Repository navigation
Macro-expanded unconfigured items are gated feature checked #32840
Description
Macro-expanded unconfigured items are gated feature checked, but ordinary unconfigured items are not. For example, the following should compile, ...
#![cfg_attr(attr, feature(rustc_attrs))]
macro_rules! mac {
{} => {
#[cfg(attr)]
mod m {
#[rustc_error] // ... but if not(attr), this complains about the lack of the rustc_attrs feature
fn f() {}
}
}
}
mac! {}If we manually expand mac! {}, it always compiles:
#![cfg_attr(attr, feature(rustc_attrs))]
#[cfg(attr)]
mod m {
#[rustc_error]
fn f() {}
}
Activity
jseyfried commentedon Apr 8, 2016
It looks like this was intentional (introduced in #22899), but I don't think it's a good idea.
cc @nrc
cc #22250
LeoTestard commentedon Apr 9, 2016
There are arguments on #32648 about why this is not a good idea:
#[cfg]is typically used by crates that need to build against both stable and nightly and use nightly-specific features when available (the most important example that I have in mind is syntax extensions using plugins on nightly and syntex on stable). Checking for use of gated features inside this#[cfg]-guarded code will break those crates, and it's not a good thing, this use case is actually useful. This check pass should be removed.nrc commentedon Apr 12, 2016
cc @rust-lang/lang