Golang Conditional Compilation With Build Tags

Sometimes we're developing Go packages that rely on specific features and want to include or exclude certain functionality. One such example is profiling[1] and debugging, which we likely want to exclude in release builds.

1: profiling

Go does not have a preprocessor like C/C++ but supports build tags. These are implemented as comments at the top of files. We can guard files we want to exclude with `// +build debug`. `debug` here can be anything. These files will be excluded by default. If we want to include them, we have to invoke `go build -tags=debug`.

Example, I'll mount a profile in debug mode via `debug.go`:

// +build debug

package main

import (
	_ "net/http/pprof"
	"runtime"

	"github.com/go-chi/chi"
	"github.com/go-chi/chi/middleware"
)

func profiler(r *chi.Mux) {
	runtime.SetBlockProfileRate(1)
	runtime.SetMutexProfileFraction(1)
	r.Mount("/debug", middleware.Profiler())
}

The release inverts the build tag in `release.go` and just implements a stub.

// +build !debug

package main

import "github.com/go-chi/chi"

func profiler(r *chi.Mux) {}

My `Makefile` then looks as follows and requires me to build releases with `make release`.

default: debug

release:
	@go build -mod=vendor .

debug:
	@go build -mod=vendor -tags=debug .

Note that build tags are for building and are therefore not exposed in the runtime. This is a feature to change things up regarding CPU arch, binary inclusion and size and similar. It is not a replacement for flags regarding logging or debug modes.

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