More accurate since the enum also encompasses:
* ALL (which isn't a prefix at all)
* fully-qualified rule codes (which aren't prefixes unless you say
they're a prefix to the empty string but that's not intuitive)
This commit fixes a bug accidentally introduced in
6cf770a692,
which resulted every `ruff --explain <code>` invocation to fail with:
thread 'main' panicked at 'Mismatch between definition and access of `explain`.
Could not downcast to ruff::registry::Rule, need to downcast to &ruff::registry::Rule',
ruff_cli/src/cli.rs:184:18
We also add an integration test for --explain to prevent such bugs from
going by unnoticed in the future.
This lets you test the ruff linters or use the ruff library
without having to compile the ~100 additional dependencies
that are needed by the CLI.
Because we set the following in the [workspace] section of Cargo.toml:
default-members = [".", "ruff_cli"]
`cargo run` still runs the CLI and `cargo test` still tests
the code in src/ as well as the code in the new ruff_cli crate.
(But you can now also run `cargo test -p ruff` to only test the linters.)
