From eed92f9df5eed311eb96d9cb3754dfb187bd25d7 Mon Sep 17 00:00:00 2001
From: Ariejan de Vroom <ariejan@ariejan.net>
Date: Mon, 12 Oct 2015 13:00:24 +0200
Subject: [PATCH] Add: Building golang cli tools update

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+date = "2015-10-12"
+title = "Building Golang CLI Tools Update"
+tags = ["golang"]
+description = "After my previous post on using a `Makefile` to set version and build info I got some valuable feedback from other Gophers. Here's an update."
+slug = "building-golang-cli-tools-update"
++++
+
+In my [previous post][previous] I discussed how to use a `Makefile` to set version and 
+build information at compile time. Although this approach may work fine for you, it has
+three drawbacks I want to discuss.
+
+### 1. Simplicity
+
+Andrew responded on the [golang-nuts mailing list][golang-nuts] with the following comment:
+
+> To me it seems like you took something simple and cross platform "go generate" + "go install/build" and turned it into something more complicated and less portable.
+
+Although I'm not sure `go generate` is relevant in this case, I agree that on some level
+a `Makefile` is complicating things unnecessarily. Let's remove it!
+
+### 2. Non-reproducable builds
+
+Guilio responded with:
+
+> I only have an issue with buildTime: it makes the build not reproducible.
+
+This is a valid point. The idea that if you compile a given version of your application, 
+the resulting binary's hash (be it MD5 or whatever) should be equal to that of any other 
+binary build from that specific version.
+
+By using `BuildTime` the binary is never the same. 
+
+Build time is also irrelevant. It does not matter _when_ a binary was compiled, but it
+_does matter_ which precise version was build. 
+
+Let's replace `BuildTime` with the current git commit hash instead.
+
+### 3. Why is there a `VERSION` file?
+
+If you're going to store version information under version control, you might as well
+put it right in the code, where it belongs. 
+
+Let's remove `VERSION` and instead create a nice `version.go` to handle everything.
+
+## Let's refactor
+
+Okay, first things to go are `Makefile` and `VERSION`.
+
+Next, I created a `core/version.go` which contains the necessary version information.
+I've also taken the liberty of creating a proper struct for the version information,
+including major, minor and patch numbers, as well as a label and release name.
+
+    package core
+
+    import "fmt"
+
+    type version struct {
+        Major, Minor, Patch int
+        Label               string
+        Name                string
+    }
+
+    var Version = version{1, 2, 3, "dev", "Chuck Norris"}
+
+    var Build string
+
+    func (v version) String() string {
+        if v.Label != "" {
+            return fmt.Sprintf("Roll version %d.%d.%d-%s \"%s\"\nGit commit hash: %s", v.Major, v.Minor, v.Patch, v.Label, v.Name, Build)
+        } else {
+            return fmt.Sprintf("Roll version %d.%d.%d \"%s\"\nGit commit hash: %s", v.Major, v.Minor, v.Patch, v.Name, Build)
+        }
+    }
+
+As you can see, it's quite easy to set and update the version numbers, label and release name.
+
+`Build` is still set at compile time and contains the current git commit hash. 
+
+Because the `go build` command is quite long, I've put it in a nice `build.sh` file that
+makes building easier.
+
+    go build -ldflags "-X github.com/ariejan/roll/core.Build=`git rev-parse HEAD`" -o roll main.go
+
+This will result in a build that reports version information like this:
+
+    $ ./roll version
+    Roll version 1.2.3-dev "Chuck Norris"
+    Git commit hash: b72b076af8b18ef4f6b10296f12840f23258acec
+
+### Check that SHA
+
+If you want, you can [grab the code][code] and run `./build.sh` yourself. The resulting binary
+ has a SHA-1 of `3ad7509279690d99e4144332dc200ede732663fd`. Yay for reproducable builds!
+
+### Naming variables in ldlags
+
+A short note on Peter Kleiweg's comment. He pointed out that I could use
+
+    "-X main.Build=`git rev-parse HEAD`"
+
+This would be true if the `Build` variable is in the `main` package. But because it's
+not (it's in `core`) I have to specify the full package name.
+
+## Thank you!
+
+Thanks to all the awesome gophers responding to my previous post! It's great to get
+feedback and get to learn more about Golang. Keep the comments coming, please!
+
+[previous]: https://ariejan.net/2015/10/03/a-makefile-for-golang-cli-tools/
+[golang-nuts]: https://groups.google.com/forum/#!forum/golang-nuts
+[code]: https://github.com/ariejan/roll