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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `proc_macro2` crate."><meta name="keywords" content="rust, rustlang, rust-lang, proc_macro2"><title>proc_macro2 - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../proc_macro2/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Crate proc_macro2</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all proc_macro2's items</p></a><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'proc_macro2', ty: 'mod', relpath: '../'};</script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/proc_macro2/lib.rs.html#1-1156' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>proc_macro2</a></span></h1><div class='docblock'><p>A wrapper around the procedural macro API of the compiler's <a href="https://doc.rust-lang.org/proc_macro/"><code>proc_macro</code></a>
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crate. This library serves three purposes:</p>
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<ul>
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<li>
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<p><strong>Bring proc-macro-like functionality to other contexts like build.rs and
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main.rs.</strong> Types from <code>proc_macro</code> are entirely specific to procedural
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macros and cannot ever exist in code outside of a procedural macro.
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Meanwhile <code>proc_macro2</code> types may exist anywhere including non-macro code.
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By developing foundational libraries like <a href="https://github.com/dtolnay/syn">syn</a> and <a href="https://github.com/dtolnay/quote">quote</a> against
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<code>proc_macro2</code> rather than <code>proc_macro</code>, the procedural macro ecosystem
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becomes easily applicable to many other use cases and we avoid
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reimplementing non-macro equivalents of those libraries.</p>
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</li>
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<li>
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<p><strong>Make procedural macros unit testable.</strong> As a consequence of being
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specific to procedural macros, nothing that uses <code>proc_macro</code> can be
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executed from a unit test. In order for helper libraries or components of
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a macro to be testable in isolation, they must be implemented using
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<code>proc_macro2</code>.</p>
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</li>
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<li>
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<p><strong>Provide the latest and greatest APIs across all compiler versions.</strong>
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Procedural macros were first introduced to Rust in 1.15.0 with an
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extremely minimal interface. Since then, many improvements have landed to
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make macros more flexible and easier to write. This library tracks the
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procedural macro API of the most recent stable compiler but employs a
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polyfill to provide that API consistently across any compiler since
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1.15.0.</p>
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</li>
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</ul>
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<h1 id="usage" class="section-header"><a href="#usage">Usage</a></h1>
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<p>The skeleton of a typical procedural macro typically looks like this:</p>
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<pre><code class="language-edition2018">extern crate proc_macro;
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# const IGNORE: &str = stringify! {
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#[proc_macro_derive(MyDerive)]
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# };
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pub fn my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
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let input = proc_macro2::TokenStream::from(input);
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let output: proc_macro2::TokenStream = {
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/* transform input */
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# input
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};
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proc_macro::TokenStream::from(output)
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}
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</code></pre>
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<p>If parsing with <a href="https://github.com/dtolnay/syn">Syn</a>, you'll use <a href="https://docs.rs/syn/0.15/syn/macro.parse_macro_input.html"><code>parse_macro_input!</code></a> instead to
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propagate parse errors correctly back to the compiler when parsing fails.</p>
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<h1 id="unstable-features" class="section-header"><a href="#unstable-features">Unstable features</a></h1>
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<p>The default feature set of proc-macro2 tracks the most recent stable
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compiler API. Functionality in <code>proc_macro</code> that is not yet stable is not
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exposed by proc-macro2 by default.</p>
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<p>To opt into the additional APIs available in the most recent nightly
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compiler, the <code>procmacro2_semver_exempt</code> config flag must be passed to
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rustc. As usual, we will polyfill those nightly-only APIs all the way back
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to Rust 1.15.0. As these are unstable APIs that track the nightly compiler,
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minor versions of proc-macro2 may make breaking changes to them at any time.</p>
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<pre><code class="language-sh">RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build
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</code></pre>
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<p>Note that this must not only be done for your crate, but for any crate that
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depends on your crate. This infectious nature is intentional, as it serves
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as a reminder that you are outside of the normal semver guarantees.</p>
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<p>Semver exempt methods are marked as such in the proc-macro2 documentation.</p>
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</div><h2 id='modules' class='section-header'><a href="#modules">Modules</a></h2>
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<table><tr class='module-item'><td><a class="mod" href="token_stream/index.html" title='proc_macro2::token_stream mod'>token_stream</a></td><td class='docblock-short'><p>Public implementation details for the <code>TokenStream</code> type, such as iterators.</p>
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</td></tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table><tr class='module-item'><td><a class="struct" href="struct.Group.html" title='proc_macro2::Group struct'>Group</a></td><td class='docblock-short'><p>A delimited token stream.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Ident.html" title='proc_macro2::Ident struct'>Ident</a></td><td class='docblock-short'><p>A word of Rust code, which may be a keyword or legal variable name.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.LexError.html" title='proc_macro2::LexError struct'>LexError</a></td><td class='docblock-short'><p>Error returned from <code>TokenStream::from_str</code>.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Literal.html" title='proc_macro2::Literal struct'>Literal</a></td><td class='docblock-short'><p>A literal string (<code>"hello"</code>), byte string (<code>b"hello"</code>), character (<code>'a'</code>),
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byte character (<code>b'a'</code>), an integer or floating point number with or without
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a suffix (<code>1</code>, <code>1u8</code>, <code>2.3</code>, <code>2.3f32</code>).</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Punct.html" title='proc_macro2::Punct struct'>Punct</a></td><td class='docblock-short'><p>An <code>Punct</code> is an single punctuation character like <code>+</code>, <code>-</code> or <code>#</code>.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Span.html" title='proc_macro2::Span struct'>Span</a></td><td class='docblock-short'><p>A region of source code, along with macro expansion information.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.TokenStream.html" title='proc_macro2::TokenStream struct'>TokenStream</a></td><td class='docblock-short'><p>An abstract stream of tokens, or more concretely a sequence of token trees.</p>
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</td></tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
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<table><tr class='module-item'><td><a class="enum" href="enum.Delimiter.html" title='proc_macro2::Delimiter enum'>Delimiter</a></td><td class='docblock-short'><p>Describes how a sequence of token trees is delimited.</p>
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</td></tr><tr class='module-item'><td><a class="enum" href="enum.Spacing.html" title='proc_macro2::Spacing enum'>Spacing</a></td><td class='docblock-short'><p>Whether an <code>Punct</code> is followed immediately by another <code>Punct</code> or followed by
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another token or whitespace.</p>
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</td></tr><tr class='module-item'><td><a class="enum" href="enum.TokenTree.html" title='proc_macro2::TokenTree enum'>TokenTree</a></td><td class='docblock-short'><p>A single token or a delimited sequence of token trees (e.g. <code>[1, (), ..]</code>).</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g., <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g., <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g., <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../";window.currentCrate = "proc_macro2";</script><script src="../aliases.js"></script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html>
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