Brian Grinstead [:bgrins] Reporter
	Description • 7 years ago

STR: Run `./mach test accessible/tests/mochitest/states/test_expandable.xul`

I see a log like:

GECKO(12686) | JavaScript error: chrome://browser/content/tabbrowser.js, line 5652: TypeError: gBrowser is null

I think what's happening here is that the TabProgressListener is initialized in the TabBrowser constructur, but gBrowser isn't yet assigned to the instance of the TabBrowser until after the constructor finishes. I can think of two relatively easy fixes:

1) Make the TabBrowser constructor do much less and then instantiate gBrowser in two steps as `gBrowser = new TabBrowser(); gBrowser.init()`
2) Pass `this` (i.e. the TabBrowser) into the TabProgressListener constructor and refer to that on the instance instead of the global gBrowser.

	Dão Gottwald [:dao] Assignee
	Comment 1 • 7 years ago

(In reply to Brian Grinstead [:bgrins] from comment #0)
> 1) Make the TabBrowser constructor do much less and then instantiate
> gBrowser in two steps as `gBrowser = new TabBrowser(); gBrowser.init()`

I'll do this, and use the opportunity to convert TabBrowser to a plain object.

> 2) Pass `this` (i.e. the TabBrowser) into the TabProgressListener
> constructor and refer to that on the instance instead of the global gBrowser.

We did this before but I think it's less preferable, as this problem might bite us again with other consumers. Or it already does, see bug 1442384 and bug 1443318. Not entirely sure if these are exactly the same issue, though. Will re-evaluate once this is fixed.

	Dão Gottwald [:dao] Assignee
	Comment 2 • 7 years ago

https://treeherder.mozilla.org/#/jobs?repo=try&revision=2af84abbdc8f8e9c9f4c53f7e965504e45f4092c

	Brian Grinstead [:bgrins] Reporter
	Comment 4 • 7 years ago
mozreview-review

Comment on attachment 8956385 [details]
Bug 1442398 - Convert the TabBrowser class to a plain object and make gBrowser available already before gBrowser.init returns.

https://reviewboard.mozilla.org/r/225264/#review231468

::: browser/base/content/browser.js:157
(Diff revision 1)
> +    }
> +    delete window.gBrowser;
> +    window.gBrowser = window._gBrowser;
> +    delete window._gBrowser;
> +    gBrowser.init();
> +    return window.gBrowser;

nit: we refer to this as `gBrowser` without window on the line above - we should be consistent and either `return gBrowser` here or do `window.gBrowser.init();` above.

	Pulsebot
	Comment 6 • 7 years ago

Pushed by dgottwald@mozilla.com:
https://hg.mozilla.org/integration/autoland/rev/f27d7eca013d
Convert the TabBrowser class to a plain object and make gBrowser available already before gBrowser.init returns. r=bgrins

	Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)
	Comment 7 • 7 years ago
bugherder

https://hg.mozilla.org/mozilla-central/rev/f27d7eca013d