multi-stage Dockerfile for rust builds that allows building stages after `cargo fetch` without network access

Dockerfile.rust

# Example usage:
# docker build --target=fetcher .
# docker build --network=none -t "$TAG" .

FROM rust-builder:0.2.1 AS fetcher
COPY Cargo.toml Cargo.lock ./
RUN mkdir src \
 && touch src/main.rs \
 && cargo fetch --locked

# The following stages can be built without network access

FROM rust-builder:0.2.1 AS builder
COPY . .
COPY --from=fetcher /usr/local/cargo/ /usr/local/cargo/
RUN cargo lichking check \
 && cargo +nightly fmt -- --check --files-with-diff \
 && cargo clippy -- -D warnings \
 && cargo build --release --frozen

FROM alpine-runtime:0.3.0
COPY --from=builder /target/release/program-name /usr/local/bin/
USER app
ENTRYPOINT ["/usr/local/bin/program-name"]