| <!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="Parsing interface for parsing a token stream into a syntax tree node."><meta name="keywords" content="rust, rustlang, rust-lang, parse"><title>syn::parse - 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" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script src="../../crates.js"></script><script defer src="../../main.js"></script> |
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| </a><h2 class="location">Module parse</h2><div class="sidebar-elems"><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li><li><a href="#types">Type Definitions</a></li></ul></div><div id="sidebar-vars" data-name="parse" 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="../../syn/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">Module <a href="../index.html">syn</a>::<wbr><a class="mod" href="#">parse</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"> |
| <a class="srclink" href="../../src/syn/parse.rs.html#1-1287" title="goto source code">source</a> · |
| <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div> |
| <div class="item-info"><div class="stab portability">This is supported on <strong>crate feature <code>parsing</code></strong> only.</div></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Parsing interface for parsing a token stream into a syntax tree node.</p> |
| <p>Parsing in Syn is built on parser functions that take in a <a href="type.ParseStream.html" title="ParseStream"><code>ParseStream</code></a> |
| and produce a <a href="type.Result.html"><code>Result<T></code></a> where <code>T</code> is some syntax tree node. Underlying |
| these parser functions is a lower level mechanism built around the |
| <a href="../buffer/struct.Cursor.html"><code>Cursor</code></a> type. <code>Cursor</code> is a cheaply copyable cursor over a range of |
| tokens in a token stream.</p> |
| <h2 id="example" class="section-header"><a href="#example">Example</a></h2> |
| <p>Here is a snippet of parsing code to get a feel for the style of the |
| library. We define data structures for a subset of Rust syntax including |
| enums (not shown) and structs, then provide implementations of the <a href="trait.Parse.html" title="Parse"><code>Parse</code></a> |
| trait to parse these syntax tree data structures from a token stream.</p> |
| <p>Once <code>Parse</code> impls have been defined, they can be called conveniently from a |
| procedural macro through <a href="../macro.parse_macro_input.html"><code>parse_macro_input!</code></a> as shown at the bottom of |
| the snippet. If the caller provides syntactically invalid input to the |
| procedural macro, they will receive a helpful compiler error message |
| pointing out the exact token that triggered the failure to parse.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">proc_macro::TokenStream</span>; |
| <span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">braced</span>, <span class="ident">parse_macro_input</span>, <span class="ident">token</span>, <span class="ident">Field</span>, <span class="ident">Ident</span>, <span class="prelude-ty">Result</span>, <span class="ident">Token</span>}; |
| <span class="kw">use</span> <span class="ident">syn::parse</span>::{<span class="ident">Parse</span>, <span class="ident">ParseStream</span>}; |
| <span class="kw">use</span> <span class="ident">syn::punctuated::Punctuated</span>; |
| |
| <span class="kw">enum</span> <span class="ident">Item</span> { |
| <span class="ident">Struct</span>(<span class="ident">ItemStruct</span>), |
| <span class="ident">Enum</span>(<span class="ident">ItemEnum</span>), |
| } |
| |
| <span class="kw">struct</span> <span class="ident">ItemStruct</span> { |
| <span class="ident">struct_token</span>: <span class="macro">Token!</span>[<span class="kw">struct</span>], |
| <span class="ident">ident</span>: <span class="ident">Ident</span>, |
| <span class="ident">brace_token</span>: <span class="ident">token::Brace</span>, |
| <span class="ident">fields</span>: <span class="ident">Punctuated</span><span class="op"><</span><span class="ident">Field</span>, <span class="macro">Token!</span>[,]<span class="op">></span>, |
| } |
| |
| <span class="kw">impl</span> <span class="ident">Parse</span> <span class="kw">for</span> <span class="ident">Item</span> { |
| <span class="kw">fn</span> <span class="ident">parse</span>(<span class="ident">input</span>: <span class="ident">ParseStream</span>) -> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span><span class="op">></span> { |
| <span class="kw">let</span> <span class="ident">lookahead</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">lookahead1</span>(); |
| <span class="kw">if</span> <span class="ident">lookahead</span>.<span class="ident">peek</span>(<span class="macro">Token!</span>[<span class="kw">struct</span>]) { |
| <span class="ident">input</span>.<span class="ident">parse</span>().<span class="ident">map</span>(<span class="ident">Item::Struct</span>) |
| } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">lookahead</span>.<span class="ident">peek</span>(<span class="macro">Token!</span>[<span class="kw">enum</span>]) { |
| <span class="ident">input</span>.<span class="ident">parse</span>().<span class="ident">map</span>(<span class="ident">Item::Enum</span>) |
| } <span class="kw">else</span> { |
| <span class="prelude-val">Err</span>(<span class="ident">lookahead</span>.<span class="ident">error</span>()) |
| } |
| } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">Parse</span> <span class="kw">for</span> <span class="ident">ItemStruct</span> { |
| <span class="kw">fn</span> <span class="ident">parse</span>(<span class="ident">input</span>: <span class="ident">ParseStream</span>) -> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span><span class="op">></span> { |
| <span class="kw">let</span> <span class="ident">content</span>; |
| <span class="prelude-val">Ok</span>(<span class="ident">ItemStruct</span> { |
| <span class="ident">struct_token</span>: <span class="ident">input</span>.<span class="ident">parse</span>()<span class="question-mark">?</span>, |
| <span class="ident">ident</span>: <span class="ident">input</span>.<span class="ident">parse</span>()<span class="question-mark">?</span>, |
| <span class="ident">brace_token</span>: <span class="macro">braced!</span>(<span class="ident">content</span> <span class="kw">in</span> <span class="ident">input</span>), |
| <span class="ident">fields</span>: <span class="ident">content</span>.<span class="ident">parse_terminated</span>(<span class="ident">Field::parse_named</span>)<span class="question-mark">?</span>, |
| }) |
| } |
| } |
| |
| <span class="attribute">#[<span class="ident">proc_macro</span>]</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">my_macro</span>(<span class="ident">tokens</span>: <span class="ident">TokenStream</span>) -> <span class="ident">TokenStream</span> { |
| <span class="kw">let</span> <span class="ident">input</span> <span class="op">=</span> <span class="macro">parse_macro_input!</span>(<span class="ident">tokens</span> <span class="kw">as</span> <span class="ident">Item</span>); |
| |
| <span class="comment">/* ... */</span> |
| }</code></pre></div> |
| <h2 id="the-synparse-functions" class="section-header"><a href="#the-synparse-functions">The <code>syn::parse*</code> functions</a></h2> |
| <p>The <a href="../fn.parse.html"><code>syn::parse</code></a>, <a href="../fn.parse2.html"><code>syn::parse2</code></a>, and <a href="../fn.parse_str.html"><code>syn::parse_str</code></a> functions serve |
| as an entry point for parsing syntax tree nodes that can be parsed in an |
| obvious default way. These functions can return any syntax tree node that |
| implements the <a href="trait.Parse.html" title="Parse"><code>Parse</code></a> trait, which includes most types in Syn.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">syn::Type</span>; |
| |
| <span class="kw">let</span> <span class="ident">t</span>: <span class="ident">Type</span> <span class="op">=</span> <span class="ident">syn::parse_str</span>(<span class="string">"std::collections::HashMap<String, Value>"</span>)<span class="question-mark">?</span>;</code></pre></div> |
| <p>The <a href="../macro.parse_quote.html"><code>parse_quote!</code></a> macro also uses this approach.</p> |
| <h2 id="the-parser-trait" class="section-header"><a href="#the-parser-trait">The <code>Parser</code> trait</a></h2> |
| <p>Some types can be parsed in several ways depending on context. For example |
| an <a href="../struct.Attribute.html"><code>Attribute</code></a> can be either “outer” like <code>#[...]</code> or “inner” like |
| <code>#![...]</code> and parsing the wrong one would be a bug. Similarly <a href="../punctuated/index.html"><code>Punctuated</code></a> |
| may or may not allow trailing punctuation, and parsing it the wrong way |
| would either reject valid input or accept invalid input.</p> |
| <p>The <code>Parse</code> trait is not implemented in these cases because there is no good |
| behavior to consider the default.</p> |
| |
| <div class='information'><div class='tooltip compile_fail'>ⓘ</div></div><div class="example-wrap"><pre class="rust rust-example-rendered compile_fail"><code><span class="comment">// Can't parse `Punctuated` without knowing whether trailing punctuation</span> |
| <span class="comment">// should be allowed in this context.</span> |
| <span class="kw">let</span> <span class="ident">path</span>: <span class="ident">Punctuated</span><span class="op"><</span><span class="ident">PathSegment</span>, <span class="macro">Token!</span>[::]<span class="op">></span> <span class="op">=</span> <span class="ident">syn::parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>;</code></pre></div> |
| <p>In these cases the types provide a choice of parser functions rather than a |
| single <code>Parse</code> implementation, and those parser functions can be invoked |
| through the <a href="trait.Parser.html" title="Parser"><code>Parser</code></a> trait.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">proc_macro::TokenStream</span>; |
| <span class="kw">use</span> <span class="ident">syn::parse::Parser</span>; |
| <span class="kw">use</span> <span class="ident">syn::punctuated::Punctuated</span>; |
| <span class="kw">use</span> <span class="ident">syn</span>::{<span class="ident">Attribute</span>, <span class="ident">Expr</span>, <span class="ident">PathSegment</span>, <span class="prelude-ty">Result</span>, <span class="ident">Token</span>}; |
| |
| <span class="kw">fn</span> <span class="ident">call_some_parser_methods</span>(<span class="ident">input</span>: <span class="ident">TokenStream</span>) -> <span class="prelude-ty">Result</span><span class="op"><</span>()<span class="op">></span> { |
| <span class="comment">// Parse a nonempty sequence of path segments separated by `::` punctuation</span> |
| <span class="comment">// with no trailing punctuation.</span> |
| <span class="kw">let</span> <span class="ident">tokens</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">clone</span>(); |
| <span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Punctuated</span>::<span class="op"><</span><span class="ident">PathSegment</span>, <span class="macro">Token!</span>[::]<span class="op">></span><span class="ident">::parse_separated_nonempty</span>; |
| <span class="kw">let</span> <span class="ident">_path</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>; |
| |
| <span class="comment">// Parse a possibly empty sequence of expressions terminated by commas with</span> |
| <span class="comment">// an optional trailing punctuation.</span> |
| <span class="kw">let</span> <span class="ident">tokens</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">clone</span>(); |
| <span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Punctuated</span>::<span class="op"><</span><span class="ident">Expr</span>, <span class="macro">Token!</span>[,]<span class="op">></span><span class="ident">::parse_terminated</span>; |
| <span class="kw">let</span> <span class="ident">_args</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>; |
| |
| <span class="comment">// Parse zero or more outer attributes but not inner attributes.</span> |
| <span class="kw">let</span> <span class="ident">tokens</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">clone</span>(); |
| <span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">Attribute::parse_outer</span>; |
| <span class="kw">let</span> <span class="ident">_attrs</span> <span class="op">=</span> <span class="ident">parser</span>.<span class="ident">parse</span>(<span class="ident">tokens</span>)<span class="question-mark">?</span>; |
| |
| <span class="prelude-val">Ok</span>(()) |
| }</code></pre></div> |
| <hr /> |
| <p><em>This module is available only if Syn is built with the <code>"parsing"</code> feature.</em></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="discouraged/index.html" title="syn::parse::discouraged mod">discouraged</a></div><div class="item-right docblock-short"><p>Extensions to the parsing API with niche applicability.</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.Error.html" title="syn::parse::Error struct">Error</a></div><div class="item-right docblock-short"><p>Error returned when a Syn parser cannot parse the input tokens.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Lookahead1.html" title="syn::parse::Lookahead1 struct">Lookahead1</a></div><div class="item-right docblock-short"><p>Support for checking the next token in a stream to decide how to parse.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Nothing.html" title="syn::parse::Nothing struct">Nothing</a></div><div class="item-right docblock-short"><p>An empty syntax tree node that consumes no tokens when parsed.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.ParseBuffer.html" title="syn::parse::ParseBuffer struct">ParseBuffer</a></div><div class="item-right docblock-short"><p>Cursor position within a buffered token stream.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.StepCursor.html" title="syn::parse::StepCursor struct">StepCursor</a></div><div class="item-right docblock-short"><p>Cursor state associated with speculative parsing.</p> |
| </div></div></div><h2 id="traits" class="small-section-header"><a href="#traits">Traits</a></h2> |
| <div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.Parse.html" title="syn::parse::Parse trait">Parse</a></div><div class="item-right docblock-short"><p>Parsing interface implemented by all types that can be parsed in a default |
| way from a token stream.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.Parser.html" title="syn::parse::Parser trait">Parser</a></div><div class="item-right docblock-short"><p>Parser that can parse Rust tokens into a particular syntax tree node.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.Peek.html" title="syn::parse::Peek trait">Peek</a></div><div class="item-right docblock-short"><p>Types that can be parsed by looking at just one token.</p> |
| </div></div></div><h2 id="types" class="small-section-header"><a href="#types">Type Definitions</a></h2> |
| <div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="type" href="type.ParseStream.html" title="syn::parse::ParseStream type">ParseStream</a></div><div class="item-right docblock-short"><p>Input to a Syn parser function.</p> |
| </div></div><div class="item-row"><div class="item-left module-item"><a class="type" href="type.Result.html" title="syn::parse::Result type">Result</a></div><div class="item-right docblock-short"><p>The result of a Syn parser.</p> |
| </div></div></div></section><section id="search" class="content hidden"></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="syn" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.60.0-nightly (1bd4fdc94 2022-01-12)" ></div> |
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