Fix crash when arguments[] occurs within getter/setter

Author: CamWass

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

@@ -149,6 +149,15 @@ public void visit(NodeTraversal traversal, Node node, Node parent) {
    * @param scope scope of the function
    */
   private void tryReplaceArguments(Node scopeRoot) {
+    Node scopeRootParent = scopeRoot.getParent();
+    // Nothing to do for getters and setters:
+    // - Getters cannot have any params.
+    // - Setters can only have one param, and it is required to be present, so we cannot synthesize
+    //   any new params.
+    if (scopeRootParent.isGetterDef() || scopeRootParent.isSetterDef()) {
+      return;
+    }
+
     // Find the number of parameters that can be accessed without using `arguments`.
     Node parametersList = NodeUtil.getFunctionParameters(scopeRoot);
     checkState(parametersList.isParamList(), parametersList);

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

@@ -352,4 +352,18 @@ public void testGlobalArgumentsReferences() {
             "  console.log(arguments);",
             "}"));
   }
+
+  @Test
+  public void testGettersCannotHaveAnyParams() {
+    // Getters cannot have any parameters; synthesizing one would be an error.
+    testSame("class Foo { get prop() { arguments[0] } }");
+    testSame("const a = { get prop() { arguments[0] } }");
+  }
+
+  @Test
+  public void testSettersCanOnlyHaveOneParam() {
+    // Setters can only have one parameter; synthesizing any more would be an error.
+    testSame("class Foo { set prop(x) { arguments[1] } }");
+    testSame("const a = { set prop(x) { arguments[1] } }");
+  }
 }