Rollup of 6 pull requests

compiler/rustc_hir_analysis/src/delegation.rs

@@ -14,6 +14,7 @@ use rustc_middle::ty::{
 use rustc_span::{ErrorGuaranteed, Span, kw};
 
 use crate::collect::ItemCtxt;
+use crate::errors::DelegationSelfTypeNotSpecified;
 use crate::hir_ty_lowering::HirTyLowerer;
 
 type RemapTable = FxHashMap<u32, u32>;
@@ -284,6 +285,12 @@ fn get_delegation_self_ty_or_err(tcx: TyCtxt<'_>, delegation_id: LocalDefId) ->
             ctx.lower_ty(tcx.hir_node(id).expect_ty())
         })
         .unwrap_or_else(|| {
+            // It is possible to attempt to get self type when it is used in signature
+            // (i.e., `fn default() -> Self`), so emit error here in addition to possible
+            // `mismatched types` error (see #156388).
+            let err = DelegationSelfTypeNotSpecified { span: tcx.def_span(delegation_id) };
+            tcx.dcx().emit_err(err);
+
             Ty::new_error_with_message(
                 tcx,
                 tcx.def_span(delegation_id),

compiler/rustc_hir_analysis/src/errors.rs

@@ -1670,6 +1670,14 @@ pub(crate) struct UnsupportedDelegation<'a> {
     pub callee_span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag("delegation self type is not specified")]
+#[help("consider explicitly specifying self type: `reuse </* Type */ as Trait>::function`")]
+pub(crate) struct DelegationSelfTypeNotSpecified {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("method should be `async` or return a future, but it is synchronous")]
 pub(crate) struct MethodShouldReturnFuture {