anchor.diff:  RUN cargo build --release
   RUN rm src/*.rs
   
  +# Build our tool for modifying Cargo.toml at runtime
  +
  +FROM dependencies as munge
  +
  +ADD modify-cargo-toml /modify-cargo-toml
  +RUN cd /modify-cargo-toml && \
  +    cargo build --release
  +
  +# Put everything together
  +
  +FROM dependencies
  +
  +ARG channel
  +
   ADD crate-information.json /playground/crate-information.json
   
   ADD postinstall.sh /root/
   RUN /root/postinstall.sh ${channel}
   ADD cargo-wasm /root/.cargo/bin/
  +COPY --from=munge /modify-cargo-toml/target/release/modify-cargo-toml /root/.cargo/bin
  
positive.code: 
  RUN curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain "${channel}"
  
  RUN cd / && \
      cargo new playground
  WORKDIR /playground
  
negative.code: FROM ubuntu:16.04 as toolchain
  
  # `build-essential` and `file` are needed for backtrace-sys
  # `cmake`, `git`, `python` are needed for wasm tools
  