Collect fulfillment errors across impls

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2261,9 +2261,9 @@ fn lookup_inherent_assoc_ty(
 
                     ocx.register_obligations(impl_obligations);
 
-                    let errors = ocx.select_where_possible();
+                    let mut errors = ocx.select_where_possible();
                     if !errors.is_empty() {
-                        fulfillment_errors = errors;
+                        fulfillment_errors.append(&mut errors);
                         return None;
                     }
 

tests/ui/associated-inherent-types/not-found-unsatisfied-bounds-in-multiple-impls.rs

@@ -0,0 +1,20 @@
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+struct S<A, B>(A, B);
+struct Featureless;
+
+trait One {}
+trait Two {}
+
+impl<T: One> S<Featureless, T> {
+    type X = ();
+}
+
+impl<T: Two> S<T, Featureless> {
+    type X = String;
+}
+
+fn main() {
+    let _: S::<Featureless, Featureless>::X; //~ ERROR the associated type `X` exists for `S<Featureless, Featureless>`, but its trait bounds were not satisfied
+}

tests/ui/associated-inherent-types/not-found-unsatisfied-bounds-in-multiple-impls.stderr

@@ -0,0 +1,20 @@
+error: the associated type `X` exists for `S<Featureless, Featureless>`, but its trait bounds were not satisfied
+  --> $DIR/not-found-unsatisfied-bounds-in-multiple-impls.rs:19:43
+   |
+LL | struct S<A, B>(A, B);
+   | -------------- associated item `X` not found for this struct
+LL | struct Featureless;
+   | ------------------
+   | |
+   | doesn't satisfy `Featureless: One`
+   | doesn't satisfy `Featureless: Two`
+...
+LL |     let _: S::<Featureless, Featureless>::X;
+   |                                           ^ associated type cannot be referenced on `S<Featureless, Featureless>` due to unsatisfied trait bounds
+   |
+   = note: the following trait bounds were not satisfied:
+           `Featureless: One`
+           `Featureless: Two`
+
+error: aborting due to previous error
+