diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs index 1f7ca48234a24..ade24259ed408 100644 --- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs +++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs @@ -135,18 +135,25 @@ impl TaitConstraintLocator<'_> { return; } - if let Some(hir_sig) = self.tcx.hir_node_by_def_id(item_def_id).fn_decl() { - if hir_sig.output.get_infer_ret_ty().is_some() { - let guar = self.tcx.dcx().span_delayed_bug( - hir_sig.output.span(), - "inferring return types and opaque types do not mix well", - ); - self.found = Some(ty::OpaqueHiddenType { - span: DUMMY_SP, - ty: Ty::new_error(self.tcx, guar), - }); - return; - } + // Function items with `_` in their return type already emit an error, skip any + // "non-defining use" errors for them. + // Note that we use `Node::fn_sig` instead of `Node::fn_decl` here, because the former + // excludes closures, which are allowed to have `_` in their return type. + let hir_node = self.tcx.hir_node_by_def_id(item_def_id); + debug_assert!( + !matches!(hir_node, Node::ForeignItem(..)), + "foreign items cannot constrain opaque types", + ); + if let Some(hir_sig) = hir_node.fn_sig() + && hir_sig.decl.output.get_infer_ret_ty().is_some() + { + let guar = self.tcx.dcx().span_delayed_bug( + hir_sig.decl.output.span(), + "inferring return types and opaque types do not mix well", + ); + self.found = + Some(ty::OpaqueHiddenType { span: DUMMY_SP, ty: Ty::new_error(self.tcx, guar) }); + return; } // Calling `mir_borrowck` can lead to cycle errors through diff --git a/tests/ui/type-alias-impl-trait/closure_infer.rs b/tests/ui/type-alias-impl-trait/closure_infer.rs new file mode 100644 index 0000000000000..04e2323ec4ae9 --- /dev/null +++ b/tests/ui/type-alias-impl-trait/closure_infer.rs @@ -0,0 +1,35 @@ +// check-pass + +// Regression test for an ICE: https://github.com/rust-lang/rust/issues/119916 + +#![feature(impl_trait_in_assoc_type)] +#![feature(type_alias_impl_trait)] + +// `impl_trait_in_assoc_type` example from the bug report. +pub trait StreamConsumer { + type BarrierStream; + fn execute() -> Self::BarrierStream; +} + +pub struct DispatchExecutor; + +impl StreamConsumer for DispatchExecutor { + type BarrierStream = impl Sized; + fn execute() -> Self::BarrierStream { + || -> _ {} + } +} + +// Functions that constrain TAITs can contain closures with an `_` in the return type. +type Foo = impl Sized; +fn foo() -> Foo { + || -> _ {} +} + +// The `_` in the closure return type can also be the TAIT itself. +type Bar = impl Sized; +fn bar() -> impl FnOnce() -> Bar { + || -> _ {} +} + +fn main() {}