Bug 1260620 - Ensure that possibleErrors are not null before attempting to check them; r=jorendorff

js/src/frontend/Parser.cpp

@@ -7587,8 +7587,11 @@ Parser<ParseHandler>::expr(InHandling inHandling, YieldHandling yieldHandling,
 
             // We begin by checking for an outer pending error since it would
             // have occurred first.
-            if (possibleError->checkForExprErrors())
-                possibleErrorInner.checkForExprErrors();
+            if (possibleError && !possibleError->checkForExprErrors())
+                return null();
+
+            // Go ahead and report the inner error.
+            possibleErrorInner.checkForExprErrors();
             return null();
         }
         handler.addList(seq, pn);

js/src/tests/ecma_6/Object/destructuring-shorthand-defaults.js

@@ -38,6 +38,7 @@ const SYNTAX_ERROR_STMTS = [
     "delete ({x=1})",
     "delete {x=1} = {}",
     "({x=1}.abc)",
+    "x > (0, {a = b} );",
     // declarations
     "var x = 0 + {a=1} = {}",
     "let o = {x=1};",