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| <h1 id="console-output"><a class="header" href="#console-output">Console Output</a></h1> |
| <p>All of Cargo’s output should go through the <a href="https://github.com/rust-lang/cargo/blob/master/src/cargo/core/shell.rs"><code>Shell</code></a> struct. You can normally |
| obtain the <code>Shell</code> instance from the <a href="https://github.com/rust-lang/cargo/blob/master/src/cargo/util/context/mod.rs"><code>GlobalContext</code></a> struct. Do <strong>not</strong> use |
| the std <code>println!</code> macros.</p> |
| <p>Most of Cargo’s output goes to stderr. When running in JSON mode, the output |
| goes to stdout.</p> |
| <p>It is important to properly handle errors when writing to the console. |
| Informational commands, like <code>cargo list</code>, should ignore any errors writing |
| the output. There are some <a href="https://github.com/rust-lang/cargo/blob/e4b65bdc80f2a293447f2f6a808fa7c84bf9a357/src/cargo/util/config/mod.rs#L1820-L1848"><code>drop_print</code></a> macros that are intended to make |
| this easier.</p> |
| <p>Messages written during compilation should handle errors, and abort the build |
| if they are unable to be displayed. This is generally automatically handled in |
| the <a href="https://github.com/rust-lang/cargo/blob/master/src/cargo/core/compiler/job_queue/mod.rs"><code>JobQueue</code></a> as it processes each message.</p> |
| <h2 id="errors"><a class="header" href="#errors">Errors</a></h2> |
| <p>Cargo uses <a href="https://docs.rs/anyhow"><code>anyhow</code></a> for managing errors. This makes it convenient to “chain” |
| errors together, so that Cargo can report how an error originated, and what it |
| was trying to do at the time.</p> |
| <p>Error helpers are implemented in the <a href="https://github.com/rust-lang/cargo/blob/master/src/cargo/util/errors.rs"><code>errors</code></a> module. Use the |
| <code>InternalError</code> error type for errors that are not expected to happen. This |
| will print a message to the user to file a bug report.</p> |
| <p>The binary side of Cargo uses the <code>CliError</code> struct to wrap the process exit |
| code. Usually Cargo exits with 101 for an error, but some commands like <code>cargo test</code> will exit with different codes.</p> |
| <h2 id="style"><a class="header" href="#style">Style</a></h2> |
| <p>Some guidelines for Cargo’s output:</p> |
| <ul> |
| <li>Keep the normal output brief. Cargo is already fairly noisy, so try to keep |
| the output as brief and clean as possible.</li> |
| <li>Good error messages are very important! Try to keep them brief and to the |
| point, but good enough that a beginner can understand what is wrong and can |
| figure out how to fix. It is a difficult balance to hit! Err on the side of |
| providing extra information.</li> |
| <li>When using any low-level routines, such as <code>std::fs</code>, <em>always</em> add error |
| context about what it is doing. For example, reading from a file should |
| include context about which file is being read if there is an error.</li> |
| <li>Cargo’s error style is usually a phrase, starting with a lowercase letter. |
| If there is a longer error message that needs multiple sentences, go ahead |
| and use multiple sentences. This should probably be improved sometime in the |
| future to be more structured.</li> |
| </ul> |
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