build: ci/doc win64-cross build via nix

ci/test/00_setup_env_win64.sh

@@ -7,9 +7,9 @@
 export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_win64
-export CI_IMAGE_NAME_TAG="mirror.gcr.io/debian:trixie"  # Check that https://packages.debian.org/trixie/g++-mingw-w64-ucrt64 can cross-compile
+export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:26.04"
 export HOST=x86_64-w64-mingw32ucrt
-export PACKAGES="g++-mingw-w64-ucrt64 nsis"
+export PACKAGES="nix-bin nix-setup-systemd"
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"

ci/test/00_setup_env_win64_msvcrt.sh

@@ -7,9 +7,9 @@
 export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_win64_msvcrt
-export CI_IMAGE_NAME_TAG="mirror.gcr.io/debian:trixie"  # Check that https://packages.debian.org/trixie/g++-mingw-w64-x86-64-posix (version 14.x, similar to guix) can cross-compile
+export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:26.04"
 export HOST=x86_64-w64-mingw32
-export PACKAGES="g++-mingw-w64-x86-64-posix nsis"
+export PACKAGES="nix-bin nix-setup-systemd"
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"

ci/test/01_base_install.sh

@@ -50,6 +50,11 @@ elif [ "$CI_OS_NAME" != "macos" ]; then
   ${CI_RETRY_EXE} apt-get install --no-install-recommends --no-upgrade -y $PACKAGES $CI_BASE_PACKAGES
 fi
 
+if [[ ${HOST:-} == x86_64-w64-mingw32* ]]; then
+  # Install Nix packages.
+  NIX_BUILD_SHELL=bash nix-shell "${BASE_ROOT_DIR}/contrib/devtools/shell-win64-cross.nix" --run true
+fi
+
 if [ -n "${APT_LLVM_V}" ]; then
   update-alternatives --install /usr/bin/clang++ clang++ "/usr/bin/clang++-${APT_LLVM_V}" 100
   update-alternatives --install /usr/bin/clang clang "/usr/bin/clang-${APT_LLVM_V}" 100

ci/test/02_run_container.py

@@ -183,7 +183,18 @@ def main():
         f"{os.environ['BASE_ROOT_DIR']}",
     ])
     ci_exec([f"{os.environ['BASE_ROOT_DIR']}/ci/test/01_base_install.sh"])
-    ci_exec([f"{os.environ['BASE_ROOT_DIR']}/ci/test/03_test_script.sh"])
+    test_script = f"{os.environ['BASE_ROOT_DIR']}/ci/test/03_test_script.sh"
+    if os.environ.get("HOST", "").startswith("x86_64-w64-mingw32"):
+        ci_exec([
+            "env",
+            "NIX_BUILD_SHELL=bash",
+            "nix-shell",
+            f"{os.environ['BASE_ROOT_DIR']}/contrib/devtools/shell-win64-cross.nix",
+            "--run",
+            f"exec bash {shlex.quote(test_script)}",
+        ])
+    else:
+        ci_exec([test_script])
 
     if not os.getenv("DANGER_RUN_CI_ON_HOST"):
         print("Stop and remove CI container by ID")

ci/test_imagefile

@@ -17,6 +17,7 @@ ENV BASE_ROOT_DIR=${BASE_ROOT_DIR}
 # Make retry available in PATH, needed for CI_RETRY_EXE
 COPY ./ci/retry/retry /usr/bin/retry
 COPY ./ci/test/00_setup_env.sh ./${FILE_ENV} ./ci/test/01_base_install.sh ${BASE_ROOT_DIR}/ci/test/
+COPY ./contrib/devtools/shell-win64-cross.nix ${BASE_ROOT_DIR}/contrib/devtools/
 COPY ./ci/test/*.patch ${BASE_ROOT_DIR}/ci/test/
 
 # Bash is required, so install it when missing

contrib/devtools/shell-win64-cross.nix

@@ -0,0 +1,45 @@
+# Copyright (c) The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+{ pkgs ? import (builtins.fetchTarball {
+    # Pin, to keep the versions of the toolchain aligned with the versions used by Guix.
+    url = "https://github.com/NixOS/nixpkgs/archive/531670d871c0e29724a02f3cbcac170adc65b58c.tar.gz";
+  }) {} }:
+
+let
+  host = builtins.getEnv "HOST";
+  crossPkgs = if host == "x86_64-w64-mingw32ucrt"
+    then pkgs.pkgsCross.ucrt64
+    else if host == "x86_64-w64-mingw32"
+      then pkgs.pkgsCross.mingwW64
+      else throw "Unsupported HOST: ${host}";
+  toolchain = crossPkgs.stdenv.cc.targetPrefix;
+  pthreads = crossPkgs.windows.pthreads;
+in
+
+pkgs.mkShellNoCC {
+  packages = [
+    crossPkgs.gcc14
+    pkgs.nsis
+  ];
+
+  shellHook = ''
+    export NIX_CFLAGS_COMPILE="-isystem ${pthreads}/include $NIX_CFLAGS_COMPILE"
+    export NIX_LDFLAGS="-L${pthreads}/lib $NIX_LDFLAGS"
+    export CC=$(command -v ${toolchain}gcc)
+    export CXX=$(command -v ${toolchain}g++)
+    export LD=$(command -v ${toolchain}ld)
+    export AR=$(command -v ${toolchain}ar)
+    export AS=$(command -v ${toolchain}as)
+    export RANLIB=$(command -v ${toolchain}ranlib)
+    export NM=$(command -v ${toolchain}nm)
+    export STRIP=$(command -v ${toolchain}strip)
+    export OBJCOPY=$(command -v ${toolchain}objcopy)
+    export OBJDUMP=$(command -v ${toolchain}objdump)
+    export READELF=$(command -v ${toolchain}readelf)
+    export SIZE=$(command -v ${toolchain}size)
+    export WINDRES=$(command -v ${toolchain}windres)
+    export RC=$(command -v ${toolchain}windres)
+  '';
+}

depends/README.md

@@ -160,14 +160,23 @@ proceeding with a cross-compile. Under the depends directory, create a
 subdirectory named `SDKs`. Then, place the extracted SDK under this new directory.
 For more information, see [SDK Extraction](../contrib/macdeploy/README.md#sdk-extraction).
 
-#### For Windows cross compilation using MSVCRT
+#### For Windows cross compilation
+
+Using MSVCRT:
 
     apt install g++-mingw-w64-x86-64-posix
 
-#### For Windows cross compilation using UCRT
+Using UCRT:
 
     apt install g++-mingw-w64-ucrt64
 
+Some Ubuntu or Debian versions may not offer a working package. In this case,
+you may install `nix-bin` and use the Nix shell from the repository root:
+
+    apt install nix-bin
+    NIX_BUILD_SHELL=bash HOST=x86_64-w64-mingw32 nix-shell contrib/devtools/shell-win64-cross.nix  # MSVCRT
+    NIX_BUILD_SHELL=bash HOST=x86_64-w64-mingw32ucrt nix-shell contrib/devtools/shell-win64-cross.nix  # UCRT
+
 #### For Linux cross compilation
 
 Please note that package availability might depend on the arch+OS you are building on.