Building Go modules

With the default configuration, you can build a Go module without issues.

But if you want to access module information at runtime (for example, through debug.BuildInfo or go version -m $binary), you need to set up GoReleaser to “proxy” that module before building it.

To do that, add this to your configuration:

gomod:
  proxy: true

In practice, what this does is:

• for each of your builds, create a dist/proxy/{{ build.id }};
• creates a go.mod for a module named after the build id;
• copy the project’s go.sum to that directory.
• runs go get module@version

In which:

• build.id: the id property in your build definition;
• main module: is the output of go list -m;
• main package: is the main module + your build’s main;
• current tag: is the tag that is being built.

So, let’s say:

• main module: github.com/goreleaser/nfpm/v2;
• build id: nfpm
• build’s main: ./cmd/nfpm/;
• current tag: v2.5.0.

GoReleaser will create a go.mod like:

module nfpm

Then it’ll copy the go.sum into this directory, and run:

go get github.com/goreleaser/nfpm/[email protected]

And, to build, it will use something like:

go build -o nfpm github.com/goreleaser/nfpm/v2/cmd/nfpm

This will resolve the source code from the defined module proxy using proxy.golang.org. Your project’s go.sum will be used to verify any modules that are downloaded, with sum.golang.org “filling in” any gaps.

Getting the version from the module

You can also get the module version at runtime using debug#ReadBuildInfo. It is useful to display the version of your program to the user, for example.

package main

import (
	"fmt"
	"runtime/debug"
)

func main() {
  if info, ok := debug.ReadBuildInfo(); ok && info.Main.Sum != "" {
    fmt.Println(info)
  }
}

You can also use go version -m my_program to display the go module information.

Limitations

1. Extra files will still be copied from the current project’s root directory and not from the proxy cache;
2. You can’t build packages that are not contained in the main module;
3. VCS info will not be available.

More information

You can find more information about it on the issue that originated it and its subsequent pull request.

Make sure to also read the relevant documentation for more options.

Real example

Source code of a working example can be found at goreleaser/example-mod-proxy.