cmd/go: export module information for binaries programmatically

[bcmills]

https://research.swtch.com/vgo-repro says:

When we do integrate versions into the main Go toolchain, we will add APIs to access this information from inside a running binary, just like runtime.Version provides access to the more limited Go version information.

I didn't see an issue filed to track that, so I'm filing it now.

[mvdan]

This would be great - I think it has been one of the biggest reasons why some projects have been using makefiles and custom build scripts.

[gopherbot]

Change https://golang.org/cl/143977 mentions this issue: cmd/go/internal/modload: fix use of //go:linkname

[hyangah]

The cl/143977 allowed us to retrieve the module information embedded during build. The API will be in the runtime/debug package.

BTW, using this info for version stamping of a binary instead of Makefiles and custom build scripts that utilize '-X' flag, works only when 1) the binary is built in the module enabled mode and 2) the binary is built through the module cache.

If the binary is built with the traditional GOPATH way, the info will not exist. If module is enabled but the binary is built out of checked in or cloned source repository, all dependency version info will be encoded but the main module's version info will remain undetermined (for the reason explained in the issue 28083).

[gopherbot]

Change https://golang.org/cl/144220 mentions this issue: runtime/debug: add API to read module info in binary