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Get rid of subst-relate incompleteness in new solver #113901

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Jul 22, 2023
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Get rid of subst-relate incompleteness in new solver #113901

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21 changes: 12 additions & 9 deletions compiler/rustc_trait_selection/src/solve/alias_relate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,24 +66,27 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
Invert::Yes,
));
// Relate via args
let subst_relate_response = self
.assemble_subst_relate_candidate(param_env, alias_lhs, alias_rhs, direction);
candidates.extend(subst_relate_response);
candidates.extend(
self.assemble_subst_relate_candidate(
param_env, alias_lhs, alias_rhs, direction,
),
);
debug!(?candidates);

if let Some(merged) = self.try_merge_responses(&candidates) {
Ok(merged)
} else {
// When relating two aliases and we have ambiguity, we prefer
// relating the generic arguments of the aliases over normalizing
// them. This is necessary for inference during typeck.
// When relating two aliases and we have ambiguity, if both
// aliases can be normalized to something, we prefer
// "bidirectionally normalizing" both of them within the same
// candidate.
//
// See <https://github.com/rust-lang/trait-system-refactor-initiative/issues/25>.
//
// As this is incomplete, we must not do so during coherence.
match self.solver_mode() {
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this comment is wrong, please also link to rust-lang/trait-system-refactor-initiative#25

SolverMode::Normal => {
if let Ok(subst_relate_response) = subst_relate_response {
Ok(subst_relate_response)
} else if let Ok(bidirectional_normalizes_to_response) = self
if let Ok(bidirectional_normalizes_to_response) = self
.assemble_bidirectional_normalizes_to_candidate(
param_env, lhs, rhs, direction,
)
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