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Auto merge of #96808 - cjgillot:impossible-trait, r=compiler-errors

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Detect trait fulfillment in `subst_and_check_impossible_predicates`

Split from https://github.com/rust-lang/rust/pull/91743
r? `@compiler-errors`
This commit is contained in:
bors 2022-05-10 05:27:54 +00:00
commit 2226f19f70
1 changed files with 14 additions and 0 deletions
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14
compiler/rustc_trait_selection/src/traits/mod.rs
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@ -432,6 +432,9 @@ pub fn impossible_predicates<'tcx>(
debug!("impossible_predicates(predicates={:?})", predicates);
let result = tcx.infer_ctxt().enter(|infcx| {
// HACK: Set tainted by errors to gracefully exit in case of overflow.
infcx.set_tainted_by_errors();
let param_env = ty::ParamEnv::reveal_all();
let mut selcx = SelectionContext::new(&infcx);
let mut fulfill_cx = FulfillmentContext::new();
@ -448,6 +451,9 @@ pub fn impossible_predicates<'tcx>(
let errors = fulfill_cx.select_all_or_error(&infcx);
// Clean up after ourselves
let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
!errors.is_empty()
});
debug!("impossible_predicates = {:?}", result);
@ -461,6 +467,14 @@ fn subst_and_check_impossible_predicates<'tcx>(
debug!("subst_and_check_impossible_predicates(key={:?})", key);
let mut predicates = tcx.predicates_of(key.0).instantiate(tcx, key.1).predicates;
// Specifically check trait fulfillment to avoid an error when trying to resolve
// associated items.
if let Some(trait_def_id) = tcx.trait_of_item(key.0) {
let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1);
predicates.push(ty::Binder::dummy(trait_ref).to_poly_trait_predicate().to_predicate(tcx));
}
predicates.retain(|predicate| !predicate.needs_subst());
let result = impossible_predicates(tcx, predicates);