chore: keep cache empty during entire build

Author: rjaegers

.devcontainer/cpp/Dockerfile

@@ -18,14 +18,15 @@ ENV CCACHE_DIR=/cache/.ccache \
     CMAKE_EXPORT_COMPILE_COMMANDS="On" \
     CMAKE_GENERATOR="Ninja" \
     CONAN_HOME=/opt/conan \
-    CPM_SOURCE_CACHE=/cache/.cpm-cache \
+    CPM_SOURCE_CACHE=/cache/.cpm \
     PATH="$PATH:/usr/lib/llvm-${CLANG_VERSION}/bin:/opt/gcc-arm-none-eabi/bin" \
-    PYTHONPYCACHEPREFIX=/cache/python
+    PYTHONPYCACHEPREFIX=/cache/.python
 
 # Install the base system with all tool dependencies
 # hadolint ignore=DL3008
 RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-base.json,target=/tmp/apt-requirements-base.json \
     --mount=type=bind,source=.devcontainer/cpp/requirements.txt,target=/tmp/requirements.txt \
+    --mount=type=cache,target=/cache,sharing=locked \
     --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \
     --mount=type=cache,target=/var/log,sharing=locked \
@@ -36,8 +37,7 @@ RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-base.json,target
  && wget -qO /usr/local/share/ca-certificates/Cisco_Umbrella_Root_CA.crt https://www.cisco.com/security/pki/certs/ciscoumbrellaroot.pem \
  && update-ca-certificates \
  # Install some tools via pip to get more recent versions
- && python3 -m pip install --break-system-packages --require-hashes --no-cache-dir --no-compile -r /tmp/requirements.txt \
- && rm -rf /cache/python/*
+ && python3 -m pip install --break-system-packages --require-hashes --no-cache-dir --no-compile -r /tmp/requirements.txt
 
 # Install clang toolchain and mull mutation testing framework
 RUN --mount=type=bind,source=.devcontainer/cpp/apt-requirements-clang.json,target=/tmp/apt-requirements-clang.json \
@@ -71,15 +71,16 @@ RUN wget -qO - "https://github.com/Jake-Shadle/xwin/releases/download/${XWIN_VER
 
 # Compile and install additional clang tools; often necessary as binary arm64 builds are lacking, or packages are out-of-date
 # Install ccache from source for a recent version
-RUN --mount=type=cache,target=/tmp,sharing=locked,mode=1777 \
+RUN --mount=type=cache,target=/cache,sharing=locked \
  wget -qO - https://github.com/ccache/ccache/archive/refs/tags/v${CCACHE_VERSION}.tar.gz | tar xz -C /tmp \
  && CC=clang CXX=clang++ cmake -DCMAKE_BUILD_TYPE=Release -DENABLE_TESTING=Off -DENABLE_DOCUMENTATION=Off -S /tmp/ccache-${CCACHE_VERSION} -B /tmp/ccache-${CCACHE_VERSION}/build \
  && cmake --build /tmp/ccache-${CCACHE_VERSION}/build --target install \
  && rm -rf /tmp/ccache-${CCACHE_VERSION}
 
 # Install include-what-you-use (iwyu) from source
 # hadolint ignore=DL3008
-RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
+RUN --mount=type=cache,target=/cache,sharing=locked \
+    --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \
  apt-get update && apt-get install -y --no-install-recommends libclang-${CLANG_VERSION}-dev llvm-${CLANG_VERSION}-dev \
  && wget -qO - https://github.com/include-what-you-use/include-what-you-use/archive/refs/tags/${INCLUDE_WHAT_YOU_USE_VERSION}.tar.gz | tar xz -C /tmp \
@@ -108,6 +109,7 @@ RUN --mount=type=cache,target=/var/log,sharing=locked \
 # Set up package managers CPM and Conan
 # - Install CPM.cmake to the CMake module path
 # - Configure a default profile for Conan and set the CMake generator to Ninja
-RUN wget -qP /usr/local/lib/python*/dist-packages/cmake/data/share/cmake-*/Modules/ https://github.com/cpm-cmake/CPM.cmake/releases/download/v${CPM_VERSION}/CPM.cmake \
+RUN --mount=type=cache,target=/cache,sharing=locked \
+ wget -qP /usr/local/lib/python*/dist-packages/cmake/data/share/cmake-*/Modules/ https://github.com/cpm-cmake/CPM.cmake/releases/download/v${CPM_VERSION}/CPM.cmake \
  && conan profile detect \
  && echo -e "\n[conf]\ntools.cmake.cmaketoolchain:generator=Ninja" >> "$(conan profile path default)"