`date -f dates.txt` is failing

[sylvestre]

$ echo "2023-03-27 08:30:00" > dates.txt
$ echo "2023-04-01 12:00:00" >> dates.txt
$ echo "2023-04-15 18:30:00" >> dates.txt

$ ./target/debug/coreutils date -f dates.txt "+%Y-%m-%d %H:%M:%S"
date: invalid date '2023-03-27 08:30:00'
date: invalid date '2023-04-01 12:00:00'
date: invalid date '2023-04-15 18:30:00'

With GNU:

2023-03-27 08:30:00
2023-04-01 12:00:00
2023-04-15 18:30:00

[tertsdiepraam]

I think that the date parsing in touch is more advanced than in date. If we share that implementation this could be fixed quite easily. (They share implementations in GNU too)

But maybe that would be done after #4600

[Benjscho]

Time parsing in date and touch for GNU is provided by parse-datetime - which is a yacc implementation of parsing. Seems as though the main parsing order is as described here. Should be possible to implement parsing in the same order and features either through if let Ok() parse success matching (as is currently done in touch and your PR @tertsdiepraam), or potentially a yacc syntax rust parser using grmtools.

I'm going to look into providing a lib function that provides this kind of loose parsing and returns a DateTime object, will see if I can make something that can drop in to date. It could then be tested against gnulib/tests/test-parse-datetime.c. I'm guessing it would be best to avoid any further dependencies, so I'll try the first approach of result based successes.

[tertsdiepraam]

Sounds good!

As a general precaution, keep this line of the contribution guidelines in mind:

uutils is original code. It cannot contain code from existing GNU or Unix-like utilities, nor should it link to or reference GNU libraries.

We have to copy the functionality without copying the code. Not looking directly at the code but only the documentation and observed behaviour is the best way to ensure that you don't (accidentally) copy it.

[Benjscho]

Thanks, that's a good reminder! I'll steer clear from the implementation.

[Benjscho]

Opened a PR that fixes this: #4917