src/lib.rs - platform/external/rust/crates/proc-macro-hack - Git at Google

 //! [![github]](https://github.com/dtolnay/proc-macro-hack)&ensp;[![crates-io]](https://crates.io/crates/proc-macro-hack)&ensp;[![docs-rs]](https://docs.rs/proc-macro-hack)
 //!
 //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
 //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
 //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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
 //!
 //! <br>
 //!
 //! <table><tr><td><hr>
 //! <b>Note:</b> <i>As of Rust 1.45 this crate is superseded by native support
 //! for #[proc_macro] in expression position. Only consider using this crate if
 //! you care about supporting compilers between 1.31 and 1.45.</i>
 //! <hr></td></tr></table>
 //!
 //! Since 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.
 //!
 //! [&raquo; 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.
 //!
 //! [&raquo; 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.
 //!
 //! [&raquo; 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
 //!   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.*
 //!
 //! - On compilers that are new enough to natively support proc macros in
 //!   expression position, proc-macro-hack does not automatically use that
 //!   support, since the hygiene can be subtly different between the two
 //!   implementations. To opt in to compiling your macro to native
 //!   `#[proc_macro]` on sufficiently new compilers, use
 //!   `#[proc_macro_hack(only_hack_old_rustc)]` on the re-export in your
 //!   declaration crate.
 //!
 //! [#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"]
 #![allow(clippy::needless_doctest_main, clippy::toplevel_ref_arg)]

 extern crate proc_macro;

 #[macro_use]
 mod quote;

 mod error;
 mod iter;
 mod parse;

 use crate::error::{compile_error, Error};
 use crate::iter::Iter;
 use crate::parse::{
     parse_define_args, parse_enum_hack, parse_export_args, parse_fake_call_site, parse_input,
 };
 use proc_macro::{Ident, Punct, Spacing, Span, TokenStream, TokenTree};
 use std::fmt::Write;

 type Visibility = Option<Ident>;

 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,
 }

 #[proc_macro_attribute]
 pub fn proc_macro_hack(args: TokenStream, input: TokenStream) -> TokenStream {
     let ref mut args = iter::new(args);
     let ref mut input = iter::new(input);
     expand_proc_macro_hack(args, input).unwrap_or_else(compile_error)
 }

 fn expand_proc_macro_hack(args: Iter, input: Iter) -> Result<TokenStream, Error> {
     match parse_input(input)? {
         Input::Export(export) => {
             let args = parse_export_args(args)?;
             Ok(expand_export(export, args))
         }
         Input::Define(define) => {
             parse_define_args(args)?;
             Ok(expand_define(define))
         }
     }
 }

 #[doc(hidden)]
 #[proc_macro_derive(ProcMacroHack)]
 pub fn enum_hack(input: TokenStream) -> TokenStream {
     let ref mut input = iter::new(input);
     parse_enum_hack(input).unwrap_or_else(compile_error)
 }

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

 #[doc(hidden)]
 #[proc_macro_attribute]
 pub fn fake_call_site(args: TokenStream, input: TokenStream) -> TokenStream {
     let ref mut args = iter::new(args);
     let ref mut input = iter::new(input);
     expand_fake_call_site(args, input).unwrap_or_else(compile_error)
 }

 fn expand_fake_call_site(args: Iter, input: Iter) -> Result<TokenStream, Error> {
     let span = match args.next() {
         Some(token) => token.span(),
         None => return Ok(input.collect()),
     };

     let input = parse_fake_call_site(input)?;
     let mut derive = input.derive;
     derive.set_span(span);
     let rest = input.rest;

     Ok(quote! {
         #[derive(#derive)]
         #rest
     })
 }

 struct ExportArgs {
     support_nested: bool,
     internal_macro_calls: u16,
     fake_call_site: bool,
     only_hack_old_rustc: bool,
 }

 fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
     if args.only_hack_old_rustc && cfg!(not(need_proc_macro_hack)) {
         return expand_export_nohack(export);
     }

     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.as_ref().map(|_| quote!($crate::));
     let enum_variant = if args.support_nested {
         if args.internal_macro_calls == 0 {
             Ident::new("Nested", Span::call_site())
         } else {
             let name = format!("Nested{}", args.internal_macro_calls);
             Ident::new(&name, Span::call_site())
         }
     } else {
         Ident::new("Value", Span::call_site())
     };

     let from = export.from;
     let mut actual_names = TokenStream::new();
     let mut export_dispatch = TokenStream::new();
     let mut export_call_site = TokenStream::new();
     let mut macro_rules = TokenStream::new();
     for Macro { name, export_as } in &export.macros {
         let hacked = hacked_proc_macro_name(&name);
         let dispatch = dispatch_macro_name(&name);
         let call_site = call_site_macro_name(&name);

         if !actual_names.is_empty() {
             actual_names.extend(quote!(,));
         }
         actual_names.extend(quote!(#hacked));

         if !export_dispatch.is_empty() {
             export_dispatch.extend(quote!(,));
         }
         export_dispatch.extend(quote!(dispatch as #dispatch));

         if !export_call_site.is_empty() {
             export_call_site.extend(quote!(,));
         }
         export_call_site.extend(quote!(fake_call_site as #call_site));

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

         let proc_macro_call = if args.support_nested {
             let extra_bangs = (0..args.internal_macro_calls)
                 .map(|_| TokenTree::Punct(Punct::new('!', Spacing::Alone)))
                 .collect::<TokenStream>();
             quote! {
                 #crate_prefix #dispatch! { ($($proc_macro)*) #extra_bangs }
             }
         } else {
             quote! {
                 proc_macro_call!()
             }
         };

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

     if export.macros.len() != 1 {
         export_dispatch = quote!({#export_dispatch});
         export_call_site = quote!({#export_call_site});
         actual_names = quote!({#actual_names});
     }

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

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

     let expanded = quote! {
         #[doc(hidden)]
         #vis use #from::#actual_names;

         #export_dispatch
         #export_call_site

         #macro_rules
     };

     wrap_in_enum_hack(dummy, expanded)
 }

 fn expand_export_nohack(export: Export) -> TokenStream {
     let attrs = export.attrs;
     let vis = export.vis;
     let from = export.from;
     let mut names = TokenStream::new();

     for Macro { name, export_as } in &export.macros {
         let pub_name = pub_proc_macro_name(&name);
         if !names.is_empty() {
             names.extend(quote!(,));
         }
         names.extend(quote!(#pub_name as #export_as));
     }

     if export.macros.len() != 1 {
         names = quote!({#names});
     }

     quote! {
         #attrs
         #vis use #from::#names;
     }
 }

 fn expand_define(define: Define) -> TokenStream {
     let attrs = define.attrs;
     let name = define.name;
     let pub_name = pub_proc_macro_name(&name);
     let hacked = hacked_proc_macro_name(&name);
     let body = define.body;

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

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

             let mut iter = input.into_iter();
             iter.next().unwrap(); // `enum`
             iter.next().unwrap(); // `ProcMacroHack`
             iter.next().unwrap(); // `#`
             iter.next().unwrap(); // `[allow(dead_code)]`

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

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

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

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

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

             // macro_rules! proc_macro_call {
             //     () => { #output }
             // }
             #pub_name::TokenStream::from_iter(vec![
                 #pub_name::TokenTree::Ident(
                     #pub_name::Ident::new("macro_rules", #pub_name::Span::call_site()),
                 ),
                 #pub_name::TokenTree::Punct(
                     #pub_name::Punct::new('!', #pub_name::Spacing::Alone),
                 ),
                 #pub_name::TokenTree::Ident(
                     #pub_name::Ident::new(
                         &if support_nested {
                             let extra_bangs = if varname == "Nested" {
                                 0
                             } else {
                                 varname["Nested".len()..].parse().unwrap()
                             };
                             format!("proc_macro_call_{}", extra_bangs + count_bangs(inner))
                         } else {
                             String::from("proc_macro_call")
                         },
                         #pub_name::Span::call_site(),
                     ),
                 ),
                 #pub_name::TokenTree::Group(
                     #pub_name::Group::new(#pub_name::Delimiter::Brace, #pub_name::TokenStream::from_iter(vec![
                         #pub_name::TokenTree::Group(
                             #pub_name::Group::new(#pub_name::Delimiter::Parenthesis, #pub_name::TokenStream::new()),
                         ),
                         #pub_name::TokenTree::Punct(
                             #pub_name::Punct::new('=', #pub_name::Spacing::Joint),
                         ),
                         #pub_name::TokenTree::Punct(
                             #pub_name::Punct::new('>', #pub_name::Spacing::Alone),
                         ),
                         #pub_name::TokenTree::Group(
                             #pub_name::Group::new(#pub_name::Delimiter::Brace, output),
                         ),
                     ])),
                 ),
             ])
         }

         #attrs
         #[proc_macro]
         pub fn #pub_name(input: #pub_name::TokenStream) -> #pub_name::TokenStream {
             #name(input)
         }

         fn #name #body
     }
 }

 fn pub_proc_macro_name(conceptual: &Ident) -> Ident {
     Ident::new(
         &format!("proc_macro_hack_{}", conceptual),
         conceptual.span(),
     )
 }

 fn hacked_proc_macro_name(conceptual: &Ident) -> Ident {
     Ident::new(
         &format!("_proc_macro_hack_{}", conceptual),
         conceptual.span(),
     )
 }

 fn dispatch_macro_name(conceptual: &Ident) -> Ident {
     Ident::new(
         &format!("proc_macro_call_{}", conceptual),
         conceptual.span(),
     )
 }

 fn call_site_macro_name(conceptual: &Ident) -> Ident {
     Ident::new(
         &format!("proc_macro_fake_call_site_{}", conceptual),
         conceptual.span(),
     )
 }

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

 fn unraw(ident: &Ident) -> Ident {
     let string = ident.to_string();
     if string.starts_with("r#") {
         Ident::new(&string[2..], ident.span())
     } else {
         ident.clone()
     }
 }

 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,
         }
     }
 }
	//! [![github]](https://github.com/dtolnay/proc-macro-hack)&ensp;[![crates-io]](https://crates.io/crates/proc-macro-hack)&ensp;[![docs-rs]](https://docs.rs/proc-macro-hack)
	//!
	//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
	//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
	//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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
	//!
	//! <br>
	//!
	//! <table><tr><td><hr>
	//! <b>Note:</b> <i>As of Rust 1.45 this crate is superseded by native support
	//! for #[proc_macro] in expression position. Only consider using this crate if
	//! you care about supporting compilers between 1.31 and 1.45.</i>
	//! <hr></td></tr></table>
	//!
	//! Since 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
	//! 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.
	//!
	//! - On compilers that are new enough to natively support proc macros in
	//! expression position, proc-macro-hack does not automatically use that
	//! support, since the hygiene can be subtly different between the two
	//! implementations. To opt in to compiling your macro to native
	//! `#[proc_macro]` on sufficiently new compilers, use
	//! `#[proc_macro_hack(only_hack_old_rustc)]` on the re-export in your
	//! declaration crate.
	//!
	//! [#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"]
	#![allow(clippy::needless_doctest_main, clippy::toplevel_ref_arg)]

	extern crate proc_macro;

	#[macro_use]
	mod quote;

	mod error;
	mod iter;
	mod parse;

	use crate::error::{compile_error, Error};
	use crate::iter::Iter;
	use crate::parse::{
	parse_define_args, parse_enum_hack, parse_export_args, parse_fake_call_site, parse_input,
	};
	use proc_macro::{Ident, Punct, Spacing, Span, TokenStream, TokenTree};
	use std::fmt::Write;

	type Visibility = Option<Ident>;

	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,
	}

	#[proc_macro_attribute]
	pub fn proc_macro_hack(args: TokenStream, input: TokenStream) -> TokenStream {
	let ref mut args = iter::new(args);
	let ref mut input = iter::new(input);
	expand_proc_macro_hack(args, input).unwrap_or_else(compile_error)
	}

	fn expand_proc_macro_hack(args: Iter, input: Iter) -> Result<TokenStream, Error> {
	match parse_input(input)? {
	Input::Export(export) => {
	let args = parse_export_args(args)?;
	Ok(expand_export(export, args))
	}
	Input::Define(define) => {
	parse_define_args(args)?;
	Ok(expand_define(define))
	}
	}
	}

	#[doc(hidden)]
	#[proc_macro_derive(ProcMacroHack)]
	pub fn enum_hack(input: TokenStream) -> TokenStream {
	let ref mut input = iter::new(input);
	parse_enum_hack(input).unwrap_or_else(compile_error)
	}

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

	#[doc(hidden)]
	#[proc_macro_attribute]
	pub fn fake_call_site(args: TokenStream, input: TokenStream) -> TokenStream {
	let ref mut args = iter::new(args);
	let ref mut input = iter::new(input);
	expand_fake_call_site(args, input).unwrap_or_else(compile_error)
	}

	fn expand_fake_call_site(args: Iter, input: Iter) -> Result<TokenStream, Error> {
	let span = match args.next() {
	Some(token) => token.span(),
	None => return Ok(input.collect()),
	};

	let input = parse_fake_call_site(input)?;
	let mut derive = input.derive;
	derive.set_span(span);
	let rest = input.rest;

	Ok(quote! {
	#[derive(#derive)]
	#rest
	})
	}

	struct ExportArgs {
	support_nested: bool,
	internal_macro_calls: u16,
	fake_call_site: bool,
	only_hack_old_rustc: bool,
	}

	fn expand_export(export: Export, args: ExportArgs) -> TokenStream {
	if args.only_hack_old_rustc && cfg!(not(need_proc_macro_hack)) {
	return expand_export_nohack(export);
	}

	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.as_ref().map(\|_\| quote!($crate::));
	let enum_variant = if args.support_nested {
	if args.internal_macro_calls == 0 {
	Ident::new("Nested", Span::call_site())
	} else {
	let name = format!("Nested{}", args.internal_macro_calls);
	Ident::new(&name, Span::call_site())
	}
	} else {
	Ident::new("Value", Span::call_site())
	};

	let from = export.from;
	let mut actual_names = TokenStream::new();
	let mut export_dispatch = TokenStream::new();
	let mut export_call_site = TokenStream::new();
	let mut macro_rules = TokenStream::new();
	for Macro { name, export_as } in &export.macros {
	let hacked = hacked_proc_macro_name(&name);
	let dispatch = dispatch_macro_name(&name);
	let call_site = call_site_macro_name(&name);

	if !actual_names.is_empty() {
	actual_names.extend(quote!(,));
	}
	actual_names.extend(quote!(#hacked));

	if !export_dispatch.is_empty() {
	export_dispatch.extend(quote!(,));
	}
	export_dispatch.extend(quote!(dispatch as #dispatch));

	if !export_call_site.is_empty() {
	export_call_site.extend(quote!(,));
	}
	export_call_site.extend(quote!(fake_call_site as #call_site));

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

	let proc_macro_call = if args.support_nested {
	let extra_bangs = (0..args.internal_macro_calls)
	.map(\|_\| TokenTree::Punct(Punct::new('!', Spacing::Alone)))
	.collect::<TokenStream>();
	quote! {
	#crate_prefix #dispatch! { ($($proc_macro)*) #extra_bangs }
	}
	} else {
	quote! {
	proc_macro_call!()
	}
	};

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

	if export.macros.len() != 1 {
	export_dispatch = quote!({#export_dispatch});
	export_call_site = quote!({#export_call_site});
	actual_names = quote!({#actual_names});
	}

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

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

	let expanded = quote! {
	#[doc(hidden)]
	#vis use #from::#actual_names;

	#export_dispatch
	#export_call_site

	#macro_rules
	};

	wrap_in_enum_hack(dummy, expanded)
	}

	fn expand_export_nohack(export: Export) -> TokenStream {
	let attrs = export.attrs;
	let vis = export.vis;
	let from = export.from;
	let mut names = TokenStream::new();

	for Macro { name, export_as } in &export.macros {
	let pub_name = pub_proc_macro_name(&name);
	if !names.is_empty() {
	names.extend(quote!(,));
	}
	names.extend(quote!(#pub_name as #export_as));
	}

	if export.macros.len() != 1 {
	names = quote!({#names});
	}

	quote! {
	#attrs
	#vis use #from::#names;
	}
	}

	fn expand_define(define: Define) -> TokenStream {
	let attrs = define.attrs;
	let name = define.name;
	let pub_name = pub_proc_macro_name(&name);
	let hacked = hacked_proc_macro_name(&name);
	let body = define.body;

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

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

	let mut iter = input.into_iter();
	iter.next().unwrap(); // `enum`
	iter.next().unwrap(); // `ProcMacroHack`
	iter.next().unwrap(); // `#`
	iter.next().unwrap(); // `[allow(dead_code)]`

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

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

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

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

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

	// macro_rules! proc_macro_call {
	// () => { #output }
	// }
	#pub_name::TokenStream::from_iter(vec![
	#pub_name::TokenTree::Ident(
	#pub_name::Ident::new("macro_rules", #pub_name::Span::call_site()),
	),
	#pub_name::TokenTree::Punct(
	#pub_name::Punct::new('!', #pub_name::Spacing::Alone),
	),
	#pub_name::TokenTree::Ident(
	#pub_name::Ident::new(
	&if support_nested {
	let extra_bangs = if varname == "Nested" {
	0
	} else {
	varname["Nested".len()..].parse().unwrap()
	};
	format!("proc_macro_call_{}", extra_bangs + count_bangs(inner))
	} else {
	String::from("proc_macro_call")
	},
	#pub_name::Span::call_site(),
	),
	),
	#pub_name::TokenTree::Group(
	#pub_name::Group::new(#pub_name::Delimiter::Brace, #pub_name::TokenStream::from_iter(vec![
	#pub_name::TokenTree::Group(
	#pub_name::Group::new(#pub_name::Delimiter::Parenthesis, #pub_name::TokenStream::new()),
	),
	#pub_name::TokenTree::Punct(
	#pub_name::Punct::new('=', #pub_name::Spacing::Joint),
	),
	#pub_name::TokenTree::Punct(
	#pub_name::Punct::new('>', #pub_name::Spacing::Alone),
	),
	#pub_name::TokenTree::Group(
	#pub_name::Group::new(#pub_name::Delimiter::Brace, output),
	),
	])),
	),
	])
	}

	#attrs
	#[proc_macro]
	pub fn #pub_name(input: #pub_name::TokenStream) -> #pub_name::TokenStream {
	#name(input)
	}

	fn #name #body
	}
	}

	fn pub_proc_macro_name(conceptual: &Ident) -> Ident {
	Ident::new(
	&format!("proc_macro_hack_{}", conceptual),
	conceptual.span(),
	)
	}

	fn hacked_proc_macro_name(conceptual: &Ident) -> Ident {
	Ident::new(
	&format!("_proc_macro_hack_{}", conceptual),
	conceptual.span(),
	)
	}

	fn dispatch_macro_name(conceptual: &Ident) -> Ident {
	Ident::new(
	&format!("proc_macro_call_{}", conceptual),
	conceptual.span(),
	)
	}

	fn call_site_macro_name(conceptual: &Ident) -> Ident {
	Ident::new(
	&format!("proc_macro_fake_call_site_{}", conceptual),
	conceptual.span(),
	)
	}

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

	fn unraw(ident: &Ident) -> Ident {
	let string = ident.to_string();
	if string.starts_with("r#") {
	Ident::new(&string[2..], ident.span())
	} else {
	ident.clone()
	}
	}

	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,
	}
	}
	}