Go Modules: finding out right pseudo-version (vX.Y.Z-<timestamp>-<commit>) of required package

Question

I am trying out Go modules. My project requires the libarary golang.org/x/net/html, so I defined this go.mod file:

module github.com/patrickbucher/prettyprint

require golang.org/x/net/html

And wrote this demo program to check if the dependency gets loaded upon compilation:

package main

import (
        "fmt"
        "log"
        "os"

        "golang.org/x/net/html"
)

func main() {
        doc, err := html.Parse(os.Stdin)
        if err != nil {
                log.Fatal(err)
        }
        fmt.Println(doc)
}

When I run go build, I get this error message:

go: errors parsing go.mod:
~/prettyprint/go.mod:3: usage: require module/path v1.2.3

Obviously, I missed the version number. But which one to take? I stumbled an article called Takig Go Modules for a Spin, where I found an example of a go.mod file containing references to golang.org/x packages:

module github.com/davecheney/httpstat

require (
        github.com/fatih/color v1.5.0
        github.com/mattn/go-colorable v0.0.9
        github.com/mattn/go-isatty v0.0.3
        golang.org/x/net v0.0.0-20170922011244-0744d001aa84
        golang.org/x/sys v0.0.0-20170922123423-429f518978ab
        golang.org/x/text v0.0.0-20170915090833-1cbadb444a80
)

The author is using version strings like v0.0.0-20170922011244-0744d001aa84, consisting of the semver indication v0.0.0, a timestamp and something that looks like a git commit ID.

How do I figure out those version strings? I guess those golang.org/x packages will be versioned according to semantic versioning at some point, but to really trying out go mod, I need to figure out those now.

Answer 1

Update

This command is the better solution to adding the replace command to go.mod rather than doing it manually using git that I initially posted:

go mod edit -replace github.com/docker/docker=github.com/docker/engine@ea84732a7725

produces a similar result but instead of using a pseudo-version, it finds the tagged engine version.

replace github.com/docker/docker => github.com/docker/engine v17.12.0-ce-rc1.0.20191113042239-ea84732a7725+incompatible

Alternatively, include a tagged docker version.

go mod edit -replace github.com/docker/[email protected]=github.com/docker/engine@ea84732a7725

for

replace github.com/docker/docker v1.13.1 => github.com/docker/engine v17.12.0-ce-rc1.0.20191113042239-ea84732a7725+incompatible

Thanks to @Shivam010 on Medium

---

Original, deprecated answer

Here's how I did it.

Checkout the repository on the desired branch/tag. e.g.

git clone -b v19.03.5 [email protected]:docker/engine.git

Then

cd engine
TZ=UTC git --no-pager show \
  --quiet \
  --abbrev=12 \
  --date='format-local:%Y%m%d%H%M%S' \
  --format="%cd-%h"

And i get

20191113042239-ea84732a7725

For use in go.mod as

replace github.com/docker/docker v1.13.1 => github.com/docker/engine v0.0.0-20191113042239-ea84732a7725