Fix NPE for creating error messages around unknown interface ancestors

This fixes a recent unreleased regression. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=246043186
google · May 1, 2019 · 8d7f876 · 8d7f876
1 parent 60f9835
commit 8d7f876
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diff --git a/src/com/google/javascript/rhino/jstype/ObjectType.java b/src/com/google/javascript/rhino/jstype/ObjectType.java
@@ -311,7 +311,9 @@ public final ObjectType getTopDefiningInterface(String propertyName) {
       }
     }
 
-    if (hasOwnProperty(propertyName) || getImplicitPrototype().hasOwnProperty(propertyName)) {
+    ObjectType implicitPrototype = getImplicitPrototype();
+    if (hasOwnProperty(propertyName)
+        || (implicitPrototype != null && implicitPrototype.hasOwnProperty(propertyName))) {
       return this;
     }
 

diff --git a/test/com/google/javascript/jscomp/TypeCheckTest.java b/test/com/google/javascript/jscomp/TypeCheckTest.java
@@ -8380,6 +8380,25 @@ public void testOverriddenPropertyWithUnknown() {
         "property bar already defined on superclass Foo; use @override to override it");
   }
 
+  @Test
+  public void testOverriddenPropertyWithUnknownInterfaceAncestor() {
+    testTypes(
+        lines(
+            "/** @interface @extends {Unknown}  */ function Foo() {}",
+            "/** @type {string} */ Foo.prototype.data;",
+            "/** @constructor @implements {Foo} */ function SubFoo() {}",
+            "/** @type {string|Object} */ ",
+            "SubFoo.prototype.data = null;"),
+        new String[] {
+          "Bad type annotation. Unknown type Unknown",
+          lines(
+              "mismatch of the data property on type SubFoo and the type "
+                  + "of the property it overrides from interface Foo",
+              "original: string",
+              "override: (Object|string)")
+        });
+  }
+
   @Test
   public void testThis2() {
     testTypes("var goog = {};" +