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Also use the RPIT back compat hack in trait projection

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This commit is contained in:
Oli Scherer 2022-02-23 13:34:39 +00:00
parent dc35d584a9
commit 360edd611d
4 changed files with 29 additions and 43 deletions
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19
compiler/rustc_trait_selection/src/traits/project.rs
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@ -214,10 +214,21 @@ fn project_and_unify_type<'cx, 'tcx>(
Err(InProgress) => return Ok(Err(InProgress)),
};
debug!(?normalized, ?obligations, "project_and_unify_type result");
match infcx
.at(&obligation.cause, obligation.param_env)
.eq(normalized, obligation.predicate.term)
{
let actual = obligation.predicate.term;
// HACK: lazy TAIT would regress src/test/ui/impl-trait/nested-return-type2.rs, so we add
// a back-compat hack hat converts the RPITs into inference vars, just like they were before
// lazy TAIT.
// This does not affect TAITs in general, as tested in the nested-return-type-tait* tests.
let InferOk { value: actual, obligations: new } =
selcx.infcx().replace_opaque_types_with_inference_vars(
actual,
obligation.cause.body_id,
obligation.cause.span,
obligation.param_env,
);
obligations.extend(new);
match infcx.at(&obligation.cause, obligation.param_env).eq(normalized, actual) {
Ok(InferOk { obligations: inferred_obligations, value: () }) => {
obligations.extend(inferred_obligations);
Ok(Ok(Some(obligations)))