Integration tests runner downloads rustc again

[jorgehermo9]

Currently, the integration tests runner uses docker.io/rust:1.81-slim-bookworm as base image, which already contains all the toolchain for rust 1.81.

But, when starting the runner, the current vector dir is mounted into the vector-test-runner container

vector/vdev/src/testing/runner.rs

Line 245 in c3d91af

&format!("{}:{MOUNT_PATH}", app::path()),

and that directory contains the rust-toolchain.toml file https://github.com/vectordotdev/vector/blob/master/rust-toolchain.toml that causes a whole new rust 1.81 toolchain installation when running the test command inside the container

vector/vdev/src/testing/runner.rs

Line 17 in c3d91af

const TEST_COMMAND: &[&str] = &[

as seen in the following screenshot:

see the "downloadin component" part, this should not happen if we are already using a base image containing all the rust components.

Given this, it makes no sense to use a versioned rustc base image, as the current version from rust-toolchain.toml will override any rust toolchain in the base image. I don't know if we can disable the usage of rust-toolchain.toml in the runner and rely only in the installed components of docker.io/rust:1.81-slim-bookworm , I can only find this open issue rust-lang/rustup#2793.

What I did in other projects is to ignore the rust-toolchain.toml file in a .dockerignore, as it was triggering this exact same issue while building my images and using a base rust image (https://github.com/jorgehermo9/gq/blob/f6e1efd7e8a73c34c0848a718198436da99f7262/docker/server.Dockerfile#L1) . But this worked because I used the COPY command in the Dockerfile and not mounting the vector root dir inside the container.

I think this could improve integration tests CI as downloading a whole new rust toolchain every time could take a few seconds