| <!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/syn-2.0.18/src/spanned.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>spanned.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="../../syn/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="../../syn/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> |
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| </pre><pre class="rust"><code><span class="doccomment">//! A trait that can provide the `Span` of the complete contents of a syntax |
| //! tree node. |
| //! |
| //! <br> |
| //! |
| //! # Example |
| //! |
| //! Suppose in a procedural macro we have a [`Type`] that we want to assert |
| //! implements the [`Sync`] trait. Maybe this is the type of one of the fields |
| //! of a struct for which we are deriving a trait implementation, and we need to |
| //! be able to pass a reference to one of those fields across threads. |
| //! |
| //! [`Type`]: crate::Type |
| //! [`Sync`]: std::marker::Sync |
| //! |
| //! If the field type does *not* implement `Sync` as required, we want the |
| //! compiler to report an error pointing out exactly which type it was. |
| //! |
| //! The following macro code takes a variable `ty` of type `Type` and produces a |
| //! static assertion that `Sync` is implemented for that type. |
| //! |
| //! ``` |
| //! # extern crate proc_macro; |
| //! # |
| //! use proc_macro::TokenStream; |
| //! use proc_macro2::Span; |
| //! use quote::quote_spanned; |
| //! use syn::Type; |
| //! use syn::spanned::Spanned; |
| //! |
| //! # const IGNORE_TOKENS: &str = stringify! { |
| //! #[proc_macro_derive(MyMacro)] |
| //! # }; |
| //! pub fn my_macro(input: TokenStream) -> TokenStream { |
| //! # let ty = get_a_type(); |
| //! /* ... */ |
| //! |
| //! let assert_sync = quote_spanned! {ty.span()=> |
| //! struct _AssertSync where #ty: Sync; |
| //! }; |
| //! |
| //! /* ... */ |
| //! # input |
| //! } |
| //! # |
| //! # fn get_a_type() -> Type { |
| //! # unimplemented!() |
| //! # } |
| //! ``` |
| //! |
| //! By inserting this `assert_sync` fragment into the output code generated by |
| //! our macro, the user's code will fail to compile if `ty` does not implement |
| //! `Sync`. The errors they would see look like the following. |
| //! |
| //! ```text |
| //! error[E0277]: the trait bound `*const i32: std::marker::Sync` is not satisfied |
| //! --> src/main.rs:10:21 |
| //! | |
| //! 10 | bad_field: *const i32, |
| //! | ^^^^^^^^^^ `*const i32` cannot be shared between threads safely |
| //! ``` |
| //! |
| //! In this technique, using the `Type`'s span for the error message makes the |
| //! error appear in the correct place underlining the right type. |
| //! |
| //! <br> |
| //! |
| //! # Limitations |
| //! |
| //! The underlying [`proc_macro::Span::join`] method is nightly-only. When |
| //! called from within a procedural macro in a nightly compiler, `Spanned` will |
| //! use `join` to produce the intended span. When not using a nightly compiler, |
| //! only the span of the *first token* of the syntax tree node is returned. |
| //! |
| //! In the common case of wanting to use the joined span as the span of a |
| //! `syn::Error`, consider instead using [`syn::Error::new_spanned`] which is |
| //! able to span the error correctly under the complete syntax tree node without |
| //! needing the unstable `join`. |
| //! |
| //! [`syn::Error::new_spanned`]: crate::Error::new_spanned |
| |
| </span><span class="kw">use </span>proc_macro2::Span; |
| <span class="kw">use </span>quote::spanned::Spanned <span class="kw">as </span>ToTokens; |
| |
| <span class="doccomment">/// A trait that can provide the `Span` of the complete contents of a syntax |
| /// tree node. |
| /// |
| /// This trait is automatically implemented for all types that implement |
| /// [`ToTokens`] from the `quote` crate, as well as for `Span` itself. |
| /// |
| /// [`ToTokens`]: quote::ToTokens |
| /// |
| /// See the [module documentation] for an example. |
| /// |
| /// [module documentation]: self |
| </span><span class="kw">pub trait </span>Spanned: private::Sealed { |
| <span class="doccomment">/// Returns a `Span` covering the complete contents of this syntax tree |
| /// node, or [`Span::call_site()`] if this node is empty. |
| /// |
| /// [`Span::call_site()`]: proc_macro2::Span::call_site |
| </span><span class="kw">fn </span>span(<span class="kw-2">&</span><span class="self">self</span>) -> Span; |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + ToTokens> Spanned <span class="kw">for </span>T { |
| <span class="kw">fn </span>span(<span class="kw-2">&</span><span class="self">self</span>) -> Span { |
| <span class="self">self</span>.__span() |
| } |
| } |
| |
| <span class="kw">mod </span>private { |
| <span class="kw">use super</span>::<span class="kw-2">*</span>; |
| |
| <span class="kw">pub trait </span>Sealed {} |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + ToTokens> Sealed <span class="kw">for </span>T {} |
| } |
| </code></pre></div> |
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