UnnecessaryQualifier: don't fire on interfaces, in deference to Dagger.

I don't think this is ironclad (abstract classes too, perhaps?) but this is probably good enough to avoid obvious Dagger-related false positives.

PiperOrigin-RevId: 782968953

Author: graememorgan

core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryQualifier.java

@@ -64,6 +64,12 @@ public Description matchMethod(MethodTree tree, VisitorState state) {
     }
 
     var enclosingClass = state.findEnclosing(ClassTree.class);
+    if (getSymbol(enclosingClass).isInterface()) {
+      // This is a sad admission of failure, and also not foolproof. Dagger dependencies can be
+      // declared in interfaces with no annotations to let us tell, or components can have
+      // innocent-looking supertypes.
+      return NO_MATCH;
+    }
     if (CLASS_ANNOTATIONS_EXEMPTING_METHODS.stream()
         .anyMatch(anno -> hasAnnotation(enclosingClass, anno, state))) {
       return NO_MATCH;

core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryQualifierTest.java

@@ -210,4 +210,18 @@ interface Test {
             """)
         .doTest();
   }
+
+  @Test
+  public void interface_noFinding() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            """
+            interface Test {
+              @Qual
+              Object frobnicator();
+            }
+            """)
+        .doTest();
+  }
 }