This seems to be working as documented/intended?

CheckFilePath passes: https://play.golang.org/p/8u7pObwsxjX

While the other 2 are documented to reject such paths:

CheckImportPath:

The element must not have a suffix of a tilde followed by one or more ASCII digits (to exclude paths elements that look like Windows short-names).

CheckPath:

A valid module path is a valid import path, as checked by CheckImportPath

CheckFilePath passes: https://play.golang.org/p/8u7pObwsxjX

You're right. CheckFilePath does not check for short names. I should have checked better.

While the other 2 are documented to reject such paths:

Yes, they are documented but in my opinion the original commit 4ab6fb1 that introduced this check was too restrictive and rejects path that are as documented but are not short-names in Windows.

in my opinion the original commit 4ab6fb1 that introduced this check was too restrictive and rejects path that are as documented but are not short-names in Windows.

Is there a specific reason we would need to allow these paths? (Are there existing widely-used packages that rely on them?)

I agree that the check may be somewhat more conservative than is strictly necessary, but I don't see a significant harm in leaving it that way.

A part from that it may be somewhat more conservative, there is not a specific reason. Having understood that this implementation is a deliberate choice, it is okay for me to close this issue.

However, I recommend mentioning the short-name requirements in the documentation on the page

https://golang.org/ref/mod#go-mod-file-ident

Having to implement a module path validator, without using existing code, I went from this documentation to the code implementing it without reading the CheckPath function comment and so I hadn't read that the behavior was intentional.

Change https://golang.org/cl/344569 mentions this issue: _content/ref/mod: document that module paths can't contain short names