ci: add Windows job #272

Remove recently introduced SpawnConnectInfo and SpawnConnectInfoToArgsFn type
aliases since they are the same on all platforms and might obscure the fact
that connect info should be treated as an opaque string.

Co-authored-by: Sjors Provoost <sjors@sprovoost.nl>

This change was written with Claude Sonnet 4.6.

Replace the Unix-only UnixListener test helper with a cross-platform
SocketListener backed by a std::variant<sockaddr_un> (TCP arm will be
added later for Wine compatibility).

- test/socketlistener.h: New header with SocketListener class extracted from
  the pattern of UnixListener but using SocketId/SocketError types,
  std::filesystem for temp dir cleanup, and mp::CloseSocket for teardown.
  Uses std::variant<sockaddr_un> so the TCP arm can be appended later without
  restructuring the class.
- test/unixlistener.h: Deleted.
- test/listen_tests.cpp: Switch to socketlistener.h and socketlistener.
- test/connect_tests.cpp: Switch to socketlistener.h and socketlistener.

This change was written with Claude Sonnet 4.6.

Move POSIX-only headers in util.cpp into a #ifndef WIN32 block so the file
compiles on Windows without modification. Guard the Unix-only helpers (MakeArgv,
MaxFd, ChildFail, SpawnError*, ReadSpawnResult, WriteSpawnError, KillAndReapChild)
with a single #ifndef WIN32 block. Guard the extern "C" environ declaration
likewise. Guard Unix-only includes in spawn_tests.cpp and connect_tests.cpp and
wrap the Unix-only spawn tests with #ifndef WIN32.

No Windows implementations are added here; those come in a later commit.

This change was written with Claude Sonnet 4.6.

Co-authored-by: Sjors Provoost <sjors@sprovoost.nl>

Add Windows-specific code to support building and running on Windows:

- util.h: Guard ProcessId/SocketId/SocketError type aliases with WIN32
  ifdefs so they use SOCKET/uintptr_t on Windows and int on Unix.
  Add winsock2.h include on Windows.
- util.cpp: Guard Unix-specific system headers with WIN32 ifdefs. Add
  Windows-specific includes (windows.h, winsock2.h). Guard MaxFd() with
  #ifndef WIN32. Add GetCurrentThreadId() branch in ThreadName(). Add
  win32Socketpair() forward-declare. Add Windows branch in SocketPair()
  using win32Socketpair(). Add CommandLineFromArgv() helper needed to
  construct CreateProcess command lines. Add Windows branch in
  SpawnProcess() using named pipes and WSADuplicateSocket to pass socket
  to child. Add Windows branch in StartSpawned() reading socket from
  named pipe. Add Windows branch in WaitProcess() using
  WaitForSingleObject/GetExitCodeProcess.
- proxy.cpp: Add SocketOutputStream class on Windows (analogous to
  FdOutputStream but using SOCKET/send()). Add Windows branch in
  EventLoop constructor to create m_post_writer using SocketOutputStream.

Co-Authored-By: ViniciusCestarii <viniciuscestari01@gmail.com>

SpawnProcess on Windows creates a named pipe with PIPE_WAIT and then calls
ConnectNamedPipe synchronously. If the child exits or crashes before
connecting, ConnectNamedPipe blocks forever with no recovery path.

Fix by opening the pipe with FILE_FLAG_OVERLAPPED and using
WaitForMultipleObjects on both the connect event and the child process
handle. If the process handle signals first, the child died without
connecting and SpawnProcess throws instead of hanging. Since the pipe is
now in overlapped mode, WriteFile also requires an OVERLAPPED structure;
use GetOverlappedResult with bWait=TRUE to handle both synchronous and
asynchronous completion.

Add a Windows-only test that spawns a child which exits immediately
without opening the named pipe and asserts SpawnProcess does not block.

(https://github.com/bitcoin-core/libmultiprocess/pull/231#discussion_r3706021950)

Co-Authored-By: ViniciusCestarii <viniciuscestari01@gmail.com>
This change was written with Claude Sonnet 4.6.

Allow code to compile without pthreads available, as required for MSVC
compatibility. Avoid unconditional POSIX calls (fork, posix_spawn,
pthread_getname_np) by moving them into #ifndef WIN32 or HAVE_PTHREAD_*
guards. When pthreads is available on Windows (detected via cmake
HAVE_PTHREAD_* checks), still use it for thread name reporting since it
provides useful information at low cost.

Also add Threads::Threads as an explicit dependency of the multiprocess
library. proxy.cpp directly uses thread_local, std::this_thread, and
std::thread, and the dependency was previously satisfied only through
transitive linkage from CapnProto::kj-async.

This change was written with Claude Sonnet 4.6.

Add TCP (sockaddr_in) support to SocketListener and platform-conditional
header guards so the class compiles and works on Windows:

- Wrap POSIX headers (arpa/inet.h, netinet/in.h, sys/socket.h, sys/un.h)
  in #else of #ifdef WIN32, with Windows equivalents (afunix.h,
  ws2tcpip.h) in the #ifdef WIN32 branch.
- Add a WsaInit static initializer on Windows that calls WSAStartup
  before any socket operations. Tests create sockets directly (not via
  StartSpawned), so Winsock must be initialized here.
- Add Init(sockaddr_in&) and Connect(const sockaddr_in&) overloads for
  TCP loopback connections.
- Use TCP on Windows to work around Wine's lack of the AcceptEx extension
  required by KJ's AF_UNIX listener; Unix platforms continue using
  AF_UNIX.
- Expand std::variant<sockaddr_un> to std::variant<sockaddr_in, sockaddr_un>.

This change was written with Claude Sonnet 4.6.

- shell.nix: add `windows` parameter that selects pkgs.pkgsCross.mingwW64
  as the cross target; also change crossPkgs default from import<nixpkgs>{}
  to null (cleaner API). When windows=true, add native pkgs.capnproto to
  nativeBuildInputs so capnp/capnpc-c++ are in PATH for cmake code generation,
  and add wine64Packages.staging so ctest can run mptest.exe via wine.
  Change llvmBase to always use pkgs (native) instead of crossPkgs.

- ci/configs/windows.bash: new config that cross-compiles with mingw,
  sets CMAKE_SYSTEM_NAME=Windows, CMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER
  (so cmake finds native capnp from PATH), CMAKE_CROSSCOMPILING_EMULATOR=wine
  (so ctest runs mptest.exe via wine), and sets MPGEN_PRE_BUILD=1.

- ci/scripts/ci.sh: add MPGEN_PRE_BUILD support: when set, build native mpgen
  in $CI_DIR-native before the main cross build, then inject
  -DMPGEN_EXECUTABLE into CMAKE_ARGS. This is needed because cmake's
  add_custom_command does not use CMAKE_CROSSCOMPILING_EMULATOR, so the
  cross-compiled mpgen.exe cannot be used as a code generator directly.

This change was written with Claude Sonnet 4.6.

The proxy-server code generated for test/mp/test/foo.capnp now has more
sections than MSVC's default object file format allows, failing the
Windows native VS CI job with "error C1128: number of sections exceeded
object file format limit: compile with /bigobj"
(https://github.com/bitcoin/bitcoin/actions/runs/36945085020/job/110645241551).
Bitcoin Core already passes /bigobj for its own debug builds.

Not reproduced locally; based on the error message.

This change was written with Claude Opus 5.5 (1M context).

Move Windows out of the general build matrix while preserving its check
name, configuration, and cache keys. Reuse the Nix environment and setup
steps with YAML anchors so both jobs keep the same build procedure.

This lets follow-up jobs depend on the Windows build without waiting for
the other configurations in the matrix.

Package test and example executables from the existing Windows cross-build
with their runtime DLL dependencies. Download them on windows-latest and
run mptest plus the calculator example on Windows.

This complements Wine execution with real Windows runtime testing and a
smoke test of spawned IPC processes.

Depend directly on the Windows cross-build so native tests can run while
the other build configurations are still in progress.