Macro tracing::stdlib::compile_error
1.20.0 · source · macro_rules! compile_error { ($msg:expr $(,)?) => { ... }; }
Expand description
Causes compilation to fail with the given error message when encountered.
This macro should be used when a crate uses a conditional compilation strategy to provide
better error messages for erroneous conditions. It’s the compiler-level form of panic!
,
but emits an error during compilation rather than at runtime.
§Examples
Two such examples are macros and #[cfg]
environments.
Emit a better compiler error if a macro is passed invalid values. Without the final branch, the compiler would still emit an error, but the error’s message would not mention the two valid values.
ⓘ
macro_rules! give_me_foo_or_bar {
(foo) => {};
(bar) => {};
($x:ident) => {
compile_error!("This macro only accepts `foo` or `bar`");
}
}
give_me_foo_or_bar!(neither);
// ^ will fail at compile time with message "This macro only accepts `foo` or `bar`"
Emit a compiler error if one of a number of features isn’t available.
ⓘ
#[cfg(not(any(feature = "foo", feature = "bar")))]
compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.");