| <!DOCTYPE HTML> |
| <html lang="en" class="light sidebar-visible" dir="ltr"> |
| <head> |
| <!-- Book generated using mdBook --> |
| <meta charset="UTF-8"> |
| <title>Attributes - 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 --> |
| |
| |
| <!-- Provide site root and default themes to javascript --> |
| <script> |
| const path_to_root = ""; |
| const default_light_theme = "light"; |
| const default_dark_theme = "navy"; |
| </script> |
| <!-- Start loading toc.js asap --> |
| <script src="toc.js"></script> |
| </head> |
| <body> |
| <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 = sidebar === 'visible'; |
| html.classList.remove('sidebar-visible'); |
| html.classList.add("sidebar-" + sidebar); |
| </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. (Shortkey: s)" 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/master/src/attributes.md" title="Suggest an edit" aria-label="Suggest an 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"> |
| <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> |
| </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="attributes"><a class="header" href="#attributes">Attributes</a></h1> |
| <p>Attributes come in two types: <em>inert</em> (or <em>built-in</em>) and <em>active</em> (<em>non-builtin</em>).</p> |
| <h2 id="builtininert-attributes"><a class="header" href="#builtininert-attributes">Builtin/inert attributes</a></h2> |
| <p>These attributes are defined in the compiler itself, in |
| <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_feature/builtin_attrs/index.html"><code>compiler/rustc_feature/src/builtin_attrs.rs</code></a>.</p> |
| <p>Examples include <code>#[allow]</code> and <code>#[macro_use]</code>.</p> |
| <p>These attributes have several important characteristics:</p> |
| <ul> |
| <li>They are always in scope, and do not participate in typical path-based resolution.</li> |
| <li>They cannot be renamed. For example, <code>use allow as foo</code> will compile, but writing <code>#[foo]</code> will |
| produce an error.</li> |
| <li>They are 'inert', meaning they are left as-is by the macro expansion code. |
| As a result, any behavior comes as a result of the compiler explicitly checking for their presence. |
| For example, lint-related code explicitly checks for <code>#[allow]</code>, <code>#[warn]</code>, <code>#[deny]</code>, and |
| <code>#[forbid]</code>, rather than the behavior coming from the expansion of the attributes themselves.</li> |
| </ul> |
| <h2 id="non-builtinactive-attributes"><a class="header" href="#non-builtinactive-attributes">'Non-builtin'/'active' attributes</a></h2> |
| <p>These attributes are defined by a crate - either the standard library, or a proc-macro crate.</p> |
| <p><strong>Important</strong>: Many non-builtin attributes, such as <code>#[derive]</code>, are still considered part of the |
| core Rust language. However, they are <strong>not</strong> called 'builtin attributes', since they have a |
| corresponding definition in the standard library.</p> |
| <p>Definitions of non-builtin attributes take two forms:</p> |
| <ol> |
| <li>Proc-macro attributes, defined via a function annotated with <code>#[proc_macro_attribute]</code> in a |
| proc-macro crate.</li> |
| <li>AST-based attributes, defined in the standard library. These attributes have special 'stub' |
| macros defined in places like <a href="https://github.com/rust-lang/rust/blob/master/library/core/src/macros/mod.rs"><code>library/core/src/macros/mod.rs</code></a>.</li> |
| </ol> |
| <p>These definitions exist to allow the macros to participate in typical path-based resolution - they |
| can be imported, re-exported, and renamed just like any other item definition. However, the body of |
| the definition is empty. Instead, the macro is annotated with the <code>#[rustc_builtin_macro]</code> |
| attribute, which tells the compiler to run a corresponding function in <code>rustc_builtin_macros</code>.</p> |
| <p>All non-builtin attributes have the following characteristics:</p> |
| <ul> |
| <li>Like all other definitions (e.g. structs), they must be brought into scope via an import. |
| Many standard library attributes are included in the prelude - this is why writing <code>#[derive]</code> |
| works without an import.</li> |
| <li>They participate in macro expansion. The implementation of the macro may leave the attribute |
| target unchanged, modify the target, produce new AST nodes, or remove the target entirely.</li> |
| </ul> |
| |
| </main> |
| |
| <nav class="nav-wrapper" aria-label="Page navigation"> |
| <!-- Mobile navigation buttons --> |
| <a rel="prev" href="name-resolution.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="test-implementation.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="name-resolution.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="test-implementation.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> |
| |
| |
| </div> |
| </body> |
| </html> |
