Fix panic on inferring field access on an enum

crates/ra_hir/src/ty.rs

@@ -688,9 +688,13 @@ pub(super) fn type_for_field(db: &impl HirDatabase, def_id: DefId, field: Name)
         Def::Struct(s) => (s.variant_data(db), s.generic_params(db)),
         Def::EnumVariant(ev) => (ev.variant_data(db), ev.parent_enum(db).generic_params(db)),
         // TODO: unions
+        Def::Enum(_) => {
+            // this can happen in (invalid) code, but enums don't have fields themselves
+            return None;
+        }
         _ => panic!(
-            "trying to get type for field in non-struct/variant {:?}",
-            def_id
+            "trying to get type for field {:?} in non-struct/variant {:?}",
+            field, def_id
         ),
     };
     let module = def_id.module(db);

crates/ra_hir/src/ty/tests.rs

@@ -507,6 +507,20 @@ fn test() -> i128 {
     );
 }
 
+#[test]
+fn no_panic_on_field_of_enum() {
+    check_inference(
+        r#"
+enum X {}
+
+fn test(x: X) {
+    x.some_field;
+}
+"#,
+        "no_panic_on_field_of_enum.txt",
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.source_file(file_id);

crates/ra_hir/src/ty/tests/data/no_panic_on_field_of_enum.txt

@@ -0,0 +1,4 @@
+[20; 21) 'x': X
+[26; 47) '{     ...eld; }': ()
+[32; 33) 'x': X
+[32; 44) 'x.some_field': [unknown]