path/filepath: walkSymlinks: return correct error for file with trailing slash

Rather than return os.ErrNotExist for /path/to/existing_file/,
walkSymLinks now returns syscall.ENOTDIR.

This is consistent with behavior of os.Lstat.

Fixes #29372

Change-Id: Id5c471d901db04b2f35d60f60a81b2a0be93cae9
Reviewed-on: https://go-review.googlesource.com/c/155597
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/path/filepath/path_test.go

@@ -15,6 +15,7 @@ import (
 	"runtime"
 	"sort"
 	"strings"
+	"syscall"
 	"testing"
 )
 
@@ -1371,3 +1372,39 @@ func TestWalkSymlink(t *testing.T) {
 	testenv.MustHaveSymlink(t)
 	testWalkSymlink(t, os.Symlink)
 }
+
+func TestIssue29372(t *testing.T) {
+	f, err := ioutil.TempFile("", "issue29372")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+	path := f.Name()
+	defer os.Remove(path)
+
+	isWin := runtime.GOOS == "windows"
+	pathSeparator := string(filepath.Separator)
+	tests := []struct {
+		path string
+		skip bool
+	}{
+		{path + strings.Repeat(pathSeparator, 1), false},
+		{path + strings.Repeat(pathSeparator, 2), false},
+		{path + strings.Repeat(pathSeparator, 1) + ".", false},
+		{path + strings.Repeat(pathSeparator, 2) + ".", false},
+		// windows.GetFinalPathNameByHandle return the directory part with trailing dot dot
+		// C:\path\to\existing_dir\existing_file\.. returns C:\path\to\existing_dir
+		{path + strings.Repeat(pathSeparator, 1) + "..", isWin},
+		{path + strings.Repeat(pathSeparator, 2) + "..", isWin},
+	}
+
+	for i, test := range tests {
+		if test.skip {
+			continue
+		}
+		_, err = filepath.EvalSymlinks(test.path)
+		if err != syscall.ENOTDIR {
+			t.Fatalf("test#%d: want %q, got %q", i, syscall.ENOTDIR, err)
+		}
+	}
+}

src/path/filepath/symlink.go

@@ -8,10 +8,13 @@ import (
 	"errors"
 	"os"
 	"runtime"
+	"syscall"
 )
 
 func walkSymlinks(path string) (string, error) {
 	volLen := volumeNameLen(path)
+	pathSeparator := string(os.PathSeparator)
+
 	if volLen < len(path) && os.IsPathSeparator(path[volLen]) {
 		volLen++
 	}
@@ -50,7 +53,7 @@ func walkSymlinks(path string) (string, error) {
 			}
 			if r < volLen {
 				if len(dest) > volLen {
-					dest += string(os.PathSeparator)
+					dest += pathSeparator
 				}
 				dest += ".."
 			} else {
@@ -62,7 +65,7 @@ func walkSymlinks(path string) (string, error) {
 		// Ordinary path component. Add it to result.
 
 		if len(dest) > volumeNameLen(dest) && !os.IsPathSeparator(dest[len(dest)-1]) {
-			dest += string(os.PathSeparator)
+			dest += pathSeparator
 		}
 
 		dest += path[start:end]
@@ -76,7 +79,7 @@ func walkSymlinks(path string) (string, error) {
 
 		if fi.Mode()&os.ModeSymlink == 0 {
 			if !fi.Mode().IsDir() && end < len(path) {
-				return "", os.ErrNotExist
+				return "", syscall.ENOTDIR
 			}
 			continue
 		}

src/path/filepath/symlink_windows.go

@@ -159,6 +159,18 @@ func evalSymlinksUsingGetFinalPathNameByHandle(path string) (string, error) {
 	return "", errors.New("GetFinalPathNameByHandle returned unexpected path=" + s)
 }
 
+func symlinkOrDir(path string) (string, error) {
+	fi, err := os.Lstat(path)
+	if err != nil {
+		return "", err
+	}
+
+	if fi.Mode()&os.ModeSymlink == 0 && !fi.Mode().IsDir() {
+		return "", syscall.ENOTDIR
+	}
+	return path, nil
+}
+
 func samefile(path1, path2 string) bool {
 	fi1, err := os.Lstat(path1)
 	if err != nil {
@@ -176,7 +188,11 @@ func evalSymlinks(path string) (string, error) {
 	if err != nil {
 		newpath2, err2 := evalSymlinksUsingGetFinalPathNameByHandle(path)
 		if err2 == nil {
-			return toNorm(newpath2, normBase)
+			normPath, toNormErr := toNorm(newpath2, normBase)
+			if toNormErr != nil {
+				return "", toNormErr
+			}
+			return symlinkOrDir(normPath)
 		}
 		return "", err
 	}