[Bug 428706] Backing out to investigate startup failures

js/src/jsobj.c

@@ -1976,7 +1976,7 @@ js_PutBlockObject(JSContext *cx, JSBool normalUnwind)
             if (!(sprop->flags & SPROP_HAS_SHORTID))
                 continue;
             if (sprop->id == ATOM_TO_JSID(cx->runtime->atomState.emptyAtom)) {
-                /* See comments in CheckDestructuring from jsparse.c. */
+                /* See comments before EnsureNonEmptyLet from jsparse.c. */
                 JS_ASSERT(sprop->shortid == 0);
                 continue;
             }

js/src/jsparse.c

@@ -1658,6 +1658,37 @@ BindLet(JSContext *cx, BindData *data, JSAtom *atom, JSTreeContext *tc)
                                    NULL);
 }
 
+#if JS_HAS_DESTRUCTURING
+/*
+ * The catch/finally handler implementation in the interpreter assumes that
+ * any operation that introduces a new scope (like a "let" or "with" block)
+ * increases the stack depth. This way, it is possible to restore the scope
+ * chain based on stack depth of the handler alone. A let block with an empty
+ * destructuring pattern like in
+ *
+ *   let [] = 1;
+ *
+ * would violate this assumption as the there would be no let locals to store
+ * on the stack. To satisfy it we add an empty property to such blocks so
+ * OBJ_BLOCK_COUNT(cx, blockObj), that gives the number of slots, would be
+ * always positive.
+ */
+static JSBool
+EnsureNonEmptyLet(JSContext *cx, JSTreeContext *tc)
+{
+    jsid id;
+
+    if (OBJ_BLOCK_COUNT(cx, tc->blockChain) != 0)
+        return JS_TRUE;
+
+    id = ATOM_TO_JSID(cx->runtime->atomState.emptyAtom);
+    return js_DefineNativeProperty(cx, tc->blockChain, id,
+                                   JSVAL_VOID, NULL, NULL,
+                                   JSPROP_PERMANENT | JSPROP_READONLY,
+                                   SPROP_HAS_SHORTID, 0, NULL);
+}
+#endif
+
 static JSBool
 BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, JSTreeContext *tc)
 {
@@ -2027,6 +2058,7 @@ CheckDestructuring(JSContext *cx, BindData *data,
         return JS_FALSE;
     }
 
+    ok = JS_TRUE;
     fpvd.table.ops = NULL;
     lhs = left->pn_head;
     if (lhs && lhs->pn_type == TOK_DEFSHARP) {
@@ -2113,43 +2145,12 @@ CheckDestructuring(JSContext *cx, BindData *data,
         }
     }
 
-    /*
-     * The catch/finally handler implementation in the interpreter assumes
-     * that any operation that introduces a new scope (like a "let" or "with"
-     * block) increases the stack depth. This way, it is possible to restore
-     * the scope chain based on stack depth of the handler alone. "let" with
-     * an empty destructuring pattern like in
-     *
-     *   let [] = 1;
-     *
-     * would violate this assumption as the there would be no let locals to
-     * store on the stack. To satisfy it we add an empty property to such
-     * blocks so that OBJ_BLOCK_COUNT(cx, blockObj), which gives the number of
-     * slots, would be always positive.
-     *
-     * Note that we add such a property even if the block has locals due to
-     * later let declarations in it. We optimize for code simplicity here,
-     * not the fastest runtime performance with empty [] or {}.
-     */
-    if (data->binder == BindLet && OBJ_BLOCK_COUNT(cx, tc->blockChain) == 0) {
-        ok = js_DefineNativeProperty(cx, tc->blockChain,
-                                     ATOM_TO_JSID(cx->runtime->
-                                                  atomState.emptyAtom),
-                                     JSVAL_VOID, NULL, NULL,
-                                     JSPROP_PERMANENT | JSPROP_READONLY,
-                                     SPROP_HAS_SHORTID, 0, NULL);
-        if (!ok)
-            goto out;
-    }
-
-    ok = JS_TRUE;
-
-  out:
+out:
     if (fpvd.table.ops)
         JS_DHashTableFinish(&fpvd.table);
     return ok;
 
-  no_var_name:
+no_var_name:
     js_ReportCompileErrorNumber(cx, TS(tc->parseContext), pn, JSREPORT_ERROR,
                                 JSMSG_NO_VARIABLE_NAME);
     ok = JS_FALSE;
@@ -3001,7 +3002,7 @@ Statement(JSContext *cx, JSTokenStream *ts, JSTreeContext *tc)
                   case TOK_LB:
                   case TOK_LC:
                     pn3 = DestructuringExpr(cx, &data, tc, tt);
-                    if (!pn3)
+                    if (!pn3 || !EnsureNonEmptyLet(cx, tc))
                         return NULL;
                     break;
 #endif
@@ -3618,6 +3619,10 @@ Variables(JSContext *cx, JSTokenStream *ts, JSTreeContext *tc)
                 tc->flags |= TCF_FUN_HEAVYWEIGHT;
         }
     } while (js_MatchToken(cx, ts, TOK_COMMA));
+#if JS_HAS_DESTRUCTURING
+    if (let && !EnsureNonEmptyLet(cx, tc))
+        return NULL;
+#endif
 
     pn->pn_pos.end = PN_LAST(pn)->pn_pos.end;
     return pn;