bjoernager/rust
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Add a separate error for dyn Trait in const fn

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Previously "trait bounds other than `Sized` on const fn parameters are unstable"
error was used for both trait bounds (<T: Trait>) and trait objects (dyn Trait).
This was pretty confusing.

This patch adds a separeta error for trait objects: "trait objects in const fn
are unstable". The error for trait bounds is otherwise intact.
This commit is contained in:
Waffle 2021-09-16 20:57:12 +03:00
parent 6ec7255d7b
commit f84000d9bc
8 changed files with 62 additions and 23 deletions
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4
compiler/rustc_const_eval/src/transform/check_consts/check.rs
View file

@ -384,11 +384,11 @@ impl Checker<'mir, 'tcx> {
match pred.skip_binder() {
ty::ExistentialPredicate::AutoTrait(_)
| ty::ExistentialPredicate::Projection(_) => {
self.check_op(ops::ty::TraitBound(kind))
self.check_op(ops::ty::DynTrait(kind))
}
ty::ExistentialPredicate::Trait(trait_ref) => {
if Some(trait_ref.def_id) != self.tcx.lang_items().sized_trait() {
self.check_op(ops::ty::TraitBound(kind))
self.check_op(ops::ty::DynTrait(kind))
}
}
}

45
compiler/rustc_const_eval/src/transform/check_consts/ops.rs
View file

@ -599,7 +599,7 @@ pub mod ty {
}
fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
let mut builder = feature_err(
let mut err = feature_err(
&ccx.tcx.sess.parse_sess,
sym::const_fn_trait_bound,
span,
@ -608,12 +608,51 @@ pub mod ty {
match ccx.fn_sig() {
Some(fn_sig) if !fn_sig.span.contains(span) => {
builder.span_label(fn_sig.span, "function declared as const here");
err.span_label(fn_sig.span, "function declared as const here");
}
_ => {}
}
builder
err
}
}
#[derive(Debug)]
pub struct DynTrait(pub mir::LocalKind);
impl NonConstOp for DynTrait {
fn importance(&self) -> DiagnosticImportance {
match self.0 {
mir::LocalKind::Var | mir::LocalKind::Temp => DiagnosticImportance::Secondary,
mir::LocalKind::ReturnPointer | mir::LocalKind::Arg => {
DiagnosticImportance::Primary
}
}
}
fn status_in_item(&self, ccx: &ConstCx<'_, '_>) -> Status {
if ccx.const_kind() != hir::ConstContext::ConstFn {
Status::Allowed
} else {
Status::Unstable(sym::const_fn_trait_bound)
}
}
fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
let mut err = feature_err(
&ccx.tcx.sess.parse_sess,
sym::const_fn_trait_bound,
span,
"trait objects in const fn are unstable",
);
match ccx.fn_sig() {
Some(fn_sig) if !fn_sig.span.contains(span) => {
err.span_label(fn_sig.span, "function declared as const here");
}
_ => {}
}
err
}
}