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| <h1 id="error-codes"><a class="header" href="#error-codes">Error codes</a></h1> |
| <p>We generally try to assign each error message a unique code like <code>E0123</code>. These |
| codes are defined in the compiler in the <code>diagnostics.rs</code> files found in each |
| crate, which basically consist of macros. All error codes have an associated |
| explanation: new error codes must include them. Note that not all <em>historical</em> |
| (no longer emitted) error codes have explanations.</p> |
| <h2 id="error-explanations"><a class="header" href="#error-explanations">Error explanations</a></h2> |
| <p>The explanations are written in Markdown (see the <a href="https://spec.commonmark.org/current/">CommonMark Spec</a> for |
| specifics around syntax), and all of them are linked in the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_error_codes/index.html"><code>rustc_error_codes</code></a> |
| crate. Please read <a href="https://github.com/rust-lang/rfcs/blob/master/text/1567-long-error-codes-explanation-normalization.md">RFC 1567</a> for details on how to format and write long error |
| codes. As of <!-- date-check --> February 2023, there is an |
| effort<sup class="footnote-reference" id="fr-new-explanations-1"><a href="#footnote-new-explanations">1</a></sup> to replace this largely outdated RFC with a new more |
| flexible standard.</p> |
| <p>Error explanations should expand on the error message and provide details about |
| <em>why</em> the error occurs. It is not helpful for users to copy-paste a quick fix; |
| explanations should help users understand why their code cannot be accepted by |
| the compiler. Rust prides itself on helpful error messages and long-form |
| explanations are no exception. However, before error explanations are |
| overhauled<sup class="footnote-reference" id="fr-new-explanations-2"><a href="#footnote-new-explanations">1</a></sup> it is a bit open as to how exactly they should be |
| written, as always: ask your reviewer or ask around on the Rust Zulip.</p> |
| <h2 id="allocating-a-fresh-code"><a class="header" href="#allocating-a-fresh-code">Allocating a fresh code</a></h2> |
| <p>Error codes are stored in <code>compiler/rustc_error_codes</code>.</p> |
| <p>To create a new error, you first need to find the next available |
| code. You can find it with <code>tidy</code>:</p> |
| <pre><code>./x test tidy |
| </code></pre> |
| <p>This will invoke the tidy script, which generally checks that your code obeys |
| our coding conventions. Some of these jobs check error codes and ensure that |
| there aren't duplicates, etc (the tidy check is defined in |
| <code>src/tools/tidy/src/error_codes.rs</code>). Once it is finished with that, tidy will |
| print out the highest used error code:</p> |
| <pre><code>... |
| tidy check |
| Found 505 error codes |
| Highest error code: `E0591` |
| ... |
| </code></pre> |
| <p>Here we see the highest error code in use is <code>E0591</code>, so we <em>probably</em> want |
| <code>E0592</code>. To be sure, run <code>rg E0592</code> and check, you should see no references.</p> |
| <p>You will have to write an extended description for your error, |
| which will go in <code>rustc_error_codes/src/error_codes/E0592.md</code>. |
| To register the error, open <code>rustc_error_codes/src/error_codes.rs</code> and add the |
| code (in its proper numerical order) into<code> register_diagnostics!</code> macro, like |
| this:</p> |
| <pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>register_diagnostics! { |
| ... |
| E0592: include_str!("./error_codes/E0592.md"), |
| } |
| <span class="boring">}</span></code></pre></pre> |
| <p>To actually issue the error, you can use the <code>struct_span_code_err!</code> macro:</p> |
| <pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>struct_span_code_err!(self.dcx(), // some path to the `DiagCtxt` here |
| span, // whatever span in the source you want |
| E0592, // your new error code |
| fluent::example::an_error_message) |
| .emit() // actually issue the error |
| <span class="boring">}</span></code></pre></pre> |
| <p>If you want to add notes or other snippets, you can invoke methods before you |
| call <code>.emit()</code>:</p> |
| <pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)] |
| </span><span class="boring">fn main() { |
| </span>struct_span_code_err!(...) |
| .span_label(another_span, fluent::example::example_label) |
| .span_note(another_span, fluent::example::separate_note) |
| .emit() |
| <span class="boring">}</span></code></pre></pre> |
| <p>For an example of a PR adding an error code, see <a href="https://github.com/rust-lang/rust/pull/76143">#76143</a>.</p> |
| <h2 id="running-error-code-doctests"><a class="header" href="#running-error-code-doctests">Running error code doctests</a></h2> |
| <p>To test the examples added in <code>rustc_error_codes/src/error_codes</code>, run the |
| error index generator using:</p> |
| <pre><code>./x test ./src/tools/error_index_generator |
| </code></pre> |
| <hr> |
| <ol class="footnote-definition"><li id="footnote-new-explanations"> |
| <p>See the draft RFC <a href="https://github.com/rust-lang/rfcs/pull/3370">here</a>. <a href="#fr-new-explanations-1">↩</a> <a href="#fr-new-explanations-2">↩2</a></p> |
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