path/filepath: keep walking if EvalSymlinks returns symlink

Fixes #13582

Change-Id: I220f3c7b9511b3c080874f5c42f2a431fdddcbb7
Reviewed-on: https://go-review.googlesource.com/17794
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/path/filepath/path_test.go

@@ -895,6 +895,75 @@ func TestEvalSymlinks(t *testing.T) {
 	}
 }
 
+func TestIssue13582(t *testing.T) {
+	switch runtime.GOOS {
+	case "android", "nacl", "plan9":
+		t.Skipf("skipping on %s", runtime.GOOS)
+	}
+	if !supportsSymlinks {
+		t.Skip("skipping because symlinks are not supported")
+	}
+
+	tmpDir, err := ioutil.TempDir("", "issue13582")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	dir := filepath.Join(tmpDir, "dir")
+	err = os.Mkdir(dir, 0755)
+	if err != nil {
+		t.Fatal(err)
+	}
+	linkToDir := filepath.Join(tmpDir, "link_to_dir")
+	err = os.Symlink(dir, linkToDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	file := filepath.Join(linkToDir, "file")
+	err = ioutil.WriteFile(file, nil, 0644)
+	if err != nil {
+		t.Fatal(err)
+	}
+	link1 := filepath.Join(linkToDir, "link1")
+	err = os.Symlink(file, link1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	link2 := filepath.Join(linkToDir, "link2")
+	err = os.Symlink(link1, link2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// /tmp may itself be a symlink!
+	realTmpDir, err := filepath.EvalSymlinks(tmpDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	realDir := filepath.Join(realTmpDir, "dir")
+	realFile := filepath.Join(realDir, "file")
+
+	tests := []struct {
+		path, want string
+	}{
+		{dir, realDir},
+		{linkToDir, realDir},
+		{file, realFile},
+		{link1, realFile},
+		{link2, realFile},
+	}
+	for _, test := range tests {
+		have, err := filepath.EvalSymlinks(test.path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if have != test.want {
+			t.Errorf("EvalSymlinks(%q) returns %q, want %q", test.path, have, test.want)
+		}
+	}
+}
+
 // Test directories relative to temporary directory.
 // The tests are run in absTestDirs[0].
 var absTestDirs = []string{

src/path/filepath/symlink.go

@@ -85,7 +85,6 @@ func walkLinks(path string, linksWalked *int) (string, error) {
 			return newpath, nil
 		}
 		return Join(newdir, newpath), nil
-
 	}
 }
 
@@ -94,9 +93,25 @@ func walkSymlinks(path string) (string, error) {
 		return path, nil
 	}
 	var linksWalked int // to protect against cycles
-	newpath, err := walkLinks(path, &linksWalked)
-	if err != nil {
-		return "", err
+	for {
+		i := linksWalked
+		newpath, err := walkLinks(path, &linksWalked)
+		if err != nil {
+			return "", err
+		}
+		if runtime.GOOS == "windows" {
+			// walkLinks(".", ...) always retuns "." on unix.
+			// But on windows it returns symlink target, if current
+			// directory is a symlink. Stop the walk, if symlink
+			// target is not absolute path, and return "."
+			// to the caller (just like unix does).
+			if path == "." && !IsAbs(newpath) {
+				return ".", nil
+			}
+		}
+		if i == linksWalked {
+			return Clean(newpath), nil
+		}
+		path = newpath
 	}
-	return Clean(newpath), nil
 }

src/path/filepath/symlink_windows.go

@@ -47,15 +47,10 @@ func toLong(path string) (string, error) {
 }
 
 func evalSymlinks(path string) (string, error) {
-	newpath, err := walkSymlinks(path)
+	path, err := walkSymlinks(path)
 	if err != nil {
 		return "", err
 	}
-	// discard the walk if path is "." and link destination is relative path (just like unix does)
-	if path != "." || IsAbs(newpath) {
-		path = newpath
-	}
-
 	p, err := toShort(path)
 	if err != nil {
 		return "", err