v0.2.0: clang + import std; isolated Windows cross-build (llvm-mingw + SDL3)

Dockerfile

@@ -1,7 +1,9 @@
 # syntax=docker/dockerfile:1
 
-# dev target: full toolchain + debug tools for development and debugging.
-# Base image and compiler are the latest stable (ubuntu:26.04 ships gcc/g++ 16).
+# Linux build environment. Isolated from the Windows cross image (Dockerfile.win)
+# so the two toolchains and their standard libraries never interfere.
+#
+# dev target: clang + libc++ (for `import std;`) + SDL3 + debug tools.
 FROM ubuntu:26.04 AS dev
 
 ENV DEBIAN_FRONTEND=noninteractive
@@ -23,44 +25,44 @@ RUN --mount=type=cache,target=/var/lib/apt,sharing=locked \
         sleep 5; \
     done \
     && apt-get -o Acquire::Retries=5 install -y --no-install-recommends \
-        build-essential \
         ca-certificates \
+        clang-21 \
+        clang-tools-21 \
         cmake \
-        g++-16 \
         gdb \
         git \
+        libc++-21-dev \
+        libc++abi-21-dev \
         libsdl3-dev \
         ninja-build \
         pkg-config \
     && rm -rf /var/lib/apt/lists/*
 
-# Pin the toolchain to GCC 16 (the distro default is still GCC 15).
-ENV CC=gcc-16
-ENV CXX=g++-16
-RUN update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-16 100 \
-    && update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-16 100 \
-    && update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-16 100
+ENV CC=clang-21
+ENV CXX=clang++-21
 
 WORKDIR /work
 COPY . .
 
-# C++26 modules need CMake >= 3.28, the Ninja generator and a module-aware gcc.
-RUN cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release \
-    && cmake --build build -j \
-    && ctest --test-dir build --output-on-failure
+RUN cmake -S . -B build/linux -G Ninja -DCMAKE_BUILD_TYPE=Release \
+    && cmake --build build/linux -j \
+    && ctest --test-dir build/linux --output-on-failure
 
 # deploy target: runtime dependencies + final binary, minimal and fast.
 FROM ubuntu:26.04 AS deploy
 
 ENV DEBIAN_FRONTEND=noninteractive
 
-RUN apt-get -o Acquire::Retries=5 update \
+RUN --mount=type=cache,target=/var/lib/apt,sharing=locked \
+    --mount=type=cache,target=/var/cache/apt,sharing=locked \
+    apt-get -o Acquire::Retries=5 update \
     && apt-get -o Acquire::Retries=5 install -y --no-install-recommends \
+        libc++1 \
+        libc++abi1 \
         libsdl3-0 \
-        libstdc++6 \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
-COPY --from=dev /work/build/bin/openra3 /app/openra3
+COPY --from=dev /work/build/linux/bin/openra3 /app/openra3
 
 ENTRYPOINT ["/app/openra3"]