Add rust-toolchain ecosystem support

[JamieMagee]

Related:

• Update rust-toolchain dependabot/dependabot-core#1702
• Add rust-toolchain support dependabot/cli#463
• Add rust_toolchain smoke tests dependabot/smoke-tests#302

[Copilot]

Pull Request Overview

Adds support for the Rust toolchain ecosystem by wiring up a new container image in the update script, the registry metadata, and providing a stub Dockerfile.

• Introduce rust_toolchain in the container manifest.
• Update containers.json with a placeholder for the new image tag.
• Add Dockerfile.rust-toolchain pointing at the new image.

Reviewed Changes

Copilot reviewed 3 out of 9 changed files in this pull request and generated 2 comments.

File	Description
src/update-containers.ts	Added rust_toolchain entry to the manifest object.
docker/containers.json	Inserted rust_toolchain key with a TODO tag.
docker/Dockerfile.rust-toolchain	Created stub Dockerfile referencing the new image.

Comments suppressed due to low confidence (1)

src/update-containers.ts:47

• [nitpick] There are no tests verifying that the new rust_toolchain key is correctly handled by update-containers.ts. Adding or updating a unit test to cover this new manifest entry would help prevent regressions.

  rust_toolchain: getImageName('Dockerfile.rust-toolchain')

[Copilot]

The TODO placeholder needs to be replaced with the actual image tag and SHA once the Rust toolchain image is published, otherwise CI and deployments will pull an invalid reference.

Suggested change

	"rust_toolchain": "ghcr.io/dependabot/dependabot-updater-rust-toolchain:TODO"
	"rust_toolchain": "ghcr.io/dependabot/dependabot-updater-rust-toolchain:v2.0.20250606230616@sha256:1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef"

[Copilot]

[nitpick] Consider parameterizing the version (e.g., via an ARG or environment variable) or updating this line with the real base image tag to avoid leaving a magic TODO value in the Dockerfile.

Suggested change

	FROM ghcr.io/dependabot/dependabot-updater-rust-toolchain:TODO
	ARG RUST_TOOLCHAIN_VERSION=latest
	FROM ghcr.io/dependabot/dependabot-updater-rust-toolchain:${RUST_TOOLCHAIN_VERSION}