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

Remove a back-compat hack on lazy TAIT

This PR's motivation is here: rust-lang#72614 (comment)
~~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 authored Jun 28, 2022
2 parents 64eb9ab + c24f063 commit c703d11
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Showing 4 changed files with 28 additions and 31 deletions.
14 changes: 6 additions & 8 deletions compiler/rustc_infer/src/infer/opaque_types.rs
Original file line number Diff line number Diff line change
Expand Up @@ -39,21 +39,19 @@ pub struct OpaqueTypeDecl<'tcx> {
}

impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
/// This is a backwards compatibility hack to prevent breaking changes from
/// lazy TAIT around RPIT handling.
pub fn replace_opaque_types_with_inference_vars<T: TypeFoldable<'tcx>>(
pub fn replace_opaque_types_with_inference_vars(
&self,
value: T,
ty: Ty<'tcx>,
body_id: HirId,
span: Span,
code: ObligationCauseCode<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> InferOk<'tcx, T> {
if !value.has_opaque_types() {
return InferOk { value, obligations: vec![] };
) -> InferOk<'tcx, Ty<'tcx>> {
if !ty.has_opaque_types() {
return InferOk { value: ty, obligations: vec![] };
}
let mut obligations = vec![];
let value = value.fold_with(&mut ty::fold::BottomUpFolder {
let value = ty.fold_with(&mut ty::fold::BottomUpFolder {
tcx: self.tcx,
lt_op: |lt| lt,
ct_op: |ct| ct,
Expand Down
21 changes: 4 additions & 17 deletions compiler/rustc_trait_selection/src/traits/project.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down
8 changes: 2 additions & 6 deletions src/test/ui/impl-trait/nested-return-type2.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
// check-pass

trait Duh {}

impl Duh for i32 {}
Expand All @@ -20,11 +18,9 @@ impl<R: Duh, F: FnMut() -> R> Trait for F {
// the hidden type. We already have obligations registered on the inference
// var to make it uphold the `: Duh` bound on `Trait::Assoc`. The opaque
// type does not implement `Duh`, even if its hidden type does.
// Lazy TAIT would error out, but we inserted a hack to make it work again,
// keeping backwards compatibility.
fn foo() -> impl Trait<Assoc = impl Send> {
//~^ ERROR `impl Send: Duh` is not satisfied
|| 42
}

fn main() {
}
fn main() {}
16 changes: 16 additions & 0 deletions src/test/ui/impl-trait/nested-return-type2.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
error[E0277]: the trait bound `impl Send: Duh` is not satisfied
--> $DIR/nested-return-type2.rs:21:13
|
LL | fn foo() -> impl Trait<Assoc = impl Send> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Duh` is not implemented for `impl Send`
|
= help: the trait `Duh` is implemented for `i32`
note: required because of the requirements on the impl of `Trait` for `[closure@$DIR/nested-return-type2.rs:23:5: 23:10]`
--> $DIR/nested-return-type2.rs:12:31
|
LL | impl<R: Duh, F: FnMut() -> R> Trait for F {
| ^^^^^ ^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.

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