cmd/go: "invalid version" error on get is unnecessarily repetitive

[mvdan]

$ go version
go version devel +2217e89ba3 Fri Mar 5 09:24:34 2021 +0000 linux/amd64
$ go get -d mvdan.cc/garble@branch/with/slash
go get: mvdan.cc/garble@branch/with/slash: invalid version: version "branch/with/slash" invalid: disallowed version string

The error line really doesn't have to be that long, especially given how it's repeating essentially the same three times.

Plus, it doesn't tell me why the version is disallowed. I had this happen with a name like feat/foo-bar and I had to think twice about what character it was upset about.

How about:

go get: mvdan.cc/garble@branch/with/slash: invalid version "branch/with/slash": version strings can't contain '/'

[mvdan]

Actually, the version is earlier in the message too, so that is also repeated. We can make it even less repetitive:

go get: mvdan.cc/garble@branch/with/slash: invalid version: version strings can't contain '/'

[mvdan]

I get that there are probably 5+ layers in this error message, but hopefully with error wrapping one could teach go get to remove the redundant layers.

[bcmills]

Error-wrapping is hard. 😞
(https://github.com/bcmills/go-experience-reports/blob/master/errors.md)

[gopherbot]

Change https://golang.org/cl/299150 mentions this issue: cmd/go: Remove unnecessarily repetitive from 'go get'

[gopherbot]

Change https://golang.org/cl/299132 mentions this issue: module: Remove unnecessarily repetitive from 'go get'