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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bootstrap_test
import (
"io"
"io/fs"
"os"
"path/filepath"
"strings"
)
// overlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
//
// TODO: Once we no longer need to support the misc module in GOPATH mode,
// factor this function out into a package to reduce duplication.
func overlayDir(dstRoot, srcRoot string) error {
dstRoot = filepath.Clean(dstRoot)
if err := os.MkdirAll(dstRoot, 0777); err != nil {
return err
}
srcRoot, err := filepath.Abs(srcRoot)
if err != nil {
return err
}
return filepath.WalkDir(srcRoot, func(srcPath string, entry fs.DirEntry, err error) error {
if err != nil || srcPath == srcRoot {
return err
}
if filepath.Base(srcPath) == "testdata" {
// We're just building, so no need to copy those.
return fs.SkipDir
}
suffix := strings.TrimPrefix(srcPath, srcRoot)
for len(suffix) > 0 && suffix[0] == filepath.Separator {
suffix = suffix[1:]
}
dstPath := filepath.Join(dstRoot, suffix)
info, err := entry.Info()
perm := info.Mode() & os.ModePerm
if info.Mode()&os.ModeSymlink != 0 {
info, err = os.Stat(srcPath)
if err != nil {
return err
}
perm = info.Mode() & os.ModePerm
}
// Always make copies of directories.
// If we add a file in the overlay, we don't want to add it in the original.
if info.IsDir() {
return os.MkdirAll(dstPath, perm|0200)
}
// If we can use a hard link, do that instead of copying bytes.
// Go builds don't like symlinks in some cases, such as go:embed.
if err := os.Link(srcPath, dstPath); err == nil {
return nil
}
// Otherwise, copy the bytes.
src, err := os.Open(srcPath)
if err != nil {
return err
}
defer src.Close()
dst, err := os.OpenFile(dstPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
if err != nil {
return err
}
_, err = io.Copy(dst, src)
if closeErr := dst.Close(); err == nil {
err = closeErr
}
return err
})
}
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