time: add to format documentation about dangers of using RFC1123{,Z} for parsing
When using time.RFC1123Z to parse the date header value out of an email,
an error is returned for dates that occur in the first 9 days of a
month. This is because the format strings for RFC 1123 defined in the
time package indicate that the day should be prefixed with a leading 0.
Reading the spec, the line that talks about it seems to indicate that
days can be either 1 or 2 digits:
`date = 1*2DIGIT month 2*4DIGIT`
So a date header with a day like `7` with no leading zero should be
accepted.
Fixes #67887
Change-Id: Ie7ee40d94da2c8c0417957e8b89f9987314949c8
GitHub-Last-Rev:
22a5a52fcb7ee25e5005bb9a014ef8a94d52fb32
GitHub-Pull-Request: golang/go#67888
Reviewed-on: https://go-review.googlesource.com/c/go/+/591335
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>