Speed up image builds with Docker cache mounts

.github/workflows/build-docker.yml

@@ -19,6 +19,8 @@ on:
       - pyproject.toml
       # And when we change this workflow itself...
       - .github/workflows/build-docker.yml
+      # Or when we change the Dockerfile!
+      - Dockerfile
 
 jobs:
   docker-publish:

Dockerfile

@@ -34,8 +34,17 @@ RUN rustup target add $(cat rust_target.txt)
 COPY crates crates
 COPY ./Cargo.toml Cargo.toml
 COPY ./Cargo.lock Cargo.lock
-RUN cargo zigbuild --bin puffin --target $(cat rust_target.txt) --release
-RUN cp target/$(cat rust_target.txt)/release/puffin /puffin
+
+# Build with mounted cache
+RUN --mount=type=cache,target=./target \
+  --mount=type=cache,target=/usr/local/cargo/git \
+  --mount=type=cache,target=/usr/local/cargo/registry \
+  cargo zigbuild --bin puffin --target $(cat rust_target.txt) --release
+
+# Copy binary into normal layer
+RUN --mount=type=cache,target=./target \
+  cp ./target/$(cat rust_target.txt)/release/puffin /puffin
+
 # TODO(konsti): Optimize binary size, with a version that also works when cross compiling
 # RUN strip --strip-all /puffin
 

crates/puffin-traits/src/lib.rs

@@ -150,7 +150,7 @@ pub enum BuildKind {
 impl Display for BuildKind {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         match self {
-            BuildKind::Wheel => f.write_str("wheel"),
+            BuildKind::Wheel => f.write_str("REVERT ME"),
             BuildKind::Editable => f.write_str("editable"),
         }
     }