time: Parse error messages may be confusing/misleading

[extemporalgenome]

What version of Go are you using (go version)?

$ go version
go version go1.19.3 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"

What did you do?

https://go.dev/play/p/PUywlZ7-BE5

func main() {
	_, err := time.Parse("2006-01-02", "22-10-25")
	fmt.Println(err)
}

What did you expect to see?

parsing time "22-10-25" as "2006-01-02": cannot parse "22" as "2006"

What did you see instead?

parsing time "22-10-25" as "2006-01-02": cannot parse "0-25" as "2006"

It appears that this the parser is doing some blocking or chunking that gets misaligned in the error reporting when fewer than the expected number of digits appear in the input.

[bcmills]

Does this still reproduce at HEAD? @dsnet has landed a bunch of Parse fixes during the 1.20 development cycle.

[extemporalgenome]

Unfortunately it's still an issue:

> ./bin/go version
go version devel go1.20-cb5534c1c6 Wed Nov 16 02:02:26 2022 +0000 linux/amd64
> ./bin/go run /tmp/timebug.go
parsing time "22-10-25" as "2006-01-02": cannot parse "0-25" as "2006"

[gopherbot]

Change https://go.dev/cl/450936 mentions this issue: time: set the correct value element of a parse error