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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="This crate provides a robust regular expression parser."><title>regex_syntax - Rust</title><script> if (window.location.protocol !== "file:") document.write(`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2">`)</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-e935ef01ae1c1829.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="regex_syntax" data-themes="" data-resource-suffix="" data-rustdoc-version="1.78.0 (9b00956e5 2024-04-29)" data-channel="1.78.0" data-search-js="search-42d8da7a6b9792c2.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-4c98445ec4002617.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-12cf3b4f4f9dc36d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-04d5337699b92874.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../regex_syntax/index.html">regex_syntax</a><span class="version">0.8.3</span></h2></div><div class="sidebar-elems"><ul class="block">
<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><li><a href="#functions">Functions</a></li></ul></section></div></nav><div class="sidebar-resizer"></div>
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../regex_syntax/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Crate <a class="mod" href="#">regex_syntax</a><button id="copy-path" title="Copy item path to clipboard"><img src="../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../src/regex_syntax/lib.rs.html#1-431">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This crate provides a robust regular expression parser.</p>
<p>This crate defines two primary types:</p>
<ul>
<li><a href="ast/enum.Ast.html" title="enum regex_syntax::ast::Ast"><code>Ast</code></a> is the abstract syntax of a regular expression.
An abstract syntax corresponds to a <em>structured representation</em> of the
concrete syntax of a regular expression, where the concrete syntax is the
pattern string itself (e.g., <code>foo(bar)+</code>). Given some abstract syntax, it
can be converted back to the original concrete syntax (modulo some details,
like whitespace). To a first approximation, the abstract syntax is complex
and difficult to analyze.</li>
<li><a href="hir/struct.Hir.html" title="struct regex_syntax::hir::Hir"><code>Hir</code></a> is the high-level intermediate representation
(“HIR” or “high-level IR” for short) of regular expression. It corresponds to
an intermediate state of a regular expression that sits between the abstract
syntax and the low level compiled opcodes that are eventually responsible for
executing a regular expression search. Given some high-level IR, it is not
possible to produce the original concrete syntax (although it is possible to
produce an equivalent concrete syntax, but it will likely scarcely resemble
the original pattern). To a first approximation, the high-level IR is simple
and easy to analyze.</li>
</ul>
<p>These two types come with conversion routines:</p>
<ul>
<li>An <a href="ast/parse/struct.Parser.html" title="struct regex_syntax::ast::parse::Parser"><code>ast::parse::Parser</code></a> converts concrete syntax (a <code>&amp;str</code>) to an
<a href="ast/enum.Ast.html" title="enum regex_syntax::ast::Ast"><code>Ast</code></a>.</li>
<li>A <a href="hir/translate/struct.Translator.html" title="struct regex_syntax::hir::translate::Translator"><code>hir::translate::Translator</code></a> converts an <a href="ast/enum.Ast.html" title="enum regex_syntax::ast::Ast"><code>Ast</code></a> to a
<a href="hir/struct.Hir.html" title="struct regex_syntax::hir::Hir"><code>Hir</code></a>.</li>
</ul>
<p>As a convenience, the above two conversion routines are combined into one via
the top-level <a href="struct.Parser.html" title="struct regex_syntax::Parser"><code>Parser</code></a> type. This <code>Parser</code> will first convert your pattern to
an <code>Ast</code> and then convert the <code>Ast</code> to an <code>Hir</code>. Its also exposed as top-level
<a href="fn.parse.html" title="fn regex_syntax::parse"><code>parse</code></a> free function.</p>
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
<p>This example shows how to parse a pattern string into its HIR:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>regex_syntax::{hir::Hir, parse};
<span class="kw">let </span>hir = parse(<span class="string">"a|b"</span>)<span class="question-mark">?</span>;
<span class="macro">assert_eq!</span>(hir, Hir::alternation(<span class="macro">vec!</span>[
Hir::literal(<span class="string">"a"</span>.as_bytes()),
Hir::literal(<span class="string">"b"</span>.as_bytes()),
]));</code></pre></div>
<h2 id="concrete-syntax-supported"><a class="doc-anchor" href="#concrete-syntax-supported">§</a>Concrete syntax supported</h2>
<p>The concrete syntax is documented as part of the public API of the
<a href="https://docs.rs/regex/%2A/regex/#syntax"><code>regex</code> crate</a>.</p>
<h2 id="input-safety"><a class="doc-anchor" href="#input-safety">§</a>Input safety</h2>
<p>A key feature of this library is that it is safe to use with end user facing
input. This plays a significant role in the internal implementation. In
particular:</p>
<ol>
<li>Parsers provide a <code>nest_limit</code> option that permits callers to control how
deeply nested a regular expression is allowed to be. This makes it possible
to do case analysis over an <code>Ast</code> or an <code>Hir</code> using recursion without
worrying about stack overflow.</li>
<li>Since relying on a particular stack size is brittle, this crate goes to
great lengths to ensure that all interactions with both the <code>Ast</code> and the
<code>Hir</code> do not use recursion. Namely, they use constant stack space and heap
space proportional to the size of the original pattern string (in bytes).
This includes the types corresponding destructors. (One exception to this
is literal extraction, but this will eventually get fixed.)</li>
</ol>
<h2 id="error-reporting"><a class="doc-anchor" href="#error-reporting">§</a>Error reporting</h2>
<p>The <code>Display</code> implementations on all <code>Error</code> types exposed in this library
provide nice human readable errors that are suitable for showing to end users
in a monospace font.</p>
<h2 id="literal-extraction"><a class="doc-anchor" href="#literal-extraction">§</a>Literal extraction</h2>
<p>This crate provides limited support for <a href="hir/literal/index.html" title="mod regex_syntax::hir::literal">literal extraction from <code>Hir</code>
values</a>. Be warned that literal extraction uses recursion, and
therefore, stack size proportional to the size of the <code>Hir</code>.</p>
<p>The purpose of literal extraction is to speed up searches. That is, if you
know a regular expression must match a prefix or suffix literal, then it is
often quicker to search for instances of that literal, and then confirm or deny
the match using the full regular expression engine. These optimizations are
done automatically in the <code>regex</code> crate.</p>
<h2 id="crate-features"><a class="doc-anchor" href="#crate-features">§</a>Crate features</h2>
<p>An important feature provided by this crate is its Unicode support. This
includes things like case folding, boolean properties, general categories,
scripts and Unicode-aware support for the Perl classes <code>\w</code>, <code>\s</code> and <code>\d</code>.
However, a downside of this support is that it requires bundling several
Unicode data tables that are substantial in size.</p>
<p>A fair number of use cases do not require full Unicode support. For this
reason, this crate exposes a number of features to control which Unicode
data is available.</p>
<p>If a regular expression attempts to use a Unicode feature that is not available
because the corresponding crate feature was disabled, then translating that
regular expression to an <code>Hir</code> will return an error. (It is still possible
construct an <code>Ast</code> for such a regular expression, since Unicode data is not
used until translation to an <code>Hir</code>.) Stated differently, enabling or disabling
any of the features below can only add or subtract from the total set of valid
regular expressions. Enabling or disabling a feature will never modify the
match semantics of a regular expression.</p>
<p>The following features are available:</p>
<ul>
<li><strong>std</strong> -
Enables support for the standard library. This feature is enabled by default.
When disabled, only <code>core</code> and <code>alloc</code> are used. Otherwise, enabling <code>std</code>
generally just enables <code>std::error::Error</code> trait impls for the various error
types.</li>
<li><strong>unicode</strong> -
Enables all Unicode features. This feature is enabled by default, and will
always cover all Unicode features, even if more are added in the future.</li>
<li><strong>unicode-age</strong> -
Provide the data for the
<a href="https://www.unicode.org/reports/tr44/tr44-24.html#Character_Age">Unicode <code>Age</code> property</a>.
This makes it possible to use classes like <code>\p{Age:6.0}</code> to refer to all
codepoints first introduced in Unicode 6.0</li>
<li><strong>unicode-bool</strong> -
Provide the data for numerous Unicode boolean properties. The full list
is not included here, but contains properties like <code>Alphabetic</code>, <code>Emoji</code>,
<code>Lowercase</code>, <code>Math</code>, <code>Uppercase</code> and <code>White_Space</code>.</li>
<li><strong>unicode-case</strong> -
Provide the data for case insensitive matching using
<a href="https://www.unicode.org/reports/tr18/#Simple_Loose_Matches">Unicodes “simple loose matches” specification</a>.</li>
<li><strong>unicode-gencat</strong> -
Provide the data for
<a href="https://www.unicode.org/reports/tr44/tr44-24.html#General_Category_Values">Unicode general categories</a>.
This includes, but is not limited to, <code>Decimal_Number</code>, <code>Letter</code>,
<code>Math_Symbol</code>, <code>Number</code> and <code>Punctuation</code>.</li>
<li><strong>unicode-perl</strong> -
Provide the data for supporting the Unicode-aware Perl character classes,
corresponding to <code>\w</code>, <code>\s</code> and <code>\d</code>. This is also necessary for using
Unicode-aware word boundary assertions. Note that if this feature is
disabled, the <code>\s</code> and <code>\d</code> character classes are still available if the
<code>unicode-bool</code> and <code>unicode-gencat</code> features are enabled, respectively.</li>
<li><strong>unicode-script</strong> -
Provide the data for
<a href="https://www.unicode.org/reports/tr24/">Unicode scripts and script extensions</a>.
This includes, but is not limited to, <code>Arabic</code>, <code>Cyrillic</code>, <code>Hebrew</code>,
<code>Latin</code> and <code>Thai</code>.</li>
<li><strong>unicode-segment</strong> -
Provide the data necessary to provide the properties used to implement the
<a href="https://www.unicode.org/reports/tr29/">Unicode text segmentation algorithms</a>.
This enables using classes like <code>\p{gcb=Extend}</code>, <code>\p{wb=Katakana}</code> and
<code>\p{sb=ATerm}</code>.</li>
<li><strong>arbitrary</strong> -
Enabling this feature introduces a public dependency on the
<a href="https://crates.io/crates/arbitrary"><code>arbitrary</code></a>
crate. Namely, it implements the <code>Arbitrary</code> trait from that crate for the
<a href="ast/enum.Ast.html" title="enum regex_syntax::ast::Ast"><code>Ast</code></a> type. This feature is disabled by default.</li>
</ul>
</div></details><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="mod" href="ast/index.html" title="mod regex_syntax::ast">ast</a></div><div class="desc docblock-short">Defines an abstract syntax for regular expressions.</div></li><li><div class="item-name"><a class="mod" href="hir/index.html" title="mod regex_syntax::hir">hir</a></div><div class="desc docblock-short">Defines a high-level intermediate (HIR) representation for regular expressions.</div></li><li><div class="item-name"><a class="mod" href="utf8/index.html" title="mod regex_syntax::utf8">utf8</a></div><div class="desc docblock-short">Converts ranges of Unicode scalar values to equivalent ranges of UTF-8 bytes.</div></li></ul><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.Parser.html" title="struct regex_syntax::Parser">Parser</a></div><div class="desc docblock-short">A convenience parser for regular expressions.</div></li><li><div class="item-name"><a class="struct" href="struct.ParserBuilder.html" title="struct regex_syntax::ParserBuilder">ParserBuilder</a></div><div class="desc docblock-short">A builder for a regular expression parser.</div></li><li><div class="item-name"><a class="struct" href="struct.UnicodeWordError.html" title="struct regex_syntax::UnicodeWordError">UnicodeWordError</a></div><div class="desc docblock-short">An error that occurs when the Unicode-aware <code>\w</code> class is unavailable.</div></li></ul><h2 id="enums" class="section-header">Enums<a href="#enums" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="enum" href="enum.Error.html" title="enum regex_syntax::Error">Error</a></div><div class="desc docblock-short">This error type encompasses any error that can be returned by this crate.</div></li></ul><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="fn" href="fn.escape.html" title="fn regex_syntax::escape">escape</a></div><div class="desc docblock-short">Escapes all regular expression meta characters in <code>text</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.escape_into.html" title="fn regex_syntax::escape_into">escape_into</a></div><div class="desc docblock-short">Escapes all meta characters in <code>text</code> and writes the result into <code>buf</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.is_escapeable_character.html" title="fn regex_syntax::is_escapeable_character">is_escapeable_character</a></div><div class="desc docblock-short">Returns true if the given character can be escaped in a regex.</div></li><li><div class="item-name"><a class="fn" href="fn.is_meta_character.html" title="fn regex_syntax::is_meta_character">is_meta_character</a></div><div class="desc docblock-short">Returns true if the given character has significance in a regex.</div></li><li><div class="item-name"><a class="fn" href="fn.is_word_byte.html" title="fn regex_syntax::is_word_byte">is_word_byte</a></div><div class="desc docblock-short">Returns true if and only if the given character is an ASCII word character.</div></li><li><div class="item-name"><a class="fn" href="fn.is_word_character.html" title="fn regex_syntax::is_word_character">is_word_character</a></div><div class="desc docblock-short">Returns true if and only if the given character is a Unicode word
character.</div></li><li><div class="item-name"><a class="fn" href="fn.parse.html" title="fn regex_syntax::parse">parse</a></div><div class="desc docblock-short">A convenience routine for parsing a regex using default options.</div></li><li><div class="item-name"><a class="fn" href="fn.try_is_word_character.html" title="fn regex_syntax::try_is_word_character">try_is_word_character</a></div><div class="desc docblock-short">Returns true if and only if the given character is a Unicode word
character.</div></li></ul></section></div></main></body></html>