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| </a><h2 class="location">Crate proc_macro2</h2><div class="block version"><div class="narrow-helper"></div><p>Version 1.0.36</p></div><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><div id="sidebar-vars" data-name="proc_macro2" data-ty="mod" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../proc_macro2/index.html"><img class="rust-logo" src="../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div> |
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| <h1 class="fqn"><span class="in-band">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></span></h1><span class="out-of-band"> |
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| <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&logoColor=white&logo=data:image/svg+xml;base64,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" 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" class="section-header"><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</span> <span class="kw">crate</span> <span class="ident">proc_macro</span>; |
| |
| <span class="attribute">#[<span class="ident">proc_macro_derive</span>(<span class="ident">MyDerive</span>)]</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">my_derive</span>(<span class="ident">input</span>: <span class="ident">proc_macro::TokenStream</span>) -> <span class="ident">proc_macro::TokenStream</span> { |
| <span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="ident">proc_macro2::TokenStream::from</span>(<span class="ident">input</span>); |
| |
| <span class="kw">let</span> <span class="ident">output</span>: <span class="ident">proc_macro2::TokenStream</span> <span class="op">=</span> { |
| <span class="comment">/* transform input */</span> |
| }; |
| |
| <span class="ident">proc_macro::TokenStream::from</span>(<span class="ident">output</span>) |
| }</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" class="section-header"><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" class="section-header"><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="token_stream/index.html" title="proc_macro2::token_stream mod">token_stream</a></div><div class="item-right docblock-short"><p>Public implementation details for the <code>TokenStream</code> type, such as iterators.</p> |
| </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"><p>A delimited token stream.</p> |
| </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"><p>A word of Rust code, which may be a keyword or legal variable name.</p> |
| </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"><p>Error returned from <code>TokenStream::from_str</code>.</p> |
| </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"><p>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>).</p> |
| </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"><p>A <code>Punct</code> is a single punctuation character like <code>+</code>, <code>-</code> or <code>#</code>.</p> |
| </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"><p>A region of source code, along with macro expansion information.</p> |
| </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"><p>An abstract stream of tokens, or more concretely a sequence of token trees.</p> |
| </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"><p>Describes how a sequence of token trees is delimited.</p> |
| </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"><p>Whether a <code>Punct</code> is followed immediately by another <code>Punct</code> or followed by |
| another token or whitespace.</p> |
| </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"><p>A single token or a delimited sequence of token trees (e.g. <code>[1, (), ..]</code>).</p> |
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