reading the code in src/cmd/go/internal/module,

That package contains a lot of code. Which function in particular are you concerned about?

Note that many of the functions in that package are now available as golang.org/x/mod/module, which can be used in the Playground. A complete code example illustrating the concern would be helpful.

@bcmills thanks for your reply, it's the case set checkPathTests used by TestCheckPath that i illustrated before. Particularly, it mainly about the result of CheckPath > SplitPathVersion .
for more clear detail, see https://play.golang.org/p/gTBzMfZUCZT, which print like following:

x.y/z/v2.0 check path got: malformed module path "x.y/z/v2.0": invalid version
x.y/z/v2.0.0-pre check path got: <nil>
x.y/z/v2.0 split path version got: x.y/z/v2.0,,false
x.y/z/v2.0.0-pre split path version got: x.y/z/v2.0.0-pre,,true

The intent is for the path suffix to include only the major version, since minor-version updates to that path will all be compatible. (So the path should be x.y/z/v2, not x.y/z/v2.0.)

So the error for x.y/z/v2.0 seems correct, although perhaps we should not treat v2.0 as a major-version suffix at all. The fact that we do not treat v2.0.0-pre the same way could be a bug.

Do you have concrete examples of paths of either form in the wild?

CC @jayconrod @hyangah @heschik @katiehockman

So the error for x.y/z/v2.0 seems correct, although perhaps we should not treat v2.0 as a major-version suffix at all. The fact that we do not treat v2.0.0-pre the same way could be a bug.

from the implementation, all version-like suffix /vX.Y[.Z]... will lead to this error, so thinking about whether other version pattern like /vX.Y[.Z]...[-prerelease[+buildmeta]] should lead to same error, + is not accepted in other place checking repo path, so looks like only prerelease is not coverd.

and the format is not need to strictly fit the semver, so may all version-like format "/vX.Y[.Z]...-SOMETHING` should be avoided?

Do you have concrete examples of paths of either form in the wild?

No, totally imagined, :)

@bcmills any news about this issue? does some more discussion need about how to address it?

(CC @matloob)