edg-l/edlang
1
1
Fork 0
mirror of https://github.com/edg-l/edlang.git synced 2024-11-23 08:28:24 +00:00
Code Issues Packages Projects Releases Wiki Activity
edlang/syn/meta/fn.parser.html

94 lines
10 KiB
HTML
Raw Normal View History

deploy: 050377daee3d5d7d14ebd9e93598f598475cf55c
2024-04-09 11:05:04 +00:00
<!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="Make a parser that is usable with `parse_macro_input!` in a `#[proc_macro_attribute]` macro."><title>parser in syn::meta - 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-5bc39a1768837dd0.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="syn" data-themes="" data-resource-suffix="" data-rustdoc-version="1.77.1 (7cf61ebde 2024-03-27)" data-channel="1.77.1" data-search-js="search-dd67cee4cfa65049.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-4c98445ec4002617.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-48f368f3872407c8.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-04d5337699b92874.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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../syn/index.html">syn</a><span class="version">2.0.58</span></h2></div><div class="sidebar-elems"><h2><a href="index.html">In syn::meta</a></h2></div></nav><div class="sidebar-resizer"></div>
deploy: cc1e3679829ec7c574392bace9092ffa4ecb73c2
2024-02-27 06:59:44 +00:00
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../syn/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">syn</a>::<wbr><a href="index.html">meta</a>::<wbr><a class="fn" href="#">parser</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/syn/meta.rs.html#132-140">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 parser(
deploy: 5e40306951b4dbd54c7ef875d67175e7a2c79124
2024-04-09 10:18:33 +00:00
logic: impl <a class="trait" href="https://doc.rust-lang.org/1.77.1/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(<a class="struct" href="struct.ParseNestedMeta.html" title="struct syn::meta::ParseNestedMeta">ParseNestedMeta</a>&lt;'_&gt;) -&gt; <a class="type" href="../parse/type.Result.html" title="type syn::parse::Result">Result</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.77.1/std/primitive.unit.html">()</a>&gt;
) -&gt; impl <a class="trait" href="../parse/trait.Parser.html" title="trait syn::parse::Parser">Parser</a>&lt;Output = <a class="primitive" href="https://doc.rust-lang.org/1.77.1/std/primitive.unit.html">()</a>&gt;</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Make a parser that is usable with <code>parse_macro_input!</code> in a
deploy: 4a83cfd6f9c58b14a87234162281aad1aef83c3e
2024-02-13 06:38:44 +00:00
<code>#[proc_macro_attribute]</code> macro.</p>
<p><em>Warning:</em> When parsing attribute args <strong>other than</strong> the
<code>proc_macro::TokenStream</code> input of a <code>proc_macro_attribute</code>, you do <strong>not</strong>
need this function. In several cases your callers will get worse error
messages if you use this function, because the surrounding delimiter’s span
is concealed from attribute macros by rustc. Use
<a href="../struct.Attribute.html#method.parse_nested_meta" title="method syn::Attribute::parse_nested_meta"><code>Attribute::parse_nested_meta</code></a> instead.</p>
deploy: 39fc7f2b9fd58ce67982b1c71c788f3b031ae3df
2024-03-27 11:12:16 +00:00
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
deploy: 4a83cfd6f9c58b14a87234162281aad1aef83c3e
2024-02-13 06:38:44 +00:00
<p>This example implements an attribute macro whose invocations look like this:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[tea(kind = <span class="string">"EarlGrey"</span>, hot)]
</span><span class="kw">struct </span>Picard {...}</code></pre></div>
<p>The “parameters” supported by the attribute are:</p>
<ul>
<li><code>kind = &quot;...&quot;</code></li>
<li><code>hot</code></li>
<li><code>with(sugar, milk, ...)</code>, a comma-separated list of ingredients</li>
</ul>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>proc_macro::TokenStream;
<span class="kw">use </span>syn::{parse_macro_input, LitStr, Path};
<span class="attr">#[proc_macro_attribute]
</span><span class="kw">pub fn </span>tea(args: TokenStream, input: TokenStream) -&gt; TokenStream {
<span class="kw">let </span><span class="kw-2">mut </span>kind: <span class="prelude-ty">Option</span>&lt;LitStr&gt; = <span class="prelude-val">None</span>;
<span class="kw">let </span><span class="kw-2">mut </span>hot: bool = <span class="bool-val">false</span>;
<span class="kw">let </span><span class="kw-2">mut </span>with: Vec&lt;Path&gt; = Vec::new();
<span class="kw">let </span>tea_parser = syn::meta::parser(|meta| {
<span class="kw">if </span>meta.path.is_ident(<span class="string">"kind"</span>) {
kind = <span class="prelude-val">Some</span>(meta.value()<span class="question-mark">?</span>.parse()<span class="question-mark">?</span>);
<span class="prelude-val">Ok</span>(())
} <span class="kw">else if </span>meta.path.is_ident(<span class="string">"hot"</span>) {
hot = <span class="bool-val">true</span>;
<span class="prelude-val">Ok</span>(())
} <span class="kw">else if </span>meta.path.is_ident(<span class="string">"with"</span>) {
meta.parse_nested_meta(|meta| {
with.push(meta.path);
<span class="prelude-val">Ok</span>(())
})
} <span class="kw">else </span>{
<span class="prelude-val">Err</span>(meta.error(<span class="string">"unsupported tea property"</span>))
}
});
<span class="macro">parse_macro_input!</span>(args with tea_parser);
<span class="macro">eprintln!</span>(<span class="string">"kind={kind:?} hot={hot} with={with:?}"</span>);
<span class="comment">/* ... */
</span>}</code></pre></div>
<p>The <code>syn::meta</code> library will take care of dealing with the commas including
trailing commas, and producing sensible error messages on unexpected input.</p>
<div class="example-wrap"><pre class="language-console"><code>error: expected `,`
--&gt; src/main.rs:3:37
|
3 | #[tea(kind = &quot;EarlGrey&quot;, with(sugar = &quot;lol&quot;, milk))]
| ^
deploy: 39fc7f2b9fd58ce67982b1c71c788f3b031ae3df
2024-03-27 11:12:16 +00:00
</code></pre></div><h2 id="example-1"><a class="doc-anchor" href="#example-1">§</a>Example</h2>
deploy: 4a83cfd6f9c58b14a87234162281aad1aef83c3e
2024-02-13 06:38:44 +00:00
<p>Same as above but we factor out most of the logic into a separate function.</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>proc_macro::TokenStream;
<span class="kw">use </span>syn::meta::ParseNestedMeta;
<span class="kw">use </span>syn::parse::{Parser, <span class="prelude-ty">Result</span>};
<span class="kw">use </span>syn::{parse_macro_input, LitStr, Path};
<span class="attr">#[proc_macro_attribute]
</span><span class="kw">pub fn </span>tea(args: TokenStream, input: TokenStream) -&gt; TokenStream {
<span class="kw">let </span><span class="kw-2">mut </span>attrs = TeaAttributes::default();
<span class="kw">let </span>tea_parser = syn::meta::parser(|meta| attrs.parse(meta));
<span class="macro">parse_macro_input!</span>(args with tea_parser);
<span class="comment">/* ... */
</span>}
<span class="attr">#[derive(Default)]
</span><span class="kw">struct </span>TeaAttributes {
kind: <span class="prelude-ty">Option</span>&lt;LitStr&gt;,
hot: bool,
with: Vec&lt;Path&gt;,
}
<span class="kw">impl </span>TeaAttributes {
<span class="kw">fn </span>parse(<span class="kw-2">&amp;mut </span><span class="self">self</span>, meta: ParseNestedMeta) -&gt; <span class="prelude-ty">Result</span>&lt;()&gt; {
<span class="kw">if </span>meta.path.is_ident(<span class="string">"kind"</span>) {
<span class="self">self</span>.kind = <span class="prelude-val">Some</span>(meta.value()<span class="question-mark">?</span>.parse()<span class="question-mark">?</span>);
<span class="prelude-val">Ok</span>(())
} <span class="kw">else </span><span class="comment">/* just like in last example */
</span>}
}</code></pre></div>
</div></details></section></div></main></body></html>
Reference in a new issue Copy permalink