1 // SPDX-License-Identifier: Apache-2.0 OR MIT
18 /// `proc_macro::TokenStream` input of a `proc_macro_attribute`, you do **not**
39 /// - `kind = "..."`
40 /// - `hot`
41 /// - `with(sugar, milk, ...)`, a comma-separated list of ingredients
52 /// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream {
58 ///             kind = Some(meta.value()?.parse()?);
82 /// trailing commas, and producing sensible error messages on unexpected input.
86 ///  --> src/main.rs:3:37
107 /// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream {
124 ///     fn parse(&mut self, meta: ParseNestedMeta) -> Result<()> {
126 ///             self.kind = Some(meta.value()?.parse()?);
134 pub fn parser(logic: impl FnMut(ParseNestedMeta) -> Result<()>) -> impl Parser<Output = ()> {  in parser()
135     |input: ParseStream| {  in parser()
136         if input.is_empty() {  in parser()
139             parse_nested_meta(input, logic)  in parser()
149 /// Refer to usage examples on the following two entry-points:
151 /// - [`Attribute::parse_nested_meta`] if you have an entire `Attribute` to
156 /// - [`syn::meta::parser`] if you are implementing a `proc_macro_attribute`
168     pub input: ParseStream<'a>,  field
172     /// Used when parsing `key = "value"` syntax.
174     /// All it does is advance `meta.input` past the `=` sign in the input. You
177     /// use `meta.value()?`.
191     ///             let value = meta.value()?;   // this parses the `=`
192     ///             let s: LitStr = value.parse()?;  // this parses `"EarlGrey"`
193     ///             if s.value() == "EarlGrey" {
204     pub fn value(&self) -> Result<ParseStream<'a>> {  in value()  method
205         self.input.parse::<Token![=]>()?;  in value()
206         Ok(self.input)  in value()
225     ///             meta.parse_nested_meta(|meta| {  // <---
263     ///             parenthesized!(content in meta.input);
275         logic: impl FnMut(ParseNestedMeta) -> Result<()>,  in parse_nested_meta()
276     ) -> Result<()> {  in parse_nested_meta()
278         parenthesized!(content in self.input);  in parse_nested_meta()
293     /// # fn example(attr: &Attribute) -> syn::Result<()> {
311     ///  --> src/main.rs:3:26
317     /// More usefully, the second place is if you've already parsed a value but
318     /// have decided not to accept the value:
323     /// # fn example(attr: &Attribute) -> syn::Result<()> {
328     ///         let expr: Expr = meta.value()?.parse()?;
348     ///  --> src/main.rs:3:7
360     /// # fn example(expr: Expr) -> syn::Result<()> {
375     ///  --> src/main.rs:3:14
380     pub fn error(&self, msg: impl Display) -> Error {  in error()
382         let end_span = self.input.cursor().prev_span();  in error()
388     input: ParseStream,  in parse_nested_meta()
389     mut logic: impl FnMut(ParseNestedMeta) -> Result<()>,  in parse_nested_meta()
390 ) -> Result<()> {  in parse_nested_meta()
392         let path = input.call(parse_meta_path)?;  in parse_nested_meta()
393         logic(ParseNestedMeta { path, input })?;  in parse_nested_meta()
394         if input.is_empty() {  in parse_nested_meta()
397         input.parse::<Token![,]>()?;  in parse_nested_meta()
398         if input.is_empty() {  in parse_nested_meta()
405 fn parse_meta_path(input: ParseStream) -> Result<Path> {  in parse_meta_path()
407         leading_colon: input.parse()?,  in parse_meta_path()
410             if input.peek(Ident::peek_any) {  in parse_meta_path()
411                 let ident = Ident::parse_any(input)?;  in parse_meta_path()
413             } else if input.is_empty() {  in parse_meta_path()
414                 return Err(input.error("expected nested attribute"));  in parse_meta_path()
415             } else if input.peek(Lit) {  in parse_meta_path()
416                 return Err(input.error("unexpected literal in nested attribute, expected ident"));  in parse_meta_path()
418                 return Err(input.error("unexpected token in nested attribute, expected ident"));  in parse_meta_path()
420             while input.peek(Token![::]) {  in parse_meta_path()
421                 let punct = input.parse()?;  in parse_meta_path()
423                 let ident = Ident::parse_any(input)?;  in parse_meta_path()