Install the Rust toolchain and target for wasm

[yutannihilation]

I noticed R-universe's wasm build installs rustc and cargo if there's the SystemRequirements.

> rwasm::build('./savvyExamples_0.0.1.tar.gz')

> Will download 1 package with unknown size.
> Will install 2 system packages:
+ cargo  - savvyExamples-deps
+ rustc  - savvyExamples-deps

https://github.com/r-universe/yutannihilation/actions/runs/7848104729/job/21418576850#step:5:324

However, the build fails because the cargo is not the supposed one.

...snip...

    cargo +nightly build --lib --release --manifest-path=./rust/Cargo.toml --target-dir ./rust/target --target wasm32-unknown-emscripten -Zbuild-std=panic_abort,std; \
  fi
error: no such command: `+nightly`

    Cargo does not handle `+toolchain` directives.
    Did you mean to invoke `cargo` through `rustup` instead?
make: *** [Makevars:18: rust/target/wasm32-unknown-emscripten/release/libsimple_savvy.a] Error 101

I'm not sure where this should be handled. Options that I came up with are

• Install Rust into the base Docker image. But, this turned out the size is not very lightweight (cf. https://github.com/r-wasm/actions/pull/13#issuecomment-1920131274)
• R-universe or r-wasm might be able to provide a PPA to override the cargo and rustc DEB packages, and add the repository to the Docker image.
• pak package might be able to handle this, treating the Rust system requirements specially. This is probably not very clean. But, as pak (and pkgdepends) doesn't provide option to customize the internal processes, we might need to ask pak for some help like this.
• rwasm package might be able to install Rust toolchain on the fly. With pkgdepends, it's easy to detect if the package requires Rust like this:

deps <- pkgdepends::new_pkg_installation_proposal(".", config = list(sysreqs = TRUE, sysreqs_lookup_system = FALSE))
deps$solve()
any(vapply(deps$get_sysreqs(), \(x) "cargo" %in% names(x), logical(1L)))

[georgestagg]

Thanks for investigating all the available options for us, I appreciate it.

Okay, so after re-reading the thread in r-wasm/actions#13 and this one I think updating the base Docker image is the best way to go. It's not ideal with the size increase, but I think once compressed it's not so bad (details below) and it means it won't have to be constantly reinstalled in GHA runs for rust R packages.

Let's install the required rust and cargo in the r-wasm/webr base Dockerfile. Since you have this working already, would you mind opening a PR there adding the required Docker RUN commands?

``` $ docker manifest inspect ghcr.io/r-wasm/webr | grep size "size": 3558, "size": 30438977, "size": 645927155, "size": 497774382, "size": 32, ``` 3558 + 30438977 + 645927155 + 497774382 + 32 = 1.17GB ``` $ docker manifest inspect ghcr.io/yutannihilation/webr-rust:main | grep size "size": 4960, "size": 30439111, "size": 629569132, "size": 509504104, "size": 32, "size": 209537935, ``` 4960 + 30439111 + 629569132 + 509504104 + 32 + 209537935 = 1.38GB

[yutannihilation]

Wow, thank you! Okay, let me try a pull request. Before that I think, I need a bit more struggle:

• The last time I tried, the CI fails with cargo: command not found error (cf. https://github.com/yutannihilation/savvy/issues/84). Probably I needed to add ENV steps to the last squashing step, but I should confirm.
  • A related apology: After I found the CI error, I reverted the Dockerfile, so the image you inspected is not the same one as I reported on https://github.com/r-wasm/actions/pull/13#issuecomment-1920131274, sorry. I'll report the result of docker manifest inspect later. I guess probably it won't change much, though.
• Reading R-universe's Docker image, I learned the trick of installing a fake package using equivs. It might be better to do this for rustc and cargo; it will not only reduce the time of rwasm::build() a bit but also prevent troubles related to the multiple Rust installations. This is optional, and I can remove if you don't like this way.