Golang - How to display modules version from inside of code - go

Question

I'm writing two binaries, and both of them use two libraries (we can call them libA and libB).
Each lib is in a dedicated git repo, with git-tags to declare versions.
For example, libA is at v1.0.9 and libB is v0.0.12.
Both binaries have CLI flags, and I would like to add a debug flag to display lib versions like that:
> ./prog -d
Used libraries:
- libA, v1.0.9
- libB, v0.0.12
I don't know how to do that.
The only way I see to set variable from "outside" is to use ldflags (go build -ldflags="-X 'main.Version=v1.0.0'" for example). But this way don't seems scalable, how to add a libC? It also imply to manage tags two times, one time for git, and one time in goreleaser.yml or makefile.
Can you help me to find a solution?

Answer 1

The Go tool includes module and dependency information in the executable binary. You may use runtime/debug.ReadBuildInfo() to acquire it. It returns you a list of dependencies, including module path and version. Each module / dependency is described by a value of type debug.Module which contains these info:
type Module struct {
Path string // module path
Version string // module version
Sum string // checksum
Replace *Module // replaced by this module
}
For example:
package main
import (
"fmt"
"log"
"runtime/debug"
"github.com/icza/bitio"
)
func main() {
_ = bitio.NewReader
bi, ok := debug.ReadBuildInfo()
if !ok {
log.Printf("Failed to read build info")
return
}
for _, dep := range bi.Deps {
fmt.Printf("Dep: %+v\n", dep)
}
}
This outputs (try it on the Go Playground):
Dep: &{Path:github.com/icza/bitio Version:v1.0.0 Sum:h1:squ/m1SHyFeCA6+6Gyol1AxV9nmPPlJFT8c2vKdj3U8= Replace:<nil>}
Also see related question: How to get Go detailed build logs, with all used packages in GOPATH and "go module" mode?