Generate overlay patches JSON for go build -overlay option.

# build this tool
go install 'github.com/yz89122/go-patcher@latest'
# use with go build to build your binary
go build -overlay "$(go-patcher the/patches/dir)" -o main ./main.go

The second argument (which is the/pathes/dir in above example) is the path to the patches directory, it's optional and default to $PWD/patches.

In the patches directory, the structure of the directories will be taken as import pathes. For example, errors/errors.go will replace the file errors.go in the standard package errors.

go-patcher example
/tmp/go-patcher574244752/patches.json

In this example, we replaced the standard errors.New() to return a new error with stack trace, and printed the stack trace in the main function.

// main.go
package main

import (
	"errors"
	"fmt"
	"os"
	"runtime"
)

func main() {
	var err = errors.New("test err")
	if replacedErr, ok := err.(interface{ Stack() []uintptr }); ok {
		fmt.Println("successfully replaced")
		for _, pc := range replacedErr.Stack() {
			var f = runtime.FuncForPC(pc)
			var filename, line = f.FileLine(pc)
			fmt.Printf("%s\n\t%s:%d\n", f.Name(), filename, line)
		}
	} else {
		fmt.Fprintln(os.Stderr, `failed to replace package "errors"`)
		os.Exit(1)
	}
}

# clone this repository
git clone '[email protected]:yz89122/go-patcher.git'
# to cloned repository
cd 'go-patcher'
# to example directory
cd 'run-example'
# run example
./run-example.sh

successfully replaced
runtime.main
        /usr/local/go/src/runtime/proc.go:264
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1582