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Auto merge of #86866 - nikomatsakis:issue-84841, r=oli-obk

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Hack: Ignore inference variables in certain queries

Fixes #84841
Fixes #86753

Some queries are not built to accept types with inference variables, which can lead to ICEs. These queries probably ought to be converted to canonical form, but as a quick workaround, we can return conservative results in the case that inference variables are found.

We should file a follow-up issue (and update the FIXMEs...) to do the proper refactoring.

cc `@arora-aman`

r? `@oli-obk`
This commit is contained in:
bors 2021-07-04 17:39:37 +00:00
commit 23c652dfe3
13 changed files with 168 additions and 58 deletions
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4
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View file

@ -2396,7 +2396,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
normalized_ty,
);
debug!("suggest_await_before_try: try_trait_obligation {:?}", try_obligation);
if self.predicate_may_hold(&try_obligation) && impls_future {
if self.predicate_may_hold(&try_obligation)
&& impls_future.must_apply_modulo_regions()
{
if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
if snippet.ends_with('?') {
err.span_suggestion_verbose(

16
compiler/rustc_trait_selection/src/traits/mod.rs
View file

@ -542,8 +542,7 @@ fn vtable_trait_first_method_offset<'tcx>(
}
/// Check whether a `ty` implements given trait(trait_def_id).
///
/// NOTE: Always return `false` for a type which needs inference.
/// See query definition for details.
fn type_implements_trait<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
@ -552,7 +551,7 @@ fn type_implements_trait<'tcx>(
SubstsRef<'tcx>,
ParamEnv<'tcx>,
),
) -> bool {
) -> EvaluationResult {
let (trait_def_id, ty, params, param_env) = key;
debug!(
@ -562,13 +561,22 @@ fn type_implements_trait<'tcx>(
let trait_ref = ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(ty, params) };
// FIXME(#86868): If there are inference variables anywhere, just give up and assume
// we don't know the answer. This works around the ICEs that would result from
// using those inference variables within the `infer_ctxt` we create below.
// Really we should be using canonicalized variables, or perhaps removing
// this query altogether.
if (trait_ref, param_env).needs_infer() {
return EvaluationResult::EvaluatedToUnknown;
}
let obligation = Obligation {
cause: ObligationCause::dummy(),
param_env,
recursion_depth: 0,
predicate: trait_ref.without_const().to_predicate(tcx),
};
tcx.infer_ctxt().enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation))
tcx.infer_ctxt().enter(|infcx| infcx.evaluate_obligation_no_overflow(&obligation))
}
pub fn provide(providers: &mut ty::query::Providers) {