Switch to using GetFinalPathNameByHandle

Author: jakebailey

go.mod

@@ -5,6 +5,7 @@ go 1.23.3
 require (
 	github.com/go-json-experiment/json v0.0.0-20241127185351-9802db03f36a
 	github.com/google/go-cmp v0.6.0
+	golang.org/x/sys v0.27.0
 	golang.org/x/tools v0.27.0
 	gotest.tools/v3 v3.5.1
 )

go.sum

@@ -6,6 +6,8 @@ golang.org/x/mod v0.22.0 h1:D4nJWe9zXqHOmWqj4VMOJhvzj7bEZg4wEYa759z1pH4=
 golang.org/x/mod v0.22.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
 golang.org/x/sync v0.9.0 h1:fEo0HyrW1GIgZdpbhCRO0PkJajUS5H9IFUztCgEo2jQ=
 golang.org/x/sync v0.9.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sys v0.27.0 h1:wBqf8DvsY9Y/2P8gAfPDEYNuS30J4lPHJxXSb/nJZ+s=
+golang.org/x/sys v0.27.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/tools v0.27.0 h1:qEKojBykQkQ4EynWy4S8Weg69NumxKdn40Fce3uc/8o=
 golang.org/x/tools v0.27.0/go.mod h1:sUi0ZgbwW9ZPAq26Ekut+weQPR5eIM6GQLQ1Yjm1H0Q=
 gotest.tools/v3 v3.5.1 h1:EENdUnS3pdur5nybKYIh2Vfgc8IUNBjxDPSjtiJcOzU=

internal/vfs/os.go

@@ -82,7 +82,7 @@ func (vfs *osFS) Realpath(path string) string {
 
 	orig := path
 	path = filepath.FromSlash(path)
-	path, err := walkSymlinks(path)
+	path, err := realpath(path)
 	if err != nil {
 		return orig
 	}

internal/vfs/realpath_other.go

@@ -0,0 +1,11 @@
+//go:build !windows
+
+package vfs
+
+import (
+	"path/filepath"
+)
+
+func realpath(path string) (string, error) {
+	return filepath.EvalSymlinks(path)
+}

internal/vfs/symlink_test.go renamed to internal/vfs/realpath_test.go

@@ -0,0 +1,87 @@
+package vfs
+
+import (
+	"errors"
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+// This implementation is based on what Node's fs.realpath.native does, via libuv: https://github.com/libuv/libuv/blob/ec5a4b54f7da7eeb01679005c615fee9633cdb3b/src/win/fs.c#L2937
+
+func realpath(path string) (string, error) {
+	h, err := openMetadata(path)
+	if err != nil {
+		return "", err
+	}
+	defer windows.CloseHandle(h) //nolint:errcheck
+
+	// based on https://github.com/golang/go/blob/f4e3ec3dbe3b8e04a058d266adf8e048bab563f2/src/os/file_windows.go#L389
+
+	const _VOLUME_NAME_DOS = 0
+
+	buf := make([]uint16, 310) // https://github.com/microsoft/go-winio/blob/3c9576c9346a1892dee136329e7e15309e82fb4f/internal/stringbuffer/wstring.go#L13
+	for {
+		n, err := windows.GetFinalPathNameByHandle(h, &buf[0], uint32(len(buf)), _VOLUME_NAME_DOS)
+		if err != nil {
+			return "", err
+		}
+		if n < uint32(len(buf)) {
+			break
+		}
+		buf = make([]uint16, n)
+	}
+
+	s := syscall.UTF16ToString(buf)
+	if len(s) > 4 && s[:4] == `\\?\` {
+		s = s[4:]
+		if len(s) > 3 && s[:3] == `UNC` {
+			// return path like \\server\share\...
+			return `\` + s[3:], nil
+		}
+		return s, nil
+	}
+
+	return "", errors.New("GetFinalPathNameByHandle returned unexpected path: " + s)
+}
+
+func openMetadata(path string) (windows.Handle, error) {
+	// based on https://github.com/microsoft/go-winio/blob/3c9576c9346a1892dee136329e7e15309e82fb4f/pkg/fs/resolve.go#L113
+
+	pathUTF16, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return windows.InvalidHandle, err
+	}
+
+	const (
+		_FILE_ANY_ACCESS = 0
+
+		_FILE_SHARE_READ   = 0x01
+		_FILE_SHARE_WRITE  = 0x02
+		_FILE_SHARE_DELETE = 0x04
+
+		_OPEN_EXISTING = 0x03
+
+		_FILE_FLAG_BACKUP_SEMANTICS = 0x0200_0000
+	)
+
+	h, err := windows.CreateFile(
+		pathUTF16,
+		_FILE_ANY_ACCESS,
+		_FILE_SHARE_READ|_FILE_SHARE_WRITE|_FILE_SHARE_DELETE,
+		nil,
+		_OPEN_EXISTING,
+		_FILE_FLAG_BACKUP_SEMANTICS,
+		0,
+	)
+
+	if err != nil {
+		return 0, &os.PathError{
+			Op:   "CreateFile",
+			Path: path,
+			Err:  err,
+		}
+	}
+	return h, nil
+}