Delay overlap errors if errors are involved

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -22,7 +22,7 @@ use crate::traits::{
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{error_code, DelayDm, Diagnostic};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
+use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
 use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
@@ -350,6 +350,10 @@ fn report_conflicting_impls<'tcx>(
         impl_span: Span,
         err: &mut Diagnostic,
     ) {
+        if (overlap.trait_ref, overlap.self_ty).references_error() {
+            err.downgrade_to_delayed_bug();
+        }
+
         match tcx.span_of_impl(overlap.with_impl) {
             Ok(span) => {
                 err.span_label(span, "first implementation here");

tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs

@@ -6,7 +6,7 @@
 struct S<const L: usize>;
 
 impl<const N: i32> Copy for S<N> {}
+//~^ ERROR the constant `N` is not of type `usize`
 impl<const M: usize> Copy for S<M> {}
-//~^ ERROR conflicting implementations of trait `Copy` for type `S<[const error]>`
 
 fn main() {}

tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr

@@ -1,11 +1,14 @@
-error[E0119]: conflicting implementations of trait `Copy` for type `S<[const error]>`
-  --> $DIR/bad-const-wf-doesnt-specialize.rs:9:1
+error: the constant `N` is not of type `usize`
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:8:29
    |
 LL | impl<const N: i32> Copy for S<N> {}
-   | -------------------------------- first implementation here
-LL | impl<const M: usize> Copy for S<M> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S<[const error]>`
+   |                             ^^^^
+   |
+note: required by a bound in `S`
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:6:10
+   |
+LL | struct S<const L: usize>;
+   |          ^^^^^^^^^^^^^^ required by this bound in `S`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0119`.