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Fix #90970, doesn't address #87437

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This commit is contained in:
Esteban Kuber 2022-03-26 21:26:02 +00:00
parent 3aac307ca6
commit ac8cbbd200
8 changed files with 115 additions and 6 deletions
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79
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
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@ -2,10 +2,11 @@ pub mod on_unimplemented;
pub mod suggestions;
use super::{
EvaluationResult, FulfillmentContext, FulfillmentError, FulfillmentErrorCode,
MismatchedProjectionTypes, Obligation, ObligationCause, ObligationCauseCode,
OnUnimplementedDirective, OnUnimplementedNote, OutputTypeParameterMismatch, Overflow,
PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
DerivedObligationCause, EvaluationResult, FulfillmentContext, FulfillmentError,
FulfillmentErrorCode, ImplDerivedObligationCause, MismatchedProjectionTypes, Obligation,
ObligationCause, ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote,
OutputTypeParameterMismatch, Overflow, PredicateObligation, SelectionContext, SelectionError,
TraitNotObjectSafe,
};
use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
@ -654,11 +655,77 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
} else if !suggested {
// Can't show anything else useful, try to find similar impls.
let impl_candidates = self.find_similar_impl_candidates(trait_ref);
self.report_similar_impl_candidates(
if !self.report_similar_impl_candidates(
impl_candidates,
trait_ref,
&mut err,
);
) {
// This is *almost* equivalent to
// `obligation.cause.code().peel_derives()`, but it gives us the
// trait predicate for that corresponding root obligation. This
// lets us get a derived obligation from a type parameter, like
// when calling `string.strip_suffix(p)` where `p` is *not* an
// implementer of `Pattern<'_>`.
let mut code = obligation.cause.code();
let mut trait_pred = trait_predicate;
let mut peeled = false;
loop {
match &*code {
ObligationCauseCode::FunctionArgumentObligation {
parent_code,
..
} => {
code = &parent_code;
}
ObligationCauseCode::ImplDerivedObligation(
box ImplDerivedObligationCause {
derived:
DerivedObligationCause {
parent_code,
parent_trait_pred,
},
..
},
)
| ObligationCauseCode::BuiltinDerivedObligation(
DerivedObligationCause {
parent_code,
parent_trait_pred,
},
)
| ObligationCauseCode::DerivedObligation(
DerivedObligationCause {
parent_code,
parent_trait_pred,
},
) => {
peeled = true;
code = &parent_code;
trait_pred = *parent_trait_pred;
}
_ => break,
};
}
let def_id = trait_pred.def_id();
// Mention *all* the `impl`s for the *top most* obligation, the
// user might have meant to use one of them, if any found. We skip
// auto-traits or fundamental traits that might not be exactly what
// the user might expect to be presented with. Instead this is
// useful for less general traits.
if peeled
&& !self.tcx.trait_is_auto(def_id)
&& !self.tcx.lang_items().items().contains(&Some(def_id))
{
let trait_ref = trait_pred.to_poly_trait_ref();
let impl_candidates =
self.find_similar_impl_candidates(trait_ref);
self.report_similar_impl_candidates(
impl_candidates,
trait_ref,
&mut err,
);
}
}
}
// Changing mutability doesn't make a difference to whether we have