build Windows with clang-cl instead of MSVC

clang-cl keeps the MSVC ABI, so the Windows SDK, the vcpkg packages and
D3D12 all still link; only the front end changes. That front end is the
one whose module support has been giving way - global module fragment
merging and type completeness at a template's instantiation point.

Switches the job to Ninja, which is where CMake's module scanning is best
supported, with vcvars64 for the SDK paths. Ninja is single-config, so
the artifacts move from build/bin/<config>/ to build/bin/.

CMakeLists: the MSVC-only blocks tested CMAKE_CXX_COMPILER_ID, which
clang-cl reports as Clang, so the version resource, the icon and /utf-8
would have been dropped silently. They test MSVC now, which is true for
both. /MAP and /MP stay behind a real-MSVC check - the first is a
link.exe spelling, the second clang-cl rejects.

.github/workflows/build_bin.yml

@@ -24,11 +24,11 @@ env:
 jobs:
 
   # ============================================================
-  # Windows / MSVC
+  # Windows / Clang (clang-cl)
   # ============================================================
 
   windows:
-    name: Windows x64 / MSVC
+    name: Windows x64 / Clang
     runs-on: windows-2022
 
     steps:
@@ -45,16 +45,27 @@ jobs:
           python-version: "3.14"
           architecture: "x64"
 
+      # clang-cl rather than plain clang: it keeps the MSVC ABI, so it links
+      # against the same Windows SDK, vcpkg packages and D3D12 libraries, and
+      # only the front end changes. Pinned to the version the Linux job uses.
+      - name: Install LLVM and Ninja
+        shell: pwsh
+        run: |
+          choco install llvm --version=22.1.8 -y --no-progress
+          choco install ninja -y --no-progress
+
       - name: Show environment
         shell: pwsh
         run: |
           python --version
           cmake --version
+          ninja --version
+          & "$env:ProgramFiles\LLVM\bin\clang-cl.exe" --version
 
           Write-Host "Python:"
           Get-Command python
 
-          Write-Host "MSVC:"
+          Write-Host "Visual Studio (for the SDK and the MSVC STL):"
           & "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe" `
             -latest `
             -products * `
@@ -67,30 +78,32 @@ jobs:
         run: |
           call setup.bat
 
+      # Ninja, not MSBuild: CMake's module dependency scanning is best supported
+      # there, and vcvars64 supplies the SDK and library paths clang-cl needs.
       - name: Configure
-        shell: pwsh
+        shell: cmd
         run: |
-          $pythonExe = "${{ steps.python.outputs.python-path }}"
+          for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do set VSPATH=%%i
-          $pythonRoot = Split-Path $pythonExe
+          call "%VSPATH%\VC\Auxiliary\Build\vcvars64.bat"
-
+          for %%p in ("${{ steps.python.outputs.python-path }}") do set PYROOT=%%~dpp
-          Write-Host "Python root: $pythonRoot"
+          cmake -S . -B build ^
-
+            -G Ninja ^
-          cmake -S . -B build `
+            -DCMAKE_BUILD_TYPE=%CONFIG_WIN% ^
-            -G "Visual Studio 17 2022" `
+            -DCMAKE_C_COMPILER="%ProgramFiles%/LLVM/bin/clang-cl.exe" ^
-            -A x64 `
+            -DCMAKE_CXX_COMPILER="%ProgramFiles%/LLVM/bin/clang-cl.exe" ^
-            "-DPython3_ROOT_DIR=$pythonRoot"
+            -DPython3_ROOT_DIR=%PYROOT%
 
       - name: Build
-        shell: pwsh
+        shell: cmd
         run: |
-          cmake --build build `
+          for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do set VSPATH=%%i
-            --config $env:CONFIG_WIN `
+          call "%VSPATH%\VC\Auxiliary\Build\vcvars64.bat"
-            --parallel
+          cmake --build build --parallel
 
       - name: Copy shaders
         shell: pwsh
         run: |
-          $output = "build/bin/$env:CONFIG_WIN"
+          $output = "build/bin"
 
           New-Item `
             -ItemType Directory `
@@ -108,7 +121,7 @@ jobs:
         with:
           name: maszyna-windows-x64-${{ env.CONFIG_WIN }}
           path: |
-            build/bin/${{ env.CONFIG_WIN }}/
+            build/bin/
           if-no-files-found: error
           retention-days: 14
 
@@ -117,18 +130,18 @@ jobs:
         with:
           name: maszyna-windows-x64-symbols-${{ env.CONFIG_WIN }}
           path: |
-            build/pdb/${{ env.CONFIG_WIN }}/*.pdb
+            build/pdb/*.pdb
-            build/bin/${{ env.CONFIG_WIN }}/*.map
+            build/bin/*.map
           if-no-files-found: warn
           retention-days: 14
 
 
   # ============================================================
-  # Linux / GCC
+  # Linux / Clang
   # ============================================================
 
   linux:
-    name: Linux x64 / GCC
+    name: Linux x64 / Clang
     runs-on: ubuntu-24.04
 
     steps:

CMakeLists.txt

@@ -17,9 +17,10 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/CMake_modules/")
 set(DEPS_DIR ${DEPS_DIR} "${CMAKE_CURRENT_SOURCE_DIR}/ref")
 project("eu07")
 
-# Clang is the only compiler this project is built and tested with on Linux
+# Clang is the compiler this project is built and tested with: clang on Linux,
-# (Clang 22 in CI); MSVC covers Windows. GCC is not supported: its lazy loading
+# clang-cl on Windows, both pinned to 22 in CI. MSVC still configures and is not
-# of module interfaces is broken here, and working around it costs roughly twice
+# rejected, but nothing verifies it. GCC is not supported: its lazy loading of
+# module interfaces is broken here, and working around it costs roughly twice
 # the memory per compiler process.
 if (NOT CMAKE_CXX_COMPILER_ID MATCHES "Clang|MSVC")
 	message(FATAL_ERROR
@@ -444,7 +445,12 @@ set(GLM_INCLUDE_DIR ${GLM_INCLUDE_DIR} "${DEPS_DIR}/glm/")
 configure_file(${CMAKE_SOURCE_DIR}/eu07.rc.in
                ${CMAKE_BINARY_DIR}/eu07.rc @ONLY)
 
-if (${CMAKE_CXX_COMPILER_ID} STREQUAL MSVC)
+# MSVC is true for clang-cl as well - it targets the same ABI and takes the same
+# command line. Testing CMAKE_CXX_COMPILER_ID instead would silently drop the
+# version resource and the icon from a clang-cl build.
+if (MSVC)
+    # the Visual Studio generators enable RC on their own; Ninja does not
+    enable_language(RC)
     set(SOURCES ${SOURCES} ${CMAKE_BINARY_DIR}/eu07.rc)
     set(SOURCES ${SOURCES} eu07.ico)
     add_compile_options("/utf-8")
@@ -508,18 +514,23 @@ target_include_directories(${PROJECT_NAME} PRIVATE
 	"${CMAKE_BINARY_DIR}/geninc"
 	"${GLOBAL_INCLUDE_DIR}")
 
-if (${CMAKE_CXX_COMPILER_ID} STREQUAL MSVC)
+if (MSVC)
 	# override cmake defaults
 	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO " /MD /Zi /O2 /DNDEBUG")
 	set(CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO " /DEBUG /INCREMENTAL:NO /OPT:REF /OPT:ICF")
 
-	target_link_options(${PROJECT_NAME} PRIVATE "/MAP")
-
 	# /wd4996: disable "deprecation" warnings
 	# /wd4244: disable warnings for conversion with possible loss of data
 	# /wd5033: disable because it is all over Python headers
 	set_target_properties(${PROJECT_NAME} PROPERTIES COMPILE_FLAGS "/wd4996 /wd4244 /wd5033")
 	set_target_properties(${PROJECT_NAME} PROPERTIES LINK_FLAGS "/LARGEADDRESSAWARE")
+
+	# /MAP is a link.exe option; lld-link, which clang-cl usually drives, spells
+	# it differently. The map only feeds the debug-symbols artifact, whose upload
+	# tolerates it being absent.
+	if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+		target_link_options(${PROJECT_NAME} PRIVATE "/MAP")
+	endif()
 endif()
 
 set_target_properties( ${PROJECT_NAME}
@@ -724,7 +735,9 @@ if(GENERATE_PDB)
     endif()
 endif()
 
-if(ENABLE_MCC AND MSVC)
+# /MP is an MSVC-only option; clang-cl rejects it, and under Ninja the generator
+# already runs one compiler process per core.
+if(ENABLE_MCC AND CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND NOT CMAKE_GENERATOR MATCHES "Ninja")
     message(STATUS "Enabling multi-processor compilation for MSVC.")
 	add_compile_options(/MP)
 endif()