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Merge the ~const and impl const checks and add some explanatory notes

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This commit is contained in:
Oli Scherer 2022-10-04 08:59:20 +00:00
parent 33bcea8f61
commit c72c6e01c8
4 changed files with 34 additions and 45 deletions
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26
compiler/rustc_trait_selection/src/traits/wf.rs
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@ -309,8 +309,30 @@ impl<'tcx> WfPredicates<'tcx> {
self.nominal_obligations_without_const(trait_ref.def_id, trait_ref.substs)
} else {
if !tcx.has_attr(trait_ref.def_id, rustc_span::sym::const_trait) {
tcx.sess
.span_err(self.span, "~const can only be applied to `#[const_trait]` traits");
if let Some(item) = self.item &&
let hir::ItemKind::Impl(impl_) = item.kind &&
let Some(trait_) = &impl_.of_trait &&
let Some(def_id) = trait_.trait_def_id() &&
def_id == trait_ref.def_id
{
let trait_name = tcx.item_name(def_id);
let mut err = tcx.sess.struct_span_err(
self.span,
&format!("const `impl` for trait `{trait_name}` which is not marked with `#[const_trait]`"),
);
if def_id.is_local() {
let sp = tcx.def_span(def_id).shrink_to_lo();
err.span_suggestion(sp, &format!("mark `{trait_name}` as const"), "#[const_trait]", rustc_errors::Applicability::MachineApplicable);
}
err.note("marking a trait with `#[const_trait]` ensures all default method bodies are `const`");
err.note("adding a non-const method body in the future would be a breaking change");
err.emit();
} else {
tcx.sess.span_err(
self.span,
"~const can only be applied to `#[const_trait]` traits",
);
}
}
self.nominal_obligations(trait_ref.def_id, trait_ref.substs)
};