dirSymLinkWindows

fn dirSymLinkWindows(
    userdata: ?*anyopaque,
    dir: Dir,
    target_path: []const u8,
    sym_link_path: []const u8,
    flags: Dir.SymLinkFlags,
) Dir.SymLinkError!void {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    _ = t;
    const w = windows;

    // Target path does not use sliceToPrefixedFileW because certain paths
    // are handled differently when creating a symlink than they would be
    // when converting to an NT namespaced path.
    var target_path_w: WindowsPathSpace = undefined;
    target_path_w.len = try w.wtf8ToWtf16Le(&target_path_w.data, target_path);
    target_path_w.data[target_path_w.len] = 0;
    // However, we need to canonicalize any path separators to `\`, since if
    // the target path is relative, then it must use `\` as the path separator.
    std.mem.replaceScalar(
        u16,
        target_path_w.data[0..target_path_w.len],
        std.mem.nativeToLittle(u16, '/'),
        std.mem.nativeToLittle(u16, '\\'),
    );

    const sym_link_path_w = try sliceToPrefixedFileW(dir.handle, sym_link_path, .{});

    const SYMLINK_DATA = extern struct {
        ReparseTag: w.IO_REPARSE_TAG,
        ReparseDataLength: w.USHORT,
        Reserved: w.USHORT,
        SubstituteNameOffset: w.USHORT,
        SubstituteNameLength: w.USHORT,
        PrintNameOffset: w.USHORT,
        PrintNameLength: w.USHORT,
        Flags: w.ULONG,
    };

    const symlink_handle = handle: {
        if (OpenFile(sym_link_path_w.span(), .{
            .access_mask = .{
                .GENERIC = .{ .READ = true, .WRITE = true },
                .STANDARD = .{ .SYNCHRONIZE = true },
            },
            .dir = dir.handle,
            .creation = .CREATE,
            .filter = if (flags.is_directory) .dir_only else .non_directory_only,
        })) |handle| {
            break :handle handle;
        } else |err| switch (err) {
            error.IsDir => return error.PathAlreadyExists,
            error.NotDir => return error.Unexpected,
            error.WouldBlock => return error.Unexpected,
            error.PipeBusy => return error.Unexpected,
            error.FileBusy => return error.Unexpected,
            error.NoDevice => return error.Unexpected,
            error.AntivirusInterference => return error.Unexpected,
            else => |e| return e,
        }
    };
    defer w.CloseHandle(symlink_handle);

    // Relevant portions of the documentation:
    // > Relative links are specified using the following conventions:
    // > - Root relative—for example, "\Windows\System32" resolves to "current drive:\Windows\System32".
    // > - Current working directory–relative—for example, if the current working directory is
    // >   C:\Windows\System32, "C:File.txt" resolves to "C:\Windows\System32\File.txt".
    // > Note: If you specify a current working directory–relative link, it is created as an absolute
    // > link, due to the way the current working directory is processed based on the user and the thread.
    // https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createsymboliclinkw
    var is_target_absolute = false;
    const final_target_path = target_path: {
        if (w.hasCommonNtPrefix(u16, target_path_w.span())) {
            // Already an NT path, no need to do anything to it
            break :target_path target_path_w.span();
        } else {
            switch (Dir.path.getWin32PathType(u16, target_path_w.span())) {
                // Rooted paths need to avoid getting put through wToPrefixedFileW
                // (and they are treated as relative in this context)
                // Note: It seems that rooted paths in symbolic links are relative to
                //       the drive that the symbolic exists on, not to the CWD's drive.
                //       So, if the symlink is on C:\ and the CWD is on D:\,
                //       it will still resolve the path relative to the root of
                //       the C:\ drive.
                .rooted => break :target_path target_path_w.span(),
                // Keep relative paths relative, but anything else needs to get NT-prefixed.
                else => if (!Dir.path.isAbsoluteWindowsWtf16(target_path_w.span()))
                    break :target_path target_path_w.span(),
            }
        }
        var prefixed_target_path = try wToPrefixedFileW(dir.handle, target_path_w.span(), .{});
        // We do this after prefixing to ensure that drive-relative paths are treated as absolute
        is_target_absolute = Dir.path.isAbsoluteWindowsWtf16(prefixed_target_path.span());
        break :target_path prefixed_target_path.span();
    };

    // prepare reparse data buffer
    var buffer: [w.MAXIMUM_REPARSE_DATA_BUFFER_SIZE]u8 = undefined;
    const buf_len = @sizeOf(SYMLINK_DATA) + final_target_path.len * 4;
    const header_len = @sizeOf(w.ULONG) + @sizeOf(w.USHORT) * 2;
    const target_is_absolute = Dir.path.isAbsoluteWindowsWtf16(final_target_path);
    const symlink_data: SYMLINK_DATA = .{
        .ReparseTag = .SYMLINK,
        .ReparseDataLength = @intCast(buf_len - header_len),
        .Reserved = 0,
        .SubstituteNameOffset = @intCast(final_target_path.len * 2),
        .SubstituteNameLength = @intCast(final_target_path.len * 2),
        .PrintNameOffset = 0,
        .PrintNameLength = @intCast(final_target_path.len * 2),
        .Flags = if (!target_is_absolute) w.SYMLINK_FLAG_RELATIVE else 0,
    };

    @memcpy(buffer[0..@sizeOf(SYMLINK_DATA)], std.mem.asBytes(&symlink_data));
    @memcpy(buffer[@sizeOf(SYMLINK_DATA)..][0 .. final_target_path.len * 2], @as([*]const u8, @ptrCast(final_target_path)));
    const paths_start = @sizeOf(SYMLINK_DATA) + final_target_path.len * 2;
    @memcpy(buffer[paths_start..][0 .. final_target_path.len * 2], @as([*]const u8, @ptrCast(final_target_path)));
    switch ((try deviceIoControl(&.{
        .file = .{ .handle = symlink_handle, .flags = .{ .nonblocking = false } },
        .code = .SET_REPARSE_POINT,
        .in = buffer[0..buf_len],
    })).u.Status) {
        .SUCCESS => {},
        .CANCELLED => unreachable,
        .INSUFFICIENT_RESOURCES => return error.SystemResources,
        .PRIVILEGE_NOT_HELD => return error.PermissionDenied,
        .ACCESS_DENIED => return error.AccessDenied,
        .INVALID_DEVICE_REQUEST => return error.FileSystem,
        else => |status| return w.unexpectedStatus(status),
    }
}