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Highlight conflicting param-env candidates

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This commit is contained in:
Michael Goulet
2022-07-02 01:30:07 +00:00
parent 9b21131278
commit 08135254dc
8 changed files with 114 additions and 19 deletions
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43
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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@@ -6,9 +6,11 @@
//!
//! [rustc dev guide]:https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly
use hir::LangItem;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_infer::traits::TraitEngine;
use rustc_infer::traits::util::elaborate_predicates_with_span;
use rustc_infer::traits::{AmbiguousSelection, TraitEngine};
use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
use rustc_lint_defs::builtin::DEREF_INTO_DYN_SUPERTRAIT;
use rustc_middle::ty::print::with_no_trimmed_paths;
@@ -199,11 +201,48 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// and report ambiguity.
if i > 1 {
debug!("multiple matches, ambig");
// Collect a list of (probable) spans that point to a param-env candidate
let tcx = self.infcx.tcx;
let owner = stack.obligation.cause.body_id.owner.to_def_id();
let predicates = tcx.predicates_of(owner).instantiate_identity(tcx);
let param_env_spans: FxHashMap<_, _> = elaborate_predicates_with_span(
tcx,
std::iter::zip(predicates.predicates, predicates.spans),
)
.filter_map(|obligation| {
let kind = obligation.predicate.kind();
if let ty::PredicateKind::Trait(trait_pred) = kind.skip_binder() {
if trait_pred.trait_ref
== ty::TraitRef::identity(tcx, trait_pred.def_id())
.skip_binder()
{
// HACK: Remap the `Self: Trait` predicate that every trait has to a more useful span
Some((
kind.rebind(trait_pred),
tcx.def_span(trait_pred.def_id()),
))
} else {
Some((kind.rebind(trait_pred), obligation.cause.span))
}
} else {
None
}
})
.collect();
return Err(Ambiguous(
candidates
.into_iter()
.filter_map(|c| match c.candidate {
SelectionCandidate::ImplCandidate(def_id) => Some(def_id),
SelectionCandidate::ImplCandidate(def_id) => {
Some(AmbiguousSelection::Impl(def_id))
}
SelectionCandidate::ParamCandidate(predicate) => {
Some(AmbiguousSelection::ParamEnv(
*param_env_spans.get(&predicate)?,
))
}
_ => None,
})
.collect(),