fastwalk: don't clean the path argument to Walk on Windows

On Windows don't attempt to clean the path argument to Walk since the
existing clean logic (cleanRootPath) transforms paths like "C:\" => "C:"
which are not equivalent.

This logic only existed to make the joining of paths simpler and should
probably be removed since we shouldn't be modifying user provided paths.

TODO: Investigate if anything relies on the current clean logic and
remove it if nothing does.

Fixes: #37

dirent_export_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io/fs"
 	"os"
+	"runtime"
 	"testing"
 	"time"
 )
@@ -29,26 +30,44 @@ func FormatFileInfo(fi fs.FileInfo) string {
 	})
 }
 
+// NB: this test lives here and not in fastwalk_test.go since we need to
+// access the internal cleanRootPath function.
 func TestCleanRootPath(t *testing.T) {
-	tests := map[string]string{
-		"":      "",
-		"/":     "/",
-		"//":    "/",
-		"/foo":  "/foo",
-		"/foo/": "/foo",
-		"a":     "a",
-		`C:/`:   `C:`,
-	}
-	if os.PathSeparator != '/' {
-		const sep = string(os.PathSeparator)
-		tests["C:"+sep] = `C:`
-		tests["C:"+sep+sep] = `C:`
-		tests[sep+sep] = sep
-	}
-	for in, want := range tests {
-		got := cleanRootPath(in)
-		if got != want {
-			t.Errorf("cleanRootPath(%q) = %q; want: %q", in, got, want)
+	test := func(t *testing.T, tests map[string]string) {
+		t.Helper()
+		for in, want := range tests {
+			got := cleanRootPath(in)
+			if got != want {
+				t.Errorf("cleanRootPath(%q) = %q; want: %q", in, got, want)
+			}
 		}
 	}
+	// NB: The name here isn't exactly correct since we run this for
+	// any non-Windows OS.
+	t.Run("Unix", func(t *testing.T) {
+		if runtime.GOOS == "windows" {
+			t.Skip("test not supported on Windows")
+		}
+		test(t, map[string]string{
+			"":      "",
+			".":     ".",
+			"/":     "/",
+			"//":    "/",
+			"/foo":  "/foo",
+			"/foo/": "/foo",
+			"a":     "a",
+		})
+	})
+	// Test that cleanRootPath is a no-op on Windows
+	t.Run("Windows", func(t *testing.T) {
+		if runtime.GOOS != "windows" {
+			t.Skip("test only supported on Windows")
+		}
+		test(t, map[string]string{
+			`C:/`:              `C:/`,
+			`C://`:             `C://`,
+			`\\?\GLOBALROOT`:   `\\?\GLOBALROOT`,
+			`\\?\GLOBALROOT\\`: `\\?\GLOBALROOT\\`,
+		})
+	})
 }

fastwalk.go

@@ -563,12 +563,14 @@ func (w *walker) joinPaths(dir, base string) string {
 	// Handle the case where the root path argument to Walk is "/"
 	// without this the returned path is prefixed with "//".
 	if os.PathSeparator == '/' {
-		if dir == "/" {
+		if len(dir) != 0 && dir[len(dir)-1] == '/' {
 			return dir + base
 		}
 		return dir + "/" + base
 	}
-	// TODO: handle the above case of the argument to Walk being "/"
+	if len(dir) != 0 && os.IsPathSeparator(dir[len(dir)-1]) {
+		return dir + base
+	}
 	if w.toSlash {
 		return dir + "/" + base
 	}
@@ -625,7 +627,17 @@ func (w *walker) walk(root string, info DirEntry, runUserCallback bool) error {
 	return nil
 }
 
+// cleanRootPath returns the root path trimmed of extraneous trailing slashes.
+// This is a no-op on Windows.
 func cleanRootPath(root string) string {
+	if runtime.GOOS == "windows" || len(filepath.VolumeName(root)) != 0 {
+		// Windows paths or any path with a volume name (which AFAIK should
+		// only be Windows) are a bit too complicated to clean.
+		return root
+	}
+	if len(filepath.VolumeName(root)) != 0 {
+		return root
+	}
 	for i := len(root) - 1; i >= 0; i-- {
 		if !os.IsPathSeparator(root[i]) {
 			return root[:i+1]

fastwalk_test.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"regexp"
 	"runtime"
 	"sort"
 	"strings"
@@ -388,6 +389,207 @@ func TestFastWalk_LongPath(t *testing.T) {
 	}
 }
 
+func TestFastWalk_WindowsRootPaths(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skip("test only supported on Windows")
+	}
+
+	sameFile := func(t *testing.T, name1, name2 string) bool {
+		fi1, err := os.Stat(name1)
+		if err != nil {
+			t.Fatal(err)
+		}
+		fi2, err := os.Stat(name2)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return os.SameFile(fi1, fi2)
+	}
+
+	walk := func(t *testing.T, root string) map[string]fs.DirEntry {
+		var mu sync.Mutex
+		seen := make(map[string]fs.DirEntry)
+		errStop := errors.New("errStop")
+		fn := func(path string, de fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+			mu.Lock()
+			seen[path] = de
+			mu.Unlock()
+			if path != root && de.IsDir() {
+				return fs.SkipDir
+			}
+			return nil
+		}
+		err := fastwalk.Walk(nil, root, fastwalk.IgnorePermissionErrors(fn))
+		if err != nil && err != errStop {
+			t.Fatal(err)
+		}
+		if len(seen) <= 1 {
+			// If we are a child of the root directory we should have visited at
+			// least two entries: the root itself and a directory that leads to,
+			// or is, our current working directory.
+			t.Fatalf("empty directory: %s", root)
+		}
+		return seen
+	}
+
+	pwd, err := filepath.Abs(".")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	vol := filepath.VolumeName(pwd)
+	if !regexp.MustCompile(`^[A-Za-z]:$`).MatchString(vol) {
+		// Ignore UNC names and other weird Windows paths to keep this simple.
+		t.Skipf("unsupported volume name: %s for path: %s", vol, pwd)
+	}
+	if !sameFile(t, pwd, vol) {
+		t.Skipf("skipping %s and %s should be considered the same file", pwd, vol)
+	}
+
+	// Test that walking the disk root ("C:\") actually walks the disk root.
+	// Previously, there was a bug where the path "C:\" was transformed to "C:"
+	// before walking which caused fastwalk to walk the current directory.
+	//
+	// https://github.com/charlievieth/fastwalk/issues/37
+	t.Run("FullyQualified", func(t *testing.T) {
+		root := vol + `\`
+		if sameFile(t, pwd, root) {
+			t.Skipf("the current working directory (%s) is the disk root: %s", pwd, root)
+		}
+		seen := walk(t, root)
+
+		// Make sure we don't append an extraneous slash to the root ("C:\" => "C:\\a").
+		for path := range seen {
+			rest := strings.TrimPrefix(path, vol)
+			if strings.Contains(rest, `\\`) {
+				t.Errorf(`path contains multiple consecutive slashes after volume (%s): "%s"`,
+					vol, path)
+			}
+			if s := filepath.Clean(path); s != path {
+				t.Errorf(`filepath.Clean("%s") == "%s"`, path, s)
+			}
+		}
+
+		// Make sure we didn't walk the current directory. This will happen if
+		// the root argument to Walk is a drive letter ("C:\") but we strip off
+		// the trailing slash ("C:\" => "C:") since this makes the path relative
+		// to the current directory on drive "C".
+		//
+		// See: https://github.com/charlievieth/fastwalk/issues/37
+		//
+		// Docs: https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#fully-qualified-vs-relative-paths
+		for path, de := range seen {
+			if path == root {
+				// Ignore root since filepath.Base("C:\") == "\" and "C:\" and "\"
+				// are equivalent.
+				continue
+			}
+			fi1, err := de.Info()
+			if err != nil {
+				if os.IsNotExist(err) || os.IsPermission(err) {
+					continue
+				}
+				t.Fatal(err)
+			}
+			name := filepath.Base(path)
+			fi2, err := os.Lstat(name)
+			if err != nil {
+				continue
+			}
+			if os.SameFile(fi1, fi2) {
+				t.Errorf("Walking root (%s) returned entries for the current working "+
+					"directory (%s): file %s is the same as %s", root, pwd, path, name)
+			}
+		}
+
+		// Add file base name mappings
+		for _, de := range seen {
+			seen[de.Name()] = de
+		}
+
+		// Make sure we read some files from the disk root.
+		des, err := os.ReadDir(root)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(des) == 0 {
+			t.Fatalf("Disk root %s contains no files!", root)
+		}
+		same := 0
+		for _, d2 := range des {
+			d1 := seen[d2.Name()]
+			if d1 == nil {
+				continue
+			}
+			fi1, err := d1.Info()
+			if err != nil {
+				t.Log(err)
+				continue
+			}
+			fi2, err := d2.Info()
+			if err != nil {
+				t.Log(err)
+				continue
+			}
+			if os.SameFile(fi1, fi2) {
+				same++
+			}
+		}
+		// TODO: Expect to see N% of files and use
+		// a more descriptive error message
+		if same == 0 {
+			t.Fatalf(`Error failed to walk dist root: "%s"`, root)
+		}
+	})
+
+	// Test that paths like "C:" are treated as a relative path.
+	t.Run("Relative", func(t *testing.T) {
+		seen := walk(t, vol)
+
+		// Make sure we don't append an extraneous slash to the root ("C:\" => "C:\\a").
+		for path := range seen {
+			rest := strings.TrimPrefix(path, vol)
+			if strings.Contains(rest, `\\`) {
+				t.Errorf(`path contains multiple consecutive slashes after volume (%s): "%s"`,
+					vol, path)
+			}
+			if path == vol {
+				continue // Clean("C:") => "C:."
+			}
+			if s := filepath.Clean(path); s != path {
+				t.Errorf(`filepath.Clean("%s") == "%s"`, path, s)
+			}
+		}
+
+		// Make sure we walk the current directory.
+		for path, de := range seen {
+			if path == vol {
+				// Ignore the volume since filepath.Base("C:") == "\" and "C:" and "\"
+				// are not equivalent.
+				continue
+			}
+			fi1, err := de.Info()
+			if err != nil {
+				t.Fatal(err)
+			}
+			name := filepath.Base(path)
+			fi2, err := os.Lstat(name)
+			if err != nil {
+				// NB: This test will fail if this file is removed while it's
+				// running. There are workarounds for this, but for now it's
+				// simpler to just error if that happens.
+				t.Fatal(err)
+			}
+			if !os.SameFile(fi1, fi2) {
+				t.Errorf("Expected files (%s) and (%s) to be the same", path, name)
+			}
+		}
+	})
+}
+
 func TestFastWalk_Symlink(t *testing.T) {
 	testFastWalk(t, map[string]string{
 		"foo/foo.go":       "one",