path/filepath: make Walk example runnable in the playground

Relates to #9679

Change-Id: I68951f664d2a03812dae309c580c181869d8af21
Reviewed-on: https://go-review.googlesource.com/122237
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/path/filepath/example_unix_test.go

@@ -8,7 +8,6 @@ package filepath_test
 
 import (
 	"fmt"
-	"os"
 	"path/filepath"
 )
 
@@ -80,25 +79,3 @@ func ExampleJoin() {
 	// a/b/c
 	// a/b/c
 }
-
-func ExampleWalk() {
-	dir := "dir/to/walk"
-	subDirToSkip := "skip" // dir/to/walk/skip
-
-	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
-		if err != nil {
-			fmt.Printf("prevent panic by handling failure accessing a path %q: %v\n", path, err)
-			return err
-		}
-		if info.IsDir() && info.Name() == subDirToSkip {
-			fmt.Printf("skipping a dir without errors: %+v \n", info.Name())
-			return filepath.SkipDir
-		}
-		fmt.Printf("visited file: %q\n", path)
-		return nil
-	})
-
-	if err != nil {
-		fmt.Printf("error walking the path %q: %v\n", dir, err)
-	}
-}

src/path/filepath/example_unix_walk_test.go

+// Copyright 2018 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.
+
+// +build !windows,!plan9
+
+package filepath_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+func prepareTestDirTree(tree string) (string, error) {
+	tmpDir, err := ioutil.TempDir("", "")
+	if err != nil {
+		return "", fmt.Errorf("error creating temp directory: %v\n", err)
+	}
+
+	err = os.MkdirAll(filepath.Join(tmpDir, tree), 0755)
+	if err != nil {
+		os.RemoveAll(tmpDir)
+		return "", err
+	}
+
+	return tmpDir, nil
+}
+
+func ExampleWalk() {
+	tmpDir, err := prepareTestDirTree("dir/to/walk/skip")
+	if err != nil {
+		fmt.Printf("unable to create test dir tree: %v\n", err)
+		return
+	}
+	defer os.RemoveAll(tmpDir)
+	os.Chdir(tmpDir)
+
+	subDirToSkip := "skip"
+
+	fmt.Println("On Unix:")
+	err = filepath.Walk(".", func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			fmt.Printf("prevent panic by handling failure accessing a path %q: %v\n", path, err)
+			return err
+		}
+		if info.IsDir() && info.Name() == subDirToSkip {
+			fmt.Printf("skipping a dir without errors: %+v \n", info.Name())
+			return filepath.SkipDir
+		}
+		fmt.Printf("visited file or dir: %q\n", path)
+		return nil
+	})
+	if err != nil {
+		fmt.Printf("error walking the path %q: %v\n", tmpDir, err)
+		return
+	}
+	// Output:
+	// On Unix:
+	// visited file or dir: "."
+	// visited file or dir: "dir"
+	// visited file or dir: "dir/to"
+	// visited file or dir: "dir/to/walk"
+	// skipping a dir without errors: skip
+}