date: fails to parse +N and -N in absolute time string as a time zone

[jfinkels]

Environment: Ubuntu 20.04, uutils main branch (git commit 88cdf16), GNU coreutils v8.30

Steps to reproduce:

TZ=UTC0 date -d '1997-01-19 08:17:48 +0'

What happens now: uutils date terminates with an error because it doesn't understand the +0 time zone:

date: invalid date '1997-01-19 08:17:48 +0'

If you remove the +0, then uutils date does successfully parse the date string.

What I expected to happen: GNU date successfully interprets the +0 as a time zone:

Sun 19 Jan 1997 08:17:48 AM UTC

Notes: this is causing a test failure in GNU test file tests/date/date.pl.

[Felle33]

Making some tests, the code can sucessfully parse the strings TZ=UTC0 date -d '1997-01-19 08:17:48 +0000' and TZ=UTC0 date -d '1997-01-19 08:17:48 +00:00'.
We could try to parse the timezone and then pass the right argument to the function parse_datetime::parse_datetime_at_date(...).
What do you think?

[jfinkels]

Maybe the parse_datetime_at_date function in https://github.com/uutils/parse_datetime just needs to be updated to understand the string "+0", etc.?

[Felle33]

Inspecting the code, I see that they try to parse also the timezone, but since %z accepts only 4 digits (i.e +0000) or 4 digits separated by : (i.e +00:00), the function returns an error