Fix PolymerPass crash (#1950)

Author: MatrixFrog

src/com/google/javascript/jscomp/PolymerPassErrors.java

@@ -58,6 +58,11 @@ final class PolymerPassErrors {
       "JSC_POLYMER_UNANNOTATED_BEHAVIOR",
       "Behavior declarations must be annotated with @polymerBehavior.");
 
+  static final DiagnosticType POLYMER_PROPERTIES_INVALID =
+      DiagnosticType.error(
+          "JSC_POLYMER_PROPERTIES_INVALID",
+          "The Polymer element 'properties' must be an object literal.");
+
   static final DiagnosticType POLYMER_CLASS_PROPERTIES_INVALID =
       DiagnosticType.error(
           "JSC_POLYMER_CLASS_PROPERTIES_INVALID",

src/com/google/javascript/jscomp/PolymerPassStaticUtils.java

@@ -18,6 +18,7 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.javascript.jscomp.PolymerPassErrors.POLYMER_MISPLACED_PROPERTY_JSDOC;
+import static com.google.javascript.jscomp.PolymerPassErrors.POLYMER_PROPERTIES_INVALID;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Ascii;
@@ -265,6 +266,10 @@ static ImmutableList<MemberDefinition> extractProperties(
     Node properties = descriptor;
     if (defType == PolymerClassDefinition.DefinitionType.ObjectLiteral) {
       properties = NodeUtil.getFirstPropMatchingKey(descriptor, "properties");
+      if (properties != null && !properties.isObjectLit()) {
+        compiler.report(JSError.make(properties, POLYMER_PROPERTIES_INVALID));
+        return ImmutableList.of();
+      }
     }
     if (properties == null) {
       return ImmutableList.of();

test/com/google/javascript/jscomp/PolymerPassTest.java

@@ -183,6 +183,22 @@ public void setUp() throws Exception {
     setGenericNameReplacements(ImmutableMap.of("Interface$UID", "Interface$"));
   }
 
+/** Regression test for https://github.com/google/closure-compiler/issues/1950 */
+  @Test
+  public void testPropertiesNotObjLit() {
+    testError(
+        srcs(
+            """
+            Polymer({
+              is: 'x-y',
+              properties: (function() {
+                return {};
+              })(),
+            })
+            """),
+        error(PolymerPassErrors.POLYMER_PROPERTIES_INVALID));
+  }
+
   @Test
   public void testPolymerRewriterGeneratesDeclarationOutsideLoadModule() {
     test(