feat(Dockerfile): make apt cache sharing configurable

This is useful to avoid locking the cache, which is desirable if
using buildah, since it has had bugs around this feature.

The tradeoff is that you could potentially find locking issues
if running multiple parallel apt commands (such as in CI).

Author: unleashed

Dockerfile

@@ -277,11 +277,13 @@ COPY --link --from=tools-script /bin/* /bin/
 ## Base images
 ##
 
+ARG APT_CACHE_SHARING=",sharing=locked"
+
 # A Go build environment.
 FROM docker.io/library/golang:${GO_TAG} as go
 RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y file jo jq
 COPY --link --from=tools-script /bin/* /usr/local/bin/
 COPY --link --from=tools-go /bin/* /usr/local/bin/
@@ -294,8 +296,8 @@ ENV PROTOC_NO_VENDOR=1 \
 # A Rust build environment.
 FROM docker.io/library/rust:${RUST_TAG}-slim-bookworm as rust
 RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y \
         cmake \
         curl \
@@ -307,8 +309,8 @@ RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
         libssl-dev \
         pkg-config
 RUN --mount=type=cache,from=apt-llvm,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-llvm,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-llvm,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-llvm,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-llvm,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y clang-19 llvm-19
 RUN rustup component add clippy rustfmt
 COPY --link --from=tools-lint /bin/checksec /usr/local/bin/
@@ -332,8 +334,8 @@ RUN rustup target add \
         aarch64-unknown-linux-musl \
         x86_64-unknown-linux-musl
 RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y \
         binutils-aarch64-linux-gnu \
         g++-aarch64-linux-gnu \
@@ -346,8 +348,8 @@ RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
 
 FROM docker.io/library/debian:bookworm as devcontainer
 RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y \
         cmake \
         curl \
@@ -384,13 +386,13 @@ RUN groupadd --gid=1000 code \
 
 # git v2.34+ has new subcommands and supports code signing via SSH.
 RUN --mount=type=cache,from=apt-base,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y -t bookworm-backports git
 
 RUN --mount=type=cache,from=apt-llvm,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-llvm,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-llvm,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-llvm,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-llvm,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y clang-19 llvm-19
 ENV CC=clang-19 \
     CXX=clang++-19
@@ -402,16 +404,16 @@ ENV CC=clang-19 \
 #
 # TODO(ver): replace this with a devcontainer feature?
 RUN --mount=type=cache,id=apt-docker,from=apt-base,source=/etc/apt,target=/etc/apt \
-    --mount=type=cache,id=apt-docker,from=apt-base,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,id=apt-docker,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,id=apt-docker,from=apt-base,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,id=apt-docker,from=apt-base,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     --mount=type=bind,from=tools,source=/bin/scurl,target=/usr/local/bin/scurl \
     scurl https://raw.githubusercontent.com/microsoft/vscode-dev-containers/main/script-library/docker-debian.sh | bash -s
 ENV DOCKER_BUILDKIT=1
 
 ARG MARKDOWNLINT_VERSION=0.15.0
 RUN --mount=type=cache,from=apt-node,source=/etc/apt,target=/etc/apt,ro \
-    --mount=type=cache,from=apt-node,source=/var/cache/apt,target=/var/cache/apt,sharing=locked \
-    --mount=type=cache,from=apt-node,source=/var/lib/apt/lists,target=/var/lib/apt/lists,sharing=locked \
+    --mount=type=cache,from=apt-node,source=/var/cache/apt,target=/var/cache/apt${APT_CACHE_SHARING} \
+    --mount=type=cache,from=apt-node,source=/var/lib/apt/lists,target=/var/lib/apt/lists${APT_CACHE_SHARING} \
     DEBIAN_FRONTEND=noninteractive apt-get install -y nodejs
 RUN npm install "markdownlint-cli2@${MARKDOWNLINT_VERSION}" --global