path/filepath: fix EvalSymlinks(".") on windows

Also new tests added. So, perhaps, this CL corrects
even more broken EvalSymlinks behaviour.

Fixes #12451

Change-Id: I81b9d92bab74bcb8eca6db6633546982fe5cec87
Reviewed-on: https://go-review.googlesource.com/16192Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/path/filepath/path_test.go

@@ -752,6 +752,18 @@ var EvalSymlinksTests = []EvalSymlinksTest{
 	{"test/linkabs", "/"},
 }
 
+// findEvalSymlinksTestDirsDest searches testDirs
+// for matching path and returns correspondent dest.
+func findEvalSymlinksTestDirsDest(t *testing.T, testDirs []EvalSymlinksTest, path string) string {
+	for _, d := range testDirs {
+		if d.path == path {
+			return d.dest
+		}
+	}
+	t.Fatalf("did not find %q in testDirs slice", path)
+	return ""
+}
+
 // simpleJoin builds a file name from the directory and path.
 // It does not use Join because we don't want ".." to be evaluated.
 func simpleJoin(dir, path string) string {
@@ -780,8 +792,22 @@ func TestEvalSymlinks(t *testing.T) {
 		t.Fatal("eval symlink for tmp dir:", err)
 	}
 
+	tests := EvalSymlinksTests
+	testdirs := EvalSymlinksTestDirs
+	if runtime.GOOS == "windows" {
+		if len(tmpDir) < 3 {
+			t.Fatalf("tmpDir path %q is too short", tmpDir)
+		}
+		if tmpDir[1] != ':' {
+			t.Fatalf("tmpDir path %q must have drive letter in it", tmpDir)
+		}
+		newtest := EvalSymlinksTest{"test/linkabswin", tmpDir[:3]}
+		tests = append(tests, newtest)
+		testdirs = append(testdirs, newtest)
+	}
+
 	// Create the symlink farm using relative paths.
-	for _, d := range EvalSymlinksTestDirs {
+	for _, d := range testdirs {
 		var err error
 		path := simpleJoin(tmpDir, d.path)
 		if d.dest == "" {
@@ -794,8 +820,13 @@ func TestEvalSymlinks(t *testing.T) {
 		}
 	}
 
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	// Evaluate the symlink farm.
-	for _, d := range EvalSymlinksTests {
+	for _, d := range tests {
 		path := simpleJoin(tmpDir, d.path)
 		dest := simpleJoin(tmpDir, d.dest)
 		if filepath.IsAbs(d.dest) || os.IsPathSeparator(d.dest[0]) {
@@ -806,6 +837,56 @@ func TestEvalSymlinks(t *testing.T) {
 		} else if filepath.Clean(p) != filepath.Clean(dest) {
 			t.Errorf("Clean(%q)=%q, want %q", path, p, dest)
 		}
+
+		// test EvalSymlinks(".")
+		func() {
+			defer func() {
+				err := os.Chdir(wd)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}()
+
+			err := os.Chdir(path)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			p, err := filepath.EvalSymlinks(".")
+			if err != nil {
+				t.Errorf(`EvalSymlinks(".") in %q directory error: %v`, d.path, err)
+				return
+			}
+			if p == "." {
+				return
+			}
+			want := filepath.Clean(findEvalSymlinksTestDirsDest(t, testdirs, d.path))
+			if p == want {
+				return
+			}
+			t.Errorf(`EvalSymlinks(".") in %q directory returns %q, want "." or %q`, d.path, p, want)
+		}()
+
+		// test EvalSymlinks where parameter is relative path
+		func() {
+			defer func() {
+				err := os.Chdir(wd)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}()
+
+			err := os.Chdir(tmpDir)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			if p, err := filepath.EvalSymlinks(d.path); err != nil {
+				t.Errorf("EvalSymlinks(%q) error: %v", d.path, err)
+			} else if filepath.Clean(p) != filepath.Clean(d.dest) {
+				t.Errorf("Clean(%q)=%q, want %q", d.path, p, d.dest)
+			}
+		}()
 	}
 }
 

src/path/filepath/symlink.go

@@ -5,68 +5,99 @@
 package filepath
 
 import (
-	"bytes"
 	"errors"
 	"os"
+	"runtime"
 )
 
-const utf8RuneSelf = 0x80
+// isRoot returns true if path is root of file system
+// (`/` on unix and `/`, `\`, `c:\` or `c:/` on windows).
+func isRoot(path string) bool {
+	if runtime.GOOS != "windows" {
+		return path == "/"
+	}
+	switch len(path) {
+	case 1:
+		return os.IsPathSeparator(path[0])
+	case 3:
+		return path[1] == ':' && os.IsPathSeparator(path[2])
+	}
+	return false
+}
 
-func walkSymlinks(path string) (string, error) {
-	const maxIter = 255
-	originalPath := path
-	// consume path by taking each frontmost path element,
-	// expanding it if it's a symlink, and appending it to b
-	var b bytes.Buffer
-	for n := 0; path != ""; n++ {
-		if n > maxIter {
-			return "", errors.New("EvalSymlinks: too many links in " + originalPath)
-		}
+// isDriveLetter returns true if path is Windows drive letter (like "c:").
+func isDriveLetter(path string) bool {
+	if runtime.GOOS != "windows" {
+		return false
+	}
+	return len(path) == 2 && path[1] == ':'
+}
 
-		// find next path component, p
-		var i = -1
-		for j, c := range path {
-			if c < utf8RuneSelf && os.IsPathSeparator(uint8(c)) {
-				i = j
-				break
-			}
-		}
-		var p string
-		if i == -1 {
-			p, path = path, ""
-		} else {
-			p, path = path[:i], path[i+1:]
-		}
+func walkLink(path string, linksWalked *int) (newpath string, islink bool, err error) {
+	if *linksWalked > 255 {
+		return "", false, errors.New("EvalSymlinks: too many links")
+	}
+	fi, err := os.Lstat(path)
+	if err != nil {
+		return "", false, err
+	}
+	if fi.Mode()&os.ModeSymlink == 0 {
+		return path, false, nil
+	}
+	newpath, err = os.Readlink(path)
+	if err != nil {
+		return "", false, err
+	}
+	*linksWalked++
+	return newpath, true, nil
+}
 
-		if p == "" {
-			if b.Len() == 0 {
-				// must be absolute path
-				b.WriteRune(Separator)
+func walkLinks(path string, linksWalked *int) (string, error) {
+	switch dir, file := Split(path); {
+	case dir == "":
+		newpath, _, err := walkLink(file, linksWalked)
+		return newpath, err
+	case file == "":
+		if isDriveLetter(dir) {
+			// appending "." to avoid bug in Join (see issue 11551)
+			return dir + ".", nil
+		}
+		if os.IsPathSeparator(dir[len(dir)-1]) {
+			if isRoot(dir) {
+				return dir, nil
 			}
-			continue
+			return walkLinks(dir[:len(dir)-1], linksWalked)
 		}
-
-		fi, err := os.Lstat(b.String() + p)
+		newpath, _, err := walkLink(dir, linksWalked)
+		return newpath, err
+	default:
+		newdir, err := walkLinks(dir, linksWalked)
 		if err != nil {
 			return "", err
 		}
-		if fi.Mode()&os.ModeSymlink == 0 {
-			b.WriteString(p)
-			if path != "" || (b.Len() == 2 && len(p) == 2 && p[1] == ':') {
-				b.WriteRune(Separator)
-			}
-			continue
-		}
-
-		// it's a symlink, put it at the front of path
-		dest, err := os.Readlink(b.String() + p)
+		newpath, islink, err := walkLink(Join(newdir, file), linksWalked)
 		if err != nil {
 			return "", err
 		}
-		if IsAbs(dest) || os.IsPathSeparator(dest[0]) {
-			b.Reset()
+		if !islink {
+			return newpath, nil
+		}
+		if IsAbs(newpath) || os.IsPathSeparator(newpath[0]) {
+			return newpath, nil
 		}
-		path = dest + string(Separator) + path
+		return Join(newdir, newpath), nil
+
+	}
+}
+
+func walkSymlinks(path string) (string, error) {
+	if path == "" {
+		return path, nil
+	}
+	var linksWalked int // to protect against cycles
+	newpath, err := walkLinks(path, &linksWalked)
+	if err != nil {
+		return "", err
 	}
-	return Clean(b.String()), nil
+	return Clean(newpath), nil
 }

src/path/filepath/symlink_windows.go

@@ -47,10 +47,14 @@ func toLong(path string) (string, error) {
 }
 
 func evalSymlinks(path string) (string, error) {
-	path, err := walkSymlinks(path)
+	newpath, 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 {