go-ifdef

Add trivial #ifdef, #else and #define macros to your go code.

go-ifdef has built-in support for GOOS in form of #ifdef GOOS:<target>

You can use any valid GOOS value.

Usage

1. Install go-ifdef with:

go install github.com/pijng/go-ifdef@latest

2. Build your project with go build while specifying go-ifdef preprocessor:

go build -a -toolexec="go-ifdef" main.go

Important:

• -a flag is required to recompile all your project, otherwise go compiler might do nothing and use cached build

3. Run the final binary:

./main

Demonstration

Suppose we have this code:

package main

import "fmt"

func main() {
	var i int

	// #ifdef GOOS:darwin
	i = 100
	// #else
	i = 727
	// #endif

	fmt.Println(i)
}

If we compile it for MacOS and apply go-ifdef as a preprocessor, then we'll get the following result:

$ env GOOS=darwin go build -a -toolexec="go-ifdef" main.go
$ ./main
100
$

But if we change the directive to linux, for example like this:

package main

import "fmt"

func main() {
	var i int

	// #ifdef GOOS:linux
	i = 100
	// #else
	i = 727
	// #endif

	fmt.Println(i)
}

and then compile it to the same MacOS, then we'll get different result:

$ env GOOS=darwin go build -a -toolexec="go-ifdef" main.go
$ ./main
727
$

Or another example with conditional struct populating:

package main

import "fmt"

func main() {
	fmt.Printf("%+v\n", someResult())
}

type result struct {
	os    string
	items []int
}

func someResult() result {
	res := result{os: "Not windows"}
	res.items = append(res.items, []int{1, 2, 3}...)

	// #ifdef GOOS:windows
	res.os = "windows!"
	res.items = append(res.items, []int{4, 5}...)
	// #endif

	return res
}

If we compile this code for a platform other than Windows, then upon execution, we will get the following:

$ env GOOS=linux go build -a -toolexec="go-ifdef" main.go
$ ./main
{os:Not windows items:[1 2 3]}
$

But if we compile it for Windows, we'll get this instead:

$ env GOOS=windows go build -a -toolexec="go-ifdef" main.go
$ ./main
{os:windows! items:[1 2 3 4 5]}
$

---

Custom directives

You can define custom directives with #define keyword. ⚠️ Only boolean values are supported

For example:

package main

import "fmt"

// #define DEBUG true

func main() {
	fmt.Printf("%d\n", someResult())
}

func someResult() int {
	// #ifdef DEBUG
	fmt.Println("DEBUGGING")
	// #else
	fmt.Println("NOT DEBUGGING")
	// #endif

	return 0
}

If we compile it and run:

$ go build -a -toolexec="go-ifdef" main.go
$ ./main
DEBUGGING
0
$

But if we change #define DEBUG to false:

package main

import "fmt"

// #define DEBUG false

func main() {
	fmt.Printf("%d\n", someResult())
}

func someResult() int {
	// #ifdef DEBUG
	fmt.Println("DEBUGGING")
	// #else
	fmt.Println("NOT DEBUGGING")
	// #endif

	return 0
}

Then the result will be different:

$ go build -a -toolexec="go-ifdef" main.go
$ ./main
NOT DEBUGGING
0
$

Or you can pass a directive value with env when invoking go build command:

package main

import "fmt"

// #define DEBUG

func main() {
	fmt.Printf("%d\n", someResult())
}

func someResult() int {
	// #ifdef DEBUG
	fmt.Println("DEBUGGING")
	// #else
	fmt.Println("NOT DEBUGGING")
	// #endif

	return 0
}

If we pass DEBUG=true with env and compile this code:

$ env DEBUG=true go build -a -toolexec="go-ifdef" main.go
$ ./main
DEBUGGING
0
$