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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="API documentation for the Rust `proc_macro_nested` crate."><meta name="keywords" content="rust, rustlang, rust-lang, proc_macro_nested"><title>proc_macro_nested - Rust</title><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="../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../ayu.css" disabled ><script id="default-settings"></script><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../proc_macro_nested/index.html'><div class='logo-container rust-logo'><img src='../rust-logo.png' alt='logo'></div></a><p class="location">Crate proc_macro_nested</p><div class="block version"><p>Version 0.1.7</p></div><div class="sidebar-elems"><a id="all-types" href="all.html"><p>See all proc_macro_nested's items</p></a><p class="location"></p><div id="sidebar-vars" data-name="proc_macro_nested" data-ty="mod" data-relpath="../"></div></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" class="help-button">?</button>
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<a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class="fqn"><span class="in-band">Crate <a class="mod" href="">proc_macro_nested</a></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../src/proc_macro_nested/lib.rs.html#1-69" title="goto source code">[src]</a></span></h1><div class="docblock"><p>Support for nested invocations of proc-macro-hack expression macros.</p>
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<p>By default, macros defined through proc-macro-hack do not support nested
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invocations, i.e. the code emitted by a proc-macro-hack macro invocation
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cannot contain recursive calls to the same proc-macro-hack macro nor calls
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to any other proc-macro-hack macros.</p>
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<p>This crate provides opt-in support for such nested invocations.</p>
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<p>To make a macro callable recursively, add a dependency on this crate from
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your declaration crate and update the <code>#[proc_macro_hack]</code> re-export as
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follows.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// Before</span>
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<span class="attribute">#[<span class="ident">proc_macro_hack</span>]</span>
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<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">demo_hack_impl</span>::<span class="ident">add_one</span>;</pre></div>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// After</span>
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<span class="attribute">#[<span class="ident">proc_macro_hack</span>(<span class="ident">support_nested</span>)]</span>
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<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">demo_hack_impl</span>::<span class="ident">add_one</span>;</pre></div>
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<p>No change is required within your definition crate, only to the re-export in
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the declaration crate.</p>
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<h1 id="limitations" class="section-header"><a href="#limitations">Limitations</a></h1>
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<ul>
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<li>
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<p>Nested invocations are preprocessed by a TT-muncher, so the caller's crate
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will be required to contain <code>#![recursion_limit = "..."]</code> if there are
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lengthy macro invocations.</p>
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</li>
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<li>
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<p>Only up to 64 nested invocations are supported.</p>
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</li>
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</ul>
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