Getting Started

Install

go get github.com/floatpane/go-patchapply

Requires Go 1.26+. Its only dependency is its sibling, go-mailpatch.

Apply a patch in three lines

p, _ := mailpatch.ParseBytes(raw)            // parse the email
fsys := patchapply.NewDirFS("/path/to/repo") // confined to this root
res, err := patchapply.ApplyPatch(fsys, p, nil)

A full program:

package main

import (
	"log"
	"os"

	"github.com/floatpane/go-mailpatch"
	"github.com/floatpane/go-patchapply"
)

func main() {
	raw, _ := os.ReadFile("fix.patch")

	p, err := mailpatch.ParseBytes(raw)
	if err != nil {
		log.Fatal(err)
	}

	fsys := patchapply.NewDirFS("/path/to/repo")
	res, err := patchapply.ApplyPatch(fsys, p, nil)
	if err != nil {
		log.Fatal(err)
	}

	for _, f := range res.Files {
		log.Printf("%s %s", f.Status, f.Path)
	}
}

The entry points

res, err := patchapply.ApplyPatch(fsys, patch, opts)
res, err := patchapply.ApplyDiff(fsys, diffText, opts)
res, err := patchapply.Apply(fsys, files, opts)
out, err := patchapply.ApplyToBytes(orig, fileChange)

opts may be nil.

The result

type Result struct {
	Files []FileResult
}

type FileResult struct {
	Path    string // resulting path (the removed path, for a deletion)
	OldPath string // previous path for a rename, else empty
	Status  Status // Created | Updated | Removed | Renamed
	Hunks   int    // hunks applied
}

Errors

import "errors"

_, err := patchapply.ApplyPatch(fsys, p, nil)
switch {
case errors.Is(err, patchapply.ErrConflict):
	// a hunk's context could not be matched
case errors.Is(err, patchapply.ErrUnsafePath):
	// a path tried to escape the DirFS root
case errors.Is(err, patchapply.ErrMissing):
	// modify/delete/rename of a file that isn't there
case errors.Is(err, patchapply.ErrExists):
	// add of a file that already exists
}