moonjectlog

Inject fmt.Println at the beginning of each function call.

Usage

1. Install moonjectlog with:

go install github.com/pijng/moonjectlog@latest

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

go build -o output -a -toolexec="moonjectlog <absolute/path/to/project>" main.go

Important:

• -a flag is required to recompile all your project, otherwise go compiler might do nothing and use cached build
• <absolute/path/to/project> is and absolute path to the root of your project. If you run go build from the root – simply specify $PWD as an argument.

3. Run the final binary:

./output

Demonstration

Suppose we have this code:

package main

import "fmt"

func main() {
	fmt.Println(someWork())
	fmt.Println(anotherWork())
	fmt.Println(finalWork())

	fmt.Println("End of main")
}

func someWork() int {
	return 1
}

func anotherWork() int {
	return 2
}

func finalWork() int {
	return 3
}

If we compile and run it, we get the expected output:

$ go build main.go
$ ./main
1
2
3
End of main
$

But if we apply moonjectlog as a preprocessor at compile time, we get the following result:

$ go build -a -toolexec="moonjectlog $PWD" main.go
$ ./main
Calling [main] func
Calling [someWork] func
1
Calling [anotherWork] func
2
Calling [finalWork] func
3
End of main
$

Thus, the preprocessor added a call to fmt.Println("Calling [%s] func") to the body of each function, while the source code remained unchanged.