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| <main> |
| <h1 id="coding-conventions"><a class="header" href="#coding-conventions">Coding conventions</a></h1> |
| <p>This chapter covers <a href="#formatting">formatting</a>, <a href="#cc">coding for correctness</a>, |
| <a href="#cio">using crates from crates.io</a>, and some tips on <a href="#er">structuring your PR for easy review</a>.</p> |
| <p><a id="formatting"></a></p> |
| <h2 id="formatting-and-the-tidy-script"><a class="header" href="#formatting-and-the-tidy-script">Formatting and the tidy script</a></h2> |
| <p>rustc is moving towards the <a href="https://github.com/rust-dev-tools/fmt-rfcs">Rust standard coding style</a>.</p> |
| <p>However, for now we don’t use stable <code>rustfmt</code>; we use a pinned version with a |
| special config, so this may result in different style from normal <a href="https://github.com/rust-lang/rustfmt"><code>rustfmt</code></a>. |
| Therefore, formatting this repository using <code>cargo fmt</code> is not recommended.</p> |
| <p>Instead, formatting should be done using <code>./x fmt</code>. |
| It’s a good habit to run <code>./x fmt</code> before every commit, as this reduces conflicts later.</p> |
| <p>Formatting is checked by the <code>tidy</code> script. |
| It runs automatically when you do <code>./x test</code> and can be run in isolation with <code>./x fmt --check</code>.</p> |
| <blockquote> |
| <p><strong>Note: Formatting and test suites</strong></p> |
| <p>Most Rust source files under <code>tests/</code> directory are not formatted for reasons |
| such as whitespace sensitivity, nature of snapshot tests, location-sensitive |
| comments and more.</p> |
| <p>Consult the <code>ignore</code> entries in |
| <a href="https://github.com/rust-lang/rust/blob/main/rustfmt.toml">https://github.com/rust-lang/rust/blob/main/rustfmt.toml</a> for which test |
| files are not formatted.</p> |
| </blockquote> |
| <p>If you want to use format-on-save in your editor, the pinned version of |
| <code>rustfmt</code> is built under <code>build/<target>/stage0/bin/rustfmt</code>.</p> |
| <h3 id="formatting-c-code"><a class="header" href="#formatting-c-code">Formatting C++ code</a></h3> |
| <p>The compiler contains some C++ code for interfacing with parts of LLVM that |
| don’t have a stable C API. |
| When modifying that code, use this command to format it:</p> |
| <pre><code class="language-console">./x test tidy --extra-checks cpp:fmt --bless |
| </code></pre> |
| <p>This uses a pinned version of <code>clang-format</code>, to avoid relying on the local environment.</p> |
| <h3 id="formatting-and-linting-python-code"><a class="header" href="#formatting-and-linting-python-code">Formatting and linting Python code</a></h3> |
| <p>The Rust repository contains quite a lot of Python code. |
| We try to keep it both linted and formatted by the <a href="https://github.com/astral-sh/ruff">ruff</a> tool.</p> |
| <p>When modifying Python code, use this command to format it:</p> |
| <pre><code class="language-console">./x test tidy --extra-checks py:fmt --bless |
| </code></pre> |
| <p>And, the following command to run lints:</p> |
| <pre><code class="language-console">./x test tidy --extra-checks py:lint |
| </code></pre> |
| <p>These use a pinned version of <code>ruff</code>, to avoid relying on the local environment.</p> |
| <p><a id="copyright"></a></p> |
| <!-- REUSE-IgnoreStart --> |
| <!-- Prevent REUSE from interpreting the heading as a copyright notice --> |
| <h3 id="copyright-notice"><a class="header" href="#copyright-notice">Copyright notice</a></h3> |
| <!-- REUSE-IgnoreEnd --> |
| <p>In the past, files began with a copyright and license notice. |
| Please <strong>omit</strong> this notice for new files licensed under the standard terms (dual |
| MIT/Apache-2.0).</p> |
| <p>All of the copyright notices should be gone by now, but if you come across one |
| in the rust-lang/rust repo, feel free to open a PR to remove it.</p> |
| <h3 id="line-length"><a class="header" href="#line-length">Line length</a></h3> |
| <p>Lines should be at most 100 characters. |
| It’s even better if you can keep things to 80.</p> |
| <p>Sometimes, and particularly for tests, it can be necessary to exempt yourself from this limit. |
| In that case, you can add a comment towards the top of the file like so:</p> |
| <pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>// ignore-tidy-linelength |
| <span class="boring">}</span></code></pre> |
| <h3 id="tabs-vs-spaces"><a class="header" href="#tabs-vs-spaces">Tabs vs spaces</a></h3> |
| <p>Prefer 4-space indents.</p> |
| <p><a id="cc"></a></p> |
| <h2 id="coding-for-correctness"><a class="header" href="#coding-for-correctness">Coding for correctness</a></h2> |
| <p>Beyond formatting, there are a few other tips that are worth following.</p> |
| <h3 id="prefer-exhaustive-matches"><a class="header" href="#prefer-exhaustive-matches">Prefer exhaustive matches</a></h3> |
| <p>Using <code>_</code> in a match is convenient, but it means that when new |
| variants are added to the enum, they may not get handled correctly. |
| Ask yourself: if a new variant were added to this enum, what’s the |
| chance that it would want to use the <code>_</code> code, versus having some other treatment? |
| Unless the answer is “low”, then prefer an exhaustive match.</p> |
| <p>The same advice applies to <code>if let</code> and <code>while let</code>, |
| which are effectively tests for a single variant.</p> |
| <h3 id="use-todo-comments-for-things-you-dont-want-to-forget"><a class="header" href="#use-todo-comments-for-things-you-dont-want-to-forget">Use “TODO” comments for things you don’t want to forget</a></h3> |
| <p>As a useful tool to yourself, you can insert a <code>// TODO</code> comment |
| for something that you want to get back to before you land your PR:</p> |
| <pre><code class="language-rust ignore">fn do_something() { |
| if something_else { |
| unimplemented!(); // TODO write this |
| } |
| }</code></pre> |
| <p>The tidy script will report an error for a <code>// TODO</code> comment, so this |
| code would not be able to land until the TODO is fixed (or removed).</p> |
| <p>This can also be useful in a PR as a way to signal from one commit that you are |
| leaving a bug that a later commit will fix:</p> |
| <pre><code class="language-rust ignore">if foo { |
| return true; // TODO wrong, but will be fixed in a later commit |
| }</code></pre> |
| <p><a id="cio"></a></p> |
| <h2 id="using-crates-from-cratesio"><a class="header" href="#using-crates-from-cratesio">Using crates from crates.io</a></h2> |
| <p>See the <a href="./crates-io.html">crates.io dependencies</a> section.</p> |
| <p><a id="er"></a></p> |
| <h2 id="how-to-structure-your-pr"><a class="header" href="#how-to-structure-your-pr">How to structure your PR</a></h2> |
| <p>How you prepare the commits in your PR can make a big difference for the reviewer. |
| Here are some tips.</p> |
| <p><strong>Isolate “pure refactorings” into their own commit.</strong> For example, if |
| you rename a method, then put that rename into its own commit, along |
| with the renames of all the uses.</p> |
| <p><strong>More commits is usually better.</strong> If you are doing a large change, |
| it’s almost always better to break it up into smaller steps that can be independently understood. |
| The one thing to be aware of is that if |
| you introduce some code following one strategy, then change it |
| dramatically (versus adding to it) in a later commit, that ‘back-and-forth’ can be confusing.</p> |
| <p><strong>Format liberally.</strong> While only the final commit of a PR must be correctly |
| formatted, it is both easier to review and less noisy to format each commit |
| individually using <code>./x fmt</code>.</p> |
| <p><strong>No merges.</strong> We do not allow merge commits into our history, other than those by bors. |
| If you get a merge conflict, rebase instead via a |
| command like <code>git rebase --interactive rust-lang/main</code> (presuming you use the |
| name <code>rust-lang</code> for your remote).</p> |
| <p><strong>Individual commits do not have to build (but it’s nice).</strong> We do not |
| require that every intermediate commit successfully builds – we only |
| expect to be able to bisect at a PR level. |
| However, if you <em>can</em> make individual commits build, that is always helpful.</p> |
| <h2 id="naming-conventions"><a class="header" href="#naming-conventions">Naming conventions</a></h2> |
| <p>Apart from normal Rust style/naming conventions, there are also some specific to the compiler.</p> |
| <ul> |
| <li> |
| <p><code>cx</code> tends to be short for “context” and is often used as a suffix. |
| For example, <code>tcx</code> is a common name for the <a href="./ty.html">Typing Context</a>.</p> |
| </li> |
| <li> |
| <p><a href="./ty.html"><code>'tcx</code></a> is used as the lifetime name for the Typing Context.</p> |
| </li> |
| <li> |
| <p>Because <code>crate</code> is a keyword, if you need a variable to represent something |
| crate-related, often the spelling is changed to <code>krate</code>.</p> |
| </li> |
| </ul> |
| |
| </main> |
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