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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="Install the provided error hook for constructing EyreHandlers when converting Errors to Reports"><title>set_hook in eyre - Rust</title><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"><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="eyre" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-feafe1bb7466e4bd.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 fn"><!--[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">&#9776;</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../eyre/index.html">eyre</a><span class="version">0.6.12</span></h2></div><div class="sidebar-elems"></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="../eyre/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>Function <a href="index.html">eyre</a>::<wbr><a class="fn" href="#">set_hook</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/eyre/lib.rs.html#583-585">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub fn set_hook(
hook: <a class="struct" href="https://doc.rust-lang.org/1.76.0/alloc/boxed/struct.Box.html" title="struct alloc::boxed::Box">Box</a>&lt;dyn <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&amp;(dyn <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/error/trait.Error.html" title="trait core::error::Error">StdError</a> + 'static)) -&gt; <a class="struct" href="https://doc.rust-lang.org/1.76.0/alloc/boxed/struct.Box.html" title="struct alloc::boxed::Box">Box</a>&lt;dyn <a class="trait" href="trait.EyreHandler.html" title="trait eyre::EyreHandler">EyreHandler</a>&gt; + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + <a class="trait" href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + 'static&gt;
) -&gt; <a class="type" href="type.Result.html" title="type eyre::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.76.0/std/primitive.unit.html">()</a>, <a class="struct" href="struct.InstallError.html" title="struct eyre::InstallError">InstallError</a>&gt;</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Install the provided error hook for constructing EyreHandlers when converting
Errors to Reports</p>
<h2 id="details"><a href="#details">Details</a></h2>
<p>To customize the format and content of error reports from <code>eyre</code> you must
first define a new <code>EyreHandler</code> type to capture and store the extra context
and to define the format of how to display the chain of errors and this
stored context. Once this type has been defined you must also define a global
hook used to construct these handlers whenever <code>Report</code>s are constructed.</p>
<h2 id="examples"><a href="#examples">Examples</a></h2>
<div class="example-wrap should_panic"><a href="#" class="tooltip" title="This example panics"></a><pre class="rust rust-example-rendered"><code><span class="kw">use </span>backtrace::Backtrace;
<span class="kw">use </span>eyre::EyreHandler;
<span class="kw">use </span>std::error::Error;
<span class="kw">use </span>std::{fmt, iter};
<span class="kw">fn </span>main() -&gt; eyre::Result&lt;()&gt; {
<span class="comment">// Install our custom eyre report hook for constructing our custom Handlers
</span>install().unwrap();
<span class="comment">// construct a report with, hopefully, our custom handler!
</span><span class="kw">let </span><span class="kw-2">mut </span>report = <span class="macro">eyre::eyre!</span>(<span class="string">"hello from custom error town!"</span>);
<span class="comment">// manually set the custom msg for this report after it has been constructed
</span><span class="kw">if let </span><span class="prelude-val">Some</span>(handler) = report.handler_mut().downcast_mut::&lt;Handler&gt;() {
handler.custom_msg = <span class="prelude-val">Some</span>(<span class="string">"you're the best users, you know that right???"</span>);
}
<span class="comment">// print that shit!!
</span><span class="prelude-val">Err</span>(report)
}
<span class="comment">// define a handler that captures backtraces unless told not to
</span><span class="kw">fn </span>install() -&gt; <span class="prelude-ty">Result</span>&lt;(), <span class="kw">impl </span>Error&gt; {
<span class="kw">let </span>capture_backtrace = std::env::var(<span class="string">"RUST_BACKWARDS_TRACE"</span>)
.map(|val| val != <span class="string">"0"</span>)
.unwrap_or(<span class="bool-val">true</span>);
<span class="kw">let </span>hook = Hook { capture_backtrace };
eyre::set_hook(Box::new(<span class="kw">move </span>|e| Box::new(hook.make_handler(e))))
}
<span class="kw">struct </span>Hook {
capture_backtrace: bool,
}
<span class="kw">impl </span>Hook {
<span class="kw">fn </span>make_handler(<span class="kw-2">&amp;</span><span class="self">self</span>, _error: <span class="kw-2">&amp;</span>(<span class="kw">dyn </span>Error + <span class="lifetime">'static</span>)) -&gt; Handler {
<span class="kw">let </span>backtrace = <span class="kw">if </span><span class="self">self</span>.capture_backtrace {
<span class="prelude-val">Some</span>(Backtrace::new())
} <span class="kw">else </span>{
<span class="prelude-val">None
</span>};
Handler {
backtrace,
custom_msg: <span class="prelude-val">None</span>,
}
}
}
<span class="kw">struct </span>Handler {
<span class="comment">// custom configured backtrace capture
</span>backtrace: <span class="prelude-ty">Option</span>&lt;Backtrace&gt;,
<span class="comment">// customizable message payload associated with reports
</span>custom_msg: <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">'static </span>str&gt;,
}
<span class="kw">impl </span>EyreHandler <span class="kw">for </span>Handler {
<span class="kw">fn </span>debug(<span class="kw-2">&amp;</span><span class="self">self</span>, error: <span class="kw-2">&amp;</span>(<span class="kw">dyn </span>Error + <span class="lifetime">'static</span>), f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">'_</span>&gt;) -&gt; fmt::Result {
<span class="kw">if </span>f.alternate() {
<span class="kw">return </span>fmt::Debug::fmt(error, f);
}
<span class="kw">let </span>errors = iter::successors(<span class="prelude-val">Some</span>(error), |error| (<span class="kw-2">*</span>error).source());
<span class="kw">for </span>(ind, error) <span class="kw">in </span>errors.enumerate() {
<span class="macro">write!</span>(f, <span class="string">"\n{:&gt;4}: {}"</span>, ind, error)<span class="question-mark">?</span>;
}
<span class="kw">if let </span><span class="prelude-val">Some</span>(backtrace) = <span class="self">self</span>.backtrace.as_ref() {
<span class="macro">writeln!</span>(f, <span class="string">"\n\nBacktrace:\n{:?}"</span>, backtrace)<span class="question-mark">?</span>;
}
<span class="kw">if let </span><span class="prelude-val">Some</span>(msg) = <span class="self">self</span>.custom_msg.as_ref() {
<span class="macro">writeln!</span>(f, <span class="string">"\n\n{}"</span>, msg)<span class="question-mark">?</span>;
}
<span class="prelude-val">Ok</span>(())
}
}</code></pre></div>
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