html_last_updated_fmt does not support UTC offset (%z)

[th0ger]

According to Sphinx docs, html_last_updated_fmt uses the strftime().
The python strftime format codes defines: %z as UTC offset in the form ±HHMM[SS[.ffffff]] (empty string if the object is naive).

However, with:

html_last_updated_fmt = '%Y-%m-%d %H:%M:%S %z'

I get a literal %z at output:

© Copyright 2020, .... Revision 81dbc58. Last updated on 2021-01-12 07:34:52 %z.

The expected output in my case is ... +0100.

Notes:

• Uppercase %Z (Time zone name) does "work". On my local box is gives GMT+01:00, but on our CI pipeline is gives the full string Coordinated Universal Time which is a bit anoying. I guess it may be platform dependent.
  The "literal %z"-issue occurs on both platforms.
• Some basic testing with Python, shows that %z works well with strftime().
• I have tested all other format tokens and they all work, except %U and %W (week numbers) which throws an exception. Someone may want to raise a separate issue for this.

[tk0miya]

Thank you for reporting. Both %z and %Z are bugs.

[th0ger]

@tk0miya thanks for fixing.
I see that test_format_date() needs a little love to fully cover https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes
For example %U and %W which fails for me. Will you create an issue for this?

[tk0miya]

Could you try to make a pull request instead of issue? Contributions are always welcome :-)