cmd/go: no clear "go get" message when requested version doesn't match suffix

[firelizzard18]

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

$ go version
go version go1.12 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
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/me/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/me/Source/Go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/tmp/test/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/qx/064gkvrd7bl0trt43gd434f0zm0rjy/T/go-build739499749=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

$ go get gitlab.example.com/my/[email protected]

What did you expect to see?

go.mod:

module test

go 1.12

require gitlab.example.com/my/pkg v2.1.0

What did you see instead?

module test

go 1.12

require gitlab.example.com/my/pkg v0.0.0-20190416182416-8556b6232906

I don't understand why go get is not respecting my tag. The correct tags exist. v1.6.1 works fine, but v2.0.0 and v2.1.0 don't work.

$ git ls-remote --tags [email protected]:my/pkg .git
...
a4ce364216755764766eb7d75518f8bf227cd106        refs/tags/v1.6.1
b2b3bfc0416ab40e30042683b9128d38b8c2eefc        refs/tags/v1.6.1^{}
be9d7c7b6e3fc68aae49cfbdd7ff78c2372b4d4c        refs/tags/v2.0.0
aa7975ba93ff643c24f6f949988ddf61ec637b90        refs/tags/v2.0.0^{}
f47456c7276fc677fdc41e18c51b3c56c7e365c2        refs/tags/v2.0.1
0209bae56a88afe277edf8ec12a10d0e2f33be17        refs/tags/v2.0.1^{}
e96fe2a02d7e4559f3d86520d7643faaec3e6c7e        refs/tags/v2.1.0
8556b6232906717785033de712aa27e4cd7a4600        refs/tags/v2.1.0^{}

[jayconrod]

Versions that start with v2 or later don't belong to the same module as v0 or v1 versions. They would belong to gitlab.example.com/my/pkg/v2. The major version suffix is required.

We should provide a clear diagnostic message for this.

[bcmills]

This might be a duplicate of #30499. (Not entirely clear to me whether the problems occur under the same conditions.)

[jayconrod]

@tbpg is working on this, but I'm not able to assign it to him.

[gopherbot]

Change https://golang.org/cl/174180 mentions this issue: cmd/go: error if mismatched major versions causes use of pseudo-version

[gopherbot]

Change https://golang.org/cl/173721 mentions this issue: cmd/go: error if mismatched major versions causes use of pseudo-version

[bcmills]

prometheus/prometheus#5356 (comment) is an interesting counter-point to this issue: it appears that some maintainers are already intentionally using mismatched module paths to avoid SemVer semantics for not-actually-SemVer repositories.

That said, it seems like the pseudo-version we choose in that case should be based on the last v1.*.* tag, not the v0.0.0 prefix that we're seeing today. (Perhaps the observed behavior for prometheus — and possibly for @firelizzard18's example in this issue — is another instance of #27171?)

[jayconrod]

Since CL 181881, we now print an error message like this:

$ GOPROXY=direct go list -m rsc.io/[email protected]
go get rsc.io/[email protected]: rsc.io/[email protected]: invalid version: module contains a go.mod file, so major version must be compatible: should be v0 or v1, not v3

Note that proxy.golang.org is still serving results based on go1.12 behavior (#32805), and we don't print this message for results received from the proxy. We probably should.

[bcmills]

we don't print this message for results received from the proxy. We probably should.

That is tracked separately as #31428.

[bcmills]

I believe this is resolved. @firelizzard18, please let us know if this is still an issue for you using Go 1.13.