fix(docker): Stop resetting the cargo-chef cache in the Dockerfile

.dockerignore

@@ -22,3 +22,12 @@
 !zebrad
 !docker/entrypoint.sh
 !docker/runtime-entrypoint.sh
+
+# TODO:
+# replace git with a supported way of resetting files modified by cargo-chef, with the correct timestamps.
+# (This will improve Docker cache performance when the changes in a PR don't impact Rust builds.)
+#
+# Background:
+# https://hackmd.io/@kobzol/S17NS71bh#Using-cargo-chef
+# https://github.com/LukeMathWalker/cargo-chef/issues/180#issuecomment-1552965888
+!.git

docker/Dockerfile

@@ -29,14 +29,15 @@ FROM chef AS deps
 SHELL ["/bin/bash", "-xo", "pipefail", "-c"]
 COPY --from=planner /opt/zebrad/recipe.json recipe.json
 
-# Install zebra build deps
+# Install zebra build deps and Dockerfile deps
 RUN apt-get -qq update && \
     apt-get -qq install -y --no-install-recommends \
     llvm \
     libclang-dev \
     clang \
     ca-certificates \
     protobuf-compiler \
+    git \
     ; \
     rm -rf /var/lib/apt/lists/* /tmp/*
 
@@ -102,15 +103,25 @@ FROM deps AS tests
 COPY --from=us-docker.pkg.dev/zealous-zebra/zebra/zcash-params /root/.zcash-params /root/.zcash-params
 COPY --from=us-docker.pkg.dev/zealous-zebra/zebra/lightwalletd /opt/lightwalletd /usr/local/bin
 
+# Copy across the source files and .git directory, so their timestamps are before the build cache timestamps.
+COPY . .
+
 # Re-hydrate the minimum project skeleton identified by `cargo chef prepare` in the planner stage,
+# over the top of the original source files,
 # and build it to cache all possible sentry and test dependencies.
 #
-# This is the caching Docker layer for Rust!
+# This is the caching Docker layer for Rust tests!
+# It creates fake empty test binaries so dependencies are built, but Zebra is not fully built.
 #
-# TODO: is it faster to use --tests here?
-RUN cargo chef cook --release --features "${TEST_FEATURES} ${FEATURES}" --workspace --recipe-path recipe.json
+# TODO: add --locked when cargo-chef supports it
+RUN cargo chef cook --tests --release --features "${TEST_FEATURES} ${FEATURES}" --workspace --recipe-path recipe.json
 
-COPY . .
+# Undo the source file changes made by cargo-chef.
+# This also invalidates the cargo cache for those files by updating their timestamps,
+# which makes sure the fake empty binaries created by cargo-chef are rebuilt.
+RUN git reset --hard HEAD
+
+# Build Zebra test binaries, but don't run them
 RUN cargo test --locked --release --features "${TEST_FEATURES} ${FEATURES}" --workspace --no-run
 RUN cp /opt/zebrad/target/release/zebrad /usr/local/bin
 RUN cp /opt/zebrad/target/release/zebra-checkpoints /usr/local/bin
@@ -127,10 +138,20 @@ ENTRYPOINT [ "/entrypoint.sh" ]
 # `test` stage. This step is a dependency for the `runtime` stage, which uses the resulting
 # zebrad binary from this step.
 FROM deps AS release
-RUN cargo chef cook --release --features "${FEATURES}" --recipe-path recipe.json
 
+# Copy the git sources as a base for the build cache.
 COPY . .
-# Build zebra
+
+# This is the caching layer for Rust zebrad builds.
+# It creates a fake empty zebrad binary, see above for details.
+#
+# TODO: add --locked when cargo-chef supports it
+RUN cargo chef cook --release --features "${FEATURES}" --package zebrad --bin zebrad --recipe-path recipe.json
+
+# Undo the source file changes made by cargo-chef, so the fake empty zebrad binary is rebuilt.
+RUN git reset --hard HEAD
+
+# Build zebrad
 RUN cargo build --locked --release --features "${FEATURES}" --package zebrad --bin zebrad
 
 COPY ./docker/runtime-entrypoint.sh /