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Rollup merge of #148173 - tiif:fix-opaque-ice, r=BoxyUwU
Emit delayed bug during wfck for stranded opaque Fixes rust-lang/trait-system-refactor-initiative#235 ## Problem The fundamental issue here is ``OpaqueTypeCollector`` operates on ``rustc_middle::Ty``, but ``check_type_wf`` operates on HIR. Since [check_type_wf](https://github.com/rust-lang/rust/blob/2f7620a5ccfea7d59d1f500e2a2e59cf1c867a1b/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L2262) operates on HIR, it can see the stranded opaque and tries to infer it's hidden type. But ``OpaqueTypeCollector`` operates on ``rustc_middle::Ty``, so the ``OpaqueTypeCollector`` can no longer see a stranded opaque, hence its hidden type could not be inferred. As a result, the tests ICE'ed at https://github.com/rust-lang/rust/blob/34a8c7368c84fc699fc83a8851a02f93fd655931/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs#L253 ## Proposed solution This PR detects stranded opaque types during wf check and emit a delayed bug for it. ## Alternative solution `@BoxyUwU` and I had considered rewriting ``OpaqueTypeCollector`` to be a HIR visitor instead of a ``rustc_middle::Ty`` visitor, but we believe a HIR-based ``OpaqueTypeCollector`` will not work and might not worth the cost of rewriting. ## Acknowledgement This PR is a joint effort with `@BoxyUwU` :3
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‎compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs‎

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@@ -242,6 +242,16 @@ pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
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owner_def_id: LocalDefId,
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opaque_types_from: DefiningScopeKind,
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) -> Ty<'tcx> {
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// When an opaque type is stranded, its hidden type cannot be inferred
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// so we should not continue.
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if !tcx.opaque_types_defined_by(owner_def_id).contains(&def_id) {
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let opaque_type_span = tcx.def_span(def_id);
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let guar = tcx
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.dcx()
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.span_delayed_bug(opaque_type_span, "cannot infer type for stranded opaque type");
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return Ty::new_error(tcx, guar);
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}
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match opaque_types_from {
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DefiningScopeKind::HirTypeck => {
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let tables = tcx.typeck(owner_def_id);

‎tests/ui/traits/next-solver/opaques/stranded_opaque.rs‎

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//@ compile-flags: -Znext-solver
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#![feature(type_alias_impl_trait)]
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use std::future::Future;
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// Test for https://github.com/rust-lang/trait-system-refactor-initiative/issues/235
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// These are cases where an opaque types become "stranded" due to
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// some errors. Make sure we don't ICE in either case.
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// Case 1: `impl Send` is stranded
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fn foo() -> impl ?Future<Output = impl Send> {
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//~^ ERROR bound modifier `?` can only be applied to `Sized`
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//~| ERROR bound modifier `?` can only be applied to `Sized`
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()
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}
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// Case 2: `Assoc = impl Trait` is stranded
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trait Trait {}
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impl Trait for i32 {}
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fn produce() -> impl Trait<Assoc = impl Trait> {
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//~^ ERROR associated type `Assoc` not found for `Trait`
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//~| ERROR associated type `Assoc` not found for `Trait`
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16
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}
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// Case 3: `impl Trait` is stranded
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fn ill_formed_string() -> String<impl Trait> {
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//~^ ERROR struct takes 0 generic arguments but 1 generic argument was supplied
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String::from("a string")
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}
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// Case 4: TAIT variant of Case 1 to 3
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type Foo = impl ?Future<Output = impl Send>;
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//~^ ERROR unconstrained opaque type
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//~| ERROR unconstrained opaque type
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//~| ERROR bound modifier `?` can only be applied to `Sized`
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//~| ERROR bound modifier `?` can only be applied to `Sized`
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type Produce = impl Trait<Assoc = impl Trait>;
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//~^ ERROR unconstrained opaque type
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//~| ERROR unconstrained opaque type
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//~| ERROR associated type `Assoc` not found for `Trait`
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//~| ERROR associated type `Assoc` not found for `Trait`
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type IllFormedString = String<impl Trait>;
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//~^ ERROR unconstrained opaque type
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//~| ERROR struct takes 0 generic arguments but 1 generic argument was supplied
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fn main() {}

‎tests/ui/traits/next-solver/opaques/stranded_opaque.stderr‎

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error: bound modifier `?` can only be applied to `Sized`
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--> $DIR/stranded_opaque.rs:11:18
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|
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LL | fn foo() -> impl ?Future<Output = impl Send> {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error[E0220]: associated type `Assoc` not found for `Trait`
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--> $DIR/stranded_opaque.rs:21:28
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|
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LL | fn produce() -> impl Trait<Assoc = impl Trait> {
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| ^^^^^ associated type `Assoc` not found
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error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
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--> $DIR/stranded_opaque.rs:28:27
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|
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LL | fn ill_formed_string() -> String<impl Trait> {
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| ^^^^^^------------ help: remove the unnecessary generics
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| |
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| expected 0 generic arguments
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error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
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--> $DIR/stranded_opaque.rs:46:25
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|
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LL | type IllFormedString = String<impl Trait>;
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| ^^^^^^------------ help: remove the unnecessary generics
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| |
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| expected 0 generic arguments
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error: bound modifier `?` can only be applied to `Sized`
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--> $DIR/stranded_opaque.rs:11:18
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|
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LL | fn foo() -> impl ?Future<Output = impl Send> {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error[E0220]: associated type `Assoc` not found for `Trait`
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--> $DIR/stranded_opaque.rs:21:28
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|
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LL | fn produce() -> impl Trait<Assoc = impl Trait> {
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| ^^^^^ associated type `Assoc` not found
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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: unconstrained opaque type
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--> $DIR/stranded_opaque.rs:34:12
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|
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LL | type Foo = impl ?Future<Output = impl Send>;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: `Foo` must be used in combination with a concrete type within the same crate
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error: bound modifier `?` can only be applied to `Sized`
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--> $DIR/stranded_opaque.rs:34:17
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|
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LL | type Foo = impl ?Future<Output = impl Send>;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: bound modifier `?` can only be applied to `Sized`
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--> $DIR/stranded_opaque.rs:34:17
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|
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LL | type Foo = impl ?Future<Output = impl Send>;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: unconstrained opaque type
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--> $DIR/stranded_opaque.rs:34:34
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|
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LL | type Foo = impl ?Future<Output = impl Send>;
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| ^^^^^^^^^
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|
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= note: `Foo` must be used in combination with a concrete type within the same crate
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error: unconstrained opaque type
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--> $DIR/stranded_opaque.rs:40:17
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|
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LL | type Produce = impl Trait<Assoc = impl Trait>;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: `Produce` must be used in combination with a concrete type within the same crate
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error[E0220]: associated type `Assoc` not found for `Trait`
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--> $DIR/stranded_opaque.rs:40:28
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|
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LL | type Produce = impl Trait<Assoc = impl Trait>;
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| ^^^^^ associated type `Assoc` not found
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error[E0220]: associated type `Assoc` not found for `Trait`
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--> $DIR/stranded_opaque.rs:40:28
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|
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LL | type Produce = impl Trait<Assoc = impl Trait>;
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| ^^^^^ associated type `Assoc` not found
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|
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= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
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error: unconstrained opaque type
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--> $DIR/stranded_opaque.rs:40:36
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|
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LL | type Produce = impl Trait<Assoc = impl Trait>;
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| ^^^^^^^^^^
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|
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= note: `Produce` must be used in combination with a concrete type within the same crate
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error: unconstrained opaque type
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--> $DIR/stranded_opaque.rs:46:32
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|
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LL | type IllFormedString = String<impl Trait>;
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| ^^^^^^^^^^
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|
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= note: `IllFormedString` must be used in combination with a concrete type within the same crate
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error: aborting due to 15 previous errors
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Some errors have detailed explanations: E0107, E0220.
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For more information about an error, try `rustc --explain E0107`.

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