# Basics for hacking on Clippy This document explains the basics for hacking on Clippy. Besides others, this includes how to build and test Clippy. For a more in depth description on the codebase take a look at [Adding Lints] or [Common Tools]. [Adding Lints]: https://github.com/rust-lang/rust-clippy/blob/master/doc/adding_lints.md [Common Tools]: https://github.com/rust-lang/rust-clippy/blob/master/doc/common_tools_writing_lints.md - [Basics for hacking on Clippy](#basics-for-hacking-on-clippy) - [Get the Code](#get-the-code) - [Building and Testing](#building-and-testing) - [`cargo dev`](#cargo-dev) - [lintcheck](#lintcheck) - [PR](#pr) - [Common Abbreviations](#common-abbreviations) - [Install from source](#install-from-source) ## Get the Code First, make sure you have checked out the latest version of Clippy. If this is your first time working on Clippy, create a fork of the repository and clone it afterwards with the following command: ```bash git clone git@github.com:/rust-clippy ``` If you've already cloned Clippy in the past, update it to the latest version: ```bash # If the upstream remote has not been added yet git remote add upstream https://github.com/rust-lang/rust-clippy # upstream has to be the remote of the rust-lang/rust-clippy repo git fetch upstream # make sure that you are on the master branch git checkout master # rebase your master branch on the upstream master git rebase upstream/master # push to the master branch of your fork git push ``` ## Building and Testing You can build and test Clippy like every other Rust project: ```bash cargo build # builds Clippy cargo test # tests Clippy ``` Since Clippy's test suite is pretty big, there are some commands that only run a subset of Clippy's tests: ```bash # only run UI tests cargo uitest # only run UI tests starting with `test_` TESTNAME="test_" cargo uitest # only run dogfood tests cargo test --test dogfood ``` If the output of a [UI test] differs from the expected output, you can update the reference file with: ```bash cargo dev bless ``` For example, this is necessary, if you fix a typo in an error message of a lint or if you modify a test file to add a test case. _Note:_ This command may update more files than you intended. In that case only commit the files you wanted to update. [UI test]: https://rustc-dev-guide.rust-lang.org/tests/adding.html#guide-to-the-ui-tests ## `cargo dev` Clippy has some dev tools to make working on Clippy more convenient. These tools can be accessed through the `cargo dev` command. Available tools are listed below. To get more information about these commands, just call them with `--help`. ```bash # formats the whole Clippy codebase and all tests cargo dev fmt # register or update lint names/groups/... cargo dev update_lints # create a new lint and register it cargo dev new_lint # automatically formatting all code before each commit cargo dev setup git-hook # (experimental) Setup Clippy to work with IntelliJ-Rust cargo dev setup intellij ``` More about intellij command usage and reasons [here](../CONTRIBUTING.md#intellij-rust) ## lintcheck `cargo lintcheck` will build and run clippy on a fixed set of crates and generate a log of the results. You can `git diff` the updated log against its previous version and see what impact your lint made on a small set of crates. If you add a new lint, please audit the resulting warnings and make sure there are no false positives and that the suggestions are valid. Refer to the tools [README] for more details. [README]: https://github.com/rust-lang/rust-clippy/blob/master/lintcheck/README.md ## PR We follow a rustc no merge-commit policy. See . ## Common Abbreviations | Abbreviation | Meaning | | ------------ | -------------------------------------- | | UB | Undefined Behavior | | FP | False Positive | | FN | False Negative | | ICE | Internal Compiler Error | | AST | Abstract Syntax Tree | | MIR | Mid-Level Intermediate Representation | | HIR | High-Level Intermediate Representation | | TCX | Type context | This is a concise list of abbreviations that can come up during Clippy development. An extensive general list can be found in the [rustc-dev-guide glossary][glossary]. Always feel free to ask if an abbreviation or meaning is unclear to you. ## Install from source If you are hacking on Clippy and want to install it from source, do the following: First, take note of the toolchain [override](https://rust-lang.github.io/rustup/overrides.html) in `/rust-toolchain`. We will use this override to install Clippy into the right toolchain. > Tip: You can view the active toolchain for the current directory with `rustup show active-toolchain`. From the Clippy project root, run the following command to build the Clippy binaries and copy them into the toolchain directory. This will override the currently installed Clippy component. ```terminal cargo build --release --bin cargo-clippy --bin clippy-driver -Zunstable-options --out-dir "$(rustc --print=sysroot)/bin" ``` Now you may run `cargo clippy` in any project, using the toolchain where you just installed Clippy. ```terminal cd my-project cargo +nightly-2021-07-01 clippy ``` ...or `clippy-driver` ```terminal clippy-driver +nightly-2021-07-01 ``` If you need to restore the default Clippy installation, run the following (from the Clippy project root). ```terminal rustup component remove clippy rustup component add clippy ``` > **DO NOT** install using `cargo install --path . --force` since this will overwrite rustup > [proxies](https://rust-lang.github.io/rustup/concepts/proxies.html). That is, `~/.cargo/bin/cargo-clippy` and > `~/.cargo/bin/clippy-driver` should be hard or soft links to `~/.cargo/bin/rustup`. You can repair these by running > `rustup update`. [glossary]: https://rustc-dev-guide.rust-lang.org/appendix/glossary.html