fix(resolve): skip panic when resolution is dummy

Author: bvanjoi

compiler/rustc_resolve/src/imports.rs

@@ -990,7 +990,10 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                         });
                         let res = binding.res();
                         if let Ok(initial_res) = initial_res {
-                            if res != initial_res && this.ambiguity_errors.is_empty() {
+                            if res != initial_res
+                                && this.ambiguity_errors.is_empty()
+                                && res != Res::Err
+                            {
                                 span_bug!(import.span, "inconsistent resolution for an import");
                             }
                         } else if res != Res::Err

tests/ui/imports/issue-113953.rs

@@ -0,0 +1,6 @@
+// edition: 2021
+use u8 as imported_u8;
+use unresolved as u8;
+//~^ ERROR unresolved import `unresolved`
+
+fn main() {}

tests/ui/imports/issue-113953.stderr

@@ -0,0 +1,9 @@
+error[E0432]: unresolved import `unresolved`
+  --> $DIR/issue-113953.rs:3:5
+   |
+LL | use unresolved as u8;
+   |     ^^^^^^^^^^^^^^^^ no external crate `unresolved`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0432`.