| <!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" 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="../../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"><!--[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="../../syn/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="../../syn/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Module parse</a></h2><div class="sidebar-elems"><section><ul class="block"><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></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">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></h1><span class="out-of-band"><a class="srclink" href="../../src/syn/parse.rs.html#1-1334">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>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"><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>proc_macro::TokenStream; |
| <span class="kw">use </span>syn::{braced, parse_macro_input, token, Field, Ident, <span class="prelude-ty">Result</span>, Token}; |
| <span class="kw">use </span>syn::parse::{Parse, ParseStream}; |
| <span class="kw">use </span>syn::punctuated::Punctuated; |
| |
| <span class="kw">enum </span>Item { |
| Struct(ItemStruct), |
| Enum(ItemEnum), |
| } |
| |
| <span class="kw">struct </span>ItemStruct { |
| struct_token: <span class="macro">Token!</span>[<span class="kw">struct</span>], |
| ident: Ident, |
| brace_token: token::Brace, |
| fields: Punctuated<Field, <span class="macro">Token!</span>[,]>, |
| } |
| |
| <span class="kw">impl </span>Parse <span class="kw">for </span>Item { |
| <span class="kw">fn </span>parse(input: ParseStream) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>> { |
| <span class="kw">let </span>lookahead = input.lookahead1(); |
| <span class="kw">if </span>lookahead.peek(<span class="macro">Token!</span>[<span class="kw">struct</span>]) { |
| input.parse().map(Item::Struct) |
| } <span class="kw">else if </span>lookahead.peek(<span class="macro">Token!</span>[<span class="kw">enum</span>]) { |
| input.parse().map(Item::Enum) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Err</span>(lookahead.error()) |
| } |
| } |
| } |
| |
| <span class="kw">impl </span>Parse <span class="kw">for </span>ItemStruct { |
| <span class="kw">fn </span>parse(input: ParseStream) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>> { |
| <span class="kw">let </span>content; |
| <span class="prelude-val">Ok</span>(ItemStruct { |
| struct_token: input.parse()<span class="question-mark">?</span>, |
| ident: input.parse()<span class="question-mark">?</span>, |
| brace_token: <span class="macro">braced!</span>(content <span class="kw">in </span>input), |
| fields: content.parse_terminated(Field::parse_named, <span class="macro">Token!</span>[,])<span class="question-mark">?</span>, |
| }) |
| } |
| } |
| |
| <span class="attribute">#[proc_macro] |
| </span><span class="kw">pub fn </span>my_macro(tokens: TokenStream) -> TokenStream { |
| <span class="kw">let </span>input = <span class="macro">parse_macro_input!</span>(tokens <span class="kw">as </span>Item); |
| |
| <span class="comment">/* ... */ |
| </span>}</code></pre></div> |
| <h2 id="the-synparse-functions"><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>syn::Type; |
| |
| <span class="kw">let </span>t: Type = syn::parse_str(<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"><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="example-wrap compile_fail"><div class='tooltip'>ⓘ</div><pre class="rust rust-example-rendered"><code><span class="comment">// Can't parse `Punctuated` without knowing whether trailing punctuation |
| // should be allowed in this context. |
| </span><span class="kw">let </span>path: Punctuated<PathSegment, <span class="macro">Token!</span>[::]> = syn::parse(tokens)<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>proc_macro::TokenStream; |
| <span class="kw">use </span>syn::parse::Parser; |
| <span class="kw">use </span>syn::punctuated::Punctuated; |
| <span class="kw">use </span>syn::{Attribute, Expr, PathSegment, <span class="prelude-ty">Result</span>, Token}; |
| |
| <span class="kw">fn </span>call_some_parser_methods(input: TokenStream) -> <span class="prelude-ty">Result</span><()> { |
| <span class="comment">// Parse a nonempty sequence of path segments separated by `::` punctuation |
| // with no trailing punctuation. |
| </span><span class="kw">let </span>tokens = input.clone(); |
| <span class="kw">let </span>parser = Punctuated::<PathSegment, <span class="macro">Token!</span>[::]>::parse_separated_nonempty; |
| <span class="kw">let </span>_path = parser.parse(tokens)<span class="question-mark">?</span>; |
| |
| <span class="comment">// Parse a possibly empty sequence of expressions terminated by commas with |
| // an optional trailing punctuation. |
| </span><span class="kw">let </span>tokens = input.clone(); |
| <span class="kw">let </span>parser = Punctuated::<Expr, <span class="macro">Token!</span>[,]>::parse_terminated; |
| <span class="kw">let </span>_args = parser.parse(tokens)<span class="question-mark">?</span>; |
| |
| <span class="comment">// Parse zero or more outer attributes but not inner attributes. |
| </span><span class="kw">let </span>tokens = input.clone(); |
| <span class="kw">let </span>parser = Attribute::parse_outer; |
| <span class="kw">let </span>_attrs = parser.parse(tokens)<span class="question-mark">?</span>; |
| |
| <span class="prelude-val">Ok</span>(()) |
| }</code></pre></div> |
| </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">Extensions to the parsing API with niche applicability.</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">Error returned when a Syn parser cannot parse the input tokens.</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">Support for checking the next token in a stream to decide how to parse.</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">An empty syntax tree node that consumes no tokens when parsed.</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">Cursor position within a buffered token stream.</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">Cursor state associated with speculative parsing.</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">Parsing interface implemented by all types that can be parsed in a default |
| way from a token stream.</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">Parser that can parse Rust tokens into a particular syntax tree node.</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">Types that can be parsed by looking at just one token.</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">Input to a Syn parser function.</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">The result of a Syn parser.</div></div></div></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="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
