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+/// Parse the input TokenStream of a macro, triggering a compile error if the
+/// tokens fail to parse.
+///
+/// Refer to the [`parse` module] documentation for more details about parsing
+/// in Syn.
+///
+/// [`parse` module]: mod@crate::parse
+///
+/// <br>
+///
+/// # Intended usage
+///
+/// This macro must be called from a function that returns
+/// `proc_macro::TokenStream`. Usually this will be your proc macro entry point,
+/// the function that has the #\[proc_macro\] / #\[proc_macro_derive\] /
+/// #\[proc_macro_attribute\] attribute.
+///
+/// ```
+/// # extern crate proc_macro;
+/// #
+/// use proc_macro::TokenStream;
+/// use syn::{parse_macro_input, Result};
+/// use syn::parse::{Parse, ParseStream};
+///
+/// struct MyMacroInput {
+/// /* ... */
+/// }
+///
+/// impl Parse for MyMacroInput {
+/// fn parse(input: ParseStream) -> Result<Self> {
+/// /* ... */
+/// # Ok(MyMacroInput {})
+/// }
+/// }
+///
+/// # const IGNORE: &str = stringify! {
+/// #[proc_macro]
+/// # };
+/// pub fn my_macro(tokens: TokenStream) -> TokenStream {
+/// let input = parse_macro_input!(tokens as MyMacroInput);
+///
+/// /* ... */
+/// # TokenStream::new()
+/// }
+/// ```
+///
+/// <br>
+///
+/// # Usage with Parser
+///
+/// This macro can also be used with the [`Parser` trait] for types that have
+/// multiple ways that they can be parsed.
+///
+/// [`Parser` trait]: crate::parse::Parser
+///
+/// ```
+/// # extern crate proc_macro;
+/// #
+/// # use proc_macro::TokenStream;
+/// # use syn::{parse_macro_input, Result};
+/// # use syn::parse::ParseStream;
+/// #
+/// # struct MyMacroInput {}
+/// #
+/// impl MyMacroInput {
+/// fn parse_alternate(input: ParseStream) -> Result<Self> {
+/// /* ... */
+/// # Ok(MyMacroInput {})
+/// }
+/// }
+///
+/// # const IGNORE: &str = stringify! {
+/// #[proc_macro]
+/// # };
+/// pub fn my_macro(tokens: TokenStream) -> TokenStream {
+/// let input = parse_macro_input!(tokens with MyMacroInput::parse_alternate);
+///
+/// /* ... */
+/// # TokenStream::new()
+/// }
+/// ```
+///
+/// <br>
+///
+/// # Expansion
+///
+/// `parse_macro_input!($variable as $Type)` expands to something like:
+///
+/// ```no_run
+/// # extern crate proc_macro;
+/// #
+/// # macro_rules! doc_test {
+/// # ($variable:ident as $Type:ty) => {
+/// match syn::parse::<$Type>($variable) {
+/// Ok(syntax_tree) => syntax_tree,
+/// Err(err) => return proc_macro::TokenStream::from(err.to_compile_error()),
+/// }
+/// # };
+/// # }
+/// #
+/// # fn test(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+/// # let _ = doc_test!(input as syn::Ident);
+/// # proc_macro::TokenStream::new()
+/// # }
+/// ```
+#[macro_export]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "proc-macro"))))]
+macro_rules! parse_macro_input {
+ ($tokenstream:ident as $ty:ty) => {
+ match $crate::parse::<$ty>($tokenstream) {
+ $crate::__private::Ok(data) => data,
+ $crate::__private::Err(err) => {
+ return $crate::__private::TokenStream::from(err.to_compile_error());
+ }
+ }
+ };
+ ($tokenstream:ident with $parser:path) => {
+ match $crate::parse::Parser::parse($parser, $tokenstream) {
+ $crate::__private::Ok(data) => data,
+ $crate::__private::Err(err) => {
+ return $crate::__private::TokenStream::from(err.to_compile_error());
+ }
+ }
+ };
+ ($tokenstream:ident) => {
+ $crate::parse_macro_input!($tokenstream as _)
+ };
+}