22     /// An attribute, like `#[repr(transparent)]`.
44     /// The `style` field of type `AttrStyle` distinguishes whether an attribute
47     /// Every attribute has a `path` that indicates the intended interpretation
48     /// of the rest of the attribute's contents. The path and the optional
50     /// attribute in three possible varieties:
53     ///   path, for example the `#[test]` attribute.
82     /// # Parsing from tokens to Attribute
87     /// [`Attribute::parse_outer`] or [`Attribute::parse_inner`] depending on
95     /// use syn::{Attribute, Ident, Result, Token};
103     ///     attrs: Vec<Attribute>,
112     ///             attrs: input.call(Attribute::parse_outer)?,
123     /// # Parsing from Attribute to structured arguments
127     /// `Meta::List` variety of attribute are held in an arbitrary `tokens:
128     /// TokenStream`. Macros are expected to check the `path` of the attribute,
131     /// attribute. Use [`parse_args()`] to parse those tokens into the expected
134     /// [`parse_args()`]: Attribute::parse_args
142     /// expanded into an attribute of the form `#[doc = r"comment"]`.
175     pub struct Attribute {
183 impl Attribute {  impl
184     /// Returns the path that identifies the interpretation of this attribute.
192     /// Parse the arguments to the attribute as a syntax tree.
210     /// use syn::{parse_quote, Attribute, Expr};
212     /// let attr: Attribute = parse_quote! {
228     /// Parse the arguments to the attribute using the given parser.
233     /// use syn::{parse_quote, Attribute};
235     /// let attr: Attribute = parse_quote! {
239     /// let bwom = attr.parse_args_with(Attribute::parse_outer)?;
241     /// // Attribute does not have a Parse impl, so we couldn't directly do:
242     /// // let bwom: Attribute = attr.parse_args()?;
253                     "expected attribute arguments in parentheses: {}[{}(...)]",  in parse_args_with()
270     /// Parse the arguments to the attribute, expecting it to follow the
273     /// The [*Meta Item Attribute Syntax*][syntax] section in the Rust reference
276     /// need to parse arbitrarily goofy attribute syntax.
278     /// [syntax]: https://doc.rust-lang.org/reference/attributes.html#meta-item-attribute-syntax
282     /// We'll parse a struct, and then parse some of Rust's `#[repr]` attribute
405     /// [*Parsing from tokens to Attribute*](#parsing-from-tokens-to-attribute).
421     /// [*Parsing from tokens to Attribute*](#parsing-from-tokens-to-attribute).
454     /// Content of a compile-time structured attribute.
478         /// A structured list within an attribute, like `derive(Copy, Clone)`.
481         /// A name-value pair within an attribute, like `feature = "nightly"`.
487     /// A structured list within an attribute, like `derive(Copy, Clone)`.
497     /// A name-value pair within an attribute, like `feature = "nightly"`.
528         Err(Error::new(error_span, "unexpected token in attribute"))  in require_path_only()
541                     "expected attribute arguments in parentheses: `{}(...)`",  in require_list()
559                     "expected a value for this attribute: `{} = ...`",  in require_name_value()
569     /// See [`Attribute::parse_args`].
576     /// See [`Attribute::parse_args_with`].
584     /// See [`Attribute::parse_nested_meta`].
597     type Ret: Iterator<Item = &'a Attribute>;
605 impl<'a> FilterAttrs<'a> for &'a [Attribute] {  implementation
606     type Ret = iter::Filter<slice::Iter<'a, Attribute>, fn(&&Attribute) -> bool>;
609         fn is_outer(attr: &&Attribute) -> bool {  in outer()
620         fn is_inner(attr: &&Attribute) -> bool {  in inner()
650     use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
661     pub(crate) fn parse_inner(input: ParseStream, attrs: &mut Vec<Attribute>) -> Result<()> {  in parse_inner()
668     pub(crate) fn single_parse_inner(input: ParseStream) -> Result<Attribute> {  in single_parse_inner()  argument
670         Ok(Attribute {  in single_parse_inner()
678     pub(crate) fn single_parse_outer(input: ParseStream) -> Result<Attribute> {  in single_parse_outer()  argument
680         Ok(Attribute {  in single_parse_outer()
713     // only the `unsafe` keyword is accepted as an attribute's outermost path.
753             return Err(input.error("unexpected attribute inside of attribute"));  in parse_meta_name_value_after_path()
792     use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
799     impl ToTokens for Attribute {  implementation