1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Standard library macros
13 //! This modules contains a set of macros which are exported from the standard
14 //! library. Each macro is available for use when linking against the standard
17 /// The entry point for panic of Rust threads.
19 /// This allows a program to to terminate immediately and provide feedback
20 /// to the caller of the program. `panic!` should be used when a program reaches
21 /// an unrecoverable problem.
23 /// This macro is the perfect way to assert conditions in example code and in
24 /// tests. `panic!` is closely tied with the `unwrap` method of both [`Option`]
25 /// and [`Result`][runwrap] enums. Both implementations call `panic!` when they are set
26 /// to None or Err variants.
28 /// This macro is used to inject panic into a Rust thread, causing the thread to
29 /// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type,
30 /// and the single-argument form of the `panic!` macro will be the value which
33 /// [`Result`] enum is often a better solution for recovering from errors than
34 /// using the `panic!` macro. This macro should be used to avoid proceeding using
35 /// incorrect values, such as from external sources. Detailed information about
36 /// error handling is found in the [book].
38 /// The multi-argument form of this macro panics with a string and has the
39 /// [`format!`] syntax for building a string.
41 /// [runwrap]: ../std/result/enum.Result.html#method.unwrap
42 /// [`Option`]: ../std/option/enum.Option.html#method.unwrap
43 /// [`Result`]: ../std/result/enum.Result.html
44 /// [`format!`]: ../std/macro.format.html
45 /// [book]: ../book/second-edition/ch09-01-unrecoverable-errors-with-panic.html
47 /// # Current implementation
49 /// If the main thread panics it will terminate all your threads and end your
50 /// program with code `101`.
55 /// # #![allow(unreachable_code)]
57 /// panic!("this is a terrible mistake!");
58 /// panic!(4); // panic with the value of 4 to be collected elsewhere
59 /// panic!("this is a {} {message}", "fancy", message = "message");
62 #[stable(feature = "rust1", since = "1.0.0")]
63 #[allow_internal_unstable]
66 panic!("explicit panic")
69 $crate::rt::begin_panic($msg, &(file!(), line!(), __rust_unstable_column!()))
74 ($fmt:expr, $($arg:tt)+) => ({
75 $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+),
76 &(file!(), line!(), __rust_unstable_column!()))
80 /// Macro for printing to the standard output.
82 /// Equivalent to the [`println!`] macro except that a newline is not printed at
83 /// the end of the message.
85 /// Note that stdout is frequently line-buffered by default so it may be
86 /// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted
89 /// Use `print!` only for the primary output of your program. Use
90 /// [`eprint!`] instead to print error and progress messages.
92 /// [`println!`]: ../std/macro.println.html
93 /// [flush]: ../std/io/trait.Write.html#tymethod.flush
94 /// [`eprint!`]: ../std/macro.eprint.html
98 /// Panics if writing to `io::stdout()` fails.
103 /// use std::io::{self, Write};
113 /// io::stdout().flush().unwrap();
115 /// print!("this string has a newline, why not choose println! instead?\n");
117 /// io::stdout().flush().unwrap();
120 #[stable(feature = "rust1", since = "1.0.0")]
121 #[allow_internal_unstable]
123 ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
126 /// Macro for printing to the standard output, with a newline.
128 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
129 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
131 /// Use the [`format!`] syntax to write data to the standard output.
132 /// See [`std::fmt`] for more information.
134 /// Use `println!` only for the primary output of your program. Use
135 /// [`eprintln!`] instead to print error and progress messages.
137 /// [`format!`]: ../std/macro.format.html
138 /// [`std::fmt`]: ../std/fmt/index.html
139 /// [`eprintln!`]: ../std/macro.eprint.html
142 /// Panics if writing to `io::stdout` fails.
147 /// println!(); // prints just a newline
148 /// println!("hello there!");
149 /// println!("format {} arguments", "some");
152 #[stable(feature = "rust1", since = "1.0.0")]
153 macro_rules! println {
154 () => (print!("\n"));
155 ($fmt:expr) => (print!(concat!($fmt, "\n")));
156 ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
159 /// Macro for printing to the standard error.
161 /// Equivalent to the [`print!`] macro, except that output goes to
162 /// [`io::stderr`] instead of `io::stdout`. See [`print!`] for
165 /// Use `eprint!` only for error and progress messages. Use `print!`
166 /// instead for the primary output of your program.
168 /// [`io::stderr`]: ../std/io/struct.Stderr.html
169 /// [`print!`]: ../std/macro.print.html
173 /// Panics if writing to `io::stderr` fails.
178 /// eprint!("Error: Could not complete task");
181 #[stable(feature = "eprint", since = "1.19.0")]
182 #[allow_internal_unstable]
183 macro_rules! eprint {
184 ($($arg:tt)*) => ($crate::io::_eprint(format_args!($($arg)*)));
187 /// Macro for printing to the standard error, with a newline.
189 /// Equivalent to the [`println!`] macro, except that output goes to
190 /// [`io::stderr`] instead of `io::stdout`. See [`println!`] for
193 /// Use `eprintln!` only for error and progress messages. Use `println!`
194 /// instead for the primary output of your program.
196 /// [`io::stderr`]: ../std/io/struct.Stderr.html
197 /// [`println!`]: ../std/macro.println.html
201 /// Panics if writing to `io::stderr` fails.
206 /// eprintln!("Error: Could not complete task");
209 #[stable(feature = "eprint", since = "1.19.0")]
210 macro_rules! eprintln {
211 () => (eprint!("\n"));
212 ($fmt:expr) => (eprint!(concat!($fmt, "\n")));
213 ($fmt:expr, $($arg:tt)*) => (eprint!(concat!($fmt, "\n"), $($arg)*));
217 #[unstable(feature = "await_macro", issue = "50547")]
218 #[allow_internal_unstable]
219 #[allow_internal_unsafe]
223 let mut pinned = unsafe { $crate::mem::PinMut::new_unchecked(&mut pinned) };
225 match $crate::future::poll_in_task_cx(&mut pinned) {
226 // FIXME(cramertj) prior to stabilizing await, we have to ensure that this
227 // can't be used to create a generator on stable via `|| await!()`.
228 $crate::task::Poll::Pending => yield,
229 $crate::task::Poll::Ready(x) => break x,
235 /// A macro to select an event from a number of receivers.
237 /// This macro is used to wait for the first event to occur on a number of
238 /// receivers. It places no restrictions on the types of receivers given to
239 /// this macro, this can be viewed as a heterogeneous select.
244 /// #![feature(mpsc_select)]
247 /// use std::sync::mpsc;
249 /// // two placeholder functions for now
250 /// fn long_running_thread() {}
251 /// fn calculate_the_answer() -> u32 { 42 }
253 /// let (tx1, rx1) = mpsc::channel();
254 /// let (tx2, rx2) = mpsc::channel();
256 /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
257 /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
260 /// _ = rx1.recv() => println!("the long running thread finished first"),
261 /// answer = rx2.recv() => {
262 /// println!("the answer was: {}", answer.unwrap());
265 /// # drop(rx1.recv());
266 /// # drop(rx2.recv());
269 /// For more information about select, see the `std::sync::mpsc::Select` structure.
271 #[unstable(feature = "mpsc_select", issue = "27800")]
272 macro_rules! select {
274 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
276 use $crate::sync::mpsc::Select;
277 let sel = Select::new();
278 $( let mut $rx = sel.handle(&$rx); )+
282 let ret = sel.wait();
283 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
289 macro_rules! assert_approx_eq {
290 ($a:expr, $b:expr) => ({
291 let (a, b) = (&$a, &$b);
292 assert!((*a - *b).abs() < 1.0e-6,
293 "{} is not approximately equal to {}", *a, *b);
297 /// Built-in macros to the compiler itself.
299 /// These macros do not have any corresponding definition with a `macro_rules!`
300 /// macro, but are documented here. Their implementations can be found hardcoded
301 /// into libsyntax itself.
305 /// Unconditionally causes compilation to fail with the given error message when encountered.
307 /// This macro should be used when a crate uses a conditional compilation strategy to provide
308 /// better error messages for erroneous conditions.
312 /// Two such examples are macros and `#[cfg]` environments.
314 /// Emit better compiler error if a macro is passed invalid values.
317 /// macro_rules! give_me_foo_or_bar {
321 /// compile_error!("This macro only accepts `foo` or `bar`");
325 /// give_me_foo_or_bar!(neither);
326 /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
329 /// Emit compiler error if one of a number of features isn't available.
332 /// #[cfg(not(any(feature = "foo", feature = "bar")))]
333 /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.")
335 #[stable(feature = "compile_error_macro", since = "1.20.0")]
337 macro_rules! compile_error {
338 ($msg:expr) => ({ /* compiler built-in */ });
339 ($msg:expr,) => ({ /* compiler built-in */ });
342 /// The core macro for formatted string creation & output.
344 /// This macro functions by taking a formatting string literal containing
345 /// `{}` for each additional argument passed. `format_args!` prepares the
346 /// additional parameters to ensure the output can be interpreted as a string
347 /// and canonicalizes the arguments into a single type. Any value that implements
348 /// the [`Display`] trait can be passed to `format_args!`, as can any
349 /// [`Debug`] implementation be passed to a `{:?}` within the formatting string.
351 /// This macro produces a value of type [`fmt::Arguments`]. This value can be
352 /// passed to the macros within [`std::fmt`] for performing useful redirection.
353 /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
354 /// proxied through this one. `format_args!`, unlike its derived macros, avoids
355 /// heap allocations.
357 /// You can use the [`fmt::Arguments`] value that `format_args!` returns
358 /// in `Debug` and `Display` contexts as seen below. The example also shows
359 /// that `Debug` and `Display` format to the same thing: the interpolated
360 /// format string in `format_args!`.
363 /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
364 /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
365 /// assert_eq!("1 foo 2", display);
366 /// assert_eq!(display, debug);
369 /// For more information, see the documentation in [`std::fmt`].
371 /// [`Display`]: ../std/fmt/trait.Display.html
372 /// [`Debug`]: ../std/fmt/trait.Debug.html
373 /// [`fmt::Arguments`]: ../std/fmt/struct.Arguments.html
374 /// [`std::fmt`]: ../std/fmt/index.html
375 /// [`format!`]: ../std/macro.format.html
376 /// [`write!`]: ../std/macro.write.html
377 /// [`println!`]: ../std/macro.println.html
384 /// let s = fmt::format(format_args!("hello {}", "world"));
385 /// assert_eq!(s, format!("hello {}", "world"));
387 #[stable(feature = "rust1", since = "1.0.0")]
389 macro_rules! format_args {
390 ($fmt:expr) => ({ /* compiler built-in */ });
391 ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ });
394 /// Inspect an environment variable at compile time.
396 /// This macro will expand to the value of the named environment variable at
397 /// compile time, yielding an expression of type `&'static str`.
399 /// If the environment variable is not defined, then a compilation error
400 /// will be emitted. To not emit a compile error, use the [`option_env!`]
403 /// [`option_env!`]: ../std/macro.option_env.html
408 /// let path: &'static str = env!("PATH");
409 /// println!("the $PATH variable at the time of compiling was: {}", path);
412 /// You can customize the error message by passing a string as the second
416 /// let doc: &'static str = env!("documentation", "what's that?!");
419 /// If the `documentation` environment variable is not defined, you'll get
420 /// the following error:
423 /// error: what's that?!
425 #[stable(feature = "rust1", since = "1.0.0")]
428 ($name:expr) => ({ /* compiler built-in */ });
429 ($name:expr,) => ({ /* compiler built-in */ });
432 /// Optionally inspect an environment variable at compile time.
434 /// If the named environment variable is present at compile time, this will
435 /// expand into an expression of type `Option<&'static str>` whose value is
436 /// `Some` of the value of the environment variable. If the environment
437 /// variable is not present, then this will expand to `None`. See
438 /// [`Option<T>`][option] for more information on this type.
440 /// A compile time error is never emitted when using this macro regardless
441 /// of whether the environment variable is present or not.
443 /// [option]: ../std/option/enum.Option.html
448 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
449 /// println!("the secret key might be: {:?}", key);
451 #[stable(feature = "rust1", since = "1.0.0")]
453 macro_rules! option_env {
454 ($name:expr) => ({ /* compiler built-in */ });
455 ($name:expr,) => ({ /* compiler built-in */ });
458 /// Concatenate identifiers into one identifier.
460 /// This macro takes any number of comma-separated identifiers, and
461 /// concatenates them all into one, yielding an expression which is a new
462 /// identifier. Note that hygiene makes it such that this macro cannot
463 /// capture local variables. Also, as a general rule, macros are only
464 /// allowed in item, statement or expression position. That means while
465 /// you may use this macro for referring to existing variables, functions or
466 /// modules etc, you cannot define a new one with it.
471 /// #![feature(concat_idents)]
474 /// fn foobar() -> u32 { 23 }
476 /// let f = concat_idents!(foo, bar);
477 /// println!("{}", f());
479 /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
482 #[unstable(feature = "concat_idents_macro", issue = "29599")]
484 macro_rules! concat_idents {
485 ($($e:ident),+) => ({ /* compiler built-in */ });
486 ($($e:ident,)+) => ({ /* compiler built-in */ });
489 /// Concatenates literals into a static string slice.
491 /// This macro takes any number of comma-separated literals, yielding an
492 /// expression of type `&'static str` which represents all of the literals
493 /// concatenated left-to-right.
495 /// Integer and floating point literals are stringified in order to be
501 /// let s = concat!("test", 10, 'b', true);
502 /// assert_eq!(s, "test10btrue");
504 #[stable(feature = "rust1", since = "1.0.0")]
506 macro_rules! concat {
507 ($($e:expr),*) => ({ /* compiler built-in */ });
508 ($($e:expr,)*) => ({ /* compiler built-in */ });
511 /// A macro which expands to the line number on which it was invoked.
513 /// With [`column!`] and [`file!`], these macros provide debugging information for
514 /// developers about the location within the source.
516 /// The expanded expression has type `u32` and is 1-based, so the first line
517 /// in each file evaluates to 1, the second to 2, etc. This is consistent
518 /// with error messages by common compilers or popular editors.
519 /// The returned line is *not necessarily* the line of the `line!` invocation itself,
520 /// but rather the first macro invocation leading up to the invocation
521 /// of the `line!` macro.
523 /// [`column!`]: macro.column.html
524 /// [`file!`]: macro.file.html
529 /// let current_line = line!();
530 /// println!("defined on line: {}", current_line);
532 #[stable(feature = "rust1", since = "1.0.0")]
534 macro_rules! line { () => ({ /* compiler built-in */ }) }
536 /// A macro which expands to the column number on which it was invoked.
538 /// With [`line!`] and [`file!`], these macros provide debugging information for
539 /// developers about the location within the source.
541 /// The expanded expression has type `u32` and is 1-based, so the first column
542 /// in each line evaluates to 1, the second to 2, etc. This is consistent
543 /// with error messages by common compilers or popular editors.
544 /// The returned column is *not necessarily* the line of the `column!` invocation itself,
545 /// but rather the first macro invocation leading up to the invocation
546 /// of the `column!` macro.
548 /// [`line!`]: macro.line.html
549 /// [`file!`]: macro.file.html
554 /// let current_col = column!();
555 /// println!("defined on column: {}", current_col);
557 #[stable(feature = "rust1", since = "1.0.0")]
559 macro_rules! column { () => ({ /* compiler built-in */ }) }
561 /// A macro which expands to the file name from which it was invoked.
563 /// With [`line!`] and [`column!`], these macros provide debugging information for
564 /// developers about the location within the source.
567 /// The expanded expression has type `&'static str`, and the returned file
568 /// is not the invocation of the `file!` macro itself, but rather the
569 /// first macro invocation leading up to the invocation of the `file!`
572 /// [`line!`]: macro.line.html
573 /// [`column!`]: macro.column.html
578 /// let this_file = file!();
579 /// println!("defined in file: {}", this_file);
581 #[stable(feature = "rust1", since = "1.0.0")]
583 macro_rules! file { () => ({ /* compiler built-in */ }) }
585 /// A macro which stringifies its arguments.
587 /// This macro will yield an expression of type `&'static str` which is the
588 /// stringification of all the tokens passed to the macro. No restrictions
589 /// are placed on the syntax of the macro invocation itself.
591 /// Note that the expanded results of the input tokens may change in the
592 /// future. You should be careful if you rely on the output.
597 /// let one_plus_one = stringify!(1 + 1);
598 /// assert_eq!(one_plus_one, "1 + 1");
600 #[stable(feature = "rust1", since = "1.0.0")]
602 macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) }
604 /// Includes a utf8-encoded file as a string.
606 /// The file is located relative to the current file. (similarly to how
607 /// modules are found)
609 /// This macro will yield an expression of type `&'static str` which is the
610 /// contents of the file.
614 /// Assume there are two files in the same directory with the following
617 /// File 'spanish.in':
625 /// ```ignore (cannot-doctest-external-file-dependency)
627 /// let my_str = include_str!("spanish.in");
628 /// assert_eq!(my_str, "adiรณs\n");
629 /// print!("{}", my_str);
633 /// Compiling 'main.rs' and running the resulting binary will print "adiรณs".
634 #[stable(feature = "rust1", since = "1.0.0")]
636 macro_rules! include_str {
637 ($file:expr) => ({ /* compiler built-in */ });
638 ($file:expr,) => ({ /* compiler built-in */ });
641 /// Includes a file as a reference to a byte array.
643 /// The file is located relative to the current file. (similarly to how
644 /// modules are found)
646 /// This macro will yield an expression of type `&'static [u8; N]` which is
647 /// the contents of the file.
651 /// Assume there are two files in the same directory with the following
654 /// File 'spanish.in':
662 /// ```ignore (cannot-doctest-external-file-dependency)
664 /// let bytes = include_bytes!("spanish.in");
665 /// assert_eq!(bytes, b"adi\xc3\xb3s\n");
666 /// print!("{}", String::from_utf8_lossy(bytes));
670 /// Compiling 'main.rs' and running the resulting binary will print "adiรณs".
671 #[stable(feature = "rust1", since = "1.0.0")]
673 macro_rules! include_bytes {
674 ($file:expr) => ({ /* compiler built-in */ });
675 ($file:expr,) => ({ /* compiler built-in */ });
678 /// Expands to a string that represents the current module path.
680 /// The current module path can be thought of as the hierarchy of modules
681 /// leading back up to the crate root. The first component of the path
682 /// returned is the name of the crate currently being compiled.
689 /// assert!(module_path!().ends_with("test"));
695 #[stable(feature = "rust1", since = "1.0.0")]
697 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
699 /// Boolean evaluation of configuration flags, at compile-time.
701 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
702 /// boolean expression evaluation of configuration flags. This frequently
703 /// leads to less duplicated code.
705 /// The syntax given to this macro is the same syntax as [the `cfg`
706 /// attribute](../book/first-edition/conditional-compilation.html).
711 /// let my_directory = if cfg!(windows) {
712 /// "windows-specific-directory"
717 #[stable(feature = "rust1", since = "1.0.0")]
719 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
721 /// Parse a file as an expression or an item according to the context.
723 /// The file is located relative to the current file (similarly to how
724 /// modules are found).
726 /// Using this macro is often a bad idea, because if the file is
727 /// parsed as an expression, it is going to be placed in the
728 /// surrounding code unhygienically. This could result in variables
729 /// or functions being different from what the file expected if
730 /// there are variables or functions that have the same name in
731 /// the current file.
735 /// Assume there are two files in the same directory with the following
738 /// File 'monkeys.in':
740 /// ```ignore (only-for-syntax-highlight)
741 /// ['๐', '๐', '๐']
745 /// .collect::<String>()
750 /// ```ignore (cannot-doctest-external-file-dependency)
752 /// let my_string = include!("monkeys.in");
753 /// assert_eq!("๐๐๐๐๐๐", my_string);
754 /// println!("{}", my_string);
758 /// Compiling 'main.rs' and running the resulting binary will print
759 /// "๐๐๐๐๐๐".
760 #[stable(feature = "rust1", since = "1.0.0")]
762 macro_rules! include {
763 ($file:expr) => ({ /* compiler built-in */ });
764 ($file:expr,) => ({ /* compiler built-in */ });
767 /// Ensure that a boolean expression is `true` at runtime.
769 /// This will invoke the [`panic!`] macro if the provided expression cannot be
770 /// evaluated to `true` at runtime.
774 /// Assertions are always checked in both debug and release builds, and cannot
775 /// be disabled. See [`debug_assert!`] for assertions that are not enabled in
776 /// release builds by default.
778 /// Unsafe code relies on `assert!` to enforce run-time invariants that, if
779 /// violated could lead to unsafety.
781 /// Other use-cases of `assert!` include [testing] and enforcing run-time
782 /// invariants in safe code (whose violation cannot result in unsafety).
784 /// # Custom Messages
786 /// This macro has a second form, where a custom panic message can
787 /// be provided with or without arguments for formatting. See [`std::fmt`]
788 /// for syntax for this form.
790 /// [`panic!`]: macro.panic.html
791 /// [`debug_assert!`]: macro.debug_assert.html
792 /// [testing]: ../book/second-edition/ch11-01-writing-tests.html#checking-results-with-the-assert-macro
793 /// [`std::fmt`]: ../std/fmt/index.html
798 /// // the panic message for these assertions is the stringified value of the
799 /// // expression given.
802 /// fn some_computation() -> bool { true } // a very simple function
804 /// assert!(some_computation());
806 /// // assert with a custom message
808 /// assert!(x, "x wasn't true!");
810 /// let a = 3; let b = 27;
811 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
813 #[stable(feature = "rust1", since = "1.0.0")]
815 macro_rules! assert {
816 ($cond:expr) => ({ /* compiler built-in */ });
817 ($cond:expr,) => ({ /* compiler built-in */ });
818 ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });
822 /// A macro for defining `#[cfg]` if-else statements.
824 /// This is similar to the `if/elif` C preprocessor macro by allowing definition
825 /// of a cascade of `#[cfg]` cases, emitting the implementation which matches
828 /// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code
829 /// without having to rewrite each clause multiple times.
830 macro_rules! cfg_if {
832 if #[cfg($($meta:meta),*)] { $($it:item)* }
838 $( ( ($($meta),*) ($($it)*) ), )*
844 macro_rules! __cfg_if_items {
845 (($($not:meta,)*) ; ) => {};
846 (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => {
847 __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* }
848 __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* }
852 macro_rules! __cfg_if_apply {
853 ($m:meta, $($it:item)*) => {