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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="proc-macro-error2"><title>proc_macro_error2 - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-492a78a4a87dcc01.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="proc_macro_error2" data-themes="" data-resource-suffix="" data-rustdoc-version="1.82.0 (f6e511eec 2024-10-15)" data-channel="1.82.0" data-search-js="search-a99f1315e7cc5121.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-118b08c4c78b968e.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-921df33f47b8780c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-3b12f09e550e0385.css"></noscript><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="../proc_macro_error2/index.html">proc_<wbr>macro_<wbr>error2</a><span class="version">2.0.1</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="#reexports">Re-exports</a></li><li><a href="#modules">Modules</a></li><li><a href="#macros">Macros</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#traits">Traits</a></li><li><a href="#functions">Functions</a></li><li><a href="#attributes">Attribute Macros</a></li></ul></section></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Crate <a class="mod" href="#">proc_macro_error2</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../src/proc_macro_error2/lib.rs.html#1-565">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"><h2 id="proc-macro-error2"><a class="doc-anchor" href="#proc-macro-error2">§</a>proc-macro-error2</h2>
<p>This crate aims to make error reporting in proc-macros simple and easy to use.
Migrate from <code>panic!</code>-based errors for as little effort as possible!</p>
<p>(Also, you can explicitly <a href="dummy/index.html">append a dummy token stream</a> to your errors).</p>
<p>To achieve his, this crate serves as a tiny shim around <code>proc_macro::Diagnostic</code> and
<code>compile_error!</code>. It detects the best way of emitting available based on compilers version.
When the underlying diagnostic type is finally stabilized, this crate will simply be
delegating to it requiring no changes in your code!</p>
<p>So you can just use this crate and have <em>both</em> some of <code>proc_macro::Diagnostic</code> functionality
available on stable ahead of time <em>and</em> your error-reporting code future-proof.</p>
<h3 id="cargo-features"><a class="doc-anchor" href="#cargo-features">§</a>Cargo features</h3>
<p>This crate provides <em>enabled by default</em> <code>syn-error</code> feature that gates
<code>impl From&lt;syn::Error&gt; for Diagnostic</code> conversion. If you dont use <code>syn</code> and want
to cut off some of compilation time, you can disable it via</p>
<div class="example-wrap"><pre class="language-toml"><code>[dependencies]
proc-macro-error2 = { version = &quot;2.0.0&quot;, default-features = false }
</code></pre></div>
<p>*<strong>Please note that disabling this feature makes sense only if you dont depend on <code>syn</code>
directly or indirectly, and you very likely do.</strong></p>
<h3 id="real-world-examples"><a class="doc-anchor" href="#real-world-examples">§</a>Real world examples</h3>
<ul>
<li><a href="https://github.com/TeXitoi/structopt/tree/master/structopt-derive"><code>structopt-derive</code></a>
(abort-like usage)</li>
<li><a href="https://github.com/auto-impl-rs/auto_impl/"><code>auto-impl</code></a> (emit-like usage)</li>
</ul>
<h3 id="limitations"><a class="doc-anchor" href="#limitations">§</a>Limitations</h3>
<ul>
<li>Warnings are emitted only on nightly, they are ignored on stable.</li>
<li>“help” suggestions cant have their own span info on stable,
(essentially inheriting the parent span).</li>
<li>If a panic occurs somewhere in your macro no errors will be displayed. This is not a
technical limitation but rather intentional design. <code>panic</code> is not for error reporting.</li>
</ul>
<h4 id="proc_macro_error-attribute"><a class="doc-anchor" href="#proc_macro_error-attribute">§</a><code>#[proc_macro_error]</code> attribute</h4>
<p><strong>This attribute MUST be present on the top level of your macro</strong> (the function
annotated with any of <code>#[proc_macro]</code>, <code>#[proc_macro_derive]</code>, <code>#[proc_macro_attribute]</code>).</p>
<p>This attribute performs the setup and cleanup necessary to make things work.</p>
<p>In most cases youll need the simple <code>#[proc_macro_error]</code> form without any
additional settings. Feel free to <a href="#macros">skip the “Syntax” section</a>.</p>
<h5 id="syntax"><a class="doc-anchor" href="#syntax">§</a>Syntax</h5>
<p><code>#[proc_macro_error]</code> or <code>#[proc_macro_error(settings...)]</code>, where <code>settings...</code>
is a comma-separated list of:</p>
<ul>
<li>
<p><code>proc_macro_hack</code>:</p>
<p>In order to correctly cooperate with <code>#[proc_macro_hack]</code>, <code>#[proc_macro_error]</code>
attribute must be placed <em>before</em> (above) it, like this:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[proc_macro_error]
#[proc_macro_hack]
#[proc_macro]
</span><span class="kw">fn </span>my_macro(input: TokenStream) -&gt; TokenStream {
<span class="macro">unimplemented!</span>()
}</code></pre></div>
<p>If, for some reason, you cant place it like that you can use
<code>#[proc_macro_error(proc_macro_hack)]</code> instead.</p>
<h2 id="note"><a class="doc-anchor" href="#note">§</a>Note</h2>
<p>If <code>proc-macro-hack</code> was detected (by any means) <code>allow_not_macro</code>
and <code>assert_unwind_safe</code> will be applied automatically.</p>
</li>
<li>
<p><code>allow_not_macro</code>:</p>
<p>By default, the attribute checks that its applied to a proc-macro.
If none of <code>#[proc_macro]</code>, <code>#[proc_macro_derive]</code> nor <code>#[proc_macro_attribute]</code> are
present it will panic. Its the intention - this crate is supposed to be used only with
proc-macros.</p>
<p>This setting is made to bypass the check, useful in certain circumstances.</p>
<p>Pay attention: the function this attribute is applied to must return
<code>proc_macro::TokenStream</code>.</p>
<p>This setting is implied if <code>proc-macro-hack</code> was detected.</p>
</li>
<li>
<p><code>assert_unwind_safe</code>:</p>
<p>By default, your code must be <a href="https://doc.rust-lang.org/std/panic/trait.UnwindSafe.html#what-is-unwind-safety">unwind safe</a>. If your code is not unwind safe,
but you believe its correct, you can use this setting to bypass the check.
You would need this for code that uses <code>lazy_static</code> or <code>thread_local</code> with
<code>Cell/RefCell</code> inside (and the like).</p>
<p>This setting is implied if <code>#[proc_macro_error]</code> is applied to a function
marked as <code>#[proc_macro]</code>, <code>#[proc_macro_derive]</code> or <code>#[proc_macro_attribute]</code>.</p>
<p>This setting is also implied if <code>proc-macro-hack</code> was detected.</p>
</li>
</ul>
<h3 id="macros"><a class="doc-anchor" href="#macros">§</a>Macros</h3>
<p>Most of the time you want to use the macros. Syntax is described in the next section below.</p>
<p>Youll need to decide how you want to emit errors:</p>
<ul>
<li>Emit the error and abort. Very much panic-like usage. Served by <a href="macro.abort.html"><code>abort!</code></a> and
<a href="macro.abort_call_site.html"><code>abort_call_site!</code></a>.</li>
<li>Emit the error but do not abort right away, looking for other errors to report.
Served by <a href="macro.emit_error.html"><code>emit_error!</code></a> and <a href="macro.emit_call_site_warning.html"><code>emit_call_site_error!</code></a>.</li>
</ul>
<p>You <strong>can</strong> mix these usages.</p>
<p><code>abort</code> and <code>emit_error</code> take a “source span” as the first argument. This source
will be used to highlight the place the error originates from. It must be one of:</p>
<ul>
<li><em>Something</em> that implements <a href="https://docs.rs/quote/1.0.3/quote/trait.ToTokens.html"><code>ToTokens</code></a> (most types in <code>syn</code> and <code>proc-macro2</code> do).
This source is the preferable one since it doesnt lose span information on multi-token
spans, see <a href="https://gitlab.com/CreepySkeleton/proc-macro-error/-/issues/6">this issue</a>
for details.</li>
<li><a href="https://doc.rust-lang.org/proc_macro/struct.Span.html"><code>proc_macro::Span</code></a></li>
<li><a href="https://docs.rs/proc-macro2/1.0.10/proc_macro2/struct.Span.html"><code>proc-macro2::Span</code></a></li>
</ul>
<p>The rest is your message in format-like style.</p>
<p>See <a href="#syntax-1">the next section</a> for detailed syntax.</p>
<ul>
<li>
<p><a href="macro.abort.html"><code>abort!</code></a>:</p>
<p>Very much panic-like usage - abort right away and show the error.
Expands to <a href="https://doc.rust-lang.org/std/primitive.never.html"><code>!</code></a> (never type).</p>
</li>
<li>
<p><a href="macro.abort_call_site.html"><code>abort_call_site!</code></a>:</p>
<p>Shortcut for <code>abort!(Span::call_site(), ...)</code>. Expands to <a href="https://doc.rust-lang.org/std/primitive.never.html"><code>!</code></a> (never type).</p>
</li>
<li>
<p><a href="macro.emit_error.html"><code>emit_error!</code></a>:</p>
<p><a href="https://doc.rust-lang.org/proc_macro/struct.Diagnostic.html"><code>proc_macro::Diagnostic</code></a>-like usage - emit the error but keep going,
looking for other errors to report.
The compilation will fail nonetheless. Expands to <a href="https://doc.rust-lang.org/std/primitive.unit.html"><code>()</code></a> (unit type).</p>
</li>
<li>
<p><a href="macro.emit_call_site_warning.html"><code>emit_call_site_error!</code></a>:</p>
<p>Shortcut for <code>emit_error!(Span::call_site(), ...)</code>. Expands to <a href="https://doc.rust-lang.org/std/primitive.unit.html"><code>()</code></a> (unit type).</p>
</li>
<li>
<p><a href="macro.emit_warning.html"><code>emit_warning!</code></a>:</p>
<p>Like <code>emit_error!</code> but emit a warning instead of error. The compilation wont fail
because of warnings.
Expands to <a href="https://doc.rust-lang.org/std/primitive.unit.html"><code>()</code></a> (unit type).</p>
<p><strong>Beware</strong>: warnings are nightly only, they are completely ignored on stable.</p>
</li>
<li>
<p><a href="macro.emit_call_site_error.html"><code>emit_call_site_warning!</code></a>:</p>
<p>Shortcut for <code>emit_warning!(Span::call_site(), ...)</code>. Expands to <a href="https://doc.rust-lang.org/std/primitive.unit.html"><code>()</code></a> (unit type).</p>
</li>
<li>
<p><a href="struct.Diagnostic.html"><code>diagnostic</code></a>:</p>
<p>Build an instance of <code>Diagnostic</code> in format-like style.</p>
</li>
</ul>
<h5 id="syntax-1"><a class="doc-anchor" href="#syntax-1">§</a>Syntax</h5>
<p>All the macros have pretty much the same syntax:</p>
<ol>
<li>
<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested"></a><pre class="rust rust-example-rendered"><code><span class="macro">abort!</span>(single_expr)</code></pre></div>
<p>Shortcut for <code>Diagnostic::from(expr).abort()</code>.</p>
</li>
<li>
<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested"></a><pre class="rust rust-example-rendered"><code><span class="macro">abort!</span>(span, message)</code></pre></div>
<p>The first argument is an expression the span info should be taken from.</p>
<p>The second argument is the error message, it must implement <a href="https://doc.rust-lang.org/std/string/trait.ToString.html"><code>ToString</code></a>.</p>
</li>
<li>
<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested"></a><pre class="rust rust-example-rendered"><code><span class="macro">abort!</span>(span, format_literal, format_args...)</code></pre></div>
<p>This form is pretty much the same as 2, except <code>format!(format_literal, format_args...)</code>
will be used to for the message instead of <a href="https://doc.rust-lang.org/std/string/trait.ToString.html"><code>ToString</code></a>.</p>
</li>
</ol>
<p>Thats it. <code>abort!</code>, <code>emit_warning</code>, <code>emit_error</code> share this exact syntax.</p>
<p><code>abort_call_site!</code>, <code>emit_call_site_warning</code>, <code>emit_call_site_error</code> lack 1 form
and do not take span in 2th and 3th forms. Those are essentially shortcuts for
<code>macro!(Span::call_site(), args...)</code>.</p>
<p><code>diagnostic!</code> requires a <a href="enum.Level.html" title="enum proc_macro_error2::Level"><code>Level</code></a> instance between <code>span</code> and second argument
(1th form is the same).</p>
<blockquote>
<p><strong>Important!</strong></p>
<p>If you have some type from <code>proc_macro</code> or <code>syn</code> to point to, do not call <code>.span()</code>
on it but rather use it directly:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>ty: syn::Type = syn::parse2(input).unwrap();
<span class="macro">abort!</span>(ty, <span class="string">"BOOM"</span>);
<span class="comment">// ^^ &lt;-- avoid .span()</span></code></pre></div>
<p><code>.span()</code> calls work too, but you may experience regressions in message quality.</p>
</blockquote>
<h5 id="note-attachments"><a class="doc-anchor" href="#note-attachments">§</a>Note attachments</h5>
<ol start="3">
<li>Every macro can have “note” attachments (only 2 and 3 form).</li>
</ol>
<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested"></a><pre class="rust rust-example-rendered"><code><span class="kw">let </span>opt_help = <span class="kw">if </span>have_some_info { <span class="prelude-val">Some</span>(<span class="string">"did you mean `this`?"</span>) } <span class="kw">else </span>{ <span class="prelude-val">None </span>};
<span class="macro">abort!</span>(
span, message; <span class="comment">// &lt;--- attachments start with `;` (semicolon)
</span>help = <span class="string">"format {} {}"</span>, <span class="string">"arg1"</span>, <span class="string">"arg2"</span>; <span class="comment">// &lt;--- every attachment ends with `;`,
// maybe except the last one
</span>note = <span class="string">"to_string"</span>; <span class="comment">// &lt;--- one arg uses `.to_string()` instead of `format!()`
</span>yay = <span class="string">"I see what {} did here"</span>, <span class="string">"you"</span>; <span class="comment">// &lt;--- "help =" and "hint =" are mapped
// to Diagnostic::help,
// anything else is Diagnostic::note
</span>wow = note_span =&gt; <span class="string">"custom span"</span>; <span class="comment">// &lt;--- attachments can have their own span
// it takes effect only on nightly though
</span>hint =<span class="question-mark">? </span>opt_help; <span class="comment">// &lt;-- "optional" attachment, get displayed only if `Some`
// must be single `Option` expression
</span>note =<span class="question-mark">? </span>note_span =&gt; opt_help <span class="comment">// &lt;-- optional attachments can have custom spans too
</span>);</code></pre></div>
<h4 id="diagnostic-type"><a class="doc-anchor" href="#diagnostic-type">§</a>Diagnostic type</h4>
<p><a href="struct.Diagnostic.html"><code>Diagnostic</code></a> type is intentionally designed to be API compatible with <a href="https://doc.rust-lang.org/proc_macro/struct.Diagnostic.html"><code>proc_macro::Diagnostic</code></a>.
Not all API is implemented, only the part that can be reasonably implemented on stable.</p>
</div></details><h2 id="reexports" class="section-header">Re-exports<a href="#reexports" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name" id="reexport.append_dummy"><code>pub use crate::dummy::<a class="fn" href="dummy/fn.append_dummy.html" title="fn proc_macro_error2::dummy::append_dummy">append_dummy</a>;</code></div></li><li><div class="item-name" id="reexport.set_dummy"><code>pub use crate::dummy::<a class="fn" href="dummy/fn.set_dummy.html" title="fn proc_macro_error2::dummy::set_dummy">set_dummy</a>;</code></div></li></ul><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="dummy/index.html" title="mod proc_macro_error2::dummy">dummy</a></div><div class="desc docblock-short">Facility to emit dummy implementations (or whatever) in case
an error happen.</div></li></ul><h2 id="macros-1" class="section-header">Macros<a href="#macros-1" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="macro" href="macro.abort.html" title="macro proc_macro_error2::abort">abort</a></div><div class="desc docblock-short">Abort proc-macro execution right now and display the error.</div></li><li><div class="item-name"><a class="macro" href="macro.abort_call_site.html" title="macro proc_macro_error2::abort_call_site">abort_<wbr>call_<wbr>site</a></div><div class="desc docblock-short">Shortcut for <code>abort!(Span::call_site(), msg...)</code>. This macro
is still preferable over plain panic, panics are not for error reporting.</div></li><li><div class="item-name"><a class="macro" href="macro.diagnostic.html" title="macro proc_macro_error2::diagnostic">diagnostic</a></div><div class="desc docblock-short">Build <a href="struct.Diagnostic.html"><code>Diagnostic</code></a> instance from provided arguments.</div></li><li><div class="item-name"><a class="macro" href="macro.emit_call_site_error.html" title="macro proc_macro_error2::emit_call_site_error">emit_<wbr>call_<wbr>site_<wbr>error</a></div><div class="desc docblock-short">Shortcut for <code>emit_error!(Span::call_site(), ...)</code>. This macro
is still preferable over plain panic, panics are not for error reporting..</div></li><li><div class="item-name"><a class="macro" href="macro.emit_call_site_warning.html" title="macro proc_macro_error2::emit_call_site_warning">emit_<wbr>call_<wbr>site_<wbr>warning</a></div><div class="desc docblock-short">Shortcut for <code>emit_warning!(Span::call_site(), ...)</code>.</div></li><li><div class="item-name"><a class="macro" href="macro.emit_error.html" title="macro proc_macro_error2::emit_error">emit_<wbr>error</a></div><div class="desc docblock-short">Emit an error while not aborting the proc-macro right away.</div></li><li><div class="item-name"><a class="macro" href="macro.emit_warning.html" title="macro proc_macro_error2::emit_warning">emit_<wbr>warning</a></div><div class="desc docblock-short">Emit a warning. Warnings are not errors and compilation wont fail because of them.</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.Diagnostic.html" title="struct proc_macro_error2::Diagnostic">Diagnostic</a></div><div class="desc docblock-short">Represents a single diagnostic message</div></li><li><div class="item-name"><a class="struct" href="struct.SpanRange.html" title="struct proc_macro_error2::SpanRange">Span<wbr>Range</a></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.Level.html" title="enum proc_macro_error2::Level">Level</a></div><div class="desc docblock-short">Represents a diagnostic level</div></li></ul><h2 id="traits" class="section-header">Traits<a href="#traits" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="trait" href="trait.DiagnosticExt.html" title="trait proc_macro_error2::DiagnosticExt">Diagnostic<wbr>Ext</a></div><div class="desc docblock-short">A collection of methods that do not exist in <code>proc_macro::Diagnostic</code>
but still useful to have around.</div></li><li><div class="item-name"><a class="trait" href="trait.OptionExt.html" title="trait proc_macro_error2::OptionExt">Option<wbr>Ext</a></div><div class="desc docblock-short">This traits expands <code>Option</code> with some handy shortcuts.</div></li><li><div class="item-name"><a class="trait" href="trait.ResultExt.html" title="trait proc_macro_error2::ResultExt">Result<wbr>Ext</a></div><div class="desc docblock-short">This traits expands <code>Result&lt;T, Into&lt;Diagnostic&gt;&gt;</code> with some handy shortcuts.</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.abort_if_dirty.html" title="fn proc_macro_error2::abort_if_dirty">abort_<wbr>if_<wbr>dirty</a></div><div class="desc docblock-short">Abort macro execution and display all the emitted errors, if any.</div></li></ul><h2 id="attributes" class="section-header">Attribute Macros<a href="#attributes" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="attr" href="attr.proc_macro_error.html" title="attr proc_macro_error2::proc_macro_error">proc_<wbr>macro_<wbr>error</a></div></li></ul></section></div></main></body></html>