Bug 157246 – ES6 Function.name inferred from property names of literal objects can break some websites

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Mark Lam]

Specifically, the library mathjs (see http://mathjs.org and https://github.com/josdejong/mathjs) uses an idiom where it created literal objects with property names that look like this: 'number | BigNumber | Unit'.  Later, this name is used in a string to create function source code that gets eval'ed.  Since 'number | BigNumber | Unit' is not a valid function name, we get a syntax error.

The nitty gritty details:

1. mathjs uses object literals with the funky property names for its function members.  For example, 

      // helper function to type check the middle value of the array
      var middle = typed({
        'number | BigNumber | Unit': function (value) {
          return value;
        }
      });

2. mathjs' getName() uses Function.name to get the name of functions (hence, picks up the ES6 behavior):

        /**
         * Retrieve the function name from a set of functions, and check
         * whether the name of all functions match (if given)
         ...
         */
        function getName (fns) {
          var name = '';

          for (var i = 0; i < fns.length; i++) {
            var fn = fns[i];
            ...
                name = fn.name;
            ...
          return name;
        }

3. mathjs uses that name to assembler new function source code that gets eval'ed:

        /**
         * Compose a function from sub-functions each handling a single type signature.
         ...
         */
        function _typed(name, signatures) {
          ...
          // generate code for the typed function
          var code = [];
          var _name = name || '';
          ...
          code.push('function ' + _name + '(' + _args.join(', ') + ') {');
          code.push('  "use strict";');
          code.push('  var name = \'' + _name + '\';');
          code.push(node.toCode(refs, '  '));
          code.push('}');

          // generate body for the factory function
          var body = [
            refs.toCode(),
            'return ' + code.join('\n')
          ].join('\n');

          // evaluate the JavaScript code and attach function references
          var factory = (new Function(refs.name, 'createError', body));  // <========= Syntax Error right here!
          var fn = factory(refs, createError);
          ...
          return fn;
        }

Until mathjs (and any other frameworks that does similar things) and sites that uses mathjs has been updated to work with ES6, we'll need a compatibility hack to work around it.

[Mark Lam]

<rdar://problem/25923995>

[Mark Lam]

Created attachment 278008 [details]
proposed patch.

Still need to run tests.

[Mark Lam]

The mac and mac-wk2 EWS' fast/workers/worker-replace-self.html failure is not due to this patch (pre-existing).

The ios-sim EWS' js/dom/regress-157246.html failure is interesting.  I'll investigate.

[Build Bot]

Comment on attachment 278008 [details]
proposed patch.

Attachment 278008 [details] did not pass ios-sim-ews (ios-simulator-wk2):
Output: http://webkit-queues.webkit.org/results/1261770

New failing tests:
js/dom/regress-157246.html

[Build Bot]

Created attachment 278010 [details]
Archive of layout-test-results from ews122 for ios-simulator-wk2

The attached test failures were seen while running run-webkit-tests on the ios-sim-ews.
Bot: ews122  Port: ios-simulator-wk2  Platform: Mac OS X 10.11.4

[Mark Lam]

Created attachment 278043 [details]
proposed patch: fixed iOS sim EWS sadness

[WebKit Commit Bot]

Attachment 278043 [details] did not pass style-queue:


WARNING: Not running on native Windows.
ERROR: Source/JavaScriptCore/ChangeLog:30:  Need whitespace between colon and description  [changelog/filechangedescriptionwhitespace] [5]
ERROR: Source/JavaScriptCore/ChangeLog:31:  Need whitespace between colon and description  [changelog/filechangedescriptionwhitespace] [5]
ERROR: Source/JavaScriptCore/ChangeLog:48:  Need whitespace between colon and description  [changelog/filechangedescriptionwhitespace] [5]
Total errors found: 3 in 16 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Geoffrey Garen]

Comment on attachment 278043 [details]
proposed patch: fixed iOS sim EWS sadness

r=me

[Mark Lam]

Thanks for the review.  Landed in r200423: <http://trac.webkit.org/r200423>.