third_party/rust_crates/vendor/proc-macro-hack/src/lib.rs - fuchsia - Git at Google

 //! As of Rust 1.30, the language supports user-defined function-like procedural
 //! macros. However these can only be invoked in item position, not in
 //! statements or expressions.
 //!
 //! This crate implements an alternative type of procedural macro that can be
 //! invoked in statement or expression position.
 //!
 //! # Defining procedural macros
 //!
 //! Two crates are required to define a procedural macro.
 //!
 //! ## The implementation crate
 //!
 //! This crate must contain nothing but procedural macros. Private helper
 //! functions and private modules are fine but nothing can be public.
 //!
 //! [> example of an implementation crate][demo-hack-impl]
 //!
 //! Just like you would use a #\[proc_macro\] attribute to define a natively
 //! supported procedural macro, use proc-macro-hack's #\[proc_macro_hack\]
 //! attribute to define a procedural macro that works in expression position.
 //! The function signature is the same as for ordinary function-like procedural
 //! macros.
 //!
 //! ```
 //! extern crate proc_macro;
 //!
 //! use proc_macro::TokenStream;
 //! use proc_macro_hack::proc_macro_hack;
 //! use quote::quote;
 //! use syn::{parse_macro_input, Expr};
 //!
 //! # const IGNORE: &str = stringify! {
 //! #[proc_macro_hack]
 //! # };
 //! pub fn add_one(input: TokenStream) -> TokenStream {
 //!     let expr = parse_macro_input!(input as Expr);
 //!     TokenStream::from(quote! {
 //!         1 + (#expr)
 //!     })
 //! }
 //! #
 //! # fn main() {}
 //! ```
 //!
 //! ## The declaration crate
 //!
 //! This crate is allowed to contain other public things if you need, for
 //! example traits or functions or ordinary macros.
 //!
 //! [> example of a declaration crate][demo-hack]
 //!
 //! Within the declaration crate there needs to be a re-export of your
 //! procedural macro from the implementation crate. The re-export also carries a
 //! \#\[proc_macro_hack\] attribute.
 //!
 //! ```
 //! use proc_macro_hack::proc_macro_hack;
 //!
 //! /// Add one to an expression.
 //! ///
 //! /// (Documentation goes here on the re-export, not in the other crate.)
 //! #[proc_macro_hack]
 //! pub use demo_hack_impl::add_one;
 //! #
 //! # fn main() {}
 //! ```
 //!
 //! Both crates depend on `proc-macro-hack`:
 //!
 //! ```toml
 //! [dependencies]
 //! proc-macro-hack = "0.5"
 //! ```
 //!
 //! Additionally, your implementation crate (but not your declaration crate) is
 //! a proc macro crate:
 //!
 //! ```toml
 //! [lib]
 //! proc-macro = true
 //! ```
 //!
 //! # Using procedural macros
 //!
 //! Users of your crate depend on your declaration crate (not your
 //! implementation crate), then use your procedural macros as usual.
 //!
 //! [> example of a downstream crate][example]
 //!
 //! ```
 //! use demo_hack::add_one;
 //!
 //! fn main() {
 //!     let two = 2;
 //!     let nine = add_one!(two) + add_one!(2 + 3);
 //!     println!("nine = {}", nine);
 //! }
 //! ```
 //!
 //! [demo-hack-impl]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
 //! [demo-hack]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack
 //! [example]: https://github.com/dtolnay/proc-macro-hack/tree/master/example
 //!
 //! # Limitations
 //!
 //! - Only proc macros in expression position are supported. Proc macros in type
 //!   position ([#10]) or pattern position ([#20]) are not supported.
 //!
 //! - By default, nested invocations are not supported i.e. the code emitted by
 //!   a proc-macro-hack macro invocation cannot contain recursive calls to the
 //!   same proc-macro-hack macro nor calls to any other proc-macro-hack macros.
 //!   Use [`proc-macro-nested`] if you require support for nested invocations.
 //!
 //! - By default, hygiene is structured such that the expanded code can't refer
 //!   to local variables other than those passed by name somewhere in the macro
 //!   input. If your macro must refer to *local* variables that don't get named
 //!   in the macro input, use `#[proc_macro_hack(fake_call_site)]` on the
 //!   re-export in your declaration crate. *Most macros won't need this.*
 //!
 //! [#10]: https://github.com/dtolnay/proc-macro-hack/issues/10
 //! [#20]: https://github.com/dtolnay/proc-macro-hack/issues/20
 //! [`proc-macro-nested`]: https://docs.rs/proc-macro-nested

 #![recursion_limit = "512"]
 #![cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints))]
 #![cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]

 extern crate proc_macro;
 extern crate proc_macro2;
 extern crate quote;
 extern crate syn;

 use std::fmt::Write;

 use proc_macro2::{Span, TokenStream, TokenTree};
 use quote::{quote, ToTokens};
 use syn::parse::{Parse, ParseStream, Result};
 use syn::{braced, bracketed, parenthesized, parse_macro_input, token, Ident, Token};

 type Visibility = Option<Token![pub]>;

 enum Input {
     Export(Export),
     Define(Define),
 }

 // pub use demo_hack_impl::{m1, m2 as qrst};
 struct Export {
     attrs: TokenStream,
     vis: Visibility,
     from: Ident,
     macros: Vec<Macro>,
 }

 // pub fn m1(input: TokenStream) -> TokenStream { ... }
 struct Define {
     attrs: TokenStream,
     name: Ident,
     body: TokenStream,
 }

 struct Macro {
     name: Ident,
     export_as: Ident,
 }

 impl Parse for Input {
     fn parse(input: ParseStream) -> Result<Self> {
         let ahead = input.fork();
         parse_attributes(&ahead)?;
         ahead.parse::<Visibility>()?;

         if ahead.peek(Token![use]) {
             input.parse().map(Input::Export)
         } else if ahead.peek(Token![fn]) {
             input.parse().map(Input::Define)
         } else {
             Err(input.error("unexpected input to #[proc_macro_hack]"))
         }
     }
 }

 impl Parse for Export {
     fn parse(input: ParseStream) -> Result<Self> {
         let attrs = input.call(parse_attributes)?;
         let vis: Visibility = input.parse()?;
         input.parse::<Token![use]>()?;
         let from: Ident = input.parse()?;
         input.parse::<Token![::]>()?;

         let mut macros = Vec::new();
         if input.peek(token::Brace) {
             let content;
             braced!(content in input);
             loop {
                 macros.push(content.parse()?);
                 if content.is_empty() {
                     break;
                 }
                 content.parse::<Token![,]>()?;
                 if content.is_empty() {
                     break;
                 }
             }
         } else {
             macros.push(input.parse()?);
         }

         input.parse::<Token![;]>()?;
         Ok(Export { attrs, vis, from, macros })
     }
 }

 impl Parse for Define {
     fn parse(input: ParseStream) -> Result<Self> {
         let attrs = input.call(parse_attributes)?;
         let vis: Visibility = input.parse()?;
         if vis.is_none() {
             return Err(input.error("functions tagged with `#[proc_macro_hack]` must be `pub`"));
         }

         input.parse::<Token![fn]>()?;
         let name: Ident = input.parse()?;
         let body: TokenStream = input.parse()?;
         Ok(Define { attrs, name, body })
     }
 }

 impl Parse for Macro {
     fn parse(input: ParseStream) -> Result<Self> {
         let name: Ident = input.parse()?;
         let renamed: Option<Token![as]> = input.parse()?;
         let export_as = if renamed.is_some() {
             input.parse()?
         } else {
             name.clone()
         };
         Ok(Macro { name, export_as })
     }
 }

 fn parse_attributes(input: ParseStream) -> Result<TokenStream> {
     let mut attrs = TokenStream::new();
     while input.peek(Token![#]) {
         let pound: Token![#] = input.parse()?;
         pound.to_tokens(&mut attrs);
         let content;
         let bracket_token = bracketed!(content in input);
         let content: TokenStream = content.parse()?;
         bracket_token.surround(&mut attrs, |tokens| content.to_tokens(tokens));
     }
     Ok(attrs)
 }

 #[proc_macro_attribute]
 pub fn proc_macro_hack(
     args: proc_macro::TokenStream,
     input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
     proc_macro::TokenStream::from(match parse_macro_input!(input) {
         Input::Export(export) => {
             let args = parse_macro_input!(args as ExportArgs);
             expand_export(export, args)
         }
         Input::Define(define) => {
             parse_macro_input!(args as DefineArgs);
             expand_define(define)
         }
     })
 }

 mod kw {
     syn::custom_keyword!(derive);
     syn::custom_keyword!(fake_call_site);
     syn::custom_keyword!(support_nested);
 }

 struct ExportArgs {
     support_nested: bool,
     fake_call_site: bool,
 }

 impl Parse for ExportArgs {
     fn parse(input: ParseStream) -> Result<Self> {
         let mut args = ExportArgs {
             support_nested: false,
             fake_call_site: false,
         };

         while !input.is_empty() {
             let ahead = input.lookahead1();
             if ahead.peek(kw::support_nested) {
                 input.parse::<kw::support_nested>()?;
                 args.support_nested = true;
             } else if ahead.peek(kw::fake_call_site) {
                 input.parse::<kw::fake_call_site>()?;
                 args.fake_call_site = true;
             } else {
                 return Err(ahead.error());
             }
             if input.is_empty() {
                 break;
             }
             input.parse::<Token![,]>()?;
         }

         Ok(args)
     }
 }

 struct DefineArgs;

 impl Parse for DefineArgs {
     fn parse(_input: ParseStream) -> Result<Self> {
         Ok(DefineArgs)
     }
 }

 struct EnumHack {
     token_stream: TokenStream,
 }

 impl Parse for EnumHack {
     fn parse(input: ParseStream) -> Result<Self> {
         input.parse::<Token![enum]>()?;
         input.parse::<Ident>()?;

         let braces;
         braced!(braces in input);
         braces.parse::<Ident>()?;
         braces.parse::<Token![=]>()?;

         let parens;
         parenthesized!(parens in braces);
         parens.parse::<Ident>()?;
         parens.parse::<Token![!]>()?;

         let inner;
         braced!(inner in parens);
         let token_stream: TokenStream = inner.parse()?;

         parens.parse::<Token![,]>()?;
         parens.parse::<TokenTree>()?;
         braces.parse::<Token![.]>()?;
         braces.parse::<TokenTree>()?;
         braces.parse::<Token![,]>()?;

         Ok(EnumHack { token_stream })
     }
 }

 #[doc(hidden)]
 #[proc_macro_derive(ProcMacroHack)]
 pub fn enum_hack(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let inner = parse_macro_input!(input as EnumHack);
     proc_macro::TokenStream::from(inner.token_stream)
 }

 struct FakeCallSite {
     derive: Ident,
     rest: TokenStream,
 }

 impl Parse for FakeCallSite {
     fn parse(input: ParseStream) -> Result<Self> {
         input.parse::<Token![#]>()?;
         let attr;
         bracketed!(attr in input);
         attr.parse::<kw::derive>()?;
         let path;
         parenthesized!(path in attr);
         Ok(FakeCallSite {
             derive: path.parse()?,
             rest: input.parse()?,
         })
     }
 }

 #[doc(hidden)]
 #[proc_macro_attribute]
 pub fn fake_call_site(
     args: proc_macro::TokenStream,
     input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
     let args = TokenStream::from(args);
     let span = match args.into_iter().next() {
         Some(token) => token.span(),
         None => return input,
     };

     let input = parse_macro_input!(input as FakeCallSite);
     let mut derive = input.derive;
     derive.set_span(span);
     let rest = input.rest;

     let expanded = quote! {
         #[derive(#derive)]
         #rest
     };

     proc_macro::TokenStream::from(expanded)
 }

 fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
     let dummy = dummy_name_for_export(&export);

     let attrs = export.attrs;
     let vis = export.vis;
     let macro_export = match vis {
         Some(_) => quote!(#[macro_export]),
         None => quote!(),
     };
     let crate_prefix = vis.map(|_| quote!($crate::));
     let enum_variant = if args.support_nested {
         quote!(Nested)
     } else {
         quote!(Value)
     };

     let from = export.from;
     let rules = export
         .macros
         .into_iter()
         .map(|Macro { name, export_as }| {
             let actual_name = actual_proc_macro_name(&name);
             let dispatch = dispatch_macro_name(&name);
             let call_site = call_site_macro_name(&name);

             let export_dispatch = if args.support_nested {
                 quote! {
                     #[doc(hidden)]
                     #vis use proc_macro_nested::dispatch as #dispatch;
                 }
             } else {
                 quote!()
             };

             let proc_macro_call = if args.support_nested {
                 quote! {
                     #crate_prefix #dispatch! { ($($proc_macro)*) }
                 }
             } else {
                 quote! {
                     proc_macro_call!()
                 }
             };

             let export_call_site = if args.fake_call_site {
                 quote! {
                     #[doc(hidden)]
                     #vis use proc_macro_hack::fake_call_site as #call_site;
                 }
             } else {
                 quote!()
             };

             let do_derive = if !args.fake_call_site {
                 quote! {
                     #[derive(#crate_prefix #actual_name)]
                 }
             } else if crate_prefix.is_some() {
                 quote! {
                     use #crate_prefix #actual_name;
                     #[#crate_prefix #call_site ($($proc_macro)*)]
                     #[derive(#actual_name)]
                 }
             } else {
                 quote! {
                     #[#call_site ($($proc_macro)*)]
                     #[derive(#actual_name)]
                 }
             };

             quote! {
                 #[doc(hidden)]
                 #vis use #from::#actual_name;

                 #export_dispatch
                 #export_call_site

                 #attrs
                 #macro_export
                 macro_rules! #export_as {
                     ($($proc_macro:tt)*) => {{
                         #do_derive
                         enum ProcMacroHack {
                             #enum_variant = (stringify! { $($proc_macro)* }, 0).1,
                         }
                         #proc_macro_call
                     }};
                 }
             }
         })
         .collect();

     wrap_in_enum_hack(dummy, rules)
 }

 fn expand_define(define: Define) -> TokenStream {
     let attrs = define.attrs;
     let name = define.name;
     let dummy = actual_proc_macro_name(&name);
     let body = define.body;

     quote! {
         mod #dummy {
             extern crate proc_macro;
             pub use self::proc_macro::*;
         }

         #attrs
         #[proc_macro_derive(#dummy)]
         pub fn #dummy(input: #dummy::TokenStream) -> #dummy::TokenStream {
             use std::iter::FromIterator;

             let mut iter = input.into_iter();
             iter.next().unwrap(); // `enum`
             iter.next().unwrap(); // `ProcMacroHack`

             let mut braces = match iter.next().unwrap() {
                 #dummy::TokenTree::Group(group) => group.stream().into_iter(),
                 _ => unimplemented!(),
             };
             let variant = braces.next().unwrap(); // `Value` or `Nested`
             let support_nested = variant.to_string() == "Nested";
             braces.next().unwrap(); // `=`

             let mut parens = match braces.next().unwrap() {
                 #dummy::TokenTree::Group(group) => group.stream().into_iter(),
                 _ => unimplemented!(),
             };
             parens.next().unwrap(); // `stringify`
             parens.next().unwrap(); // `!`

             let inner = match parens.next().unwrap() {
                 #dummy::TokenTree::Group(group) => group.stream(),
                 _ => unimplemented!(),
             };

             let output: #dummy::TokenStream = #name(inner.clone());

             fn count_bangs(input: #dummy::TokenStream) -> usize {
                 let mut count = 0;
                 for token in input {
                     match token {
                         #dummy::TokenTree::Punct(punct) => {
                             if punct.as_char() == '!' {
                                 count += 1;
                             }
                         }
                         #dummy::TokenTree::Group(group) => {
                             count += count_bangs(group.stream());
                         }
                         _ => {}
                     }
                 }
                 count
             }

             // macro_rules! proc_macro_call {
             //     () => { #output }
             // }
             #dummy::TokenStream::from_iter(vec![
                 #dummy::TokenTree::Ident(
                     #dummy::Ident::new("macro_rules", #dummy::Span::call_site()),
                 ),
                 #dummy::TokenTree::Punct(
                     #dummy::Punct::new('!', #dummy::Spacing::Alone),
                 ),
                 #dummy::TokenTree::Ident(
                     #dummy::Ident::new(
                         &if support_nested {
                             format!("proc_macro_call_{}", count_bangs(inner))
                         } else {
                             String::from("proc_macro_call")
                         },
                         #dummy::Span::call_site(),
                     ),
                 ),
                 #dummy::TokenTree::Group(
                     #dummy::Group::new(#dummy::Delimiter::Brace, #dummy::TokenStream::from_iter(vec![
                         #dummy::TokenTree::Group(
                             #dummy::Group::new(#dummy::Delimiter::Parenthesis, #dummy::TokenStream::new()),
                         ),
                         #dummy::TokenTree::Punct(
                             #dummy::Punct::new('=', #dummy::Spacing::Joint),
                         ),
                         #dummy::TokenTree::Punct(
                             #dummy::Punct::new('>', #dummy::Spacing::Alone),
                         ),
                         #dummy::TokenTree::Group(
                             #dummy::Group::new(#dummy::Delimiter::Brace, output),
                         ),
                     ])),
                 ),
             ])
         }

         fn #name #body
     }
 }

 fn actual_proc_macro_name(conceptual: &Ident) -> Ident {
     let actual_name = format!("proc_macro_hack_{}", conceptual);
     Ident::new(&actual_name, Span::call_site())
 }

 fn dispatch_macro_name(conceptual: &Ident) -> Ident {
     let dispatch = format!("proc_macro_call_{}", conceptual);
     Ident::new(&dispatch, Span::call_site())
 }

 fn call_site_macro_name(conceptual: &Ident) -> Ident {
     let dispatch = format!("proc_macro_fake_call_site_{}", conceptual);
     Ident::new(&dispatch, Span::call_site())
 }

 fn dummy_name_for_export(export: &Export) -> String {
     let mut dummy = String::new();
     write!(dummy, "_{}{}", export.from.to_string().len(), export.from).unwrap();
     for m in &export.macros {
         write!(dummy, "_{}{}", m.name.to_string().len(), m.name).unwrap();
     }
     dummy
 }

 fn wrap_in_enum_hack(dummy: String, inner: TokenStream) -> TokenStream {
     let dummy = Ident::new(&dummy, Span::call_site());
     quote! {
         #[derive(proc_macro_hack::ProcMacroHack)]
         enum #dummy {
             Value = (stringify! { #inner }, 0).1,
         }
     }
 }
	//! As of Rust 1.30, the language supports user-defined function-like procedural
	//! macros. However these can only be invoked in item position, not in
	//! statements or expressions.
	//!
	//! This crate implements an alternative type of procedural macro that can be
	//! invoked in statement or expression position.
	//!
	//! # Defining procedural macros
	//!
	//! Two crates are required to define a procedural macro.
	//!
	//! ## The implementation crate
	//!
	//! This crate must contain nothing but procedural macros. Private helper
	//! functions and private modules are fine but nothing can be public.
	//!
	//! [> example of an implementation crate][demo-hack-impl]
	//!
	//! Just like you would use a #\[proc_macro\] attribute to define a natively
	//! supported procedural macro, use proc-macro-hack's #\[proc_macro_hack\]
	//! attribute to define a procedural macro that works in expression position.
	//! The function signature is the same as for ordinary function-like procedural
	//! macros.
	//!
	//! ```
	//! extern crate proc_macro;
	//!
	//! use proc_macro::TokenStream;
	//! use proc_macro_hack::proc_macro_hack;
	//! use quote::quote;
	//! use syn::{parse_macro_input, Expr};
	//!
	//! # const IGNORE: &str = stringify! {
	//! #[proc_macro_hack]
	//! # };
	//! pub fn add_one(input: TokenStream) -> TokenStream {
	//! let expr = parse_macro_input!(input as Expr);
	//! TokenStream::from(quote! {
	//! 1 + (#expr)
	//! })
	//! }
	//! #
	//! # fn main() {}
	//! ```
	//!
	//! ## The declaration crate
	//!
	//! This crate is allowed to contain other public things if you need, for
	//! example traits or functions or ordinary macros.
	//!
	//! [> example of a declaration crate][demo-hack]
	//!
	//! Within the declaration crate there needs to be a re-export of your
	//! procedural macro from the implementation crate. The re-export also carries a
	//! \#\[proc_macro_hack\] attribute.
	//!
	//! ```
	//! use proc_macro_hack::proc_macro_hack;
	//!
	//! /// Add one to an expression.
	//! ///
	//! /// (Documentation goes here on the re-export, not in the other crate.)
	//! #[proc_macro_hack]
	//! pub use demo_hack_impl::add_one;
	//! #
	//! # fn main() {}
	//! ```
	//!
	//! Both crates depend on `proc-macro-hack`:
	//!
	//! ```toml
	//! [dependencies]
	//! proc-macro-hack = "0.5"
	//! ```
	//!
	//! Additionally, your implementation crate (but not your declaration crate) is
	//! a proc macro crate:
	//!
	//! ```toml
	//! [lib]
	//! proc-macro = true
	//! ```
	//!
	//! # Using procedural macros
	//!
	//! Users of your crate depend on your declaration crate (not your
	//! implementation crate), then use your procedural macros as usual.
	//!
	//! [> example of a downstream crate][example]
	//!
	//! ```
	//! use demo_hack::add_one;
	//!
	//! fn main() {
	//! let two = 2;
	//! let nine = add_one!(two) + add_one!(2 + 3);
	//! println!("nine = {}", nine);
	//! }
	//! ```
	//!
	//! [demo-hack-impl]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
	//! [demo-hack]: https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack
	//! [example]: https://github.com/dtolnay/proc-macro-hack/tree/master/example
	//!
	//! # Limitations
	//!
	//! - Only proc macros in expression position are supported. Proc macros in type
	//! position ([#10]) or pattern position ([#20]) are not supported.
	//!
	//! - By default, nested invocations are not supported i.e. the code emitted by
	//! a proc-macro-hack macro invocation cannot contain recursive calls to the
	//! same proc-macro-hack macro nor calls to any other proc-macro-hack macros.
	//! Use [`proc-macro-nested`] if you require support for nested invocations.
	//!
	//! - By default, hygiene is structured such that the expanded code can't refer
	//! to local variables other than those passed by name somewhere in the macro
	//! input. If your macro must refer to local variables that don't get named
	//! in the macro input, use `#[proc_macro_hack(fake_call_site)]` on the
	//! re-export in your declaration crate. Most macros won't need this.
	//!
	//! [#10]: https://github.com/dtolnay/proc-macro-hack/issues/10
	//! [#20]: https://github.com/dtolnay/proc-macro-hack/issues/20
	//! [`proc-macro-nested`]: https://docs.rs/proc-macro-nested

	#![recursion_limit = "512"]
	#![cfg_attr(feature = "cargo-clippy", allow(renamed_and_removed_lints))]
	#![cfg_attr(feature = "cargo-clippy", allow(needless_pass_by_value))]

	extern crate proc_macro;
	extern crate proc_macro2;
	extern crate quote;
	extern crate syn;

	use std::fmt::Write;

	use proc_macro2::{Span, TokenStream, TokenTree};
	use quote::{quote, ToTokens};
	use syn::parse::{Parse, ParseStream, Result};
	use syn::{braced, bracketed, parenthesized, parse_macro_input, token, Ident, Token};

	type Visibility = Option<Token![pub]>;

	enum Input {
	Export(Export),
	Define(Define),
	}

	// pub use demo_hack_impl::{m1, m2 as qrst};
	struct Export {
	attrs: TokenStream,
	vis: Visibility,
	from: Ident,
	macros: Vec<Macro>,
	}

	// pub fn m1(input: TokenStream) -> TokenStream { ... }
	struct Define {
	attrs: TokenStream,
	name: Ident,
	body: TokenStream,
	}

	struct Macro {
	name: Ident,
	export_as: Ident,
	}

	impl Parse for Input {
	fn parse(input: ParseStream) -> Result<Self> {
	let ahead = input.fork();
	parse_attributes(&ahead)?;
	ahead.parse::<Visibility>()?;

	if ahead.peek(Token![use]) {
	input.parse().map(Input::Export)
	} else if ahead.peek(Token![fn]) {
	input.parse().map(Input::Define)
	} else {
	Err(input.error("unexpected input to #[proc_macro_hack]"))
	}
	}
	}

	impl Parse for Export {
	fn parse(input: ParseStream) -> Result<Self> {
	let attrs = input.call(parse_attributes)?;
	let vis: Visibility = input.parse()?;
	input.parse::<Token![use]>()?;
	let from: Ident = input.parse()?;
	input.parse::<Token![::]>()?;

	let mut macros = Vec::new();
	if input.peek(token::Brace) {
	let content;
	braced!(content in input);
	loop {
	macros.push(content.parse()?);
	if content.is_empty() {
	break;
	}
	content.parse::<Token![,]>()?;
	if content.is_empty() {
	break;
	}
	}
	} else {
	macros.push(input.parse()?);
	}

	input.parse::<Token![;]>()?;
	Ok(Export { attrs, vis, from, macros })
	}
	}

	impl Parse for Define {
	fn parse(input: ParseStream) -> Result<Self> {
	let attrs = input.call(parse_attributes)?;
	let vis: Visibility = input.parse()?;
	if vis.is_none() {
	return Err(input.error("functions tagged with `#[proc_macro_hack]` must be `pub`"));
	}

	input.parse::<Token![fn]>()?;
	let name: Ident = input.parse()?;
	let body: TokenStream = input.parse()?;
	Ok(Define { attrs, name, body })
	}
	}

	impl Parse for Macro {
	fn parse(input: ParseStream) -> Result<Self> {
	let name: Ident = input.parse()?;
	let renamed: Option<Token![as]> = input.parse()?;
	let export_as = if renamed.is_some() {
	input.parse()?
	} else {
	name.clone()
	};
	Ok(Macro { name, export_as })
	}
	}

	fn parse_attributes(input: ParseStream) -> Result<TokenStream> {
	let mut attrs = TokenStream::new();
	while input.peek(Token![#]) {
	let pound: Token![#] = input.parse()?;
	pound.to_tokens(&mut attrs);
	let content;
	let bracket_token = bracketed!(content in input);
	let content: TokenStream = content.parse()?;
	bracket_token.surround(&mut attrs, \|tokens\| content.to_tokens(tokens));
	}
	Ok(attrs)
	}

	#[proc_macro_attribute]
	pub fn proc_macro_hack(
	args: proc_macro::TokenStream,
	input: proc_macro::TokenStream,
	) -> proc_macro::TokenStream {
	proc_macro::TokenStream::from(match parse_macro_input!(input) {
	Input::Export(export) => {
	let args = parse_macro_input!(args as ExportArgs);
	expand_export(export, args)
	}
	Input::Define(define) => {
	parse_macro_input!(args as DefineArgs);
	expand_define(define)
	}
	})
	}

	mod kw {
	syn::custom_keyword!(derive);
	syn::custom_keyword!(fake_call_site);
	syn::custom_keyword!(support_nested);
	}

	struct ExportArgs {
	support_nested: bool,
	fake_call_site: bool,
	}

	impl Parse for ExportArgs {
	fn parse(input: ParseStream) -> Result<Self> {
	let mut args = ExportArgs {
	support_nested: false,
	fake_call_site: false,
	};

	while !input.is_empty() {
	let ahead = input.lookahead1();
	if ahead.peek(kw::support_nested) {
	input.parse::<kw::support_nested>()?;
	args.support_nested = true;
	} else if ahead.peek(kw::fake_call_site) {
	input.parse::<kw::fake_call_site>()?;
	args.fake_call_site = true;
	} else {
	return Err(ahead.error());
	}
	if input.is_empty() {
	break;
	}
	input.parse::<Token![,]>()?;
	}

	Ok(args)
	}
	}

	struct DefineArgs;

	impl Parse for DefineArgs {
	fn parse(_input: ParseStream) -> Result<Self> {
	Ok(DefineArgs)
	}
	}

	struct EnumHack {
	token_stream: TokenStream,
	}

	impl Parse for EnumHack {
	fn parse(input: ParseStream) -> Result<Self> {
	input.parse::<Token![enum]>()?;
	input.parse::<Ident>()?;

	let braces;
	braced!(braces in input);
	braces.parse::<Ident>()?;
	braces.parse::<Token![=]>()?;

	let parens;
	parenthesized!(parens in braces);
	parens.parse::<Ident>()?;
	parens.parse::<Token![!]>()?;

	let inner;
	braced!(inner in parens);
	let token_stream: TokenStream = inner.parse()?;

	parens.parse::<Token![,]>()?;
	parens.parse::<TokenTree>()?;
	braces.parse::<Token![.]>()?;
	braces.parse::<TokenTree>()?;
	braces.parse::<Token![,]>()?;

	Ok(EnumHack { token_stream })
	}
	}

	#[doc(hidden)]
	#[proc_macro_derive(ProcMacroHack)]
	pub fn enum_hack(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
	let inner = parse_macro_input!(input as EnumHack);
	proc_macro::TokenStream::from(inner.token_stream)
	}

	struct FakeCallSite {
	derive: Ident,
	rest: TokenStream,
	}

	impl Parse for FakeCallSite {
	fn parse(input: ParseStream) -> Result<Self> {
	input.parse::<Token![#]>()?;
	let attr;
	bracketed!(attr in input);
	attr.parse::<kw::derive>()?;
	let path;
	parenthesized!(path in attr);
	Ok(FakeCallSite {
	derive: path.parse()?,
	rest: input.parse()?,
	})
	}
	}

	#[doc(hidden)]
	#[proc_macro_attribute]
	pub fn fake_call_site(
	args: proc_macro::TokenStream,
	input: proc_macro::TokenStream,
	) -> proc_macro::TokenStream {
	let args = TokenStream::from(args);
	let span = match args.into_iter().next() {
	Some(token) => token.span(),
	None => return input,
	};

	let input = parse_macro_input!(input as FakeCallSite);
	let mut derive = input.derive;
	derive.set_span(span);
	let rest = input.rest;

	let expanded = quote! {
	#[derive(#derive)]
	#rest
	};

	proc_macro::TokenStream::from(expanded)
	}

	fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
	let dummy = dummy_name_for_export(&export);

	let attrs = export.attrs;
	let vis = export.vis;
	let macro_export = match vis {
	Some(_) => quote!(#[macro_export]),
	None => quote!(),
	};
	let crate_prefix = vis.map(\|_\| quote!($crate::));
	let enum_variant = if args.support_nested {
	quote!(Nested)
	} else {
	quote!(Value)
	};

	let from = export.from;
	let rules = export
	.macros
	.into_iter()
	.map(\|Macro { name, export_as }\| {
	let actual_name = actual_proc_macro_name(&name);
	let dispatch = dispatch_macro_name(&name);
	let call_site = call_site_macro_name(&name);

	let export_dispatch = if args.support_nested {
	quote! {
	#[doc(hidden)]
	#vis use proc_macro_nested::dispatch as #dispatch;
	}
	} else {
	quote!()
	};

	let proc_macro_call = if args.support_nested {
	quote! {
	#crate_prefix #dispatch! { ($($proc_macro)*) }
	}
	} else {
	quote! {
	proc_macro_call!()
	}
	};

	let export_call_site = if args.fake_call_site {
	quote! {
	#[doc(hidden)]
	#vis use proc_macro_hack::fake_call_site as #call_site;
	}
	} else {
	quote!()
	};

	let do_derive = if !args.fake_call_site {
	quote! {
	#[derive(#crate_prefix #actual_name)]
	}
	} else if crate_prefix.is_some() {
	quote! {
	use #crate_prefix #actual_name;
	#[#crate_prefix #call_site ($($proc_macro)*)]
	#[derive(#actual_name)]
	}
	} else {
	quote! {
	#[#call_site ($($proc_macro)*)]
	#[derive(#actual_name)]
	}
	};

	quote! {
	#[doc(hidden)]
	#vis use #from::#actual_name;

	#export_dispatch
	#export_call_site

	#attrs
	#macro_export
	macro_rules! #export_as {
	($($proc_macro:tt)*) => {{
	#do_derive
	enum ProcMacroHack {
	#enum_variant = (stringify! { $($proc_macro)* }, 0).1,
	}
	#proc_macro_call
	}};
	}
	}
	})
	.collect();

	wrap_in_enum_hack(dummy, rules)
	}

	fn expand_define(define: Define) -> TokenStream {
	let attrs = define.attrs;
	let name = define.name;
	let dummy = actual_proc_macro_name(&name);
	let body = define.body;

	quote! {
	mod #dummy {
	extern crate proc_macro;
	pub use self::proc_macro::*;
	}

	#attrs
	#[proc_macro_derive(#dummy)]
	pub fn #dummy(input: #dummy::TokenStream) -> #dummy::TokenStream {
	use std::iter::FromIterator;

	let mut iter = input.into_iter();
	iter.next().unwrap(); // `enum`
	iter.next().unwrap(); // `ProcMacroHack`

	let mut braces = match iter.next().unwrap() {
	#dummy::TokenTree::Group(group) => group.stream().into_iter(),
	_ => unimplemented!(),
	};
	let variant = braces.next().unwrap(); // `Value` or `Nested`
	let support_nested = variant.to_string() == "Nested";
	braces.next().unwrap(); // `=`

	let mut parens = match braces.next().unwrap() {
	#dummy::TokenTree::Group(group) => group.stream().into_iter(),
	_ => unimplemented!(),
	};
	parens.next().unwrap(); // `stringify`
	parens.next().unwrap(); // `!`

	let inner = match parens.next().unwrap() {
	#dummy::TokenTree::Group(group) => group.stream(),
	_ => unimplemented!(),
	};

	let output: #dummy::TokenStream = #name(inner.clone());

	fn count_bangs(input: #dummy::TokenStream) -> usize {
	let mut count = 0;
	for token in input {
	match token {
	#dummy::TokenTree::Punct(punct) => {
	if punct.as_char() == '!' {
	count += 1;
	}
	}
	#dummy::TokenTree::Group(group) => {
	count += count_bangs(group.stream());
	}
	_ => {}
	}
	}
	count
	}

	// macro_rules! proc_macro_call {
	// () => { #output }
	// }
	#dummy::TokenStream::from_iter(vec![
	#dummy::TokenTree::Ident(
	#dummy::Ident::new("macro_rules", #dummy::Span::call_site()),
	),
	#dummy::TokenTree::Punct(
	#dummy::Punct::new('!', #dummy::Spacing::Alone),
	),
	#dummy::TokenTree::Ident(
	#dummy::Ident::new(
	&if support_nested {
	format!("proc_macro_call_{}", count_bangs(inner))
	} else {
	String::from("proc_macro_call")
	},
	#dummy::Span::call_site(),
	),
	),
	#dummy::TokenTree::Group(
	#dummy::Group::new(#dummy::Delimiter::Brace, #dummy::TokenStream::from_iter(vec![
	#dummy::TokenTree::Group(
	#dummy::Group::new(#dummy::Delimiter::Parenthesis, #dummy::TokenStream::new()),
	),
	#dummy::TokenTree::Punct(
	#dummy::Punct::new('=', #dummy::Spacing::Joint),
	),
	#dummy::TokenTree::Punct(
	#dummy::Punct::new('>', #dummy::Spacing::Alone),
	),
	#dummy::TokenTree::Group(
	#dummy::Group::new(#dummy::Delimiter::Brace, output),
	),
	])),
	),
	])
	}

	fn #name #body
	}
	}

	fn actual_proc_macro_name(conceptual: &Ident) -> Ident {
	let actual_name = format!("proc_macro_hack_{}", conceptual);
	Ident::new(&actual_name, Span::call_site())
	}

	fn dispatch_macro_name(conceptual: &Ident) -> Ident {
	let dispatch = format!("proc_macro_call_{}", conceptual);
	Ident::new(&dispatch, Span::call_site())
	}

	fn call_site_macro_name(conceptual: &Ident) -> Ident {
	let dispatch = format!("proc_macro_fake_call_site_{}", conceptual);
	Ident::new(&dispatch, Span::call_site())
	}

	fn dummy_name_for_export(export: &Export) -> String {
	let mut dummy = String::new();
	write!(dummy, "_{}{}", export.from.to_string().len(), export.from).unwrap();
	for m in &export.macros {
	write!(dummy, "_{}{}", m.name.to_string().len(), m.name).unwrap();
	}
	dummy
	}

	fn wrap_in_enum_hack(dummy: String, inner: TokenStream) -> TokenStream {
	let dummy = Ident::new(&dummy, Span::call_site());
	quote! {
	#[derive(proc_macro_hack::ProcMacroHack)]
	enum #dummy {
	Value = (stringify! { #inner }, 0).1,
	}
	}
	}