I think this is not supposed to work, independent of the version. This is a cyclic dependency, and golang doesn't support that as far as I know.

Go allows cyclic dependencies in modules, just not packages.

Can I suggest a new title?

"x/exp/cmd/gorelease: when main module has cycle to itself, only allow versions greater than latest in cycle"

Or, something to that affect? The current title and description don't seem to match: the title says "cycles are not allowed", the description says "cycles are allowed but version has to be greater than greatest in cycle".

Change https://golang.org/cl/273288 mentions this issue: x/exp/cmd/gorelease: when main module has cycle to itself, only allow versions

Thoughts after looking into this for a while:

• Ignore if v0
• Else,
  1. go mod graph
  2. Look for same module path
  3. Throw away versions not in same major as suggested
  4. Get latest
  5. See if suggested > latest, report err if not

Does that sound about right @jayconrod ?

@jadekler I don't think that's quite right: it's okay if a module requires a lower version of itself; a higher version should be an error though.

For example, suppose we're running gorelease in module A with -version=v0.5.0. A requires B at v0.1.0, and B requires A at v0.6.0. That should be an error because if anyone requires module A at v0.5.0, they'll get v0.6.0 instead because A v0.5.0 transitively requires a higher version of itself. So the v0.5.0 won't be usable. It would be okay if B required A at v0.4.0 instead, or if we were preparing to tag A v0.6.1.

The approach you outlined should work except the condition at the end needs to be flipped. Also, this should apply at all major versions including v0.

Also, this should apply at all major versions including v0.

SG!

Rewriting step v in more clear logic:

// version == suggested or requested version
if version < latestVersion {
  // report err
}

For example, suppose we're running gorelease in module A with -version=v0.5.0. A requires B at v0.1.0, and B requires A at v0.6.0. That should be an error because if anyone requires module A at v0.5.0, they'll get v0.6.0 instead because A v0.5.0 transitively requires a higher version of itself. [...]

The approach you outlined should work except the condition at the end needs to be flipped.

Logic above seems to hold, AFAICT? version = v0.5.0, latestVersion = v0.6.0, version < latestVersion == true so we err.

Probably missing something though - please let me know if I am!