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    // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! A support library for macro authors when defining new macros.
    //!
    //! This library, provided by the standard distribution, provides the types
    //! consumed in the interfaces of procedurally defined macro definitions.
    //! Currently the primary use of this crate is to provide the ability to define
    //! new custom derive modes through `#[proc_macro_derive]`.
    //!
    //! Note that this crate is intentionally very bare-bones currently. The main
    //! type, `TokenStream`, only supports `fmt::Display` and `FromStr`
    //! implementations, indicating that it can only go to and come from a string.
    //! This functionality is intended to be expanded over time as more surface
    //! area for macro authors is stabilized.
    //!
    //! See [the book](../book/procedural-macros.html) for more.

    #![crate_name = "proc_macro"]
    #![stable(feature = "proc_macro_lib", since = "1.15.0")]
    #![crate_type = "rlib"]
    #![crate_type = "dylib"]
    #![deny(warnings)]
    #![deny(missing_docs)]
    #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
           html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
           html_root_url = "https://doc.rust-lang.org/nightly/",
           html_playground_url = "https://play.rust-lang.org/",
           issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
           test(no_crate_inject, attr(deny(warnings))),
           test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]

    #![feature(rustc_private)]
    #![feature(staged_api)]
    #![feature(lang_items)]

    extern crate syntax;

    use std::fmt;
    use std::str::FromStr;

    use syntax::errors::DiagnosticBuilder;
    use syntax::parse;
    use syntax::tokenstream::TokenStream as TokenStream_;

    /// The main type provided by this crate, representing an abstract stream of
    /// tokens.
    ///
    /// This is both the input and output of `#[proc_macro_derive]` definitions.
    /// Currently it's required to be a list of valid Rust items, but this
    /// restriction may be lifted in the future.
    ///
    /// The API of this type is intentionally bare-bones, but it'll be expanded over
    /// time!
    #[stable(feature = "proc_macro_lib", since = "1.15.0")]
    pub struct TokenStream {
        inner: TokenStream_,
    }

    /// Error returned from `TokenStream::from_str`.
    #[derive(Debug)]
    #[stable(feature = "proc_macro_lib", since = "1.15.0")]
    pub struct LexError {
        _inner: (),
    }

    /// Permanently unstable internal implementation details of this crate. This
    /// should not be used.
    ///
    /// These methods are used by the rest of the compiler to generate instances of
    /// `TokenStream` to hand to macro definitions, as well as consume the output.
    ///
    /// Note that this module is also intentionally separate from the rest of the
    /// crate. This allows the `#[unstable]` directive below to naturally apply to
    /// all of the contents.
    #[unstable(feature = "proc_macro_internals", issue = "27812")]
    #[doc(hidden)]
    pub mod __internal {
        use std::cell::Cell;
        use std::rc::Rc;

        use syntax::ast;
        use syntax::ptr::P;
        use syntax::parse::{self, token, ParseSess};
        use syntax::tokenstream::{TokenTree, TokenStream as TokenStream_};

        use super::{TokenStream, LexError};

        pub fn new_token_stream(item: P<ast::Item>) -> TokenStream {
            TokenStream {
                inner: TokenTree::Token(item.span, token::Interpolated(Rc::new(token::NtItem(item))))
                    .into()
            }
        }

        pub fn token_stream_wrap(inner: TokenStream_) -> TokenStream {
            TokenStream {
                inner: inner
            }
        }

        pub fn token_stream_parse_items(stream: TokenStream) -> Result<Vec<P<ast::Item>>, LexError> {
            with_parse_sess(move |sess| {
                let mut parser = parse::stream_to_parser(sess, stream.inner);
                let mut items = Vec::new();

                while let Some(item) = try!(parser.parse_item().map_err(super::parse_to_lex_err)) {
                    items.push(item)
                }

                Ok(items)
            })
        }

        pub fn token_stream_inner(stream: TokenStream) -> TokenStream_ {
            stream.inner
        }

        pub trait Registry {
            fn register_custom_derive(&mut self,
                                      trait_name: &str,
                                      expand: fn(TokenStream) -> TokenStream,
                                      attributes: &[&'static str]);

            fn register_attr_proc_macro(&mut self,
                                        name: &str,
                                        expand: fn(TokenStream, TokenStream) -> TokenStream);

            fn register_bang_proc_macro(&mut self,
                                        name: &str,
                                        expand: fn(TokenStream) -> TokenStream);
        }

        // Emulate scoped_thread_local!() here essentially
        thread_local! {
            static CURRENT_SESS: Cell<*const ParseSess> = Cell::new(0 as *const _);
        }

        pub fn set_parse_sess<F, R>(sess: &ParseSess, f: F) -> R
            where F: FnOnce() -> R
        {
            struct Reset { prev: *const ParseSess }

            impl Drop for Reset {
                fn drop(&mut self) {
                    CURRENT_SESS.with(|p| p.set(self.prev));
                }
            }

            CURRENT_SESS.with(|p| {
                let _reset = Reset { prev: p.get() };
                p.set(sess);
                f()
            })
        }

        pub fn with_parse_sess<F, R>(f: F) -> R
            where F: FnOnce(&ParseSess) -> R
        {
            let p = CURRENT_SESS.with(|p| p.get());
            assert!(!p.is_null(), "proc_macro::__internal::with_parse_sess() called \
                                   before set_parse_sess()!");
            f(unsafe { &*p })
        }
    }

    fn parse_to_lex_err(mut err: DiagnosticBuilder) -> LexError {
        err.cancel();
        LexError { _inner: () }
    }

    #[stable(feature = "proc_macro_lib", since = "1.15.0")]
    impl FromStr for TokenStream {
        type Err = LexError;

        fn from_str(src: &str) -> Result<TokenStream, LexError> {
            __internal::with_parse_sess(|sess| {
                let src = src.to_string();
                let name = "<proc-macro source code>".to_string();
                let stream = parse::parse_stream_from_source_str(name, src, sess);
                Ok(__internal::token_stream_wrap(stream))
            })
        }
    }

    #[stable(feature = "proc_macro_lib", since = "1.15.0")]
    impl fmt::Display for TokenStream {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            self.inner.fmt(f)
        }
    }

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