path/filepath: return special error from EvalSymlinks

CL 155597 attempted to fix #29372. But it failed to make all new
test cases pass. Also CL 155597 broke some existing code
(see #29449 for details).

Make small adjustment to CL 155597 that fixes both #29372 and #29449.

Suggested by Ian.

Updates #29372
Fixes #29449

Change-Id: I9777a615514d3f152af5acb65fb1239e696607b6
Reviewed-on: https://go-review.googlesource.com/c/156398
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

5 files changed, 54 insertions, 41 deletions

diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index 1b9f286c4d..cbddda88b6 100644
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -1382,27 +1382,18 @@ func TestIssue29372(t *testing.T) {
 	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},
+	tests := []string{
+		path + strings.Repeat(pathSeparator, 1),
+		path + strings.Repeat(pathSeparator, 2),
+		path + strings.Repeat(pathSeparator, 1) + ".",
+		path + strings.Repeat(pathSeparator, 2) + ".",
+		path + strings.Repeat(pathSeparator, 1) + "..",
+		path + strings.Repeat(pathSeparator, 2) + "..",
 	}
 
 	for i, test := range tests {
-		if test.skip {
-			continue
-		}
-		_, err = filepath.EvalSymlinks(test.path)
+		_, err = filepath.EvalSymlinks(test)
 		if err != syscall.ENOTDIR {
 			t.Fatalf("test#%d: want %q, got %q", i, syscall.ENOTDIR, err)
 		}
diff --git a/src/path/filepath/path_windows_test.go b/src/path/filepath/path_windows_test.go
index 63eab18116..3fcccfab78 100644
--- a/src/path/filepath/path_windows_test.go
+++ b/src/path/filepath/path_windows_test.go
@@ -536,17 +536,39 @@ func TestNTNamespaceSymlink(t *testing.T) {
 	}
 	target := strings.Trim(string(output), " \n\r")
 
-	link := filepath.Join(tmpdir, "link")
-	output, err = exec.Command("cmd", "/c", "mklink", "/J", link, target).CombinedOutput()
+	dirlink := filepath.Join(tmpdir, "dirlink")
+	output, err = exec.Command("cmd", "/c", "mklink", "/J", dirlink, target).CombinedOutput()
 	if err != nil {
-		t.Fatalf("failed to run mklink %v %v: %v %q", link, target, err, output)
+		t.Fatalf("failed to run mklink %v %v: %v %q", dirlink, target, err, output)
 	}
 
-	got, err := filepath.EvalSymlinks(link)
+	got, err := filepath.EvalSymlinks(dirlink)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if want := vol + `\`; got != want {
-		t.Errorf(`EvalSymlinks(%q): got %q, want %q`, link, got, want)
+		t.Errorf(`EvalSymlinks(%q): got %q, want %q`, dirlink, got, want)
+	}
+
+	file := filepath.Join(tmpdir, "file")
+	err = ioutil.WriteFile(file, []byte(""), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	target += file[len(filepath.VolumeName(file)):]
+
+	filelink := filepath.Join(tmpdir, "filelink")
+	output, err = exec.Command("cmd", "/c", "mklink", filelink, target).CombinedOutput()
+	if err != nil {
+		t.Fatalf("failed to run mklink %v %v: %v %q", filelink, target, err, output)
+	}
+
+	got, err = filepath.EvalSymlinks(filelink)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := file; got != want {
+		t.Errorf(`EvalSymlinks(%q): got %q, want %q`, filelink, got, want)
 	}
 }
diff --git a/src/path/filepath/symlink.go b/src/path/filepath/symlink.go
index a08b85a29c..4b41039e25 100644
--- a/src/path/filepath/symlink.go
+++ b/src/path/filepath/symlink.go
@@ -8,7 +8,6 @@ import (
 	"errors"
 	"os"
 	"runtime"
-	"syscall"
 )
 
 func walkSymlinks(path string) (string, error) {
@@ -79,7 +78,7 @@ func walkSymlinks(path string) (string, error) {
 
 		if fi.Mode()&os.ModeSymlink == 0 {
 			if !fi.Mode().IsDir() && end < len(path) {
-				return "", syscall.ENOTDIR
+				return "", slashAfterFilePathError
 			}
 			continue
 		}
diff --git a/src/path/filepath/symlink_unix.go b/src/path/filepath/symlink_unix.go
index d20e63a987..b57e7f2277 100644
--- a/src/path/filepath/symlink_unix.go
+++ b/src/path/filepath/symlink_unix.go
@@ -2,6 +2,15 @@
 
 package filepath
 
+import (
+	"syscall"
+)
+
+// walkSymlinks returns slashAfterFilePathError error for paths like
+// //path/to/existing_file/ and /path/to/existing_file/. and /path/to/existing_file/..
+
+var slashAfterFilePathError = syscall.ENOTDIR
+
 func evalSymlinks(path string) (string, error) {
 	return walkSymlinks(path)
 }
diff --git a/src/path/filepath/symlink_windows.go b/src/path/filepath/symlink_windows.go
index 1108b3ddff..531dc26fc0 100644
--- a/src/path/filepath/symlink_windows.go
+++ b/src/path/filepath/symlink_windows.go
@@ -159,18 +159,6 @@ 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 {
@@ -183,16 +171,20 @@ func samefile(path1, path2 string) bool {
 	return os.SameFile(fi1, fi2)
 }
 
+// walkSymlinks returns slashAfterFilePathError error for paths like
+// //path/to/existing_file/ and /path/to/existing_file/. and /path/to/existing_file/..
+
+var slashAfterFilePathError = errors.New("attempting to walk past file path.")
+
 func evalSymlinks(path string) (string, error) {
 	newpath, err := walkSymlinks(path)
+	if err == slashAfterFilePathError {
+		return "", syscall.ENOTDIR
+	}
 	if err != nil {
 		newpath2, err2 := evalSymlinksUsingGetFinalPathNameByHandle(path)
 		if err2 == nil {
-			normPath, toNormErr := toNorm(newpath2, normBase)
-			if toNormErr != nil {
-				return "", toNormErr
-			}
-			return symlinkOrDir(normPath)
+			return toNorm(newpath2, normBase)
 		}
 		return "", err
 	}