repl: Prevent REPL crash when tab-completed with Proxy objects

[thefourtheye]

If the proxy objects don't have a valid hasOwnPropertyNames trap,
REPL crashes with a TypeError, as per the bug report
#2119

> var proxy = Proxy.create({ fix: function() { return {}; } });
undefined
> proxy.<tab>
TypeError: Proxy handler #<Object> has no 'getOwnPropertyNames' trap
    at Function.getOwnPropertyNames (native)
    at repl.js:644:40
    at REPLServer.defaultEval (repl.js:169:5)
    at bound (domain.js:254:14)
    at REPLServer.runBound [as eval] (domain.js:267:12)
    at REPLServer.complete (repl.js:639:14)
    at REPLServer.complete [as completer] (repl.js:207:10)
    at REPLServer.Interface._tabComplete (readline.js:377:8)
    at REPLServer.Interface._ttyWrite (readline.js:845:14)
    at ReadStream.onkeypress (readline.js:105:10)

This patch traps the error thrown and issues Error message.

[thefourtheye]

I don't know how to write a test for this, as we need to

1. enable --harmony-proxies
2. do tab complete

I am not sure how to do both of them in the same test.

[evanlucas]

To force the flags, take a look at https://github.com/nodejs/io.js/blob/master/test/sequential/test-debug-args.js#L2

[rlidwka]

Can something else except proxy objects cause TypeError? That error check seems a bit too broad.

Also, I'm not sure adding an error message is useful. Maybe just silencing that particular error would be better.

[thefourtheye]

@evanlucas I tried that now and it doesn't work. This is the patch which I tried,

diff --git a/test/parallel/test-repl-tab-complete.js b/test/parallel/test-repl-tab-complete.js
index 1bf0c70..c560a3f 100644
--- a/test/parallel/test-repl-tab-complete.js
+++ b/test/parallel/test-repl-tab-complete.js
@@ -1,4 +1,6 @@
 'use strict';
+// Flags: --harmony-proxies
+
 var common = require('../common');
 var assert = require('assert');
 var util = require('util');
@@ -242,3 +244,14 @@ testMe.complete('cus', function(error, data) {
   completionCount++;
   assert.deepEqual(data, [['custom'], 'cus']);
 });
+
+// Make sure tab completion doesn't crash REPL with proxy objects
+putIn.run(['.clear']);
+
+putIn.run([
+  'var proxy = Proxy.create({});'
+]);
+
+testMe.complete('proxy.', function(error, data) {
+  console.error(arguments);
+});

It still throws a ReferenceError for Proxy. Is there anything else I need to include?

@rlidwka We can tighten the error checking, but silencing it will not give a hint to the user. Will that be okay?

[evanlucas]

Did you still get the ReferenceError running it with python tools/test.py?

[thefourtheye]

@evanlucas Awesome, it works :-) Thanks for the help. I removed the error check as suggested by @rlidwka now.

[cjihrig]

Please use either the referenceErrors or completionCount variable here (see the rest of the test). This test is known to fail silently.

[thefourtheye]

@cjihrig Oh, why not common.mustCall then? That should work here, right? I think that would make the tests better, without explicitly counting.

[cjihrig]

That should work for the tests using completionCount.

[thefourtheye]

@cjihrig Can you PTAL at #2122? I PRed that idea.

[cjihrig]

This can no longer be merged.

[cjihrig]

Not a huge fan of just dropping errors, but it's also just REPL tab completion. LGTM

[thefourtheye]

@cjihrig Thanks for reviewing and notifying about the merge conflict :-)

I rebased and squashed the commits.

@rlidwka @evanlucas PTAL :-)

[evanlucas]

CI: https://jenkins-iojs.nodesource.com/job/iojs+any-pr+multi/139/

LGTM if CI is happy

[evanlucas]

Landed in 59f6b5d with a slightly modified commit message to conform to the collaborator guidelines. Thanks @thefourtheye!