| <!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/meta.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>meta.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">//! Facility for interpreting structured content inside of an `Attribute`. |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::ext::IdentExt; |
| <span class="kw">use </span><span class="kw">crate</span>::lit::Lit; |
| <span class="kw">use </span><span class="kw">crate</span>::parse::{Error, ParseStream, Parser, <span class="prelude-ty">Result</span>}; |
| <span class="kw">use </span><span class="kw">crate</span>::path::{Path, PathSegment}; |
| <span class="kw">use </span><span class="kw">crate</span>::punctuated::Punctuated; |
| <span class="kw">use </span>proc_macro2::Ident; |
| <span class="kw">use </span>std::fmt::Display; |
| |
| <span class="doccomment">/// Make a parser that is usable with `parse_macro_input!` in a |
| /// `#[proc_macro_attribute]` macro. |
| /// |
| /// *Warning:* When parsing attribute args **other than** the |
| /// `proc_macro::TokenStream` input of a `proc_macro_attribute`, you do **not** |
| /// 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 |
| /// [`Attribute::parse_nested_meta`] instead. |
| /// |
| /// [`Attribute::parse_nested_meta`]: crate::Attribute::parse_nested_meta |
| /// |
| /// # Example |
| /// |
| /// This example implements an attribute macro whose invocations look like this: |
| /// |
| /// ``` |
| /// # const IGNORE: &str = stringify! { |
| /// #[tea(kind = "EarlGrey", hot)] |
| /// struct Picard {...} |
| /// # }; |
| /// ``` |
| /// |
| /// The "parameters" supported by the attribute are: |
| /// |
| /// - `kind = "..."` |
| /// - `hot` |
| /// - `with(sugar, milk, ...)`, a comma-separated list of ingredients |
| /// |
| /// ``` |
| /// # extern crate proc_macro; |
| /// # |
| /// use proc_macro::TokenStream; |
| /// use syn::{parse_macro_input, LitStr, Path}; |
| /// |
| /// # const IGNORE: &str = stringify! { |
| /// #[proc_macro_attribute] |
| /// # }; |
| /// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream { |
| /// let mut kind: Option<LitStr> = None; |
| /// let mut hot: bool = false; |
| /// let mut with: Vec<Path> = Vec::new(); |
| /// let tea_parser = syn::meta::parser(|meta| { |
| /// if meta.path.is_ident("kind") { |
| /// kind = Some(meta.value()?.parse()?); |
| /// Ok(()) |
| /// } else if meta.path.is_ident("hot") { |
| /// hot = true; |
| /// Ok(()) |
| /// } else if meta.path.is_ident("with") { |
| /// meta.parse_nested_meta(|meta| { |
| /// with.push(meta.path); |
| /// Ok(()) |
| /// }) |
| /// } else { |
| /// Err(meta.error("unsupported tea property")) |
| /// } |
| /// }); |
| /// |
| /// parse_macro_input!(args with tea_parser); |
| /// eprintln!("kind={kind:?} hot={hot} with={with:?}"); |
| /// |
| /// /* ... */ |
| /// # TokenStream::new() |
| /// } |
| /// ``` |
| /// |
| /// The `syn::meta` library will take care of dealing with the commas including |
| /// trailing commas, and producing sensible error messages on unexpected input. |
| /// |
| /// ```console |
| /// error: expected `,` |
| /// --> src/main.rs:3:37 |
| /// | |
| /// 3 | #[tea(kind = "EarlGrey", with(sugar = "lol", milk))] |
| /// | ^ |
| /// ``` |
| /// |
| /// # Example |
| /// |
| /// Same as above but we factor out most of the logic into a separate function. |
| /// |
| /// ``` |
| /// # extern crate proc_macro; |
| /// # |
| /// use proc_macro::TokenStream; |
| /// use syn::meta::ParseNestedMeta; |
| /// use syn::parse::{Parser, Result}; |
| /// use syn::{parse_macro_input, LitStr, Path}; |
| /// |
| /// # const IGNORE: &str = stringify! { |
| /// #[proc_macro_attribute] |
| /// # }; |
| /// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream { |
| /// let mut attrs = TeaAttributes::default(); |
| /// let tea_parser = syn::meta::parser(|meta| attrs.parse(meta)); |
| /// parse_macro_input!(args with tea_parser); |
| /// |
| /// /* ... */ |
| /// # TokenStream::new() |
| /// } |
| /// |
| /// #[derive(Default)] |
| /// struct TeaAttributes { |
| /// kind: Option<LitStr>, |
| /// hot: bool, |
| /// with: Vec<Path>, |
| /// } |
| /// |
| /// impl TeaAttributes { |
| /// fn parse(&mut self, meta: ParseNestedMeta) -> Result<()> { |
| /// if meta.path.is_ident("kind") { |
| /// self.kind = Some(meta.value()?.parse()?); |
| /// Ok(()) |
| /// } else /* just like in last example */ |
| /// # { unimplemented!() } |
| /// |
| /// } |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>parser(logic: <span class="kw">impl </span>FnMut(ParseNestedMeta) -> <span class="prelude-ty">Result</span><()>) -> <span class="kw">impl </span>Parser<Output = ()> { |
| |input: ParseStream| { |
| <span class="kw">if </span>input.is_empty() { |
| <span class="prelude-val">Ok</span>(()) |
| } <span class="kw">else </span>{ |
| parse_nested_meta(input, logic) |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Context for parsing a single property in the conventional syntax for |
| /// structured attributes. |
| /// |
| /// # Examples |
| /// |
| /// Refer to usage examples on the following two entry-points: |
| /// |
| /// - [`Attribute::parse_nested_meta`] if you have an entire `Attribute` to |
| /// parse. Always use this if possible. Generally this is able to produce |
| /// better error messages because `Attribute` holds span information for all |
| /// of the delimiters therein. |
| /// |
| /// - [`syn::meta::parser`] if you are implementing a `proc_macro_attribute` |
| /// macro and parsing the arguments to the attribute macro, i.e. the ones |
| /// written in the same attribute that dispatched the macro invocation. Rustc |
| /// does not pass span information for the surrounding delimiters into the |
| /// attribute macro invocation in this situation, so error messages might be |
| /// less precise. |
| /// |
| /// [`Attribute::parse_nested_meta`]: crate::Attribute::parse_nested_meta |
| /// [`syn::meta::parser`]: crate::meta::parser |
| </span><span class="attribute">#[non_exhaustive] |
| </span><span class="kw">pub struct </span>ParseNestedMeta<<span class="lifetime">'a</span>> { |
| <span class="kw">pub </span>path: Path, |
| <span class="kw">pub </span>input: ParseStream<<span class="lifetime">'a</span>>, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> ParseNestedMeta<<span class="lifetime">'a</span>> { |
| <span class="doccomment">/// Used when parsing `key = "value"` syntax. |
| /// |
| /// All it does is advance `meta.input` past the `=` sign in the input. You |
| /// could accomplish the same effect by writing |
| /// `meta.parse::<Token![=]>()?`, so at most it is a minor convenience to |
| /// use `meta.value()?`. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use syn::{parse_quote, Attribute, LitStr}; |
| /// |
| /// let attr: Attribute = parse_quote! { |
| /// #[tea(kind = "EarlGrey")] |
| /// }; |
| /// // conceptually: |
| /// if attr.path().is_ident("tea") { // this parses the `tea` |
| /// attr.parse_nested_meta(|meta| { // this parses the `(` |
| /// if meta.path.is_ident("kind") { // this parses the `kind` |
| /// let value = meta.value()?; // this parses the `=` |
| /// let s: LitStr = value.parse()?; // this parses `"EarlGrey"` |
| /// if s.value() == "EarlGrey" { |
| /// // ... |
| /// } |
| /// Ok(()) |
| /// } else { |
| /// Err(meta.error("unsupported attribute")) |
| /// } |
| /// })?; |
| /// } |
| /// # anyhow::Ok(()) |
| /// ``` |
| </span><span class="kw">pub fn </span>value(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><ParseStream<<span class="lifetime">'a</span>>> { |
| <span class="self">self</span>.input.parse::<<span class="macro">Token!</span>[=]>()<span class="question-mark">?</span>; |
| <span class="prelude-val">Ok</span>(<span class="self">self</span>.input) |
| } |
| |
| <span class="doccomment">/// Used when parsing `list(...)` syntax **if** the content inside the |
| /// nested parentheses is also expected to conform to Rust's structured |
| /// attribute convention. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use syn::{parse_quote, Attribute}; |
| /// |
| /// let attr: Attribute = parse_quote! { |
| /// #[tea(with(sugar, milk))] |
| /// }; |
| /// |
| /// if attr.path().is_ident("tea") { |
| /// attr.parse_nested_meta(|meta| { |
| /// if meta.path.is_ident("with") { |
| /// meta.parse_nested_meta(|meta| { // <--- |
| /// if meta.path.is_ident("sugar") { |
| /// // Here we can go even deeper if needed. |
| /// Ok(()) |
| /// } else if meta.path.is_ident("milk") { |
| /// Ok(()) |
| /// } else { |
| /// Err(meta.error("unsupported ingredient")) |
| /// } |
| /// }) |
| /// } else { |
| /// Err(meta.error("unsupported tea property")) |
| /// } |
| /// })?; |
| /// } |
| /// # anyhow::Ok(()) |
| /// ``` |
| /// |
| /// # Counterexample |
| /// |
| /// If you don't need `parse_nested_meta`'s help in parsing the content |
| /// written within the nested parentheses, keep in mind that you can always |
| /// just parse it yourself from the exposed ParseStream. Rust syntax permits |
| /// arbitrary tokens within those parentheses so for the crazier stuff, |
| /// `parse_nested_meta` is not what you want. |
| /// |
| /// ``` |
| /// use syn::{parenthesized, parse_quote, Attribute, LitInt}; |
| /// |
| /// let attr: Attribute = parse_quote! { |
| /// #[repr(align(32))] |
| /// }; |
| /// |
| /// let mut align: Option<LitInt> = None; |
| /// if attr.path().is_ident("repr") { |
| /// attr.parse_nested_meta(|meta| { |
| /// if meta.path.is_ident("align") { |
| /// let content; |
| /// parenthesized!(content in meta.input); |
| /// align = Some(content.parse()?); |
| /// Ok(()) |
| /// } else { |
| /// Err(meta.error("unsupported repr")) |
| /// } |
| /// })?; |
| /// } |
| /// # anyhow::Ok(()) |
| /// ``` |
| </span><span class="kw">pub fn </span>parse_nested_meta( |
| <span class="kw-2">&</span><span class="self">self</span>, |
| logic: <span class="kw">impl </span>FnMut(ParseNestedMeta) -> <span class="prelude-ty">Result</span><()>, |
| ) -> <span class="prelude-ty">Result</span><()> { |
| <span class="kw">let </span>content; |
| <span class="macro">parenthesized!</span>(content <span class="kw">in </span><span class="self">self</span>.input); |
| parse_nested_meta(<span class="kw-2">&</span>content, logic) |
| } |
| |
| <span class="doccomment">/// Report that the attribute's content did not conform to expectations. |
| /// |
| /// The span of the resulting error will cover `meta.path` *and* everything |
| /// that has been parsed so far since it. |
| /// |
| /// There are 2 ways you might call this. First, if `meta.path` is not |
| /// something you recognize: |
| /// |
| /// ``` |
| /// # use syn::Attribute; |
| /// # |
| /// # fn example(attr: &Attribute) -> syn::Result<()> { |
| /// attr.parse_nested_meta(|meta| { |
| /// if meta.path.is_ident("kind") { |
| /// // ... |
| /// Ok(()) |
| /// } else { |
| /// Err(meta.error("unsupported tea property")) |
| /// } |
| /// })?; |
| /// # Ok(()) |
| /// # } |
| /// ``` |
| /// |
| /// In this case, it behaves exactly like |
| /// `syn::Error::new_spanned(&meta.path, "message...")`. |
| /// |
| /// ```console |
| /// error: unsupported tea property |
| /// --> src/main.rs:3:26 |
| /// | |
| /// 3 | #[tea(kind = "EarlGrey", wat = "foo")] |
| /// | ^^^ |
| /// ``` |
| /// |
| /// More usefully, the second place is if you've already parsed a value but |
| /// have decided not to accept the value: |
| /// |
| /// ``` |
| /// # use syn::Attribute; |
| /// # |
| /// # fn example(attr: &Attribute) -> syn::Result<()> { |
| /// use syn::Expr; |
| /// |
| /// attr.parse_nested_meta(|meta| { |
| /// if meta.path.is_ident("kind") { |
| /// let expr: Expr = meta.value()?.parse()?; |
| /// match expr { |
| /// Expr::Lit(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// Expr::Path(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// Expr::Macro(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// _ => Err(meta.error("tea kind must be a string literal, path, or macro")), |
| /// } |
| /// } else /* as above */ |
| /// # { unimplemented!() } |
| /// |
| /// })?; |
| /// # Ok(()) |
| /// # } |
| /// ``` |
| /// |
| /// ```console |
| /// error: tea kind must be a string literal, path, or macro |
| /// --> src/main.rs:3:7 |
| /// | |
| /// 3 | #[tea(kind = async { replicator.await })] |
| /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| /// ``` |
| /// |
| /// Often you may want to use `syn::Error::new_spanned` even in this |
| /// situation. In the above code, that would be: |
| /// |
| /// ``` |
| /// # use syn::{Error, Expr}; |
| /// # |
| /// # fn example(expr: Expr) -> syn::Result<()> { |
| /// match expr { |
| /// Expr::Lit(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// Expr::Path(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// Expr::Macro(expr) => /* ... */ |
| /// # unimplemented!(), |
| /// _ => Err(Error::new_spanned(expr, "unsupported expression type for `kind`")), |
| /// } |
| /// # } |
| /// ``` |
| /// |
| /// ```console |
| /// error: unsupported expression type for `kind` |
| /// --> src/main.rs:3:14 |
| /// | |
| /// 3 | #[tea(kind = async { replicator.await })] |
| /// | ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| /// ``` |
| </span><span class="kw">pub fn </span>error(<span class="kw-2">&</span><span class="self">self</span>, msg: <span class="kw">impl </span>Display) -> Error { |
| <span class="kw">let </span>start_span = <span class="self">self</span>.path.segments[<span class="number">0</span>].ident.span(); |
| <span class="kw">let </span>end_span = <span class="self">self</span>.input.cursor().prev_span(); |
| <span class="kw">crate</span>::error::new2(start_span, end_span, msg) |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>parse_nested_meta( |
| input: ParseStream, |
| <span class="kw-2">mut </span>logic: <span class="kw">impl </span>FnMut(ParseNestedMeta) -> <span class="prelude-ty">Result</span><()>, |
| ) -> <span class="prelude-ty">Result</span><()> { |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>path = input.call(parse_meta_path)<span class="question-mark">?</span>; |
| logic(ParseNestedMeta { path, input })<span class="question-mark">?</span>; |
| <span class="kw">if </span>input.is_empty() { |
| <span class="kw">return </span><span class="prelude-val">Ok</span>(()); |
| } |
| input.parse::<<span class="macro">Token!</span>[,]>()<span class="question-mark">?</span>; |
| <span class="kw">if </span>input.is_empty() { |
| <span class="kw">return </span><span class="prelude-val">Ok</span>(()); |
| } |
| } |
| } |
| |
| <span class="comment">// Like Path::parse_mod_style, but accepts keywords in the path. |
| </span><span class="kw">fn </span>parse_meta_path(input: ParseStream) -> <span class="prelude-ty">Result</span><Path> { |
| <span class="prelude-val">Ok</span>(Path { |
| leading_colon: input.parse()<span class="question-mark">?</span>, |
| segments: { |
| <span class="kw">let </span><span class="kw-2">mut </span>segments = Punctuated::new(); |
| <span class="kw">if </span>input.peek(Ident::peek_any) { |
| <span class="kw">let </span>ident = Ident::parse_any(input)<span class="question-mark">?</span>; |
| segments.push_value(PathSegment::from(ident)); |
| } <span class="kw">else if </span>input.is_empty() { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(input.error(<span class="string">"expected nested attribute"</span>)); |
| } <span class="kw">else if </span>input.peek(Lit) { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(input.error(<span class="string">"unexpected literal in nested attribute, expected ident"</span>)); |
| } <span class="kw">else </span>{ |
| <span class="kw">return </span><span class="prelude-val">Err</span>(input.error(<span class="string">"unexpected token in nested attribute, expected ident"</span>)); |
| } |
| <span class="kw">while </span>input.peek(<span class="macro">Token!</span>[::]) { |
| <span class="kw">let </span>punct = input.parse()<span class="question-mark">?</span>; |
| segments.push_punct(punct); |
| <span class="kw">let </span>ident = Ident::parse_any(input)<span class="question-mark">?</span>; |
| segments.push_value(PathSegment::from(ident)); |
| } |
| segments |
| }, |
| }) |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="syn" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
