| <!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-macro-error-1.0.4/src/dummy.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>dummy.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_macro_error/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_macro_error/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> |
| <span id="76">76</span> |
| <span id="77">77</span> |
| <span id="78">78</span> |
| <span id="79">79</span> |
| <span id="80">80</span> |
| <span id="81">81</span> |
| <span id="82">82</span> |
| <span id="83">83</span> |
| <span id="84">84</span> |
| <span id="85">85</span> |
| <span id="86">86</span> |
| <span id="87">87</span> |
| <span id="88">88</span> |
| <span id="89">89</span> |
| <span id="90">90</span> |
| <span id="91">91</span> |
| <span id="92">92</span> |
| <span id="93">93</span> |
| <span id="94">94</span> |
| <span id="95">95</span> |
| <span id="96">96</span> |
| <span id="97">97</span> |
| <span id="98">98</span> |
| <span id="99">99</span> |
| <span id="100">100</span> |
| <span id="101">101</span> |
| <span id="102">102</span> |
| <span id="103">103</span> |
| <span id="104">104</span> |
| <span id="105">105</span> |
| <span id="106">106</span> |
| <span id="107">107</span> |
| <span id="108">108</span> |
| <span id="109">109</span> |
| <span id="110">110</span> |
| <span id="111">111</span> |
| <span id="112">112</span> |
| <span id="113">113</span> |
| <span id="114">114</span> |
| <span id="115">115</span> |
| <span id="116">116</span> |
| <span id="117">117</span> |
| <span id="118">118</span> |
| <span id="119">119</span> |
| <span id="120">120</span> |
| <span id="121">121</span> |
| <span id="122">122</span> |
| <span id="123">123</span> |
| <span id="124">124</span> |
| <span id="125">125</span> |
| <span id="126">126</span> |
| <span id="127">127</span> |
| <span id="128">128</span> |
| <span id="129">129</span> |
| <span id="130">130</span> |
| <span id="131">131</span> |
| <span id="132">132</span> |
| <span id="133">133</span> |
| <span id="134">134</span> |
| <span id="135">135</span> |
| <span id="136">136</span> |
| <span id="137">137</span> |
| <span id="138">138</span> |
| <span id="139">139</span> |
| <span id="140">140</span> |
| <span id="141">141</span> |
| <span id="142">142</span> |
| <span id="143">143</span> |
| <span id="144">144</span> |
| <span id="145">145</span> |
| <span id="146">146</span> |
| <span id="147">147</span> |
| <span id="148">148</span> |
| <span id="149">149</span> |
| <span id="150">150</span> |
| </pre><pre class="rust"><code><span class="doccomment">//! Facility to emit dummy implementations (or whatever) in case |
| //! an error happen. |
| //! |
| //! `compile_error!` does not abort a compilation right away. This means |
| //! `rustc` doesn't just show you the error and abort, it carries on the |
| //! compilation process looking for other errors to report. |
| //! |
| //! Let's consider an example: |
| //! |
| //! ```rust,ignore |
| //! use proc_macro::TokenStream; |
| //! use proc_macro_error::*; |
| //! |
| //! trait MyTrait { |
| //! fn do_thing(); |
| //! } |
| //! |
| //! // this proc macro is supposed to generate MyTrait impl |
| //! #[proc_macro_derive(MyTrait)] |
| //! #[proc_macro_error] |
| //! fn example(input: TokenStream) -> TokenStream { |
| //! // somewhere deep inside |
| //! abort!(span, "something's wrong"); |
| //! |
| //! // this implementation will be generated if no error happened |
| //! quote! { |
| //! impl MyTrait for #name { |
| //! fn do_thing() {/* whatever */} |
| //! } |
| //! } |
| //! } |
| //! |
| //! // ================ |
| //! // in main.rs |
| //! |
| //! // this derive triggers an error |
| //! #[derive(MyTrait)] // first BOOM! |
| //! struct Foo; |
| //! |
| //! fn main() { |
| //! Foo::do_thing(); // second BOOM! |
| //! } |
| //! ``` |
| //! |
| //! The problem is: the generated token stream contains only `compile_error!` |
| //! invocation, the impl was not generated. That means user will see two compilation |
| //! errors: |
| //! |
| //! ```text |
| //! error: something's wrong |
| //! --> $DIR/probe.rs:9:10 |
| //! | |
| //! 9 |#[proc_macro_derive(MyTrait)] |
| //! | ^^^^^^^ |
| //! |
| //! error[E0599]: no function or associated item named `do_thing` found for type `Foo` in the current scope |
| //! --> src\main.rs:3:10 |
| //! | |
| //! 1 | struct Foo; |
| //! | ----------- function or associated item `do_thing` not found for this |
| //! 2 | fn main() { |
| //! 3 | Foo::do_thing(); // second BOOM! |
| //! | ^^^^^^^^ function or associated item not found in `Foo` |
| //! ``` |
| //! |
| //! But the second error is meaningless! We definitely need to fix this. |
| //! |
| //! Most used approach in cases like this is "dummy implementation" - |
| //! omit `impl MyTrait for #name` and fill functions bodies with `unimplemented!()`. |
| //! |
| //! This is how you do it: |
| //! |
| //! ```rust,ignore |
| //! use proc_macro::TokenStream; |
| //! use proc_macro_error::*; |
| //! |
| //! trait MyTrait { |
| //! fn do_thing(); |
| //! } |
| //! |
| //! // this proc macro is supposed to generate MyTrait impl |
| //! #[proc_macro_derive(MyTrait)] |
| //! #[proc_macro_error] |
| //! fn example(input: TokenStream) -> TokenStream { |
| //! // first of all - we set a dummy impl which will be appended to |
| //! // `compile_error!` invocations in case a trigger does happen |
| //! set_dummy(quote! { |
| //! impl MyTrait for #name { |
| //! fn do_thing() { unimplemented!() } |
| //! } |
| //! }); |
| //! |
| //! // somewhere deep inside |
| //! abort!(span, "something's wrong"); |
| //! |
| //! // this implementation will be generated if no error happened |
| //! quote! { |
| //! impl MyTrait for #name { |
| //! fn do_thing() {/* whatever */} |
| //! } |
| //! } |
| //! } |
| //! |
| //! // ================ |
| //! // in main.rs |
| //! |
| //! // this derive triggers an error |
| //! #[derive(MyTrait)] // first BOOM! |
| //! struct Foo; |
| //! |
| //! fn main() { |
| //! Foo::do_thing(); // no more errors! |
| //! } |
| //! ``` |
| |
| </span><span class="kw">use </span>proc_macro2::TokenStream; |
| <span class="kw">use </span>std::cell::RefCell; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::check_correctness; |
| |
| <span class="macro">thread_local! </span>{ |
| <span class="kw">static </span>DUMMY_IMPL: RefCell<<span class="prelude-ty">Option</span><TokenStream>> = RefCell::new(<span class="prelude-val">None</span>); |
| } |
| |
| <span class="doccomment">/// Sets dummy token stream which will be appended to `compile_error!(msg);...` |
| /// invocations in case you'll emit any errors. |
| /// |
| /// See [guide](../index.html#guide). |
| </span><span class="kw">pub fn </span>set_dummy(dummy: TokenStream) -> <span class="prelude-ty">Option</span><TokenStream> { |
| check_correctness(); |
| DUMMY_IMPL.with(|old_dummy| old_dummy.replace(<span class="prelude-val">Some</span>(dummy))) |
| } |
| |
| <span class="doccomment">/// Same as [`set_dummy`] but, instead of resetting, appends tokens to the |
| /// existing dummy (if any). Behaves as `set_dummy` if no dummy is present. |
| </span><span class="kw">pub fn </span>append_dummy(dummy: TokenStream) { |
| check_correctness(); |
| DUMMY_IMPL.with(|old_dummy| { |
| <span class="kw">let </span><span class="kw-2">mut </span>cell = old_dummy.borrow_mut(); |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(ts) = cell.as_mut() { |
| ts.extend(dummy); |
| } <span class="kw">else </span>{ |
| <span class="kw-2">*</span>cell = <span class="prelude-val">Some</span>(dummy); |
| } |
| }); |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>cleanup() -> <span class="prelude-ty">Option</span><TokenStream> { |
| DUMMY_IMPL.with(|old_dummy| old_dummy.replace(<span class="prelude-val">None</span>)) |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="proc_macro_error" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
