<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="Error returned when a Syn parser cannot parse the input tokens."><title>Error in syn - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../static.files/rustdoc-ac92e1bbe349e143.css"><metaname="rustdoc-vars"data-root-path="../"data-static-root-path="../static.files/"data-current-crate="syn"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"><scriptsrc="../static.files/storage-f2adc0d6ca4d09fb.js"></script><scriptdefersrc="sidebar-items.js"></script><scriptdefersrc="../static.files/main-305769736d49e732.js"></script><noscript><linkrel="stylesheet"href="../static.files/noscript-feafe1bb7466e4bd.css"></noscript><linkrel="alternate icon"type="image/png"href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc struct"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle">☰</button></nav><navclass="sidebar"><divclass="sidebar-crate"><h2><ahref="../syn/index.html">syn</a><spanclass="version">2.0.51</span></h2></div><h2class="location"><ahref="#">Error</a></h2><divclass="sidebar-elems"><section><h3><ahref="#implementations">Methods</a></h3><ulclass="block method"><li><ahref="#method.combine">combine</a></li><li><ahref="#method.into_compile_error">into_compile_error</a></li><li><ahref="#method.new">new</a></li><li><ahref="#method.new_spanned">new_spanned</a></li><li><ahref="#method.span">span</a></li><li><ahref="#method.to_compile_error">to_compile_error</a></li></ul><h3><ahref="#trait-implementations">Trait Implementations</a></h3><ulclass="block trait-implementation"><li><ahref="#impl-Clone-for-Error">Clone</a></li><li><ahref="#impl-Debug-for-Error">Debug</a></li><li><ahref="#impl-Display-for-Error">Display</a></li><li><ahref="#impl-Error-for-Error">Error</a></li><li><ahref="#impl-Extend%3CError%3E-for-Error">Extend<Error></a></li><li><ahref="#impl-From%3CLexError%3E-for-Error">From<LexError></a></li><li><ahref="#impl-IntoIterator-for-%26Error">IntoIterator</a></li><li><ahref="#impl-IntoIterator-for-Error">IntoIterator</a></li></ul><h3><ahref="#synthetic-implementations">Auto Trait Implementations</a></h3><ulclass="block synthetic-implementation"><li><ahref="#impl-RefUnwindSafe-for-Error">RefUnwindSafe</a></li><li><ahref="#impl-Send-for-Error">Send</a></li><li><ahref="#impl-Sync-for-Error">Sync</a></li><li><ahref="#impl-Unpin-for-Error">Unpin</a></li><li><ahref="#impl-UnwindSafe-for-Error">UnwindSafe</a></li></ul><h3><ahref="#blanket-implementations">Blanket Implementations</a></h3><ulclass="block blanket-implementation"><li><ahref="#impl-Any-for-T">Any</a></li><li><ahref="#impl-Borrow%3CT%3E-for-T">Borrow<T></a></li><li><ahref="#impl-BorrowMut%3CT%3E
<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../syn/all.html"title="show sidebar"></a></div><inputclass="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"><divid="help-button"tabindex="-1"><ahref="../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Struct <ahref="index.html">syn</a>::<wbr><aclass="struct"href="#">Error</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../src/syn/error.rs.html#100-102">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code>pub struct Error { <spanclass="comment">/* private fields */</span> }</code></pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>Error returned when a Syn parser cannot parse the input tokens.</p>
<h2id="error-reporting-in-proc-macros"><ahref="#error-reporting-in-proc-macros">Error reporting in proc macros</a></h2>
<p>The correct way to report errors back to the compiler from a procedural
macro is by emitting an appropriately spanned invocation of
<ahref="https://doc.rust-lang.org/1.76.0/core/macro.compile_error.html"title="macro core::compile_error"><code>compile_error!</code></a> in the generated code. This produces a better diagnostic
message than simply panicking the macro.</p>
<p>When parsing macro input, the <ahref="macro.parse_macro_input.html"title="macro syn::parse_macro_input"><code>parse_macro_input!</code></a> macro handles the
conversion to <code>compile_error!</code> automatically.</p>
<p>For errors that arise later than the initial parsing stage, the
<ahref="parse/struct.Error.html#method.to_compile_error"title="method syn::parse::Error::to_compile_error"><code>.to_compile_error()</code></a> or <ahref="parse/struct.Error.html#method.into_compile_error"title="method syn::parse::Error::into_compile_error"><code>.into_compile_error()</code></a> methods can be used to
perform an explicit conversion to <code>compile_error!</code>.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.new_spanned"class="method"><aclass="src rightside"href="../src/syn/error.rs.html#189-203">source</a><h4class="code-header">pub fn <ahref="#method.new_spanned"class="fn">new_spanned</a><T: <aclass="trait"href="../quote/to_tokens/trait.ToTokens.html"title="trait quote::to_tokens::ToTokens">ToTokens</a>, U: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/fmt/trait.Display.html"title="trait core::fmt::Display">Display</a>>(tokens: T, message: U) -> Self</h4></section></summary><divclass="docblock"><p>Creates an error with the specified message spanning the given syntax
tree node.</p>
<p>Unlike the <code>Error::new</code> constructor, this constructor takes an argument
<code>tokens</code> which is a syntax tree node. This allows the resulting <code>Error</code>
to attempt to span all tokens inside of <code>tokens</code>. While you would
typically be able to use the <code>Spanned</code> trait with the above <code>Error::new</code>
constructor, implementation limitations today mean that
<code>Error::new_spanned</code> may provide a higher-quality error message on
stable Rust.</p>
<p>When in doubt it’s recommended to stick to <code>Error::new</code> (or
<code>ParseStream::error</code>)!</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.span"class="method"><aclass="src rightside"href="../src/syn/error.rs.html#210-216">source</a><h4class="code-header">pub fn <ahref="#method.span"class="fn">span</a>(&self) -><aclass="struct"href="../proc_macro2/struct.Span.html"title="struct proc_macro2::Span">Span</a></h4></section></summary><divclass="docblock"><p>The source location of the error.</p>
<p>Spans are not thread-safe so this function returns <code>Span::call_site()</code>
if called from a different thread than the one on which the <code>Error</code> was
originally created.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.to_compile_error"class="method"><aclass="src rightside"href="../src/syn/error.rs.html#225-230">source</a><h4class="code-header">pub fn <ahref="#method.to_compile_error"class="fn">to_compile_error</a>(&self) -><aclass="struct"href="../proc_macro2/struct.TokenStream.html"title="struct proc_macro2::TokenStream">TokenStream</a></h4></section></summary><divclass="docblock"><p>Render the error as an invocation of <ahref="https://doc.rust-lang.org/1.76.0/core/macro.compile_error.html"title="macro core::compile_error"><code>compile_error!</code></a>.</p>
<p>The <ahref="macro.parse_macro_input.html"title="macro syn::parse_macro_input"><code>parse_macro_input!</code></a> macro provides a convenient way to invoke
this method correctly in a procedural macro.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.into_compile_error"class="method"><aclass="src rightside"href="../src/syn/error.rs.html#264-266">source</a><h4class="code-header">pub fn <ahref="#method.into_compile_error"class="fn">into_compile_error</a>(self) -><aclass="struct"href="../proc_macro2/struct.TokenStream.html"title="struct proc_macro2::TokenStream">TokenStream</a></h4></section></summary><divclass="docblock"><p>Render the error as an invocation of <ahref="https://doc.rust-lang.org/1.76.0/core/macro.compile_error.html"title="macro core::compile_error"><code>compile_error!</code></a>.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.combine"class="method"><aclass="src rightside"href="../src/syn/error.rs.html#270-272">source</a><h4class="code-header">pub fn <ahref="#method.combine"class="fn">combine</a>(&mut self, another: <aclass="struct"href="parse/struct.Error.html"title="struct syn::parse::Error">Error</a>)</h4></section></summary><divclass="docblock"><p>Add another error message to self such that when <code>to_compile_error()</code> is
<p>That is, this conversion is whatever the implementation of
<code><ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.From.html"title="trait core::convert::From">From</a><T> for U</code> chooses to do.</p>
</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-ToOwned-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#83-85">source</a><ahref="#impl-ToOwned-for-T"class="anchor">§</a><h3class="code-header">impl<T><aclass="trait"href="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html"title="trait alloc::borrow::ToOwned">ToOwned</a> for T<divclass="where">where
T: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/clone/trait.Clone.html"title="trait core::clone::Clone">Clone</a>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Owned"class="associatedtype trait-impl"><ahref="#associatedtype.Owned"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#associatedtype.Owned"class="associatedtype">Owned</a> = T</h4></section></summary><divclass='docblock'>The resulting type after obtaining ownership.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.to_owned"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#88">source</a><ahref="#method.to_owned"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#tymethod.to_owned"class="fn">to_owned</a>(&self) -> T</h4></section></summary><divclass='docblock'>Creates owned data from borrowed data, usually by cloning. <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#tymethod.to_owned">Read more</a></div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.clone_into"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/borrow.rs.html#92">source</a><ahref="#method.clone_into"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#method.clone_into"class="fn">clone_into</a>(&self, target: <aclass="primitive"href="https://doc.rust-lang.org/1.76.0/std/primitive.reference.html">&mut T</a>)</h4></section></summary><divclass='docblock'>Uses borrowed data to replace owned data, usually by cloning. <ahref="https://doc.rust-lang.org/1.76.0/alloc/borrow/trait.ToOwned.html#method.clone_into">Read more</a></div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-ToString-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/string.rs.html#2600">source</a><ahref="#impl-ToString-for-T"class="anchor">§</a><h3class="code-header">impl<T><aclass="trait"href="https://doc.rust-lang.org/1.76.0/alloc/string/trait.ToString.html"title="trait alloc::string::ToString">ToString</a> for T<divclass="where">where
T: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/fmt/trait.Display.html"title="trait core::fmt::Display">Display</a> + ?<aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/marker/trait.Sized.html"title="trait core::marker::Sized">Sized</a>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle method-toggle"open><summary><sectionid="method.to_string"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/alloc/string.rs.html#2606">source</a><ahref="#method.to_string"class="anchor">§</a><h4class="code-header">default fn <ahref="https://doc.rust-lang.org/1.76.0/alloc/string/trait.ToString.html#tymethod.to_string"class="fn">to_string</a>(&self) -><aclass="struct"href="https://doc.rust-lang.org/1.76.0/alloc/string/struct.String.html"title="struct alloc::string::String">String</a></h4></section></summary><divclass='docblock'>Converts the given value to a <code>String</code>. <ahref="https://doc.rust-lang.org/1.76.0/alloc/string/trait.ToString.html#tymethod.to_string">Read more</a></div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryFrom%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#803-805">source</a><ahref="#impl-TryFrom%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.Into.html"title="trait core::convert::Into">Into</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error"class="associatedtype trait-impl"><ahref="#associatedtype.Error"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"class="associatedtype">Error</a> = <aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/convert/enum.Infallible.html"title="enum core::convert::Infallible">Infallible</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_from"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#810">source</a><ahref="#method.try_from"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#tymethod.try_from"class="fn">try_from</a>(value: U) -><aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><T, <T as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryInto%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#788-790">source</a><ahref="#impl-TryInto%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html"title="trait core::convert::TryInto">TryInto</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error-1"class="associatedtype trait-impl"><ahref="#associatedtype.Error-1"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html#associatedtype.Error"class="associatedtype">Error</a> = <U as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_into"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.76.0/src/core/convert/mod.rs.html#795">source</a><ahref="#method.try_into"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryInto.html#tymethod.try_into"class="fn">try_into</a>(self) -><aclass="enum"href="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><U, <U as <aclass="trait"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.76.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details></div></section></div></main></body></html>
