modpath provides an API to detect the module path from the go.mod file underneath the given directory or its root.

go get github.com/nakabonne/modpath

package main

import (
	"fmt"

	"github.com/nakabonne/modpath"
)

func main() {
	modulePath, _ := modpath.Run("/path/to/foo/bar")
	fmt.Println(modulePath) // -> "example.com/foo/bar"
}

Unlike go list -m, you can inspect any directories except for the current directory.

$ cat /path/to/foo/bar/go.mod
module example.com/foo/bar

go 1.13

$ modpath /path/to/foo/bar/
example.com/foo/bar

If no directory is explicitly given, the module containing the current directory is emitted as go list -m does.