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normalizes-to rework rigid alias handling

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This commit is contained in:
lcnr
2025-02-11 10:37:04 +01:00
committed by Michael Goulet
parent c241e14650
commit de273e459e
7 changed files with 77 additions and 99 deletions
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31
compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
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@@ -797,11 +797,12 @@ where
/// treat the alias as rigid.
///
/// See trait-system-refactor-initiative#124 for more details.
#[instrument(level = "debug", skip(self), ret)]
#[instrument(level = "debug", skip(self, inject_normalize_to_rigid_candidate), ret)]
pub(super) fn merge_candidates(
&mut self,
proven_via: Option<TraitGoalProvenVia>,
candidates: Vec<Candidate<I>>,
inject_normalize_to_rigid_candidate: impl FnOnce(&mut EvalCtxt<'_, D>) -> QueryResult<I>,
) -> QueryResult<I> {
let Some(proven_via) = proven_via else {
// We don't care about overflow. If proving the trait goal overflowed, then
@@ -818,13 +819,27 @@ where
// FIXME(const_trait_impl): should this behavior also be used by
// constness checking. Doing so is *at least theoretically* breaking,
// see github.com/rust-lang/rust/issues/133044#issuecomment-2500709754
TraitGoalProvenVia::ParamEnv | TraitGoalProvenVia::AliasBound => candidates
.iter()
.filter(|c| {
matches!(c.source, CandidateSource::AliasBound | CandidateSource::ParamEnv(_))
})
.map(|c| c.result)
.collect(),
TraitGoalProvenVia::ParamEnv | TraitGoalProvenVia::AliasBound => {
let mut candidates_from_env: Vec<_> = candidates
.iter()
.filter(|c| {
matches!(
c.source,
CandidateSource::AliasBound | CandidateSource::ParamEnv(_)
)
})
.map(|c| c.result)
.collect();
// If the trait goal has been proven by using the environment, we want to treat
// aliases as rigid if there are no applicable projection bounds in the environment.
if candidates_from_env.is_empty() {
if let Ok(response) = inject_normalize_to_rigid_candidate(self) {
candidates_from_env.push(response);
}
}
candidates_from_env
}
TraitGoalProvenVia::Misc => candidates.iter().map(|c| c.result).collect(),
};