cmd/go: don't use retracted versions as pseudo-version base versions

[jayconrod]

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

1.16 tip (in development)

Does this issue reproduce with the latest release?

No, just tip.

What operating system and processor architecture are you using (go env)?

n/a

What did you do?

Suppose a module example.com/m tags v1.0.0, then tags v1.0.1 which retracts (#24031) both v1.0.0 and v1.0.1. Both tags refer to commits on the default branch. No other releases are tagged.

A user runs go get -d example.com/m@latest.

What did you expect to see?

The user should get a requirement on a pseudo-version based on v0.0.0, as they would if no versions are tagged.

What did you see instead?

The user gets a requirement on a pseudo-version based on v1.0.2.

Note that a pseudo-version based on v1.0.2 should still be valid; retraction shouldn't invalidate existing pseudo-versions.

[gopherbot]

Change https://golang.org/cl/261079 mentions this issue: cmd/go: ignore retracted versions when converting revisions to versions