bjoernager/rust
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better errors when a Copy impl is not coherent

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This commit is contained in:
Michael Goulet 2022-02-21 21:26:37 -08:00
parent a4a5e79814
commit c8cbd3d03c
5 changed files with 100 additions and 4 deletions
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4
compiler/rustc_trait_selection/src/traits/misc.rs
View file

@ -11,7 +11,7 @@ use crate::traits::error_reporting::InferCtxtExt;
#[derive(Clone)]
pub enum CopyImplementationError<'tcx> {
InfrigingFields(Vec<&'tcx ty::FieldDef>),
InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>)>),
NotAnAdt,
HasDestructor,
}
@ -67,7 +67,7 @@ pub fn can_type_implement_copy<'tcx>(
match traits::fully_normalize(&infcx, ctx, cause, param_env, ty) {
Ok(ty) => {
if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
infringing.push(field);
infringing.push((field, ty));
}
}
Err(errors) => {

36
compiler/rustc_typeck/src/coherence/builtin.rs
View file

@ -91,8 +91,40 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
E0204,
"the trait `Copy` may not be implemented for this type"
);
for span in fields.iter().map(|f| tcx.def_span(f.did)) {
err.span_label(span, "this field does not implement `Copy`");
for (field, ty) in fields {
let field_span = tcx.def_span(field.did);
err.span_label(field_span, "this field does not implement `Copy`");
// Spin up a new FulfillmentContext, so we can get the _precise_ reason
// why this field does not implement Copy. This is useful because sometimes
// it is not immediately clear why Copy is not implemented for a field, since
// all we point at is the field itself.
tcx.infer_ctxt().enter(|infcx| {
let mut fulfill_cx = traits::FulfillmentContext::new_ignoring_regions();
fulfill_cx.register_bound(
&infcx,
param_env,
ty,
tcx.lang_items().copy_trait().unwrap(),
traits::ObligationCause::dummy_with_span(field_span),
);
for error in fulfill_cx.select_all_or_error(&infcx) {
let error_predicate = error.obligation.predicate;
// Only note if it's not the root obligation, otherwise it's trivial and
// should be self-explanatory (i.e. a field literally doesn't implement Copy).
// FIXME: This error could be more descriptive, especially if the error_predicate
// contains a foreign type or if it's a deeply nested type...
if error_predicate != error.root_obligation.predicate {
err.span_note(
error.obligation.cause.span,
&format!(
"the `Copy` impl for `{}` requires that `{}`",
ty, error_predicate
),
);
}
}
});
}
err.emit();
}