I was able to reproduce this on 1.13.6 from my home connection with no specific network setup either.

 -> git clone https://github.com/fluxcd/helm-operator && cd helm-operator
 -> go env -w GOPROXY=direct GOSUMDB=off
 -> go env GOPROXY GOSUMDB
direct
off
 -> go mod tidy
go: github.com/fluxcd/flux@v1.17.1-0.20200109130101-ca3e8f451dd0: invalid version: unknown revision ca3e8f451dd0

The commit in question does exist on GitHub.

Tl;dr - The upstream users fluxcd/helm-operator should update the version of fluxcd/flux that they are referencing.

Ok. Dug a bit further and solved the problem. It's not an issue with the go toolchain itself.

• The top-level module that is being build, fluxcd/helm-operator, references fluxcd/flux@ca3e8f451dd0 in its requires.
• That commit, although it still can be accessed via the GitHub UI is no longer part of the actual git history of the fluxcd/flux repo. It is still visible most likely as part of a fork (as you can access commits from all forks from any repo in the network via the web UI).
• This pseudo-version was however appropriately cached by the module proxy. Protecting users against the disappearance of the underlying commit, as it is intended to do.
• The forced setting in Fedora's DNF package for Go of GOPROXY=direct instead of the usual GOPROXY=https://proxy.golang.org then resulted in the case of @carlpett to bypass the proxy and instead try to clone the actual repo and find the appropriate revision which had already been deleted.

I believe this means we can close this issue.

As @Helcaraxan found out, the commit is not part of any branch, so the error message is correct. Not much to do here, probably.

FYI @hyangah @katiehockman.

It would be interesting to say what the Fedora people have to say about this. I expect it will only happen more often as time goes on and more things are deleted.

I'm using docker to test my repo, under centos 8.0, the go build works well, while under centos 6.5, I go the error unknown revision d71410dd73eb.

Under centos8.0, the Git version is 2.18.2, while under centos 6.5, Git version is 1.7.1, does git releated to the issue?

I'm using docker to test my repo, under centos 8.0, the go build works well, while under centos 6.5, I go the error unknown revision d71410dd73eb.

Under centos8.0, the Git version is 2.18.2, while under centos 6.5, Git version is 1.7.1, does git releated to the issue?
@coanor

Yes. The go mod tidy command uses git ls-remote -q origin to load refs.
see: https://github.com/golang/go/blob/go1.15/src/cmd/go/internal/modfetch/codehost/git.go#L178

But the -q option was added to git in git v1.7.2-rc0.
see: git/git@cefb2a5

So if your git version is older then v1.7.2-rc0, this error is inevitable.

If you run go get your-repo, you will see the error from git:

$ go get a-repo
go get a-repo: module a-repo: git ls-remote -q origin in /go/pkg/mod/cache/vcs/f93901d37beed0fcdb30950985bd386107757c23046f467642803dcf63e192ee: exit status 129:
        usage: git ls-remote [--heads] [--tags]  [-u <exec> | --upload-pack <exec>] <repository> <refs>...