| <!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="github crates-io docs-rs"><meta name="keywords" content="rust, rustlang, rust-lang, proc_macro2"><title>proc_macro2 - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="../crates.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.svg"></head><body class="rustdoc mod crate"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../proc_macro2/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../proc_macro2/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate proc_macro2</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 1.0.59</li><li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Crate <a class="mod" href="#">proc_macro2</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/proc_macro2/lib.rs.html#1-1340">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p><a href="https://github.com/dtolnay/proc-macro2"><img src="https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github" alt="github" /></a> <a href="https://crates.io/crates/proc-macro2"><img src="https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust" alt="crates-io" /></a> <a href="index.html"><img src="https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" alt="docs-rs" /></a></p> |
| <br> |
| <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> |
| crate. This library serves two purposes:</p> |
| <ul> |
| <li> |
| <p><strong>Bring proc-macro-like functionality to other contexts like build.rs and |
| main.rs.</strong> Types from <code>proc_macro</code> are entirely specific to procedural |
| macros and cannot ever exist in code outside of a procedural macro. |
| Meanwhile <code>proc_macro2</code> types may exist anywhere including non-macro code. |
| 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 |
| <code>proc_macro2</code> rather than <code>proc_macro</code>, the procedural macro ecosystem |
| becomes easily applicable to many other use cases and we avoid |
| reimplementing non-macro equivalents of those libraries.</p> |
| </li> |
| <li> |
| <p><strong>Make procedural macros unit testable.</strong> As a consequence of being |
| specific to procedural macros, nothing that uses <code>proc_macro</code> can be |
| executed from a unit test. In order for helper libraries or components of |
| a macro to be testable in isolation, they must be implemented using |
| <code>proc_macro2</code>.</p> |
| </li> |
| </ul> |
| <h2 id="usage"><a href="#usage">Usage</a></h2> |
| <p>The skeleton of a typical procedural macro typically looks like this:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">extern crate </span>proc_macro; |
| |
| <span class="attribute">#[proc_macro_derive(MyDerive)] |
| </span><span class="kw">pub fn </span>my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream { |
| <span class="kw">let </span>input = proc_macro2::TokenStream::from(input); |
| |
| <span class="kw">let </span>output: proc_macro2::TokenStream = { |
| <span class="comment">/* transform input */ |
| </span>}; |
| |
| proc_macro::TokenStream::from(output) |
| }</code></pre></div> |
| <p>If parsing with <a href="https://github.com/dtolnay/syn">Syn</a>, you’ll use <a href="https://docs.rs/syn/1.0/syn/macro.parse_macro_input.html"><code>parse_macro_input!</code></a> instead to |
| propagate parse errors correctly back to the compiler when parsing fails.</p> |
| <h2 id="unstable-features"><a href="#unstable-features">Unstable features</a></h2> |
| <p>The default feature set of proc-macro2 tracks the most recent stable |
| compiler API. Functionality in <code>proc_macro</code> that is not yet stable is not |
| exposed by proc-macro2 by default.</p> |
| <p>To opt into the additional APIs available in the most recent nightly |
| compiler, the <code>procmacro2_semver_exempt</code> config flag must be passed to |
| rustc. We will polyfill those nightly-only APIs back to Rust 1.31.0. As |
| these are unstable APIs that track the nightly compiler, minor versions of |
| proc-macro2 may make breaking changes to them at any time.</p> |
| <div class="example-wrap"><pre class="language-sh"><code>RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build</code></pre></div> |
| <p>Note that this must not only be done for your crate, but for any crate that |
| depends on your crate. This infectious nature is intentional, as it serves |
| as a reminder that you are outside of the normal semver guarantees.</p> |
| <p>Semver exempt methods are marked as such in the proc-macro2 documentation.</p> |
| <h2 id="thread-safety"><a href="#thread-safety">Thread-Safety</a></h2> |
| <p>Most types in this crate are <code>!Sync</code> because the underlying compiler |
| types make use of thread-local memory, meaning they cannot be accessed from |
| a different thread.</p> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="extra/index.html" title="proc_macro2::extra mod">extra</a></div><div class="item-right docblock-short">Items which do not have a correspondence to any API in the proc_macro crate, |
| but are necessary to include in proc-macro2.</div></div><div class="item-row"><div class="item-left module-item"><a class="mod" href="token_stream/index.html" title="proc_macro2::token_stream mod">token_stream</a></div><div class="item-right docblock-short">Public implementation details for the <code>TokenStream</code> type, such as iterators.</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Group.html" title="proc_macro2::Group struct">Group</a></div><div class="item-right docblock-short">A delimited token stream.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Ident.html" title="proc_macro2::Ident struct">Ident</a></div><div class="item-right docblock-short">A word of Rust code, which may be a keyword or legal variable name.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.LexError.html" title="proc_macro2::LexError struct">LexError</a></div><div class="item-right docblock-short">Error returned from <code>TokenStream::from_str</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Literal.html" title="proc_macro2::Literal struct">Literal</a></div><div class="item-right docblock-short">A literal string (<code>"hello"</code>), byte string (<code>b"hello"</code>), character (<code>'a'</code>), |
| byte character (<code>b'a'</code>), an integer or floating point number with or without |
| a suffix (<code>1</code>, <code>1u8</code>, <code>2.3</code>, <code>2.3f32</code>).</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Punct.html" title="proc_macro2::Punct struct">Punct</a></div><div class="item-right docblock-short">A <code>Punct</code> is a single punctuation character like <code>+</code>, <code>-</code> or <code>#</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Span.html" title="proc_macro2::Span struct">Span</a></div><div class="item-right docblock-short">A region of source code, along with macro expansion information.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.TokenStream.html" title="proc_macro2::TokenStream struct">TokenStream</a></div><div class="item-right docblock-short">An abstract stream of tokens, or more concretely a sequence of token trees.</div></div></div><h2 id="enums" class="small-section-header"><a href="#enums">Enums</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="enum" href="enum.Delimiter.html" title="proc_macro2::Delimiter enum">Delimiter</a></div><div class="item-right docblock-short">Describes how a sequence of token trees is delimited.</div></div><div class="item-row"><div class="item-left module-item"><a class="enum" href="enum.Spacing.html" title="proc_macro2::Spacing enum">Spacing</a></div><div class="item-right docblock-short">Whether a <code>Punct</code> is followed immediately by another <code>Punct</code> or followed by |
| another token or whitespace.</div></div><div class="item-row"><div class="item-left module-item"><a class="enum" href="enum.TokenTree.html" title="proc_macro2::TokenTree enum">TokenTree</a></div><div class="item-right docblock-short">A single token or a delimited sequence of token trees (e.g. <code>[1, (), ..]</code>).</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="proc_macro2" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
