hyper: cache dependencies to reduce build time

This change reduces the time it takes to build the hyper Docker image by
caching the dependency builds. This is done by building a dummy binary
before copying the source code into the image.

Author: joshka

frameworks/Rust/hyper/hyper.dockerfile

@@ -1,8 +1,17 @@
 FROM rust:1.85 AS hyper
 
 WORKDIR /src
-COPY . .
-RUN RUSTFLAGS="-C target-cpu=native" cargo install --path . --locked
+ENV RUSTFLAGS="-C target-cpu=native"
+
+# Cache dependency builds (requires passing --force-rm False to tfb command)
+COPY Cargo.toml Cargo.lock /src/
+RUN mkdir src \
+    && echo "fn main() {println!(\"if you see this, the build broke\")}" > src/main.rs \
+    && cargo build --release \
+    && rm -rfv src/ target/release/hyper-techempower* target/release/deps/hyper_techempower*
+
+COPY . /src/
+RUN cargo install --path . --locked
 EXPOSE 8080
 CMD ["hyper-techempower"]
 HEALTHCHECK CMD curl --fail http://localhost:8080/ping || exit 1