Add a statistics option to makemessages

[Vlastimil Zíma]

Command makemessage has serious downfall - it always changes at least one *.po file. In order to use makemessages to validate whether gettext catalog is up to date, i.e. all translated messages are in the catalog and there are no extra, the actual change of the *.po file is unwanted.

There should be either option to generate *.pot files only, which would allow msgcmp to be used, or validation mode which would check if the catalog contains all the messages.

[Claude Paroz]

What change do you talk about? The date field in the po header?

[Vlastimil Zíma]

Not only the po header. All the file changes - new messages are added, obsolete are removed or marked, etc.

[Claude Paroz]

What about a --stats-only option which would not touch existing po files, but merge po files in a temporary directory and output translation statistics for each file? Would it fulfill your use case?

[Vlastimil Zíma]

If it also returns appropriate exit code, similar to makemigrations --exit, then yes.

[Sergey Kolosov]

Looking into this during DjangoCon EU 2017 sprints.

[Sergey Kolosov]

Posted a PR: ​https://github.com/django/django/pull/11226

Exit code part is not that straightforward to implement so that it is reliable enough.

[Baptiste Mispelon]

I closed #31048 as a partial duplicate. It suggested using --dry-run instead of --exit which seems more consistent with other commands.