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Rollup merge of #136948 - workingjubilee:split-off-extern-system-varargs, r=compiler-errors

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Split out the `extern_system_varargs` feature

After the stabilization PR was opened, `extern "system"` functions were added to `extended_varargs_abi_support`. This has a number of questions regarding it that were not discussed and were somewhat surprising. It deserves to be considered as its own feature, separate from `extended_varargs_abi_support`.

Tracking issue:
- https://github.com/rust-lang/rust/issues/136946
This commit is contained in:
Jacob Pratt 2025-02-13 03:53:32 -05:00 • committed by GitHub
commit 36d37966df
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13 changed files with 63 additions and 53 deletions
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42
compiler/rustc_hir_analysis/src/lib.rs
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@ -122,28 +122,42 @@ fn require_c_abi_if_c_variadic(
const UNSTABLE_EXPLAIN: &str =
"using calling conventions other than `C` or `cdecl` for varargs functions is unstable";
// ABIs which can stably use varargs
if !decl.c_variadic || matches!(abi, ExternAbi::C { .. } | ExternAbi::Cdecl { .. }) {
return;
}
// ABIs with feature-gated stability
let extended_abi_support = tcx.features().extended_varargs_abi_support();
let conventions = match (extended_abi_support, abi.supports_varargs()) {
// User enabled additional ABI support for varargs and function ABI matches those ones.
(true, true) => return,
let extern_system_varargs = tcx.features().extern_system_varargs();
// Using this ABI would be ok, if the feature for additional ABI support was enabled.
// Return CONVENTIONS_STABLE, because we want the other error to look the same.
(false, true) => {
feature_err(&tcx.sess, sym::extended_varargs_abi_support, span, UNSTABLE_EXPLAIN)
.emit();
CONVENTIONS_STABLE
}
(false, false) => CONVENTIONS_STABLE,
(true, false) => CONVENTIONS_UNSTABLE,
// If the feature gate has been enabled, we can stop here
if extern_system_varargs && let ExternAbi::System { .. } = abi {
return;
};
if extended_abi_support && abi.supports_varargs() {
return;
};
tcx.dcx().emit_err(errors::VariadicFunctionCompatibleConvention { span, conventions });
// Looks like we need to pick an error to emit.
// Is there any feature which we could have enabled to make this work?
match abi {
ExternAbi::System { .. } => {
feature_err(&tcx.sess, sym::extern_system_varargs, span, UNSTABLE_EXPLAIN)
}
abi if abi.supports_varargs() => {
feature_err(&tcx.sess, sym::extended_varargs_abi_support, span, UNSTABLE_EXPLAIN)
}
_ => tcx.dcx().create_err(errors::VariadicFunctionCompatibleConvention {
span,
conventions: if tcx.sess.opts.unstable_features.is_nightly_build() {
CONVENTIONS_UNSTABLE
} else {
CONVENTIONS_STABLE
},
}),
}
.emit();
}
pub fn provide(providers: &mut Providers) {