Some datetime timezone combinations don't parse

[simpoir]

We've started to notice some parsing errors on Ubuntu with some specific date and timezone combinations. Those combinations do work against gnu coreutils. e.g.

# This one doesn't work:
TZ=America/Toronto date -d "$(LC_ALL=C TZ=UTC0 gnudate -d 'Fri Oct 31 22:52:02 UTC 2025')"
date: invalid date 'Fri Oct 31 22:52:02 UTC 2025'

#While the same datetime works for paris:
TZ=Europe/Paris date -d "$(LC_ALL=C TZ=UTC0 gnudate -d 'Fri Oct 31 22:52:02 UTC 2025')"
Fri Oct 31 23:52:02 CET 2025

#While the first TZ works with some different date:
TZ=America/Toronto date -d "$(LC_ALL=C TZ=UTC0 gnudate -d 'Wed Oct 21 22:52:02 UTC 2025')"
Wed Oct 22 00:52:02 CEST 2025

Ref: https://bugs.launchpad.net/ubuntu/+source/tzdata/+bug/2130471

[simpoir]

Looks like failures are every other 31st.

for i in `seq 1000`; do TZ=America/Toronto date -d "$(LC_ALL=C TZ=UTC0 gnudate -d "Fri Oct 31 22:52:02 UTC 2025 + $i day")" > /dev/null ; done
date: invalid date 'Sat Jan 31 22:52:02 UTC 2026'
date: invalid date 'Tue Mar 31 22:52:02 UTC 2026'
date: invalid date 'Sun May 31 22:52:02 UTC 2026'
date: invalid date 'Mon Aug 31 22:52:02 UTC 2026'
date: invalid date 'Sat Oct 31 22:52:02 UTC 2026'
date: invalid date 'Sun Jan 31 22:52:02 UTC 2027'
date: invalid date 'Wed Mar 31 22:52:02 UTC 2027'
date: invalid date 'Mon May 31 22:52:02 UTC 2027'
date: invalid date 'Tue Aug 31 22:52:02 UTC 2027'
date: invalid date 'Sun Oct 31 22:52:02 UTC 2027'
date: invalid date 'Mon Jan 31 22:52:02 UTC 2028'
date: invalid date 'Fri Mar 31 22:52:02 UTC 2028'
date: invalid date 'Wed May 31 22:52:02 UTC 2028'

[naoNao89]

podman run --rm ubuntu:25.10 /bin/bash -c "apt update && apt install -y tzdata && TZ=America/Toronto date -d 'Fri Oct 31 22:52:02 UTC 2025'"

date: invalid date 'Fri Oct 31 22:52:02 UTC 2025'

[uhop]

December 31st is coming. People will have problems again parsing that date.

[simpoir]

not quite yet, December and July are impervious due to being the first of consecutive 31day months. Jan 31 is going to fail though.