proposal: cmd/api: a mechanical approach to compatibility issues

[hirochachacha]

This is related to #5778.

I think core tool support API compatibility checking is reasonable.
One of the implementations is extending current tool "go tool api".

Like this:

$ go tool api -version 1 local_file_or_directory

version 0 means "go 1.0," 1 means "go 1.1" ... and so on.

I'm not so sure in detail, but I guess implementation is not so hard work.

Walk third party import paths recursively, and check it compatible or not.
We already know location of api.txt.

Thank you.

hiro