Watch.zig: remove realpath call, prefer NtCreateFile over CreateFileW

Author: jayrod246

lib/std/Build/Watch.zig

@@ -340,19 +340,55 @@ const Os = switch (builtin.os.tag) {
                     const reaction_set = rs: {
                         const gop = try w.dir_table.getOrPut(gpa, path);
                         if (!gop.found_existing) {
-                            var realpath_buf: [std.fs.max_path_bytes]u8 = undefined;
-                            const realpath = try path.root_dir.handle.realpath(path.sub_path, &realpath_buf);
-                            const realpath_w = try windows.sliceToPrefixedFileW(null, realpath);
-                            const dir_handle = windows.kernel32.CreateFileW(
-                                realpath_w.span().ptr,
-                                windows.GENERIC_READ,
-                                windows.FILE_SHARE_DELETE | windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE,
+                            // The following code is a drawn out NtCreateFile call. (mostly adapted from std.fs.Dir.makeOpenDirAccessMaskW)
+                            // It's necessary in order to get the flags are required when calling ReadDirectoryChangesW.
+                            const root_fd = path.root_dir.handle.fd;
+                            const sub_path = path.subPathOrDot();
+                            const sub_path_w = try windows.sliceToPrefixedFileW(root_fd, sub_path);
+                            const path_len_bytes = std.math.cast(u16, sub_path_w.len * 2) orelse return error.NameTooLong;
+
+                            var nt_name = windows.UNICODE_STRING{
+                                .Length = @intCast(path_len_bytes),
+                                .MaximumLength = @intCast(path_len_bytes),
+                                .Buffer = @constCast(sub_path_w.span().ptr),
+                            };
+                            var attr = windows.OBJECT_ATTRIBUTES{
+                                .Length = @sizeOf(windows.OBJECT_ATTRIBUTES),
+                                .RootDirectory = if (std.fs.path.isAbsoluteWindowsW(sub_path_w.span())) null else root_fd,
+                                .Attributes = 0, // Note we do not use OBJ_CASE_INSENSITIVE here.
+                                .ObjectName = &nt_name,
+                                .SecurityDescriptor = null,
+                                .SecurityQualityOfService = null,
+                            };
+                            var io: windows.IO_STATUS_BLOCK = undefined;
+                            var dir_handle: windows.HANDLE = undefined;
+                            const rc = windows.ntdll.NtCreateFile(
+                                &dir_handle,
+                                windows.SYNCHRONIZE | windows.GENERIC_READ | windows.FILE_LIST_DIRECTORY,
+                                &attr,
+                                &io,
                                 null,
-                                windows.OPEN_EXISTING,
-                                windows.FILE_FLAG_BACKUP_SEMANTICS | windows.FILE_FLAG_OVERLAPPED,
+                                0,
+                                windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE | windows.FILE_SHARE_DELETE,
+                                windows.FILE_OPEN,
+                                windows.FILE_DIRECTORY_FILE | windows.FILE_OPEN_FOR_BACKUP_INTENT,
                                 null,
+                                0,
                             );
 
+                            switch (rc) {
+                                .SUCCESS => {},
+                                .OBJECT_NAME_INVALID => return error.BadPathName,
+                                .OBJECT_NAME_NOT_FOUND => return error.FileNotFound,
+                                .OBJECT_NAME_COLLISION => return error.PathAlreadyExists,
+                                .OBJECT_PATH_NOT_FOUND => return error.FileNotFound,
+                                .NOT_A_DIRECTORY => return error.NotDir,
+                                // This can happen if the directory has 'List folder contents' permission set to 'Deny'
+                                .ACCESS_DENIED => return error.AccessDenied,
+                                .INVALID_PARAMETER => unreachable,
+                                else => return windows.unexpectedStatus(rc),
+                            }
+
                             assert(dir_handle != windows.INVALID_HANDLE_VALUE);
 
                             // `dir_handle` may already be present in the table in