cmd/cgo: merge overlayDir into one package

There are many copies of overlaydir_test.go between the cgo tests
from when these couldn't share code. Now that they can, merge these
copies into a cmd/cgo/internal/cgotest package.

Change-Id: I203217f5d08e6306cb049a13718652cf7c447b80
Reviewed-on: https://go-review.googlesource.com/c/go/+/497078
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

2 files changed, 2 insertions, 79 deletions

diff --git a/src/cmd/cgo/internal/testplugin/overlaydir_test.go b/src/cmd/cgo/internal/testplugin/overlaydir_test.go
deleted file mode 100644
index e2c32d83ce..0000000000
--- a/src/cmd/cgo/internal/testplugin/overlaydir_test.go
+++ /dev/null
@@ -1,78 +0,0 @@
-// 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 plugin_test
-
-import (
-	"io"
-	"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.Walk(srcRoot, func(srcPath string, info os.FileInfo, err error) error {
-		if err != nil || srcPath == srcRoot {
-			return err
-		}
-
-		suffix := strings.TrimPrefix(srcPath, srcRoot)
-		for len(suffix) > 0 && suffix[0] == filepath.Separator {
-			suffix = suffix[1:]
-		}
-		dstPath := filepath.Join(dstRoot, suffix)
-
-		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 copy directories (don't symlink them).
-		// 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 the OS supports symlinks, use them instead of copying bytes.
-		if err := os.Symlink(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
-	})
-}
diff --git a/src/cmd/cgo/internal/testplugin/plugin_test.go b/src/cmd/cgo/internal/testplugin/plugin_test.go
index e211a96304..4c8e3d7833 100644
--- a/src/cmd/cgo/internal/testplugin/plugin_test.go
+++ b/src/cmd/cgo/internal/testplugin/plugin_test.go
@@ -6,6 +6,7 @@ package plugin_test
 
 import (
 	"bytes"
+	"cmd/cgo/internal/cgotest"
 	"context"
 	"flag"
 	"fmt"
@@ -80,7 +81,7 @@ func testMain(m *testing.M) int {
 		"testdata":                           modRoot,
 		filepath.Join("altpath", "testdata"): altRoot,
 	} {
-		if err := overlayDir(dstRoot, srcRoot); err != nil {
+		if err := cgotest.OverlayDir(dstRoot, srcRoot); err != nil {
 			log.Panic(err)
 		}
 		prettyPrintf("mkdir -p %s\n", dstRoot)