Rust Cache Action

A GitHub Action that implements smart caching for rust/cargo projects

Inputs

key - An optional key for the target cache. This is useful in case you have different jobs for test / check / clippy, etc

- uses: Swatinem/rust-cache@v1
  with:
    key: test

This action tries to be better than just caching the following directories:

~/.cargo/registry
~/.cargo/git
target

It disables incremental compilation and only caches dependencies. The assumption is that we will likely recompile the own crate(s) anyway.

It also separates the cache into 4 groups, each treated differently:

Index: ~/.cargo/registry/index/<registry>:

This is always restored from its latest snapshot, and persisted based on the most recent revision.
Registry / Cache: ~/.cargo/registry/cache/<registry>:

Automatically keyed by the lockfile/toml hash, and is being pruned to only persist the dependencies that are being used.
Registry / Git: ~/.cargo/registry/git/<registry>:

Automatically keyed by the lockfile/toml hash. Pruning is still TODO.
target: ./target

Automatically keyed by the lockfile/toml hash, and is being pruned to only persist the dependencies that are being used. This is especially throwing away any intermediate artifacts.