nsAutoConfig

[Nicholas Nethercote]

Hi,

I was just looking at the extensions/pref/autoconfig/ directory and trying
to understand what it does.

As far as I can tell, the code is there to allow custom deployments with
particular prefs set, as described at
https://developer.mozilla.org/en-US/Firefox/Enterprise_deployment#Configuration

It's initialized by modules/libpref/Preferences.cpp if a
"general.config.filename" pref is found:
http://searchfox.org/mozilla-central/rev/1ebd2eff44617df3b82eea7d2f3ca1b60cc591a0/modules/libpref/Preferences.cpp#3907-3920

There is also some MozHarness code relating to it here:
http://searchfox.org/mozilla-central/source/testing/mozharness/mozharness/mozilla/firefox/autoconfig.py

Just to check: is this still supported functionality?

Thanks.

Nick

[Marco Castelluccio]

It is not covered by any automated test:
https://codecov.io/gh/marco-c/gecko-dev/src/9ca76dcb7a5c61d33750e9718c02b11ba35c1032/extensions/pref/autoconfig/src/nsAutoConfig.cpp
(this doesn't mean it isn't actually used ever, but it can be a clue).

- Marco.

[Masatoshi Kimura]

On 2017/10/31 19:22, Marco Castelluccio wrote:
> It is not covered by any automated test:
> https://codecov.io/gh/marco-c/gecko-dev/src/9ca76dcb7a5c61d33750e9718c02b11ba35c1032/extensions/pref/autoconfig/src/nsAutoConfig.cpp
> (this doesn't mean it isn't actually used ever, but it can be a clue).

Actually I wrote an automated test, although it is difficult for
coverage tools to find the usage:
https://bugzilla.mozilla.org/show_bug.cgi?id=1267567

[Marco Castelluccio]

Are you sure the test you wrote is testing nsAutoConfig and not
nsReadConfig?

nsReadConfig does not instantiate nsAutoConfig unless
autoadmin.global_config_url exists and is not emtpy:

https://codecov.io/gh/marco-c/gecko-dev/src/9ca76dcb7a5c61d33750e9718c02b11ba35c1032/extensions/pref/autoconfig/src/nsReadConfig.cpp#L205

https://dxr.mozilla.org/mozilla-central/rev/1c618b1a13662de7cec429f606367db3827b6dc7/extensions/pref/autoconfig/src/nsReadConfig.cpp#208

- Marco.

[mka...@mozilla.com]

Yes, this is very much supported functionality. It is our primary means of enterprise customization right now.

The reason there are very few tests is because when it was first developed, it wasn't possible to write tests that involved putting down files before startup. There are some tests now:

http://searchfox.org/mozilla-central/source/extensions/pref/autoconfig/test/unit

Mike Kaply

[Nicholas Nethercote]

Thank you for the info! I will leave that code alone :)

Nick

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[mcaste...@mozilla.com]

Hey Mike,
according to our code coverage report, nsAutoConfig is never executed during tests.

As far as I can see, it is actually not tested, as the test you mentioned is not setting the autoadmin.global_config_url pref that would make nsReadConfig instantiate nsAutoConfig. Is that correct?

I'd like to understand whether this is a problem in our coverage collection tools that are not picking up this file for some reason or if it actually is not tested. I've opened https://bugzilla.mozilla.org/show_bug.cgi?id=1413600.

- Marco.

[Mike Kaply]

I didn't write the test, so I honestly don't know. I'll try to make time to
take a look.

Mike