The suggested regexp doesn't work because it matches 3m0m, m, s and doesn't match 0.

My previous suggestion doesn't work too because it matches 3m0m or 3s0m.

I think the right expression is ^(\d+m\d+s|\d+m|\d+s|\d)$

Inside time.ParseDuration we can found this regexp [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+.
https://github.com/golang/go/blob/0312e31ed197b3bf1434e8dbb283f0d2374d7457/src/time/format.go#L1622

But this regexp is not a validation regexp because it accepts everything. https://regex101.com/r/odfWT9/1

In the context of run.timeout:

• The values that use "ns", "us" (or "µs"), "ms" are off-topic.
• The value "0" is accepted.
• The negative values are off-topic.

So the best compromise is ^((\d+h)?(\d+m)?(\d+(?:\.\d)?s)?|0)$.

https://regex101.com/r/1Zse4r/1

The duration parsing is a bit surprising: https://go.dev/play/p/-NSON-ylfvm
ex: 3m3m3m -> 9m0s

So, at the end the regexp can be ^((\d+[hms])+|0)$.

I don't know if I want to follow the "official" duration format (without negative numbers and too small units) or keep my latest suggestion with something more "logical". 🤔

🤔 I think it's better to have something more strict and less human error prone.
Using 3m3m3m as value to have 9m for the timeout is "unexpected", I cannot see a use-case for that.
Same thing for 30s5m, except if you are a Yoda fan, I cannot see a use-case for that too.

Thanks! that was quick