Enforce the use of the trimmed option for blocktranslate

Below is the original issue which has been taken care of in #8226.

What remain is to enforce the use of the block option so we don’t end up back to square one.

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Is your proposal related to a problem?

In most (all?) cases, new lines and spaces are irrelevant (they are ignored in HTML), but they aren’t handled consistently in Transifex.

As a result, it lowers the confidence of translators that they are doing the right thing.

Describe the solution you’d like

No leading or trailing whitespace characters (new lines, tabs and spaces) in source translation strings. This was done in #5633 by setting the trimmed option on blocktrans blocks, but we need some linting option to make sure it is enforced in the future.

Additional context

Screenshots	Notes
	New lines are clearly identified. Spaces not so much.
	Missing new lines produce an error
	Missing new spaces do not produce any error or warning

Next Steps

The proposed solution was discussed and agreed in Core Team meetings, however no changes will be made to the codebase until we have a way to enforce the style.

Therefore, the next step is to work on some sort of linter (run as either an actual linter or a test in the test suite) to enforce the use of the trimmed option for blocktrans.

Only then we can open a PR to fix the existing source strings.

WARNING

Removing whitespace would make old translation strings invalid. Therefore, we should wait for the beginning of a release cycle (maybe a week or two after a new release) and notify translators immediately in order to give them as much time as possible to go through the now broken/missing translations.

[thibaudcolas]

I’ve been working on a linter for Django Templates (https://github.com/thibaudcolas/curlylint), I think it would be pretty straightforward to add a rule to it that checks trimmed is always used with blocktrans. Wagtail already uses the pre-existing linter I based mine on: https://github.com/wagtail/wagtail/blob/f8299885aa916becb9109c881f3ab28408af794e/.circleci/config.yml#L25, so switching over should be very straightforward.

Otherwise – wouldn’t it be even simpler for us to have our custom blocktrans_trimmed block, and move all blocks over?

[lb-]

A few updates.

• https://github.com/thibaudcolas/curlylint/issues/131 raised to see if we can or can create a way to lint our templates
• https://github.com/wagtail/wagtail/issues/8217 has been created (kind of a dupe of this) and implemented via https://github.com/wagtail/wagtail/pull/8226

I recommend we revise this issue to cover the linting enforcement and filling any gaps that are picked up in that process.