Switch to C++20

glibc compatibility remains the same.

We now use clang and static libc++ for the Aarch64 build
because clang-11 offers better C++20 support than GCC 10.

.github/workflows/Linux_aarch64.yml

@@ -29,19 +29,40 @@ jobs:
       with:
         fetch-depth: 0
 
-    - name: Create Build Environment
+    # Work around the somewhat broken packages in the GitHub Actions Ubuntu 20.04 image.
+    # https://github.com/actions/runner-images/issues/4620#issuecomment-981333260
+    - name: Work around broken packages
+      run: sudo apt-get -y install --allow-downgrades libpcre2-8-0=10.34-7
+
+    - name: Add clang repo
+      run: |
+        wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+        sudo tee /etc/apt/sources.list.d/clang.list <<LIST
+        deb [arch=amd64,arm64] http://apt.llvm.org/focal/ llvm-toolchain-focal main
+        deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal main
+        LIST
+
+    # Installs dependencies, including arm64 libraries (runs `sudo apt-get update` as part of it)
+    - name: Install dependencies
+      run: Packaging/nix/debian-cross-aarch64-prep.sh --no-gcc
+
+    - name: Install clang-18
       run: |
-        # Work around the somewhat broken packages in the GitHub Actions Ubuntu 20.04 image.
-        # https://github.com/actions/runner-images/issues/4620#issuecomment-981333260
-        sudo apt-get -y install --allow-downgrades libpcre2-8-0=10.34-7
-        Packaging/nix/debian-cross-aarch64-prep.sh
+        sudo apt-get install -yq --no-install-recommends clang-18 lld-18 libc++-18-dev:arm64 && \
+        sudo update-alternatives --install \
+          /usr/bin/clang++ clang++ /usr/bin/clang++-18 100 && \
+        sudo update-alternatives --install \
+          /usr/bin/clang clang /usr/bin/clang-18 100 \
+          --slave /usr/bin/lld lld /usr/bin/lld-18 \
+          --slave /usr/bin/ld.lld ld.lld /usr/bin/ld.lld-18 && \
+        cat /var/lib/dpkg/alternatives/clang && cat /var/lib/dpkg/alternatives/clang++
 
     - name: Cache CMake build folder
       uses: actions/cache@v3
       with:
         path: build
-        key: ${{ github.workflow }}-v2-${{ github.sha }}
-        restore-keys: ${{ github.workflow }}-v2-
+        key: ${{ github.workflow }}-v6-${{ github.sha }}
+        restore-keys: ${{ github.workflow }}-v6-
 
     - name: Build
       working-directory: ${{github.workspace}}
@@ -51,7 +72,7 @@ jobs:
       # We set DEVILUTIONX_SYSTEM_LIBFMT=OFF because its soversion changes frequently.
       # We set DEVILUTIONX_SYSTEM_SIMPLEINI=OFF because we require v4.19+, still missing from many distributions.
       run: |
-        cmake -S. -Bbuild -DCMAKE_TOOLCHAIN_FILE=../CMake/platforms/aarch64-linux-gnu.toolchain.cmake \
+        cmake -S. -Bbuild -DCMAKE_TOOLCHAIN_FILE=../CMake/platforms/aarch64-linux-gnu-clang-static-libc++.toolchain.cmake \
           -DCMAKE_BUILD_TYPE=${{env.CMAKE_BUILD_TYPE}} -DCMAKE_INSTALL_PREFIX=/usr -DCPACK=ON \
           -DDEVILUTIONX_SYSTEM_LIBFMT=OFF -DDEVILUTIONX_SYSTEM_SIMPLEINI=OFF && \
         cmake --build build -j $(getconf _NPROCESSORS_ONLN) --target package

.github/workflows/Linux_x86.yml

@@ -29,19 +29,31 @@ jobs:
       with:
         fetch-depth: 0
 
-    - name: Create Build Environment
+    # Work around the somewhat broken packages in the GitHub Actions Ubuntu 20.04 image.
+    # https://github.com/actions/runner-images/issues/4620#issuecomment-981333260
+    - name: Work around broken packages
+      run: sudo apt-get -y install --allow-downgrades libpcre2-8-0=10.34-7
+
+    - name: Add gcc repo
+      run: sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+
+    # Installs dependencies, including x86 libraries (runs `sudo apt-get update` as part of it)
+    - name: Install dependencies
+      run: Packaging/nix/debian-cross-i386-prep.sh --no-gcc
+
+    - name: Install gcc-13
       run: |
-        # Work around the somewhat broken packages in the GitHub Actions Ubuntu 20.04 image.
-        # https://github.com/actions/runner-images/issues/4620#issuecomment-981333260
-        sudo apt-get -y install --allow-downgrades libpcre2-8-0=10.34-7
-        Packaging/nix/debian-cross-i386-prep.sh
+        sudo apt-get install -yq --no-install-recommends gcc-13 g++-13 g++-13-multilib && \
+        sudo update-alternatives --install \
+          /usr/bin/gcc gcc /usr/bin/gcc-13 13 \
+          --slave /usr/bin/g++ g++ /usr/bin/g++-13
 
     - name: Cache CMake build folder
       uses: actions/cache@v3
       with:
         path: build
-        key: ${{ github.workflow }}-v3-${{ github.sha }}
-        restore-keys: ${{ github.workflow }}-v3-
+        key: ${{ github.workflow }}-v5-${{ github.sha }}
+        restore-keys: ${{ github.workflow }}-v5-
 
     - name: Build
       working-directory: ${{github.workspace}}

.github/workflows/Linux_x86_64.yml

@@ -29,15 +29,29 @@ jobs:
       with:
         fetch-depth: 0
 
+    - name: Add gcc repo
+      run: sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+
+    # Installs dependencies and runs `sudo apt-get update` as part of it.
+    - name: Install dependencies
+      run: Packaging/nix/debian-host-prep.sh --no-gcc
+
+    - name: Install gcc-13
+      run: |
+        sudo apt-get install -yq --no-install-recommends gcc-13 g++-13 && \
+        sudo update-alternatives --install \
+          /usr/bin/gcc gcc /usr/bin/gcc-13 13 \
+          --slave /usr/bin/g++ g++ /usr/bin/g++-13
+
     - name: Create Build Environment
-      run: Packaging/nix/debian-host-prep.sh
+      run: Packaging/nix/debian-host-prep.sh --no-gcc
 
     - name: Cache CMake build folder
       uses: actions/cache@v3
       with:
         path: build
-        key: ${{ github.workflow }}-v2-${{ github.sha }}
-        restore-keys: ${{ github.workflow }}-v2-
+        key: ${{ github.workflow }}-v5-${{ github.sha }}
+        restore-keys: ${{ github.workflow }}-v5-
 
     - name: Build
       working-directory: ${{github.workspace}}

.github/workflows/Linux_x86_64_test.yml

@@ -18,7 +18,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
     - uses: actions/checkout@v3

CMake/platforms/aarch64-linux-gnu-clang-static-libc++.toolchain.cmake

@@ -0,0 +1,26 @@
+set(CMAKE_SYSTEM_NAME Linux)
+set(CMAKE_SYSTEM_PROCESSOR aarch64)
+
+set(triple aarch64-linux-gnu)
+
+set(CMAKE_C_COMPILER "/usr/bin/clang")
+set(CMAKE_C_COMPILER_TARGET "${triple}")
+set(CMAKE_CXX_COMPILER "/usr/bin/clang++")
+set(CMAKE_CXX_FLAGS_INIT "-stdlib=libc++")
+set(CMAKE_CXX_COMPILER_TARGET "${triple}")
+set(CMAKE_ASM_COMPILER "/usr/bin/clang")
+set(CMAKE_ASM_COMPILER_TARGET "${triple}")
+set(CMAKE_EXE_LINKER_FLAGS_INIT "-fuse-ld=/usr/bin/ld.lld -static-libstdc++ -static-libgcc")
+
+set(CMAKE_FIND_ROOT_PATH "/usr/aarch64-linux-gnu;/usr")
+set(CMAKE_LIBRARY_ARCHITECTURE "${triple}")
+
+set(PKG_CONFIG_EXECUTABLE "${CMAKE_CURRENT_LIST_DIR}/aarch64-linux-gnu-pkg-config" CACHE STRING "Path to pkg-config")
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+
+set(CPACK_DEBIAN_PACKAGE_ARCHITECTURE arm64)

CMake/platforms/debian-cross-pkg-config.sh

@@ -14,11 +14,13 @@ if [ x"${PKG_CONFIG_LIBDIR+set}" = x ]; then
   # Normalized multiarch path if any, e.g. i386-linux-gnu for i386
   multiarch="`dpkg-architecture -t"${triplet}" -qDEB_HOST_MULTIARCH 2>/dev/null`"
   # Native multiarch path
-  native_multiarch="$(cat /usr/lib/pkg-config.multiarch)"
+  if [ -f /usr/lib/pkg-config.multiarch ]; then
+    native_multiarch="$(cat /usr/lib/pkg-config.multiarch)"
 
-  # This can be used for native builds as well, in that case, just exec pkg-config "$@" directly.
-  if [ "$native_multiarch" = "$multiarch" ]; then
-     exec pkg-config "$@"
+    # This can be used for native builds as well, in that case, just exec pkg-config "$@" directly.
+    if [ "$native_multiarch" = "$multiarch" ]; then
+       exec pkg-config "$@"
+    fi
   fi
 
   PKG_CONFIG_LIBDIR="/usr/local/${triplet}/lib/pkgconfig"

CMakeLists.txt

@@ -293,12 +293,9 @@ if(GPERF)
   endif()
 endif()
 
-# Despite setting C++ standard to 20, features from this version are not being used.
-# DevilutionX is compatible with C++ 17.
-# Here we set it to 20 only to take advantage of the fmt::format build time errors.
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_EXTENSIONS OFF)
-set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON) # for clang-tidy
 set(CMAKE_THREAD_PREFER_PTHREAD ON)
 set(THREADS_PREFER_PTHREAD_FLAG ON)

Packaging/nix/debian-cross-aarch64-prep.sh

@@ -18,8 +18,18 @@ LIST
 	cat /etc/apt/sources.list
 fi
 
+
+PACKAGES=(
+  cmake git smpq gettext dpkg-cross libc-dev-arm64-cross
+  libsdl2-dev:arm64 libsdl2-image-dev:arm64 libsodium-dev:arm64
+  libsimpleini-dev:arm64 libpng-dev:arm64 libbz2-dev:arm64 libfmt-dev:arm64
+)
+
+if (( $# < 1 )) || [[ "$1" != --no-gcc ]]; then
+  PACKAGES+=(crossbuild-essential-arm64)
+fi
+
+
 sudo dpkg --add-architecture arm64
 sudo apt-get update
-sudo apt-get install -y cmake git smpq gettext crossbuild-essential-arm64 \
-  libsdl2-dev:arm64 libsdl2-image-dev:arm64 libsodium-dev:arm64 \
-  libsimpleini-dev:arm64 libpng-dev:arm64 libbz2-dev:arm64 libfmt-dev:arm64
+sudo apt-get install -y "${PACKAGES[@]}"

Packaging/nix/debian-cross-i386-prep.sh

@@ -2,9 +2,17 @@
 set -euo pipefail
 set -x
 
+PACKAGES=(
+  cmake git smpq gettext
+  libsdl2-dev:i386 libsdl2-image-dev:i386 libsodium-dev:i386
+  libpng-dev:i386 libbz2-dev:i386 libfmt-dev:i386
+)
+
+if (( $# < 1 )) || [[ "$1" != --no-gcc ]]; then
+  PACKAGES+=(g++-multilib)
+fi
+
 sudo dpkg --add-architecture i386
 sudo apt-get update
-sudo apt-get install --ignore-hold -y \
-  cmake g++-multilib git smpq gettext \
-  libsdl2-dev:i386 libsdl2-image-dev:i386 libsodium-dev:i386 \
-  libpng-dev:i386 libbz2-dev:i386 libfmt-dev:i386
+sudo apt-get install --ignore-hold -y "${PACKAGES[@]}"
+

Packaging/nix/debian-host-prep.sh

@@ -2,7 +2,15 @@
 set -euo pipefail
 set -x
 
-sudo apt-get update
-sudo apt-get install -y \
-  rpm pkg-config cmake g++ git smpq gettext libsdl2-dev libsdl2-image-dev libsodium-dev \
+PACKAGES=(
+  rpm pkg-config cmake git smpq gettext libsdl2-dev libsdl2-image-dev libsodium-dev
   libpng-dev libbz2-dev libfmt-dev
+)
+
+if (( $# < 1 )) || [[ "$1" != --no-gcc ]]; then
+  PACKAGES+=(g++)
+fi
+
+sudo apt-get update
+sudo apt-get install -y "${PACKAGES[@]}"
+