[DevTools] Better heuristic for detecting object literals

third_party/WebKit/Source/devtools/front_end/sdk/ConsoleModel.js

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 194 matching lines @@
     {
         if (!result)
             return;
 
         WebInspector.console.showPromise().then(reportUponEvaluation);
         function reportUponEvaluation()
         {
             target.consoleModel.dispatchEventToListeners(WebInspector.ConsoleModel.Events.CommandEvaluated, {result: result, wasThrown: wasThrown, text: text, commandMessage: commandMessage, exceptionDetails: exceptionDetails});
         }
     }
-    if (/^\s*\{/.test(text) && /\}\s*$/.test(text))
-        text = '(' + text + ')';
+
+    /**
+     * @param {string} code
+     * @suppress {uselessCode}
+     * @return {boolean}
+     */
+    function looksLikeAnObjectLiteral(code) {
+        // Only parenthesize what appears to be an object literal.
+        if (!(/^\s*\{/.test(code) && /\}\s*$/.test(code))) {
+            return false;
+        }
+
+        try {
+            // Check if the code can be interpreted as an expression.
+            Function("return " + code + ";");

[kozy, 2016/04/11 19:17:32]

We can't execute user code in frontend. It can produce different problems like
DevTools freeze on expression like { while(true) {} } or ReferencedError if user
execute var a = 42 and then { b: a }.
And we don't to execute code twice it can produce hard detectable issues, e.g.
{ let a = 42; ++window.i; eval("}"); 
This expression will produce SyntaxError with and without parentheses but
window.i will be incremented twice. 

+        }
+        catch (e) {
+            return false;
+        }
+
+        // No syntax error! Does it work parenthesized?
+        try {
+            Function("(" + code + ")");
+            return true;
+        }
+        catch (e) {
+            return false;
+        }
+    }
+    if (looksLikeAnObjectLiteral(text)) {
+        text = "(" + text + ")";
+        WebInspector.console.warn("Evaluating input as an object literal.");
+    }
     executionContext.evaluate(text, "console", !!useCommandLineAPI, false, false, true, printResult);
 
     WebInspector.userMetrics.actionTaken(WebInspector.UserMetrics.Action.ConsoleEvaluated);
 }
 
 WebInspector.ConsoleModel.clearConsole = function()
 {
     var targets = WebInspector.targetManager.targets();
     for (var i = 0; i < targets.length; ++i)
         targets[i].consoleModel.requestClearMessages();
@@ skipping 376 matching lines @@
         this.dispatchEventToListeners(WebInspector.ConsoleModel.Events.CommandEvaluated, event.data);
     },
 
     __proto__: WebInspector.Object.prototype
 }
 
 /**
  * @type {!WebInspector.MultitargetConsoleModel}
  */
 WebInspector.multitargetConsoleModel;