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Rollup merge of #97495 - clarfonthey:e0788-no-coverage, r=nagisa

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Add E0788 for improper #[no_coverage] usage

Essentially, this adds proper checking for the attribute (tracking issue #84605) and throws errors when it's put in obviously-wrong places, like on struct or const definitions. Most of the code is taken directly from the checks for the `#[inline]` attribute, since it's very similar.

Right now, the code only checks at the function level, but it seems reasonable to allow adding `#[no_coverage]` to individual blocks or expressions, so, for now those just throw `unused_attributes` warnings. Similarly, since there was a lot of desire to eventually allow recursive definitions as well on modules and impl blocks, these also throw `unused_attributes` instead of an error.

I'm not sure if anything has to be done since this error is technically for an unstable feature, but since an error for using unstable features will show up anyway, I think it's okay.

This is the first big piece needed for stabilising this attribute, although I personally would like to explore renaming it to `#[coverage(never)]` on a separate PR, which I will offer soon. There's a lot of discussion still to be had about that, which is why it will be kept separate.

I don't think much is needed besides adding this simple check and a UI test, but let me know if there's something else that should be added to make this happen.
This commit is contained in:
Dylan DPC 2022-06-06 14:34:56 +02:00 • committed by GitHub
commit cb787bea46
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52
compiler/rustc_passes/src/check_attr.rs
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@ -77,6 +77,7 @@ impl CheckAttrVisitor<'_> {
for attr in attrs {
let attr_is_valid = match attr.name_or_empty() {
sym::inline => self.check_inline(hir_id, attr, span, target),
sym::no_coverage => self.check_no_coverage(hir_id, attr, span, target),
sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target),
sym::marker => self.check_marker(hir_id, attr, span, target),
sym::rustc_must_implement_one_of => {
@ -291,6 +292,57 @@ impl CheckAttrVisitor<'_> {
}
}
/// Checks if a `#[no_coverage]` is applied directly to a function
fn check_no_coverage(
&self,
hir_id: HirId,
attr: &Attribute,
span: Span,
target: Target,
) -> bool {
match target {
// no_coverage on function is fine
Target::Fn
| Target::Closure
| Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
// function prototypes can't be covered
Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
lint.build("`#[no_coverage]` is ignored on function prototypes").emit();
});
true
}
Target::Mod | Target::ForeignMod | Target::Impl | Target::Trait => {
self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
lint.build("`#[no_coverage]` does not propagate into items and must be applied to the contained functions directly").emit();
});
true
}
Target::Expression | Target::Statement | Target::Arm => {
self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
lint.build("`#[no_coverage]` may only be applied to function definitions")
.emit();
});
true
}
_ => {
struct_span_err!(
self.tcx.sess,
attr.span,
E0788,
"`#[no_coverage]` must be applied to coverable code",
)
.span_label(span, "not coverable code")
.emit();
false
}
}
}
fn check_generic_attr(
&self,
hir_id: HirId,