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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_passes/src/check_const.rs
View file

@ -191,32 +191,6 @@ impl<'tcx> Visitor<'tcx> for CheckConstVisitor<'tcx> {
self.tcx.hir()
}
fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
let tcx = self.tcx;
if let hir::ItemKind::Impl(hir::Impl {
constness: hir::Constness::Const,
of_trait: Some(trait_ref),
..
}) = item.kind
&& let Some(def_id) = trait_ref.trait_def_id()
{
let source_map = tcx.sess.source_map();
if !tcx.has_attr(def_id, sym::const_trait) {
tcx.sess
.struct_span_err(
source_map.guess_head_span(item.span),
"const `impl`s must be for traits marked with `#[const_trait]`",
)
.span_note(
source_map.guess_head_span(tcx.def_span(def_id)),
"this trait must be annotated with `#[const_trait]`",
)
.emit();
}
}
intravisit::walk_item(self, item);
}
fn visit_anon_const(&mut self, anon: &'tcx hir::AnonConst) {
let kind = Some(hir::ConstContext::Const);
self.recurse_into(kind, None, |this| intravisit::walk_anon_const(this, anon));

26
compiler/rustc_trait_selection/src/traits/wf.rs
View file

@ -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)
};

5
src/test/ui/rfc-2632-const-trait-impl/const-impl-requires-const-trait.rs
View file

@ -1,10 +1,9 @@
#![feature(const_trait_impl)]
pub trait A {}
//~^ NOTE: this trait must be annotated with `#[const_trait]`
//~^ HELP: mark `A` as const
impl const A for () {}
//~^ ERROR: const `impl`s must be for traits marked with `#[const_trait]`
//~| ERROR: ~const can only be applied to `#[const_trait]` traits
//~^ ERROR: const `impl` for trait `A` which is not marked with `#[const_trait]`
fn main() {}

22
src/test/ui/rfc-2632-const-trait-impl/const-impl-requires-const-trait.stderr
View file

@ -1,20 +1,14 @@
error: const `impl`s must be for traits marked with `#[const_trait]`
--> $DIR/const-impl-requires-const-trait.rs:6:1
|
LL | impl const A for () {}
| ^^^^^^^^^^^^^^^^^^^
|
note: this trait must be annotated with `#[const_trait]`
--> $DIR/const-impl-requires-const-trait.rs:3:1
|
LL | pub trait A {}
| ^^^^^^^^^^^
error: ~const can only be applied to `#[const_trait]` traits
error: const `impl` for trait `A` which is not marked with `#[const_trait]`
--> $DIR/const-impl-requires-const-trait.rs:6:12
|
LL | pub trait A {}
| - help: mark `A` as const: `#[const_trait]`
...
LL | impl const A for () {}
| ^
|
= note: marking a trait with `#[const_trait]` ensures all default method bodies are `const`
= note: adding a non-const method body in the future would be a breaking change
error: aborting due to 2 previous errors
error: aborting due to previous error