time: Parse of RFC3339 is incorrect for hour field

[dsnet]

RFC 3339, section 5.6 specifies that the time-hour field must be two digits wide.

However, Parse permits that field having only a single digit:

Parse(time.RFC3339, "0000-01-01T0:00:00+00:00")

reports nil rather than an error.

[seankhliao]

same as #29911 ?

[dsnet]

It's related. If we're unwilling to change the meaning of "15", we could detect that the format is RFC3339 and perform a stricter check.

[gopherbot]

Change https://go.dev/cl/425044 mentions this issue: time: fix Parse to reject single digit hour in RFC3339

[gopherbot]

Change https://go.dev/cl/426154 mentions this issue: time: parse time with two digits hour for RFC3339 format.

[gopherbot]

Change https://go.dev/cl/444277 mentions this issue: time: implement strict RFC 3339 during marshal and unmarshal

[dsnet]

Closing as dupe of #29911. The Unmarshal methods have been modified to perform strict checking. That change is more justifiable since they're explicitly documented as using RFC 3339 and the Marshal methods already have some checks for strict RFC 3339 compliance.