| <!DOCTYPE HTML> |
| <html lang="en" class="light sidebar-visible" dir="ltr"> |
| <head> |
| <!-- Book generated using mdBook --> |
| <meta charset="UTF-8"> |
| <title>Translation - Rust Compiler Development Guide</title> |
| |
| |
| <!-- Custom HTML head --> |
| |
| <meta name="description" content="A guide to developing the Rust compiler (rustc)"> |
| <meta name="viewport" content="width=device-width, initial-scale=1"> |
| <meta name="theme-color" content="#ffffff"> |
| |
| <link rel="icon" href="../favicon.svg"> |
| <link rel="shortcut icon" href="../favicon.png"> |
| <link rel="stylesheet" href="../css/variables.css"> |
| <link rel="stylesheet" href="../css/general.css"> |
| <link rel="stylesheet" href="../css/chrome.css"> |
| <link rel="stylesheet" href="../css/print.css" media="print"> |
| |
| <!-- Fonts --> |
| <link rel="stylesheet" href="../FontAwesome/css/font-awesome.css"> |
| <link rel="stylesheet" href="../fonts/fonts.css"> |
| |
| <!-- Highlight.js Stylesheets --> |
| <link rel="stylesheet" id="highlight-css" href="../highlight.css"> |
| <link rel="stylesheet" id="tomorrow-night-css" href="../tomorrow-night.css"> |
| <link rel="stylesheet" id="ayu-highlight-css" href="../ayu-highlight.css"> |
| |
| <!-- Custom theme stylesheets --> |
| <link rel="stylesheet" href="../pagetoc.css"> |
| |
| |
| <!-- Provide site root and default themes to javascript --> |
| <script> |
| const path_to_root = "../"; |
| const default_light_theme = "light"; |
| const default_dark_theme = "navy"; |
| window.path_to_searchindex_js = "../searchindex.js"; |
| </script> |
| <!-- Start loading toc.js asap --> |
| <script src="../toc.js"></script> |
| </head> |
| <body> |
| <div id="mdbook-help-container"> |
| <div id="mdbook-help-popup"> |
| <h2 class="mdbook-help-title">Keyboard shortcuts</h2> |
| <div> |
| <p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p> |
| <p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p> |
| <p>Press <kbd>?</kbd> to show this help</p> |
| <p>Press <kbd>Esc</kbd> to hide this help</p> |
| </div> |
| </div> |
| </div> |
| <div id="body-container"> |
| <!-- Work around some values being stored in localStorage wrapped in quotes --> |
| <script> |
| try { |
| let theme = localStorage.getItem('mdbook-theme'); |
| let sidebar = localStorage.getItem('mdbook-sidebar'); |
| |
| if (theme.startsWith('"') && theme.endsWith('"')) { |
| localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1)); |
| } |
| |
| if (sidebar.startsWith('"') && sidebar.endsWith('"')) { |
| localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1)); |
| } |
| } catch (e) { } |
| </script> |
| |
| <!-- Set the theme before any content is loaded, prevents flash --> |
| <script> |
| const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme; |
| let theme; |
| try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { } |
| if (theme === null || theme === undefined) { theme = default_theme; } |
| const html = document.documentElement; |
| html.classList.remove('light') |
| html.classList.add(theme); |
| html.classList.add("js"); |
| </script> |
| |
| <input type="checkbox" id="sidebar-toggle-anchor" class="hidden"> |
| |
| <!-- Hide / unhide sidebar before it is displayed --> |
| <script> |
| let sidebar = null; |
| const sidebar_toggle = document.getElementById("sidebar-toggle-anchor"); |
| if (document.body.clientWidth >= 1080) { |
| try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } |
| sidebar = sidebar || 'visible'; |
| } else { |
| sidebar = 'hidden'; |
| sidebar_toggle.checked = false; |
| } |
| if (sidebar === 'visible') { |
| sidebar_toggle.checked = true; |
| } else { |
| html.classList.remove('sidebar-visible'); |
| } |
| </script> |
| |
| <nav id="sidebar" class="sidebar" aria-label="Table of contents"> |
| <!-- populated by js --> |
| <mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox> |
| <noscript> |
| <iframe class="sidebar-iframe-outer" src="../toc.html"></iframe> |
| </noscript> |
| <div id="sidebar-resize-handle" class="sidebar-resize-handle"> |
| <div class="sidebar-resize-indicator"></div> |
| </div> |
| </nav> |
| |
| <div id="page-wrapper" class="page-wrapper"> |
| |
| <div class="page"> |
| <div id="menu-bar-hover-placeholder"></div> |
| <div id="menu-bar" class="menu-bar sticky"> |
| <div class="left-buttons"> |
| <label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar"> |
| <i class="fa fa-bars"></i> |
| </label> |
| <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list"> |
| <i class="fa fa-paint-brush"></i> |
| </button> |
| <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu"> |
| <li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="light">Light</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li> |
| </ul> |
| <button id="search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="searchbar"> |
| <i class="fa fa-search"></i> |
| </button> |
| </div> |
| |
| <h1 class="menu-title">Rust Compiler Development Guide</h1> |
| |
| <div class="right-buttons"> |
| <a href="../print.html" title="Print this book" aria-label="Print this book"> |
| <i id="print-button" class="fa fa-print"></i> |
| </a> |
| <a href="https://github.com/rust-lang/rustc-dev-guide" title="Git repository" aria-label="Git repository"> |
| <i id="git-repository-button" class="fa fa-github"></i> |
| </a> |
| <a href="https://github.com/rust-lang/rustc-dev-guide/edit/main/src/diagnostics/translation.md" title="Suggest an edit" aria-label="Suggest an edit" rel="edit"> |
| <i id="git-edit-button" class="fa fa-edit"></i> |
| </a> |
| |
| </div> |
| </div> |
| |
| <div id="search-wrapper" class="hidden"> |
| <form id="searchbar-outer" class="searchbar-outer"> |
| <div class="search-wrapper"> |
| <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> |
| <div class="spinner-wrapper"> |
| <i class="fa fa-spinner fa-spin"></i> |
| </div> |
| </div> |
| </form> |
| <div id="searchresults-outer" class="searchresults-outer hidden"> |
| <div id="searchresults-header" class="searchresults-header"></div> |
| <ul id="searchresults"> |
| </ul> |
| </div> |
| </div> |
| |
| <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> |
| <script> |
| document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); |
| document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); |
| Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { |
| link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); |
| }); |
| </script> |
| |
| <div id="content" class="content"> |
| <main> |
| <h1 id="translation"><a class="header" href="#translation">Translation</a></h1> |
| <div class="warning"> |
| rustc's current diagnostics translation infrastructure (as of |
| <!-- date-check --> October 2024 |
| ) unfortunately causes some friction for compiler contributors, and the current |
| infrastructure is mostly pending a redesign that better addresses needs of both |
| compiler contributors and translation teams. Note that there is no current |
| active redesign proposals (as of |
| <!-- date-check --> October 2024 |
| )! |
| <p>Please see the tracking issue <a href="https://github.com/rust-lang/rust/issues/132181">https://github.com/rust-lang/rust/issues/132181</a> |
| for status updates.</p> |
| <p>We have downgraded the internal lints <code>untranslatable_diagnostic</code> and |
| <code>diagnostic_outside_of_impl</code>. Those internal lints previously required new code |
| to use the current translation infrastructure. However, because the translation |
| infra is waiting for a yet-to-be-proposed redesign and thus rework, we are not |
| mandating usage of current translation infra. Use the infra if you <em>want to</em> or |
| otherwise makes the code cleaner, but otherwise sidestep the translation infra |
| if you need more flexibility.</p> |
| </div> |
| <p>rustc's diagnostic infrastructure supports translatable diagnostics using |
| <a href="https://projectfluent.org">Fluent</a>.</p> |
| <h2 id="writing-translatable-diagnostics"><a class="header" href="#writing-translatable-diagnostics">Writing translatable diagnostics</a></h2> |
| <p>There are two ways of writing translatable diagnostics:</p> |
| <ol> |
| <li>For simple diagnostics, using a diagnostic (or subdiagnostic) derive. |
| ("Simple" diagnostics being those that don't require a lot of logic in |
| deciding to emit subdiagnostics and can therefore be represented as |
| diagnostic structs). See <a href="./diagnostic-structs.html">the diagnostic and subdiagnostic structs |
| documentation</a>.</li> |
| <li>Using typed identifiers with <code>Diag</code> APIs (in |
| <code>Diagnostic</code> or <code>Subdiagnostic</code> or <code>LintDiagnostic</code> implementations).</li> |
| </ol> |
| <p>When adding or changing a translatable diagnostic, |
| you don't need to worry about the translations. |
| Only updating the original English message is required. |
| Currently, |
| each crate which defines translatable diagnostics has its own Fluent resource, |
| which is a file named <code>messages.ftl</code>, |
| located in the root of the crate |
| (such as<code>compiler/rustc_expand/messages.ftl</code>).</p> |
| <h2 id="fluent"><a class="header" href="#fluent">Fluent</a></h2> |
| <p>Fluent is built around the idea of "asymmetric localization", which aims to |
| decouple the expressiveness of translations from the grammar of the source |
| language (English in rustc's case). Prior to translation, rustc's diagnostics |
| relied heavily on interpolation to build the messages shown to the users. |
| Interpolated strings are hard to translate because writing a natural-sounding |
| translation might require more, less, or just different interpolation than the |
| English string, all of which would require changes to the compiler's source |
| code to support.</p> |
| <p>Diagnostic messages are defined in Fluent resources. A combined set of Fluent |
| resources for a given locale (e.g. <code>en-US</code>) is known as Fluent bundle.</p> |
| <pre><code class="language-fluent">typeck_address_of_temporary_taken = cannot take address of a temporary |
| </code></pre> |
| <p>In the above example, <code>typeck_address_of_temporary_taken</code> is the identifier for |
| a Fluent message and corresponds to the diagnostic message in English. Other |
| Fluent resources can be written which would correspond to a message in another |
| language. Each diagnostic therefore has at least one Fluent message.</p> |
| <pre><code class="language-fluent">typeck_address_of_temporary_taken = cannot take address of a temporary |
| .label = temporary value |
| </code></pre> |
| <p>By convention, diagnostic messages for subdiagnostics are specified as |
| "attributes" on Fluent messages (additional related messages, denoted by the |
| <code>.<attribute-name></code> syntax). In the above example, <code>label</code> is an attribute of |
| <code>typeck_address_of_temporary_taken</code> which corresponds to the message for the |
| label added to this diagnostic.</p> |
| <p>Diagnostic messages often interpolate additional context into the message shown |
| to the user, such as the name of a type or of a variable. Additional context to |
| Fluent messages is provided as an "argument" to the diagnostic.</p> |
| <pre><code class="language-fluent">typeck_struct_expr_non_exhaustive = |
| cannot create non-exhaustive {$what} using struct expression |
| </code></pre> |
| <p>In the above example, the Fluent message refers to an argument named <code>what</code> |
| which is expected to exist (how arguments are provided to diagnostics is |
| discussed in detail later).</p> |
| <p>You can consult the <a href="https://projectfluent.org">Fluent</a> documentation for other usage examples of Fluent |
| and its syntax.</p> |
| <h3 id="guideline-for-message-naming"><a class="header" href="#guideline-for-message-naming">Guideline for message naming</a></h3> |
| <p>Usually, fluent uses <code>-</code> for separating words inside a message name. However, |
| <code>_</code> is accepted by fluent as well. As <code>_</code> fits Rust's use cases better, due to |
| the identifiers on the Rust side using <code>_</code> as well, inside rustc, <code>-</code> is not |
| allowed for separating words, and instead <code>_</code> is recommended. The only exception |
| is for leading <code>-</code>s, for message names like <code>-passes_see_issue</code>.</p> |
| <h3 id="guidelines-for-writing-translatable-messages"><a class="header" href="#guidelines-for-writing-translatable-messages">Guidelines for writing translatable messages</a></h3> |
| <p>For a message to be translatable into different languages, all of the |
| information required by any language must be provided to the diagnostic as an |
| argument (not just the information required in the English message).</p> |
| <p>As the compiler team gain more experience writing diagnostics that have all of |
| the information necessary to be translated into different languages, this page |
| will be updated with more guidance. For now, the <a href="https://projectfluent.org">Fluent</a> documentation has |
| excellent examples of translating messages into different locales and the |
| information that needs to be provided by the code to do so.</p> |
| <h3 id="compile-time-validation-and-typed-identifiers"><a class="header" href="#compile-time-validation-and-typed-identifiers">Compile-time validation and typed identifiers</a></h3> |
| <p>rustc's <code>fluent_messages</code> macro performs compile-time validation of Fluent |
| resources and generates code to make it easier to refer to Fluent messages in |
| diagnostics.</p> |
| <p>Compile-time validation of Fluent resources will emit any parsing errors |
| from Fluent resources while building the compiler, preventing invalid Fluent |
| resources from causing panics in the compiler. Compile-time validation also |
| emits an error if multiple Fluent messages have the same identifier.</p> |
| <h2 id="internals"><a class="header" href="#internals">Internals</a></h2> |
| <p>Various parts of rustc's diagnostic internals are modified in order to support |
| translation.</p> |
| <h3 id="messages"><a class="header" href="#messages">Messages</a></h3> |
| <p>All of rustc's traditional diagnostic APIs (e.g. <code>struct_span_err</code> or <code>note</code>) |
| take any message that can be converted into a <code>DiagMessage</code> (or |
| <code>SubdiagMessage</code>).</p> |
| <p><a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_error_messages/enum.DiagMessage.html"><code>rustc_error_messages::DiagMessage</code></a> can represent legacy non-translatable |
| diagnostic messages and translatable messages. Non-translatable messages are |
| just <code>String</code>s. Translatable messages are just a <code>&'static str</code> with the |
| identifier of the Fluent message (sometimes with an additional <code>&'static str</code> |
| with an attribute).</p> |
| <p><code>DiagMessage</code> never needs to be interacted with directly: |
| <code>DiagMessage</code> constants are created for each diagnostic message in a |
| Fluent resource (described in more detail below), or <code>DiagMessage</code>s will |
| either be created in the macro-generated code of a diagnostic derive.</p> |
| <p><code>rustc_error_messages::SubdiagMessage</code> is similar, it can correspond to a |
| legacy non-translatable diagnostic message or the name of an attribute to a |
| Fluent message. Translatable <code>SubdiagMessage</code>s must be combined with a |
| <code>DiagMessage</code> (using <code>DiagMessage::with_subdiagnostic_message</code>) to |
| be emitted (an attribute name on its own is meaningless without a corresponding |
| message identifier, which is what <code>DiagMessage</code> provides).</p> |
| <p>Both <code>DiagMessage</code> and <code>SubdiagMessage</code> implement <code>Into</code> for any |
| type that can be converted into a string, and converts these into |
| non-translatable diagnostics - this keeps all existing diagnostic calls |
| working.</p> |
| <h3 id="arguments"><a class="header" href="#arguments">Arguments</a></h3> |
| <p>Additional context for Fluent messages which are interpolated into message |
| contents needs to be provided to translatable diagnostics.</p> |
| <p>Diagnostics have a <code>set_arg</code> function that can be used to provide this |
| additional context to a diagnostic.</p> |
| <p>Arguments have both a name (e.g. "what" in the earlier example) and a value. |
| Argument values are represented using the <code>DiagArgValue</code> type, which is |
| just a string or a number. rustc types can implement <code>IntoDiagArg</code> with |
| conversion into a string or a number, and common types like <code>Ty<'tcx></code> already |
| have such implementations.</p> |
| <p><code>set_arg</code> calls are handled transparently by diagnostic derives but need to be |
| added manually when using diagnostic builder APIs.</p> |
| <h3 id="loading"><a class="header" href="#loading">Loading</a></h3> |
| <p>rustc makes a distinction between the "fallback bundle" for <code>en-US</code> that is used |
| by default and when another locale is missing a message; and the primary fluent |
| bundle which is requested by the user.</p> |
| <p>Diagnostic emitters implement the <code>Emitter</code> trait which has two functions for |
| accessing the fallback and primary fluent bundles (<code>fallback_fluent_bundle</code> and |
| <code>fluent_bundle</code> respectively).</p> |
| <p><code>Emitter</code> also has member functions with default implementations for performing |
| translation of a <code>DiagMessage</code> using the results of |
| <code>fallback_fluent_bundle</code> and <code>fluent_bundle</code>.</p> |
| <p>All of the emitters in rustc load the fallback Fluent bundle lazily, only |
| reading Fluent resources and parsing them when an error message is first being |
| translated (for performance reasons - it doesn't make sense to do this if no |
| error is being emitted). <code>rustc_error_messages::fallback_fluent_bundle</code> returns |
| a <code>std::lazy::Lazy<FluentBundle></code> which is provided to emitters and evaluated |
| in the first call to <code>Emitter::fallback_fluent_bundle</code>.</p> |
| <p>The primary Fluent bundle (for the user's desired locale) is expected to be |
| returned by <code>Emitter::fluent_bundle</code>. This bundle is used preferentially when |
| translating messages, the fallback bundle is only used if the primary bundle is |
| missing a message or not provided.</p> |
| <p>There are no locale bundles distributed with the compiler, |
| but mechanisms are implemented for loading them.</p> |
| <ul> |
| <li><code>-Ztranslate-additional-ftl</code> can be used to load a specific resource as the |
| primary bundle for testing purposes.</li> |
| <li><code>-Ztranslate-lang</code> can be provided a language identifier (something like |
| <code>en-US</code>) and will load any Fluent resources found in |
| <code>$sysroot/share/locale/$locale/</code> directory (both the user provided |
| sysroot and any sysroot candidates).</li> |
| </ul> |
| <p>Primary bundles are not currently loaded lazily and if requested will be loaded |
| at the start of compilation regardless of whether an error occurs. Lazily |
| loading primary bundles is possible if it can be assumed that loading a bundle |
| won't fail. Bundle loading can fail if a requested locale is missing, Fluent |
| files are malformed, or a message is duplicated in multiple resources.</p> |
| |
| </main> |
| |
| <nav class="nav-wrapper" aria-label="Page navigation"> |
| <!-- Mobile navigation buttons --> |
| <a rel="prev" href="../diagnostics/diagnostic-structs.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <i class="fa fa-angle-left"></i> |
| </a> |
| |
| <a rel="next prefetch" href="../diagnostics/lintstore.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <i class="fa fa-angle-right"></i> |
| </a> |
| |
| <div style="clear: both"></div> |
| </nav> |
| </div> |
| </div> |
| |
| <nav class="nav-wide-wrapper" aria-label="Page navigation"> |
| <a rel="prev" href="../diagnostics/diagnostic-structs.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <i class="fa fa-angle-left"></i> |
| </a> |
| |
| <a rel="next prefetch" href="../diagnostics/lintstore.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <i class="fa fa-angle-right"></i> |
| </a> |
| </nav> |
| |
| </div> |
| |
| |
| |
| |
| <script> |
| window.playground_copyable = true; |
| </script> |
| |
| |
| <script src="../elasticlunr.min.js"></script> |
| <script src="../mark.min.js"></script> |
| <script src="../searcher.js"></script> |
| |
| <script src="../clipboard.min.js"></script> |
| <script src="../highlight.js"></script> |
| <script src="../book.js"></script> |
| |
| <!-- Custom JS scripts --> |
| <script src="../mermaid.min.js"></script> |
| <script src="../mermaid-init.js"></script> |
| <script src="../pagetoc.js"></script> |
| |
| |
| |
| </div> |
| </body> |
| </html> |
