Delay span bug when failing to normalize negative coherence impl subject due to other malformed impls

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -307,7 +307,13 @@ fn negative_impl<'cx, 'tcx>(
             tcx.impl_subject(impl1_def_id),
         ) {
             Ok(s) => s,
-            Err(err) => bug!("failed to fully normalize {:?}: {:?}", impl1_def_id, err),
+            Err(err) => {
+                tcx.sess.delay_span_bug(
+                    tcx.def_span(impl1_def_id),
+                    format!("failed to fully normalize {:?}: {:?}", impl1_def_id, err),
+                );
+                return false;
+            }
         };
 
         // Attempt to prove that impl2 applies, given all of the above.

src/test/ui/coherence/issue-100191-2.rs

@@ -0,0 +1,12 @@
+//~ ERROR overflow evaluating the requirement `T: Trait<_>`
+
+#![feature(specialization, with_negative_coherence)]
+#![allow(incomplete_features)]
+
+pub trait Trait<T> {}
+
+default impl<T, U> Trait<T> for U {}
+
+impl<T> Trait<<T as Iterator>::Item> for T {}
+
+fn main() {}

src/test/ui/coherence/issue-100191-2.stderr

@@ -0,0 +1,14 @@
+error[E0275]: overflow evaluating the requirement `T: Trait<_>`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_100191_2`)
+note: required because of the requirements on the impl of `Trait<_>` for `T`
+  --> $DIR/issue-100191-2.rs:8:20
+   |
+LL | default impl<T, U> Trait<T> for U {}
+   |                    ^^^^^^^^     ^
+   = note: 128 redundant requirements hidden
+   = note: required because of the requirements on the impl of `Trait<_>` for `T`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.

src/test/ui/coherence/issue-100191.rs

@@ -0,0 +1,21 @@
+#![crate_type = "lib"]
+#![feature(specialization, with_negative_coherence)]
+#![allow(incomplete_features)]
+
+trait X {}
+trait Y: X {}
+trait Z {
+    type Assoc: Y;
+}
+struct A<T>(T);
+
+impl<T> Y for T where T: X {}
+impl<T: X> Z for A<T> {
+    type Assoc = T;
+}
+
+// this impl is invalid, but causes an ICE anyway
+impl<T> From<<A<T> as Z>::Assoc> for T {}
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
+
+fn main() {}

src/test/ui/coherence/issue-100191.stderr

@@ -0,0 +1,12 @@
+error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g., `MyStruct<T>`)
+  --> $DIR/issue-100191.rs:18:6
+   |
+LL | impl<T> From<<A<T> as Z>::Assoc> for T {}
+   |      ^ type parameter `T` must be used as the type parameter for some local type
+   |
+   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local
+   = note: only traits defined in the current crate can be implemented for a type parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0210`.