Windows caching

.github/workflows/unit_tests.yml

@@ -145,6 +145,17 @@ jobs:
       BUILD_TYPE: ${{ matrix.RELEASE && 'RelWithDebInfo' || 'Debug' }}
       TEST_USE_ROCKSDB: ${{ matrix.BACKEND == 'rocksdb' && '1' || '0' }}
       DEADLINE_SCALE_FACTOR: ${{ matrix.BACKEND == 'rocksdb' && '2' || '1' }}
+      # The Visual Studio generator ignores compiler launchers, so caching requires Ninja.
+      CMAKE_GENERATOR: Ninja
+      CMAKE_C_COMPILER_LAUNCHER: sccache
+      CMAKE_CXX_COMPILER_LAUNCHER: sccache
+      SCCACHE_GHA_ENABLED: "true"
+      # Both backends compile identically, so they share a namespace.
+      SCCACHE_GHA_VERSION: windows-${{ matrix.RELEASE }}
+      # TEMPORARY - REVERT BEFORE MERGING TO DEVELOP.
+      # Forced READ_WRITE so this branch can populate and exercise the cache.
+      # Restore: ${{ github.ref == 'refs/heads/develop' && 'READ_WRITE' || 'READ_ONLY' }}
+      SCCACHE_GHA_RW_MODE: READ_WRITE
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
     steps:
       - name: Checkout
@@ -155,11 +166,22 @@ jobs:
       - name: Prepare
         run: ci/prepare/windows/prepare.ps1
 
+      # Ninja invokes the compiler directly, so cl.exe must be on PATH.
+      - name: Setup MSVC
+        uses: ilammy/msvc-dev-cmd@v1
+
+      - name: Setup sccache
+        uses: mozilla-actions/sccache-action@v0.0.9
+
       - name: Build Tests
         id: build
         run: ci/build-tests.sh
         shell: bash
 
+      - name: Build cache stats
+        if: always()
+        run: sccache --show-stats
+
       - name: Setup Core Dumps
         if: steps.build.outcome == 'success' && (success() || failure())
         run: ci/tests/setup-core-dumps.sh

CMakeLists.txt

@@ -41,6 +41,26 @@ if(MSVC)
   add_definitions(/MP)
   add_definitions(
     -D_SILENCE_STDEXT_ARR_ITERS_DEPRECATION_WARNING) # Suppress iterator warning
+
+  # RocksDB enables the generic ASM language, which otherwise claims the .asm
+  # extension ahead of MASM and leaves Boost.Context's sources without a compile
+  # rule, as CMake has no generic ASM support for MSVC. The Visual Studio
+  # generator hides this; Ninja fails to generate. Nothing here assembles .s
+  # files on Windows, so narrow the generic language to leave .asm to MASM.
+  set(CMAKE_ASM_SOURCE_FILE_EXTENSIONS s;S)
+
+  # Compiler caches cannot handle /Zi, which writes debug info to a PDB shared
+  # by every translation unit of a target. Embed the debug info in the object
+  # files instead so each compilation is a self-contained, cacheable artifact.
+  if(CMAKE_C_COMPILER_LAUNCHER OR CMAKE_CXX_COMPILER_LAUNCHER)
+    message(STATUS "Compiler launcher in use - embedding MSVC debug info (/Z7)")
+    foreach(flags_var
+            CMAKE_C_FLAGS_DEBUG CMAKE_CXX_FLAGS_DEBUG
+            CMAKE_C_FLAGS_RELWITHDEBINFO CMAKE_CXX_FLAGS_RELWITHDEBINFO)
+      string(REPLACE "/ZI" "/Z7" ${flags_var} "${${flags_var}}")
+      string(REPLACE "/Zi" "/Z7" ${flags_var} "${${flags_var}}")
+    endforeach()
+  endif()
 endif()
 
 set(CPACK_PACKAGE_VENDOR "Nano Currency")
@@ -519,6 +539,9 @@ else()
       1
       CACHE BOOL "" FORCE)
 endif()
+# Runs inside RocksDB's scope to drop MSVC flags that defeat compiler caching
+set(CMAKE_PROJECT_rocksdb_INCLUDE
+    ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules/RocksDBMsvcCache.cmake)
 add_subdirectory(submodules/rocksdb EXCLUDE_FROM_ALL)
 
 # cpptoml

ci/build.sh

@@ -77,17 +77,8 @@ number_of_processors() {
     esac
 }
 
-parallel_build_flag() {
-    case "$(uname -s)" in
-        CYGWIN*|MINGW32*|MSYS*|MINGW*)
-            echo "-- -m"
-            ;;
-        *)
-            echo "--parallel $(number_of_processors)"
-            ;;
-    esac
-}
-
-cmake --build ${PWD} ${BUILD_TARGET} $(parallel_build_flag)
+# Works for every generator: CMake forwards it as /m:N to MSBuild and -j N to
+# Ninja and Make.
+cmake --build ${PWD} ${BUILD_TARGET} --parallel $(number_of_processors)
 
 popd

ci/prepare/windows/prepare.ps1

@@ -1,4 +1,5 @@
 $ErrorActionPreference = "Stop"
 
 & "$PSScriptRoot\disable-defender.ps1"
-& "$PSScriptRoot\install-qt.ps1"
+& "$PSScriptRoot\install-qt.ps1"
+& "$PSScriptRoot\remove-git-link.ps1"

ci/prepare/windows/remove-git-link.ps1

@@ -0,0 +1,9 @@
+$ErrorActionPreference = "Continue"
+
+# Git ships a coreutils `link.exe` that shadows the MSVC linker of the same name
+# whenever CMake configures from a bash shell, because bash puts its own /usr/bin
+# ahead of the MSVC toolchain on PATH.
+$gitLink = "C:\Program Files\Git\usr\bin\link.exe"
+if (Test-Path $gitLink) {
+    Remove-Item $gitLink -Force
+}

cmake/Modules/RocksDBMsvcCache.cmake

@@ -0,0 +1,39 @@
+# Included via CMAKE_PROJECT_rocksdb_INCLUDE, so this runs inside RocksDB's own
+# directory scope right after its project() call.
+#
+# RocksDB unconditionally appends /Zi and /d2Zi+ to CMAKE_CXX_FLAGS for MSVC, and
+# both defeat compiler caching. /Zi points every translation unit at a single
+# PDB shared by the whole target, which cannot be cached per compilation, and the
+# undocumented /d2Zi+ is misparsed by sccache badly enough that it rejects the
+# command line as having "multiple input files". Together they account for a
+# third of the object files in a Windows build.
+#
+# The flags are added well after this file is included, so schedule the cleanup
+# to run once RocksDB has finished with its directory. Debug info is not lost:
+# /Z7 embeds it in the object files instead.
+
+if(NOT MSVC)
+  return()
+endif()
+
+if(NOT CMAKE_C_COMPILER_LAUNCHER AND NOT CMAKE_CXX_COMPILER_LAUNCHER)
+  return()
+endif()
+
+# cmake_language(DEFER) requires CMake 3.19; without it RocksDB simply stays
+# uncached rather than failing to build.
+if(CMAKE_VERSION VERSION_LESS 3.19)
+  message(
+    STATUS "RocksDB: CMake < 3.19, leaving MSVC debug flags uncacheable")
+  return()
+endif()
+
+function(nano_strip_rocksdb_uncacheable_flags)
+  foreach(flags_var CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+    string(REPLACE "/d2Zi+" "" ${flags_var} "${${flags_var}}")
+    string(REPLACE "/Zi" "" ${flags_var} "${${flags_var}}")
+    set(${flags_var} "${${flags_var}}" PARENT_SCOPE)
+  endforeach()
+endfunction()
+
+cmake_language(DEFER CALL nano_strip_rocksdb_uncacheable_flags)