Allow blocktrans to set a context variable

[Mitar]

Currently, we can use {% trans "string" as var %} to set var to translated string. Nothing similar exists for blocktrans.

[Tim Graham]

Do any other block tags support as var? I'm not sure it's a good idea (or feasible for that matter). Could you describe your use case? Do you have interest in trying to implement it?

[Mitar]

Ehm, use case is string interpolation. I cannot use {% trans "foo {{ bar }}" as var %}. Having only constant translated strings are vars is a bit problematic.

I use that for setting title of the page ({% blocktrans %}{{ username }}'s block{% endblocktrans %}) and I would like to set it to the context variable so that I can reuse it around (title, heading, links ...).

Currently I am using ​this custom tag to achieve this. But I think this would be useful in the tag itself. Or maybe {% trans "foo {{ bar }}" as var %} should be supported at least? And _("foo {{ bar }}").

[bmihelac]

Here is a link to branch that implements this feature and two simple tests:

​https://github.com/bmihelac/django-1/compare/fix-21695-allow-blocktrans-to-set-a-context-variable?expand=1

Please note that assigning option is named asvar contrary to usual as to avoid confusion between legacy format for using with.

If there is interest in merging this I will add docs and changelog and any more tests if needed.

[Aymeric Augustin]

It seems that every tag is going to gain this feature eventually...

[Mitar]

This is why I created ​this tag which simply sets the context based on whatever is in there. Then there is no need to modify all tags to be able to set context. DRY. :-)

[Matthew Somerville]

I have rebased bmihelac's patch on current master, made a few changes, added more tests and documentation, and submitted a PR at ​https://github.com/django/django/pull/4854

I have a need for this at the moment - exactly the same situation as why it's useful for trans, using the output in multiple places (most commonly, title element and heading). It works great for trans, but if the title happens to include a variable, I'm stuck.

[Tim Graham <timograham@…>]

In 839edceb:

Fixed #21695 -- Added asvar option to blocktrans.

Thanks Bojan Mihelac for the initial patch.