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Rollup merge of #97346 - JohnTitor:remove-back-compat-hacks, r=oli-obk

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Remove a back-compat hack on lazy TAIT

This PR's motivation is here: https://github.com/rust-lang/rust/issues/72614#issuecomment-1134595446
~~But removing a hack doesn't seem to reject the code on the issue, there're some more hacks?~~
r? ``@oli-obk``
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Dylan DPC 2022-06-28 15:30:00 +05:30 • committed by GitHub
commit c703d11dcc
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4 changed files with 28 additions and 31 deletions
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21
compiler/rustc_trait_selection/src/traits/project.rs
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@ -28,7 +28,6 @@ use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::resolve::OpportunisticRegionResolver;
use rustc_infer::traits::ObligationCauseCode;
use rustc_middle::traits::select::OverflowError;
use rustc_middle::ty::fold::{MaxUniverse, TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::subst::Subst;
@ -252,22 +251,10 @@ fn project_and_unify_type<'cx, 'tcx>(
Err(InProgress) => return ProjectAndUnifyResult::Recursive,
};
debug!(?normalized, ?obligations, "project_and_unify_type result");
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,
ObligationCauseCode::MiscObligation,
obligation.param_env,
);
obligations.extend(new);
match infcx.at(&obligation.cause, obligation.param_env).eq(normalized, actual) {
match infcx
.at(&obligation.cause, obligation.param_env)
.eq(normalized, obligation.predicate.term)
{
Ok(InferOk { obligations: inferred_obligations, value: () }) => {
obligations.extend(inferred_obligations);
ProjectAndUnifyResult::Holds(obligations)