| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.59/src/detection.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>detection.rs - source</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="../../source-script.js"></script><script defer src="../../source-files.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 source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../proc_macro2/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../proc_macro2/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
| <span id="2">2</span> |
| <span id="3">3</span> |
| <span id="4">4</span> |
| <span id="5">5</span> |
| <span id="6">6</span> |
| <span id="7">7</span> |
| <span id="8">8</span> |
| <span id="9">9</span> |
| <span id="10">10</span> |
| <span id="11">11</span> |
| <span id="12">12</span> |
| <span id="13">13</span> |
| <span id="14">14</span> |
| <span id="15">15</span> |
| <span id="16">16</span> |
| <span id="17">17</span> |
| <span id="18">18</span> |
| <span id="19">19</span> |
| <span id="20">20</span> |
| <span id="21">21</span> |
| <span id="22">22</span> |
| <span id="23">23</span> |
| <span id="24">24</span> |
| <span id="25">25</span> |
| <span id="26">26</span> |
| <span id="27">27</span> |
| <span id="28">28</span> |
| <span id="29">29</span> |
| <span id="30">30</span> |
| <span id="31">31</span> |
| <span id="32">32</span> |
| <span id="33">33</span> |
| <span id="34">34</span> |
| <span id="35">35</span> |
| <span id="36">36</span> |
| <span id="37">37</span> |
| <span id="38">38</span> |
| <span id="39">39</span> |
| <span id="40">40</span> |
| <span id="41">41</span> |
| <span id="42">42</span> |
| <span id="43">43</span> |
| <span id="44">44</span> |
| <span id="45">45</span> |
| <span id="46">46</span> |
| <span id="47">47</span> |
| <span id="48">48</span> |
| <span id="49">49</span> |
| <span id="50">50</span> |
| <span id="51">51</span> |
| <span id="52">52</span> |
| <span id="53">53</span> |
| <span id="54">54</span> |
| <span id="55">55</span> |
| <span id="56">56</span> |
| <span id="57">57</span> |
| <span id="58">58</span> |
| <span id="59">59</span> |
| <span id="60">60</span> |
| <span id="61">61</span> |
| <span id="62">62</span> |
| <span id="63">63</span> |
| <span id="64">64</span> |
| <span id="65">65</span> |
| <span id="66">66</span> |
| <span id="67">67</span> |
| <span id="68">68</span> |
| <span id="69">69</span> |
| <span id="70">70</span> |
| <span id="71">71</span> |
| <span id="72">72</span> |
| <span id="73">73</span> |
| <span id="74">74</span> |
| <span id="75">75</span> |
| </pre><pre class="rust"><code><span class="kw">use </span>core::sync::atomic::{AtomicUsize, Ordering}; |
| <span class="kw">use </span>std::sync::Once; |
| |
| <span class="kw">static </span>WORKS: AtomicUsize = AtomicUsize::new(<span class="number">0</span>); |
| <span class="kw">static </span>INIT: Once = Once::new(); |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>inside_proc_macro() -> bool { |
| <span class="kw">match </span>WORKS.load(Ordering::Relaxed) { |
| <span class="number">1 </span>=> <span class="kw">return </span><span class="bool-val">false</span>, |
| <span class="number">2 </span>=> <span class="kw">return </span><span class="bool-val">true</span>, |
| <span class="kw">_ </span>=> {} |
| } |
| |
| INIT.call_once(initialize); |
| inside_proc_macro() |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>force_fallback() { |
| WORKS.store(<span class="number">1</span>, Ordering::Relaxed); |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>unforce_fallback() { |
| initialize(); |
| } |
| |
| <span class="attribute">#[cfg(not(no_is_available))] |
| </span><span class="kw">fn </span>initialize() { |
| <span class="kw">let </span>available = proc_macro::is_available(); |
| WORKS.store(available <span class="kw">as </span>usize + <span class="number">1</span>, Ordering::Relaxed); |
| } |
| |
| <span class="comment">// Swap in a null panic hook to avoid printing "thread panicked" to stderr, |
| // then use catch_unwind to determine whether the compiler's proc_macro is |
| // working. When proc-macro2 is used from outside of a procedural macro all |
| // of the proc_macro crate's APIs currently panic. |
| // |
| // The Once is to prevent the possibility of this ordering: |
| // |
| // thread 1 calls take_hook, gets the user's original hook |
| // thread 1 calls set_hook with the null hook |
| // thread 2 calls take_hook, thinks null hook is the original hook |
| // thread 2 calls set_hook with the null hook |
| // thread 1 calls set_hook with the actual original hook |
| // thread 2 calls set_hook with what it thinks is the original hook |
| // |
| // in which the user's hook has been lost. |
| // |
| // There is still a race condition where a panic in a different thread can |
| // happen during the interval that the user's original panic hook is |
| // unregistered such that their hook is incorrectly not called. This is |
| // sufficiently unlikely and less bad than printing panic messages to stderr |
| // on correct use of this crate. Maybe there is a libstd feature request |
| // here. For now, if a user needs to guarantee that this failure mode does |
| // not occur, they need to call e.g. `proc_macro2::Span::call_site()` from |
| // the main thread before launching any other threads. |
| </span><span class="attribute">#[cfg(no_is_available)] |
| </span><span class="kw">fn </span>initialize() { |
| <span class="kw">use </span>std::panic::{<span class="self">self</span>, PanicInfo}; |
| |
| <span class="kw">type </span>PanicHook = <span class="kw">dyn </span>Fn(<span class="kw-2">&</span>PanicInfo) + Sync + Send + <span class="lifetime">'static</span>; |
| |
| <span class="kw">let </span>null_hook: Box<PanicHook> = Box::new(|_panic_info| { <span class="comment">/* ignore */ </span>}); |
| <span class="kw">let </span>sanity_check = <span class="kw-2">&*</span>null_hook <span class="kw">as </span><span class="kw-2">*const </span>PanicHook; |
| <span class="kw">let </span>original_hook = panic::take_hook(); |
| panic::set_hook(null_hook); |
| |
| <span class="kw">let </span>works = panic::catch_unwind(proc_macro::Span::call_site).is_ok(); |
| WORKS.store(works <span class="kw">as </span>usize + <span class="number">1</span>, Ordering::Relaxed); |
| |
| <span class="kw">let </span>hopefully_null_hook = panic::take_hook(); |
| panic::set_hook(original_hook); |
| <span class="kw">if </span>sanity_check != <span class="kw-2">&*</span>hopefully_null_hook { |
| <span class="macro">panic!</span>(<span class="string">"observed race condition in proc_macro2::inside_proc_macro"</span>); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="proc_macro2" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
