Bug 794059. Allow pages to be activated per locale.

[pmclanahan]

Going to a page at a non en-US locale will now redirect
to en-US unless the corresponding .lang file for that
template and locale has ## active ## as its first
line. This will allow localizers to only publish a
localized page after it's confirmed to be fully and
correctly translated.

[pmclanahan]

Not sure if this should get some caching or not. It should be pretty quick to check the first line of a file, but if you guys think that storing the results in memcache for a minute or so might help with load then it can be easily added.

[Osmose]

IMO it's worth given how easy this would be to cache, although I'm curious why you'd only cache it for a minute. How often do these files change on production? Is memcache cleared when we push?

[pmclanahan]

That was based on the value in our settings for DOTLANG_CACHE being 60. I think we should consider increasing that as well to at least the length of time between the cron runs.

[rik]

Note: This PR should not be merged before making sure the appropriate .lang files have been updated with the ## active ## header.

[pmclanahan]

Agreed. @rik any thoughts on the performance implications?

[rik]

I'll let others review this :)

[Osmose]

There's a possible race condition between here and when you actually open the file below. You should probably use a try clause instead and catch the IOError

[pmclanahan]

Yeah, but only if the file doesn't exist right? So we might get one more false negative before we see the locale activated. This doesn't seem like a big enough deal to worry with. This should almost never happen anyway as these files are automatically created.

[pmclanahan]

@Osmose updated for your approval.

[Osmose]

Looks good, although some tests for the cache logic would be nice. :D

r+

[pascalchevrel]

FYI, The .lang files for python templates are all updated with the ## active ## tag