问题
Is there a way to tell Cargo to install and build all my dependencies, but not attempt to build my application?
I thought cargo install would do that, but it actually goes all the way to building my app too. I want to get to a state where cargo build would find all dependencies ready to use, but without touching the /src directory.
What I'm really trying to accomplish:
I'm trying to build a Docker image for a Rust application, where I'd like to do the following steps:
Build time (docker build .):
- import a docker image with rust tooling installed
- add my Cargo.toml and Cargo.lock files
- download and build all dependencies
- add my source directory to the image
- build my source code
Run time (docker run ...):
- run the application
I've tried the following Dockerfile, but the indicated step builds my application as well (which of course fails since the source directory isn't there yet):
FROM jimmycuadra/rust
ADD Cargo.toml /source
ADD Cargo.lock /source
RUN cargo install # <-- failure here
ADD src /source/src
RUN cargo build
ENTRYPOINT cargo run
The reason I want to separate the install dependencies step from actually building my application, is that if I don't change the dependencies, I want Docker to be able use a cached image with all dependencies already installed and built. Thus, I can't ADD /src /source/src until after installing the dependecies, as that would invalidate the cached image when I change my own code.
回答1:
There is no native support for building just the dependencies in Cargo, as far as I know. There is an open issue for it. I wouldn't be surprised if you could submit something to Cargo to accomplish it though, or perhaps create a third-party Cargo addon. I've wanted this functionality for cargo doc as well, when my own code is too broken to compile ;-)
However, the Rust playground that I maintain does accomplish your end goal. There's a base Docker container that installs Rustup and copies in a Cargo.toml with all of the crates available for the playground. The build steps create a blank project (with a dummy src/lib.rs), then calls cargo build and cargo build --release to compile the crates:
RUN cd / && \
cargo new playground
WORKDIR /playground
ADD Cargo.toml /playground/Cargo.toml
RUN cargo build
RUN cargo build --release
RUN rm src/*.rs
All of the downloaded crates are stored in the Docker image's $HOME/.cargo directory and all of the built crates are stored in the applications target/{debug,release} directories.
Later on, the real source files are copied into the container and cargo build / cargo run can be executed again, using the now-compiled crates.
If you were building an executable project, you'd want to copy in the Cargo.lock as well.
回答2:
If you add a dummy main or lib file, you can use cargo build to just pull down the dependencies. I'm currently using this solution for my Docker based project:
COPY Cargo.toml .
RUN mkdir src \
&& echo "// dummy file" > src/lib.rs \
&& cargo build
I'm using --volumes, so I'm done at this point. The host volumes come in and blow away the dummy file, and cargo uses the cached dependencies when I go to build the source later. This solution will work just as well if you want to add a COPY (or ADD) later and use the cached dependencies though.
回答3:
Based on a GitHub comment
FROM rust:1.37
WORKDIR /usr/src
# Create blank project
RUN USER=root cargo new PROJ
# We want dependencies cached, so copy those first.
COPY Cargo.toml /usr/src/PROJ/
COPY Cargo.lock /usr/src/PROJ/
WORKDIR /usr/src/PROJ
# This is a dummy build to get the dependencies cached.
RUN cargo build --release
# Now copy in the rest of the sources
COPY MyPROJECT/src /usr/src/PROJ/src/
# This is the actual build.
RUN cargo build --release \
&& mv target/release/appname /bin \
&& rm -rf /usr/src/PROJ
WORKDIR /
EXPOSE 8888
CMD ["/bin/appname"]
来源：https://stackoverflow.com/questions/42130132/can-cargo-download-and-build-dependencies-without-also-building-the-application