///
909 /// This macro should be used when a crate uses a conditional compilation strategy to provide
910 /// better error messages for erroneous conditions. It's the compiler-level form of [`panic!`],
911 /// but emits an error during *compilation* rather than at *runtime*.
912 ///
913 /// # Examples
914 ///
915 /// Two such examples are macros and `#[cfg]` environments.
916 ///
917 /// Emit a better compiler error if a macro is passed invalid values. Without the final branch,
918 /// the compiler would still emit an error, but the error's message would not mention the two
919 /// valid values.
920 ///
921 /// ```compile_fail
922 /// macro_rules! give_me_foo_or_bar {
923 /// (foo) => {};
924 /// (bar) => {};
925 /// ($x:ident) => {
926 /// compile_error!("This macro only accepts `foo` or `bar`");
927 /// }
928 /// }
929 ///
930 /// give_me_foo_or_bar!(neither);
931 /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
932 /// ```
933 ///
934 /// Emit a compiler error if one of a number of features isn't available.
935 ///
936 /// ```compile_fail
937 /// #[cfg(not(any(feature = "foo", feature = "bar")))]
938 /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.");
939 /// ```
940 #[stable(feature = "compile_error_macro", since = "1.20.0")]
941 #[rustc_builtin_macro]
942 #[macro_export]
943 macro_rules! compile_error {
944 ($msg:expr $(,)?) => {{ /* compiler built-in */ }};
945 }
946
947 /// Constructs parameters for the other string-formatting macros.
948 ///
949 /// This macro functions by taking a formatting string literal containing
950 /// `{}` for each additional argument passed. `format_args!` prepares the
951 /// additional parameters to ensure the output can be interpreted as a string
952 /// and canonicalizes the arguments into a single type. Any value that implements
953 /// the [`Display`] trait can be passed to `format_args!`, as can any
954 /// [`Debug`] implementation be passed to a `{:?}` within the formatting string.
955 ///
956 /// This macro produces a value of type [`fmt::Arguments`]. This value can be
957 /// passed to the macros within [`std::fmt`] for performing useful redirection.
958 /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
959 /// proxied through this one. `format_args!`, unlike its derived macros, avoids
960 /// heap allocations.
961 ///
962 /// You can use the [`fmt::Arguments`] value that `format_args!` returns
963 /// in `Debug` and `Display` contexts as seen below. The example also shows
964 /// that `Debug` and `Display` format to the same thing: the interpolated
965 /// format string in `format_args!`.
966 ///
967 /// ```rust
968 /// let args = format_args!("{} foo {:?}", 1, 2);
969 /// let debug = format!("{args:?}");
970 /// let display = format!("{args}");
971 /// assert_eq!("1 foo 2", display);
972 /// assert_eq!(display, debug);
973 /// ```
974 ///
975 /// See [the formatting documentation in `std::fmt`](../std/fmt/index.html)
976 /// for details of the macro argument syntax, and further information.
977 ///
978 /// [`Display`]: crate::fmt::Display
979 /// [`Debug`]: crate::fmt::Debug
980 /// [`fmt::Arguments`]: crate::fmt::Arguments
981 /// [`std::fmt`]: ../std/fmt/index.html
982 /// [`format!`]: ../std/macro.format.html
983 /// [`println!`]: ../std/macro.println.html
984 ///
985 /// # Examples
986 ///
987 /// ```
988 /// use std::fmt;
989 ///
990 /// let s = fmt::format(format_args!("hello {}", "world"));
991 /// assert_eq!(s, format!("hello {}", "world"));
992 /// ```
993 ///
994 /// # Argument lifetimes
995 ///
996 /// Except when no formatting arguments are used,
997 /// the produced `fmt::Arguments` value borrows temporary values.
998 /// To allow it to be stored for later use, the arguments' lifetimes, as well as those of
999 /// temporaries they borrow, may be [extended] when `format_args!` appears in the initializer
1000 /// expression of a `let` statement. The syntactic rules used to determine when temporaries'
1001 /// lifetimes are extended are documented in the [Reference].
1002 ///
1003 /// [extended]: ../reference/destructors.html#temporary-lifetime-extension
1004 /// [Reference]: ../reference/destructors.html#extending-based-on-expressions
1005 #[stable(feature = "rust1", since = "1.0.0")]
1006 #[rustc_diagnostic_item = "format_args_macro"]
1007 #[allow_internal_unsafe]
1008 #[allow_internal_unstable(fmt_internals)]
1009 #[rustc_builtin_macro]
1010 #[macro_export]
1011 macro_rules! format_args {
1012 ($fmt:expr) => {{ /* compiler built-in */ }};
1013 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1014 }
1015
1016 /// Same as [`format_args`], but can be used in some const contexts.
1017 ///
1018 /// This macro is used by the panic macros for the `const_panic` feature.
1019 ///
1020 /// This macro will be removed once `format_args` is allowed in const contexts.
1021 #[unstable(feature = "const_format_args", issue = "none")]
1022 #[allow_internal_unstable(fmt_internals, const_fmt_arguments_new)]
1023 #[rustc_builtin_macro]
1024 #[macro_export]
1025 macro_rules! const_format_args {
1026 ($fmt:expr) => {{ /* compiler built-in */ }};
1027 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1028 }
1029
1030 /// Same as [`format_args`], but adds a newline in the end.
1031 #[unstable(
1032 feature = "format_args_nl",
1033 issue = "none",
1034 reason = "`format_args_nl` is only for internal \
1035 language use and is subject to change"
1036 )]
1037 #[allow_internal_unstable(fmt_internals)]
1038 #[rustc_builtin_macro]
1039 #[doc(hidden)]
1040 #[macro_export]
1041 macro_rules! format_args_nl {
1042 ($fmt:expr) => {{ /* compiler built-in */ }};
1043 ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
1044 }
1045
1046 /// Inspects an environment variable at compile time.
1047 ///
1048 /// This macro will expand to the value of the named environment variable at
1049 /// compile time, yielding an expression of type `&'static str`. Use
1050 /// [`std::env::var`] instead if you want to read the value at runtime.
1051 ///
1052 /// [`std::env::var`]: ../std/env/fn.var.html
1053 ///
1054 /// If the environment variable is not defined, then a compilation error
1055 /// will be emitted. To not emit a compile error, use the [`option_env!`]
1056 /// macro instead. A compilation error will also be emitted if the
1057 /// environment variable is not a valid Unicode string.
1058 ///
1059 /// # Examples
1060 ///
1061 /// ```
1062 /// let path: &'static str = env!("PATH");
1063 /// println!("the $PATH variable at the time of compiling was: {path}");
1064 /// ```
1065 ///
1066 /// You can customize the error message by passing a string as the second
1067 /// parameter:
1068 ///
1069 /// ```compile_fail
1070 /// let doc: &'static str = env!("documentation", "what's that?!");
1071 /// ```
1072 ///
1073 /// If the `documentation` environment variable is not defined, you'll get
1074 /// the following error:
1075 ///
1076 /// ```text
1077 /// error: what's that?!
1078 /// ```
1079 #[stable(feature = "rust1", since = "1.0.0")]
1080 #[rustc_builtin_macro]
1081 #[macro_export]
1082 #[rustc_diagnostic_item = "env_macro"] // useful for external lints
1083 macro_rules! env {
1084 ($name:expr $(,)?) => {{ /* compiler built-in */ }};
1085 ($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
1086 }
1087
1088 /// Optionally inspects an environment variable at compile time.
1089 ///
1090 /// If the named environment variable is present at compile time, this will
1091 /// expand into an expression of type `Option<&'static str>` whose value is
1092 /// `Some` of the value of the environment variable (a compilation error
1093 /// will be emitted if the environment variable is not a valid Unicode
1094 /// string). If the environment variable is not present, then this will
1095 /// expand to `None`. See [`Option<T>`][Option] for more information on this
1096 /// type. Use [`std::env::var`] instead if you want to read the value at
1097 /// runtime.
1098 ///
1099 /// [`std::env::var`]: ../std/env/fn.var.html
1100 ///
1101 /// A compile time error is only emitted when using this macro if the
1102 /// environment variable exists and is not a valid Unicode string. To also
1103 /// emit a compile error if the environment variable is not present, use the
1104 /// [`env!`] macro instead.
1105 ///
1106 /// # Examples
1107 ///
1108 /// ```
1109 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
1110 /// println!("the secret key might be: {key:?}");
1111 /// ```
1112 #[stable(feature = "rust1", since = "1.0.0")]
1113 #[rustc_builtin_macro]
1114 #[macro_export]
1115 #[rustc_diagnostic_item = "option_env_macro"] // useful for external lints
1116 macro_rules! option_env {
1117 ($name:expr $(,)?) => {{ /* compiler built-in */ }};
1118 }
1119
1120 /// Concatenates literals into a byte slice.
1121 ///
1122 /// This macro takes any number of comma-separated literals, and concatenates them all into
1123 /// one, yielding an expression of type `&[u8; _]`, which represents all of the literals
1124 /// concatenated left-to-right. The literals passed can be any combination of:
1125 ///
1126 /// - byte literals (`b'r'`)
1127 /// - byte strings (`b"Rust"`)
1128 /// - arrays of bytes/numbers (`[b'A', 66, b'C']`)
1129 ///
1130 /// # Examples
1131 ///
1132 /// ```
1133 /// #![feature(concat_bytes)]
1134 ///
1135 /// # fn main() {
1136 /// let s: &[u8; 6] = concat_bytes!(b'A', b"BC", [68, b'E', 70]);
1137 /// assert_eq!(s, b"ABCDEF");
1138 /// # }
1139 /// ```
1140 #[unstable(feature = "concat_bytes", issue = "87555")]
1141 #[rustc_builtin_macro]
1142 #[macro_export]
1143 macro_rules! concat_bytes {
1144 ($($e:literal),+ $(,)?) => {{ /* compiler built-in */ }};
1145 }
1146
1147 /// Concatenates literals into a static string slice.
1148 ///
1149 /// This macro takes any number of comma-separated literals, yielding an
1150 /// expression of type `&'static str` which represents all of the literals
1151 /// concatenated left-to-right.
1152 ///
1153 /// Integer and floating point literals are [stringified](core::stringify) in order to be
1154 /// concatenated.
1155 ///
1156 /// # Examples
1157 ///
1158 /// ```
1159 /// let s = concat!("test", 10, 'b', true);
1160 /// assert_eq!(s, "test10btrue");
1161 /// ```
1162 #[stable(feature = "rust1", since = "1.0.0")]
1163 #[rustc_builtin_macro]
1164 #[rustc_diagnostic_item = "macro_concat"]
1165 #[macro_export]
1166 macro_rules! concat {
1167 ($($e:expr),* $(,)?) => {{ /* compiler built-in */ }};
1168 }
1169
1170 /// Expands to the line number on which it was invoked.
1171 ///
1172 /// With [`column!`] and [`file!`], these macros provide debugging information for
1173 /// developers about the location within the source.
1174 ///
1175 /// The expanded expression has type `u32` and is 1-based, so the first line
1176 /// in each file evaluates to 1, the second to 2, etc. This is consistent
1177 /// with error messages by common compilers or popular editors.
1178 /// The returned line is *not necessarily* the line of the `line!` invocation itself,
1179 /// but rather the first macro invocation leading up to the invocation
1180 /// of the `line!` macro.
1181 ///
1182 /// # Examples
1183 ///
1184 /// ```
1185 /// let current_line = line!();
1186 /// println!("defined on line: {current_line}");
1187 /// ```
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 #[rustc_builtin_macro]
1190 #[macro_export]
1191 macro_rules! line {
1192 () => {
1193 /* compiler built-in */
1194 };
1195 }
1196
1197 /// Expands to the column number at which it was invoked.
1198 ///
1199 /// With [`line!`] and [`file!`], these macros provide debugging information for
1200 /// developers about the location within the source.
1201 ///
1202 /// The expanded expression has type `u32` and is 1-based, so the first column
1203 /// in each line evaluates to 1, the second to 2, etc. This is consistent
1204 /// with error messages by common compilers or popular editors.
1205 /// The returned column is *not necessarily* the line of the `column!` invocation itself,
1206 /// but rather the first macro invocation leading up to the invocation
1207 /// of the `column!` macro.
1208 ///
1209 /// # Examples
1210 ///
1211 /// ```
1212 /// let current_col = column!();
1213 /// println!("defined on column: {current_col}");
1214 /// ```
1215 ///
1216 /// `column!` counts Unicode code points, not bytes or graphemes. As a result, the first two
1217 /// invocations return the same value, but the third does not.
1218 ///
1219 /// ```
1220 /// let a = ("foobar", column!()).1;
1221 /// let b = ("人之初性本善", column!()).1;
1222 /// let c = ("f̅o̅o̅b̅a̅r̅", column!()).1; // Uses combining overline (U+0305)
1223 ///
1224 /// assert_eq!(a, b);
1225 /// assert_ne!(b, c);
1226 /// ```
1227 #[stable(feature = "rust1", since = "1.0.0")]
1228 #[rustc_builtin_macro]
1229 #[macro_export]
1230 macro_rules! column {
1231 () => {
1232 /* compiler built-in */
1233 };
1234 }
1235
1236 /// Expands to the file name in which it was invoked.
1237 ///
1238 /// With [`line!`] and [`column!`], these macros provide debugging information for
1239 /// developers about the location within the source.
1240 ///
1241 /// The expanded expression has type `&'static str`, and the returned file
1242 /// is not the invocation of the `file!` macro itself, but rather the
1243 /// first macro invocation leading up to the invocation of the `file!`
1244 /// macro.
1245 ///
1246 /// The file name is derived from the crate root's source path passed to the Rust compiler
1247 /// and the sequence the compiler takes to get from the crate root to the
1248 /// module containing `file!`, modified by any flags passed to the Rust compiler (e.g.
1249 /// `--remap-path-prefix`). If the crate's source path is relative, the initial base
1250 /// directory will be the working directory of the Rust compiler. For example, if the source
1251 /// path passed to the compiler is `./src/lib.rs` which has a `mod foo;` with a source path of
1252 /// `src/foo/mod.rs`, then calling `file!` inside `mod foo;` will return `./src/foo/mod.rs`.
1253 ///
1254 /// Future compiler options might make further changes to the behavior of `file!`,
1255 /// including potentially making it entirely empty. Code (e.g. test libraries)
1256 /// relying on `file!` producing an openable file path would be incompatible
1257 /// with such options, and might wish to recommend not using those options.
1258 ///
1259 /// # Examples
1260 ///
1261 /// ```
1262 /// let this_file = file!();
1263 /// println!("defined in file: {this_file}");
1264 /// ```
1265 #[stable(feature = "rust1", since = "1.0.0")]
1266 #[rustc_builtin_macro]
1267 #[macro_export]
1268 macro_rules! file {
1269 () => {
1270 /* compiler built-in */
1271 };
1272 }
1273
1274 /// Stringifies its arguments.
1275 ///
1276 /// This macro will yield an expression of type `&'static str` which is the
1277 /// stringification of all the tokens passed to the macro. No restrictions
1278 /// are placed on the syntax of the macro invocation itself.
1279 ///
1280 /// Note that the expanded results of the input tokens may change in the
1281 /// future. You should be careful if you rely on the output.
1282 ///
1283 /// # Examples
1284 ///
1285 /// ```
1286 /// let one_plus_one = stringify!(1 + 1);
1287 /// assert_eq!(one_plus_one, "1 + 1");
1288 /// ```
1289 #[stable(feature = "rust1", since = "1.0.0")]
1290 #[rustc_builtin_macro]
1291 #[macro_export]
1292 macro_rules! stringify {
1293 ($($t:tt)*) => {
1294 /* compiler built-in */
1295 };
1296 }
1297
1298 /// Includes a UTF-8 encoded file as a string.
1299 ///
1300 /// The file is located relative to the current file (similarly to how
1301 /// modules are found). The provided path is interpreted in a platform-specific
1302 /// way at compile time. So, for instance, an invocation with a Windows path
1303 /// containing backslashes `\` would not compile correctly on Unix.
1304 ///
1305 /// This macro will yield an expression of type `&'static str` which is the
1306 /// contents of the file.
1307 ///
1308 /// # Examples
1309 ///
1310 /// Assume there are two files in the same directory with the following
1311 /// contents:
1312 ///
1313 /// File 'spanish.in':
1314 ///
1315 /// ```text
1316 /// adiós
1317 /// ```
1318 ///
1319 /// File 'main.rs':
1320 ///
1321 /// ```ignore (cannot-doctest-external-file-dependency)
1322 /// fn main() {
1323 /// let my_str = include_str!("spanish.in");
1324 /// assert_eq!(my_str, "adiós\n");
1325 /// print!("{my_str}");
1326 /// }
1327 /// ```
1328 ///
1329 /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1330 #[stable(feature = "rust1", since = "1.0.0")]
1331 #[rustc_builtin_macro]
1332 #[macro_export]
1333 #[rustc_diagnostic_item = "include_str_macro"]
1334 macro_rules! include_str {
1335 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1336 }
1337
1338 /// Includes a file as a reference to a byte array.
1339 ///
1340 /// The file is located relative to the current file (similarly to how
1341 /// modules are found). The provided path is interpreted in a platform-specific
1342 /// way at compile time. So, for instance, an invocation with a Windows path
1343 /// containing backslashes `\` would not compile correctly on Unix.
1344 ///
1345 /// This macro will yield an expression of type `&'static [u8; N]` which is
1346 /// the contents of the file.
1347 ///
1348 /// # Examples
1349 ///
1350 /// Assume there are two files in the same directory with the following
1351 /// contents:
1352 ///
1353 /// File 'spanish.in':
1354 ///
1355 /// ```text
1356 /// adiós
1357 /// ```
1358 ///
1359 /// File 'main.rs':
1360 ///
1361 /// ```ignore (cannot-doctest-external-file-dependency)
1362 /// fn main() {
1363 /// let bytes = include_bytes!("spanish.in");
1364 /// assert_eq!(bytes, b"adi\xc3\xb3s\n");
1365 /// print!("{}", String::from_utf8_lossy(bytes));
1366 /// }
1367 /// ```
1368 ///
1369 /// Compiling 'main.rs' and running the resulting binary will print "adiós".
1370 #[stable(feature = "rust1", since = "1.0.0")]
1371 #[rustc_builtin_macro]
1372 #[macro_export]
1373 #[rustc_diagnostic_item = "include_bytes_macro"]
1374 macro_rules! include_bytes {
1375 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1376 }
1377
1378 /// Expands to a string that represents the current module path.
1379 ///
1380 /// The current module path can be thought of as the hierarchy of modules
1381 /// leading back up to the crate root. The first component of the path
1382 /// returned is the name of the crate currently being compiled.
1383 ///
1384 /// # Examples
1385 ///
1386 /// ```
1387 /// mod test {
1388 /// pub fn foo() {
1389 /// assert!(module_path!().ends_with("test"));
1390 /// }
1391 /// }
1392 ///
1393 /// test::foo();
1394 /// ```
1395 #[stable(feature = "rust1", since = "1.0.0")]
1396 #[rustc_builtin_macro]
1397 #[macro_export]
1398 macro_rules! module_path {
1399 () => {
1400 /* compiler built-in */
1401 };
1402 }
1403
1404 /// Evaluates boolean combinations of configuration flags at compile-time.
1405 ///
1406 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
1407 /// boolean expression evaluation of configuration flags. This frequently
1408 /// leads to less duplicated code.
1409 ///
1410 /// The syntax given to this macro is the same syntax as the [`cfg`]
1411 /// attribute.
1412 ///
1413 /// `cfg!`, unlike `#[cfg]`, does not remove any code and only evaluates to true or false. For
1414 /// example, all blocks in an if/else expression need to be valid when `cfg!` is used for
1415 /// the condition, regardless of what `cfg!` is evaluating.
1416 ///
1417 /// [`cfg`]: ../reference/conditional-compilation.html#the-cfg-attribute
1418 ///
1419 /// # Examples
1420 ///
1421 /// ```
1422 /// let my_directory = if cfg!(windows) {
1423 /// "windows-specific-directory"
1424 /// } else {
1425 /// "unix-directory"
1426 /// };
1427 /// ```
1428 #[stable(feature = "rust1", since = "1.0.0")]
1429 #[rustc_builtin_macro]
1430 #[macro_export]
1431 macro_rules! cfg {
1432 ($($cfg:tt)*) => {
1433 /* compiler built-in */
1434 };
1435 }
1436
1437 /// Parses a file as an expression or an item according to the context.
1438 ///
1439 /// **Warning**: For multi-file Rust projects, the `include!` macro is probably not what you
1440 /// are looking for. Usually, multi-file Rust projects use
1441 /// [modules](https://doc.rust-lang.org/reference/items/modules.html). Multi-file projects and
1442 /// modules are explained in the Rust-by-Example book
1443 /// [here](https://doc.rust-lang.org/rust-by-example/mod/split.html) and the module system is
1444 /// explained in the Rust Book
1445 /// [here](https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html).
1446 ///
1447 /// The included file is placed in the surrounding code
1448 /// [unhygienically](https://doc.rust-lang.org/reference/macros-by-example.html#hygiene). If
1449 /// the included file is parsed as an expression and variables or functions share names across
1450 /// both files, it could result in variables or functions being different from what the
1451 /// included file expected.
1452 ///
1453 /// The included file is located relative to the current file (similarly to how modules are
1454 /// found). The provided path is interpreted in a platform-specific way at compile time. So,
1455 /// for instance, an invocation with a Windows path containing backslashes `\` would not
1456 /// compile correctly on Unix.
1457 ///
1458 /// # Uses
1459 ///
1460 /// The `include!` macro is primarily used for two purposes. It is used to include
1461 /// documentation that is written in a separate file and it is used to include [build artifacts
1462 /// usually as a result from the `build.rs`
1463 /// script](https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script).
1464 ///
1465 /// When using the `include` macro to include stretches of documentation, remember that the
1466 /// included file still needs to be a valid Rust syntax. It is also possible to
1467 /// use the [`include_str`] macro as `#![doc = include_str!("...")]` (at the module level) or
1468 /// `#[doc = include_str!("...")]` (at the item level) to include documentation from a plain
1469 /// text or markdown file.
1470 ///
1471 /// # Examples
1472 ///
1473 /// Assume there are two files in the same directory with the following contents:
1474 ///
1475 /// File 'monkeys.in':
1476 ///
1477 /// ```ignore (only-for-syntax-highlight)
1478 /// ['🙈', '🙊', '🙉']
1479 /// .iter()
1480 /// .cycle()
1481 /// .take(6)
1482 /// .collect::<String>()
1483 /// ```
1484 ///
1485 /// File 'main.rs':
1486 ///
1487 /// ```ignore (cannot-doctest-external-file-dependency)
1488 /// fn main() {
1489 /// let my_string = include!("monkeys.in");
1490 /// assert_eq!("🙈🙊🙉🙈🙊🙉", my_string);
1491 /// println!("{my_string}");
1492 /// }
1493 /// ```
1494 ///
1495 /// Compiling 'main.rs' and running the resulting binary will print
1496 /// "🙈🙊🙉🙈🙊🙉".
1497 #[stable(feature = "rust1", since = "1.0.0")]
1498 #[rustc_builtin_macro]
1499 #[macro_export]
1500 #[rustc_diagnostic_item = "include_macro"] // useful for external lints
1501 macro_rules! include {
1502 ($file:expr $(,)?) => {{ /* compiler built-in */ }};
1503 }
1504
1505 /// This macro uses forward-mode automatic differentiation to generate a new function.
1506 /// It may only be applied to a function. The new function will compute the derivative
1507 /// of the function to which the macro was applied.
1508 ///
1509 /// The expected usage syntax is:
1510 /// `#[autodiff_forward(NAME, INPUT_ACTIVITIES, OUTPUT_ACTIVITY)]`
1511 ///
1512 /// - `NAME`: A string that represents a valid function name.
1513 /// - `INPUT_ACTIVITIES`: Specifies one valid activity for each input parameter.
1514 /// - `OUTPUT_ACTIVITY`: Must not be set if the function implicitly returns nothing
1515 /// (or explicitly returns `-> ()`). Otherwise, it must be set to one of the allowed activities.
1516 #[unstable(feature = "autodiff", issue = "124509")]
1517 #[allow_internal_unstable(rustc_attrs)]
1518 #[allow_internal_unstable(core_intrinsics)]
1519 #[rustc_builtin_macro]
1520 pub macro autodiff_forward($item:item) {
1521 /* compiler built-in */
1522 }
1523
1524 /// This macro uses reverse-mode automatic differentiation to generate a new function.
1525 /// It may only be applied to a function. The new function will compute the derivative
1526 /// of the function to which the macro was applied.
1527 ///
1528 /// The expected usage syntax is:
1529 /// `#[autodiff_reverse(NAME, INPUT_ACTIVITIES, OUTPUT_ACTIVITY)]`
1530 ///
1531 /// - `NAME`: A string that represents a valid function name.
1532 /// - `INPUT_ACTIVITIES`: Specifies one valid activity for each input parameter.
1533 /// - `OUTPUT_ACTIVITY`: Must not be set if the function implicitly returns nothing
1534 /// (or explicitly returns `-> ()`). Otherwise, it must be set to one of the allowed activities.
1535 #[unstable(feature = "autodiff", issue = "124509")]
1536 #[allow_internal_unstable(rustc_attrs)]
1537 #[allow_internal_unstable(core_intrinsics)]
1538 #[rustc_builtin_macro]
1539 pub macro autodiff_reverse($item:item) {
1540 /* compiler built-in */
1541 }
1542
1543 /// Asserts that a boolean expression is `true` at runtime.
1544 ///
1545 /// This will invoke the [`panic!`] macro if the provided expression cannot be
1546 /// evaluated to `true` at runtime.
1547 ///
1548 /// # Uses
1549 ///
1550 /// Assertions are always checked in both debug and release builds, and cannot
1551 /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
1552 /// release builds by default.
1553 ///
1554 /// Unsafe code may rely on `assert!` to enforce run-time invariants that, if
1555 /// violated could lead to unsafety.
1556 ///
1557 /// Other use-cases of `assert!` include testing and enforcing run-time
1558 /// invariants in safe code (whose violation cannot result in unsafety).
1559 ///
1560 /// # Custom Messages
1561 ///
1562 /// This macro has a second form, where a custom panic message can
1563 /// be provided with or without arguments for formatting. See [`std::fmt`]
1564 /// for syntax for this form. Expressions used as format arguments will only
1565 /// be evaluated if the assertion fails.
1566 ///
1567 /// [`std::fmt`]: ../std/fmt/index.html
1568 ///
1569 /// # Examples
1570 ///
1571 /// ```
1572 /// // the panic message for these assertions is the stringified value of the
1573 /// // expression given.
1574 /// assert!(true);
1575 ///
1576 /// fn some_computation() -> bool {
1577 /// // Some expensive computation here
1578 /// true
1579 /// }
1580 ///
1581 /// assert!(some_computation());
1582 ///
1583 /// // assert with a custom message
1584 /// let x = true;
1585 /// assert!(x, "x wasn't true!");
1586 ///
1587 /// let a = 3; let b = 27;
1588 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
1589 /// ```
1590 #[stable(feature = "rust1", since = "1.0.0")]
1591 #[rustc_builtin_macro]
1592 #[macro_export]
1593 #[rustc_diagnostic_item = "assert_macro"]
1594 #[allow_internal_unstable(
1595 core_intrinsics,
1596 panic_internals,
1597 edition_panic,
1598 generic_assert_internals
1599 )]
1600 macro_rules! assert {
1601 ($cond:expr $(,)?) => {{ /* compiler built-in */ }};
1602 ($cond:expr, $($arg:tt)+) => {{ /* compiler built-in */ }};
1603 }
1604
1605 /// Prints passed tokens into the standard output.
1606 #[unstable(
1607 feature = "log_syntax",
1608 issue = "29598",
1609 reason = "`log_syntax!` is not stable enough for use and is subject to change"
1610 )]
1611 #[rustc_builtin_macro]
1612 #[macro_export]
1613 macro_rules! log_syntax {
1614 ($($arg:tt)*) => {
1615 /* compiler built-in */
1616 };
1617 }
1618
1619 /// Enables or disables tracing functionality used for debugging other macros.
1620 #[unstable(
1621 feature = "trace_macros",
1622 issue = "29598",
1623 reason = "`trace_macros` is not stable enough for use and is subject to change"
1624 )]
1625 #[rustc_builtin_macro]
1626 #[macro_export]
1627 macro_rules! trace_macros {
1628 (true) => {{ /* compiler built-in */ }};
1629 (false) => {{ /* compiler built-in */ }};
1630 }
1631
1632 /// Attribute macro used to apply derive macros.
1633 ///
1634 /// See [the reference] for more info.
1635 ///
1636 /// [the reference]: ../../../reference/attributes/derive.html
1637 #[stable(feature = "rust1", since = "1.0.0")]
1638 #[rustc_builtin_macro]
1639 pub macro derive($item:item) {
1640 /* compiler built-in */
1641 }
1642
1643 /// Attribute macro used to apply derive macros for implementing traits
1644 /// in a const context.
1645 ///
1646 /// See [the reference] for more info.
1647 ///
1648 /// [the reference]: ../../../reference/attributes/derive.html
1649 #[unstable(feature = "derive_const", issue = "118304")]
1650 #[rustc_builtin_macro]
1651 pub macro derive_const($item:item) {
1652 /* compiler built-in */
1653 }
1654
1655 /// Attribute macro applied to a function to turn it into a unit test.
1656 ///
1657 /// See [the reference] for more info.
1658 ///
1659 /// [the reference]: ../../../reference/attributes/testing.html#the-test-attribute
1660 #[stable(feature = "rust1", since = "1.0.0")]
1661 #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
1662 #[rustc_builtin_macro]
1663 pub macro test($item:item) {
1664 /* compiler built-in */
1665 }
1666
1667 /// Attribute macro applied to a function to turn it into a benchmark test.
1668 #[unstable(
1669 feature = "test",
1670 issue = "50297",
1671 reason = "`bench` is a part of custom test frameworks which are unstable"
1672 )]
1673 #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]
1674 #[rustc_builtin_macro]
1675 pub macro bench($item:item) {
1676 /* compiler built-in */
1677 }
1678
1679 /// An implementation detail of the `#[test]` and `#[bench]` macros.
1680 #[unstable(
1681 feature = "custom_test_frameworks",
1682 issue = "50297",
1683 reason = "custom test frameworks are an unstable feature"
1684 )]
1685 #[allow_internal_unstable(test, rustc_attrs)]
1686 #[rustc_builtin_macro]
1687 pub macro test_case($item:item) {
1688 /* compiler built-in */
1689 }
1690
1691 /// Attribute macro applied to a static to register it as a global allocator.
1692 ///
1693 /// See also [`std::alloc::GlobalAlloc`](../../../std/alloc/trait.GlobalAlloc.html).
1694 #[stable(feature = "global_allocator", since = "1.28.0")]
1695 #[allow_internal_unstable(rustc_attrs)]
1696 #[rustc_builtin_macro]
1697 pub macro global_allocator($item:item) {
1698 /* compiler built-in */
1699 }
1700
1701 /// Attribute macro applied to a function to give it a post-condition.
1702 ///
1703 /// The attribute carries an argument token-tree which is
1704 /// eventually parsed as a unary closure expression that is
1705 /// invoked on a reference to the return value.
1706 #[unstable(feature = "contracts", issue = "128044")]
1707 #[allow_internal_unstable(contracts_internals)]
1708 #[rustc_builtin_macro]
1709 pub macro contracts_ensures($item:item) {
1710 /* compiler built-in */
1711 }
1712
1713 /// Attribute macro applied to a function to give it a precondition.
1714 ///
1715 /// The attribute carries an argument token-tree which is
1716 /// eventually parsed as an boolean expression with access to the
1717 /// function's formal parameters
1718 #[unstable(feature = "contracts", issue = "128044")]
1719 #[allow_internal_unstable(contracts_internals)]
1720 #[rustc_builtin_macro]
1721 pub macro contracts_requires($item:item) {
1722 /* compiler built-in */
1723 }
1724
1725 /// Attribute macro applied to a function to register it as a handler for allocation failure.
1726 ///
1727 /// See also [`std::alloc::handle_alloc_error`](../../../std/alloc/fn.handle_alloc_error.html).
1728 #[unstable(feature = "alloc_error_handler", issue = "51540")]
1729 #[allow_internal_unstable(rustc_attrs)]
1730 #[rustc_builtin_macro]
1731 pub macro alloc_error_handler($item:item) {
1732 /* compiler built-in */
1733 }
1734
1735 /// Keeps the item it's applied to if the passed path is accessible, and removes it otherwise.
1736 #[unstable(
1737 feature = "cfg_accessible",
1738 issue = "64797",
1739 reason = "`cfg_accessible` is not fully implemented"
1740 )]
1741 #[rustc_builtin_macro]
1742 pub macro cfg_accessible($item:item) {
1743 /* compiler built-in */
1744 }
1745
1746 /// Expands all `#[cfg]` and `#[cfg_attr]` attributes in the code fragment it's applied to.
1747 #[unstable(
1748 feature = "cfg_eval",
1749 issue = "82679",
1750 reason = "`cfg_eval` is a recently implemented feature"
1751 )]
1752 #[rustc_builtin_macro]
1753 pub macro cfg_eval($($tt:tt)*) {
1754 /* compiler built-in */
1755 }
1756
1757 /// Provide a list of type aliases and other opaque-type-containing type definitions
1758 /// to an item with a body. This list will be used in that body to define opaque
1759 /// types' hidden types.
1760 /// Can only be applied to things that have bodies.
1761 #[unstable(
1762 feature = "type_alias_impl_trait",
1763 issue = "63063",
1764 reason = "`type_alias_impl_trait` has open design concerns"
1765 )]
1766 #[rustc_builtin_macro]
1767 pub macro define_opaque($($tt:tt)*) {
1768 /* compiler built-in */
1769 }
1770
1771 /// Unstable placeholder for type ascription.
1772 #[allow_internal_unstable(builtin_syntax)]
1773 #[unstable(
1774 feature = "type_ascription",
1775 issue = "23416",
1776 reason = "placeholder syntax for type ascription"
1777 )]
1778 #[rustfmt::skip]
1779 pub macro type_ascribe($expr:expr, $ty:ty) {
1780 builtin # type_ascribe($expr, $ty)
1781 }
1782
1783 /// Unstable placeholder for deref patterns.
1784 #[allow_internal_unstable(builtin_syntax)]
1785 #[unstable(
1786 feature = "deref_patterns",
1787 issue = "87121",
1788 reason = "placeholder syntax for deref patterns"
1789 )]
1790 pub macro deref($pat:pat) {
1791 builtin # deref($pat)
1792 }
1793
1794 /// Derive macro generating an impl of the trait `From`.
1795 /// Currently, it can only be used on single-field structs.
1796 // Note that the macro is in a different module than the `From` trait,
1797 // to avoid triggering an unstable feature being used if someone imports
1798 // `std::convert::From`.
1799 #[rustc_builtin_macro]
1800 #[unstable(feature = "derive_from", issue = "144889")]
1801 pub macro From($item: item) {
1802 /* compiler built-in */
1803 }
1804}