touch: Incorrect "months ago" calculation with `-d` options

[sylvestre]

touch: Incorrect "months ago" calculation with -d options

Component

touch

Description

When using touch -d "X months ago", uutils touch calculates the date differently from GNU coreutils, resulting in a 1-day discrepancy.

Test / Reproduction Steps

$ touch -d "2025-12-30" /tmp/date
$ touch -r /tmp/date -d "1 month ago" /tmp/t; stat t
# ...
Access: 2025-11-30 00:00:00.000000000 +0000
Modify: 2025-11-30 00:00:00.000000000 +0000

$ coreutils touch -r /tmp/date -d "1 month ago" /tmp/tt; stat tt
# ...
Access: 2025-11-29 00:00:00.000000000 +0000
Modify: 2025-11-29 00:00:00.000000000 +0000

Impact

Files may be modified with unintended dates, breaking compatibility with GNU coreutils.

Recommendations

Fix the relative month calculation algorithm to match GNU's implementation using proper calendar month arithmetic.

[cerdelen]

If i debugged correctly the bug lies in the dependency parse_datetime v0.13.3.

In line 670 of file src/uu/touch/src/touch.rs the function 'parse_datetime::parse_datetime_at_date(ref_zoned, s)' is called which internally applies the relative date change.

In the dependency file items/builder.rs line 278-286 the relative date adjustments are made. This seems to be the source of the bug.

Edit: I tested println!() debugging wise and the atime/mtime were correct before line 670 in touch.rs being 12.1 but after the call of parse_datetime in line 670 in touch.rs it was 11.11 if given a 2 months ago input (should be 12.11).