module directive in go.mod is missing version number

[exklamationmark]

Proposal

Hi,

I was trying to import some packages from the repos at v2.8.0 and noticed that Go module didn't resolve to the tagged version. Instead, it resolved to a pseudo-version number
(v0.0.0-20190312040920-59369491cfdf).

While the hash is still correct (59369491cfdf is tagged with v2.8.0), it took a while to understand and verify when working with Go module.

The cause was the module directive in go.mod, which didn't match strategies
for release > v2 in Go module.

This is probably not that important if we just want to build the binary. However, it can be annoying when importing packages from Prometheus.

A proper fix would probably need to have the correct major version number in go.mod.
For now, it could simply mean having

module github.com/prometheus/prometheus/v2

Bug Report

What did you do?

Import github.com/prometheus/prometheus/promql and github.com/prometheus/prometheus/storage at version v2.8.0

What did you expect to see?

$ GO111MODULE=on go get -v -x github.com/prometheus/prometheus@v2.8.0
$ cat go.mod | grep 'prometheus/prometheus'
        github.com/prometheus/prometheus v2.8.0 // indirect

What did you see instead? Under which circumstances?

$ GO111MODULE=on go get -v -x github.com/prometheus/prometheus@v2.8.0
$ cat go.mod | grep 'prometheus/prometheus'
        github.com/prometheus/prometheus v0.0.0-20190312040920-59369491cfdf

Environment

• System information:

  Linux 4.15.0-46-generic x86_64

• Prometheus version:

  prometheus, version 2.8.0 (branch: HEAD, revision: 5936949)

• Alertmanager version:

  N/A

• Prometheus configuration file:

  N/A

• Alertmanager configuration file:

  N/A

• Logs:

  N/A

[simonpasquier]

We can't (don't want to) guarantee any API stability on the github.com/prometheus/prometheus/* packages so github.com/prometheus/prometheus/pkg/foo@v2.9.0 could break its API compared to v2.8.0 if we need it. Following SemVer and the Go modules conventions would be misleading and worth than the current situation IMHO.

[exklamationmark]

I see. Indeed it would be misleading to follow SemVer in that case.
Should we add some notes to about this, or just leave it as is?

[simonpasquier]

I'd leave as it is now since the note would probably be hard to find for people anyway.