Golang - How to display modules version from inside of code

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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?

go-modules go
1 Answers

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?

user_17055980
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