lib.rs.html -- source
Description: Source to the Rust file `src/libproc_macro/lib.rs`.
Keywords: rust, rustlang, rust-lang

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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/first-edition/procedural-macros.html) for more.

    #![stable(feature = "proc_macro_lib", since = "1.15.0")]
    #![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(i128_type)]
    #![feature(rustc_private)]
    #![feature(staged_api)]
    #![feature(lang_items)]

    #[macro_use]
    extern crate syntax;
    extern crate syntax_pos;

    use std::{ascii, fmt, iter};
    use std::str::FromStr;

    use syntax::ast;
    use syntax::errors::DiagnosticBuilder;
    use syntax::parse::{self, token, parse_stream_from_source_str};
    use syntax::print::pprust;
    use syntax::symbol::Symbol;
    use syntax::tokenstream;
    use syntax_pos::DUMMY_SP;
    use syntax_pos::SyntaxContext;
    use syntax_pos::hygiene::Mark;

    /// 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")]
    #[derive(Clone, Debug)]
    pub struct TokenStream(tokenstream::TokenStream);

    /// Error returned from `TokenStream::from_str`.
    #[stable(feature = "proc_macro_lib", since = "1.15.0")]
    #[derive(Debug)]
    pub struct 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_sess(|(sess, mark)| {
                let src = src.to_string();
                let name = "<proc-macro source code>".to_string();
                let expn_info = mark.expn_info().unwrap();
                let call_site = expn_info.call_site;
                // notify the expansion info that it is unhygienic
                let mark = Mark::fresh(mark);
                mark.set_expn_info(expn_info);
                let span = syntax_pos::Span {
                    ctxt: SyntaxContext::empty().apply_mark(mark),
                    ..call_site
                };
                let stream = parse::parse_stream_from_source_str(name, src, sess, Some(span));
                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.0.fmt(f)
        }
    }

    /// `quote!(..)` accepts arbitrary tokens and expands into a `TokenStream` describing the input.
    /// For example, `quote!(a + b)` will produce a expression, that, when evaluated, constructs
    /// the `TokenStream` `[Word("a"), Op('+', Alone), Word("b")]`.
    ///
    /// Unquoting is done with `$`, and works by taking the single next ident as the unquoted term.
    /// To quote `$` itself, use `$$`.
    #[unstable(feature = "proc_macro", issue = "38356")]
    #[macro_export]
    macro_rules! quote { () => {} }

    #[unstable(feature = "proc_macro_internals", issue = "27812")]
    #[doc(hidden)]
    mod quote;

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl From<TokenTree> for TokenStream {
        fn from(tree: TokenTree) -> TokenStream {
            TokenStream(tree.to_internal())
        }
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl From<TokenNode> for TokenStream {
        fn from(kind: TokenNode) -> TokenStream {
            TokenTree::from(kind).into()
        }
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl<T: Into<TokenStream>> iter::FromIterator<T> for TokenStream {
        fn from_iter<I: IntoIterator<Item = T>>(streams: I) -> Self {
            let mut builder = tokenstream::TokenStreamBuilder::new();
            for stream in streams {
                builder.push(stream.into().0);
            }
            TokenStream(builder.build())
        }
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl IntoIterator for TokenStream {
        type Item = TokenTree;
        type IntoIter = TokenTreeIter;

        fn into_iter(self) -> TokenTreeIter {
            TokenTreeIter { cursor: self.0.trees(), next: None }
        }
    }

    impl TokenStream {
        /// Returns an empty `TokenStream`.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn empty() -> TokenStream {
            TokenStream(tokenstream::TokenStream::empty())
        }

        /// Checks if this `TokenStream` is empty.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn is_empty(&self) -> bool {
            self.0.is_empty()
        }
    }

    /// A region of source code, along with macro expansion information.
    #[unstable(feature = "proc_macro", issue = "38356")]
    #[derive(Copy, Clone, Debug)]
    pub struct Span(syntax_pos::Span);

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl Default for Span {
        fn default() -> Span {
            ::__internal::with_sess(|(_, mark)| Span(syntax_pos::Span {
                ctxt: SyntaxContext::empty().apply_mark(mark),
                ..mark.expn_info().unwrap().call_site
            }))
        }
    }

    /// Quote a `Span` into a `TokenStream`.
    /// This is needed to implement a custom quoter.
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub fn quote_span(span: Span) -> TokenStream {
        TokenStream(quote::Quote::quote(&span.0))
    }

    impl Span {
        /// The span of the invocation of the current procedural macro.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn call_site() -> Span {
            ::__internal::with_sess(|(_, mark)| Span(mark.expn_info().unwrap().call_site))
        }
    }

    /// A single token or a delimited sequence of token trees (e.g. `[1, (), ..]`).
    #[unstable(feature = "proc_macro", issue = "38356")]
    #[derive(Clone, Debug)]
    pub struct TokenTree {
        /// The `TokenTree`'s span
        pub span: Span,
        /// Description of the `TokenTree`
        pub kind: TokenNode,
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl From<TokenNode> for TokenTree {
        fn from(kind: TokenNode) -> TokenTree {
            TokenTree { span: Span::default(), kind: kind }
        }
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl fmt::Display for TokenTree {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            TokenStream::from(self.clone()).fmt(f)
        }
    }

    /// Description of a `TokenTree`
    #[derive(Clone, Debug)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub enum TokenNode {
        /// A delimited tokenstream.
        Group(Delimiter, TokenStream),
        /// A unicode identifier.
        Term(Term),
        /// A punctuation character (`+`, `,`, `$`, etc.).
        Op(char, Spacing),
        /// A literal character (`'a'`), string (`"hello"`), or number (`2.3`).
        Literal(Literal),
    }

    /// Describes how a sequence of token trees is delimited.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub enum Delimiter {
        /// `( ... )`
        Parenthesis,
        /// `{ ... }`
        Brace,
        /// `[ ... ]`
        Bracket,
        /// An implicit delimiter, e.g. `$var`, where $var is  `...`.
        None,
    }

    /// An interned string.
    #[derive(Copy, Clone, Debug)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub struct Term(Symbol);

    impl Term {
        /// Intern a string into a `Term`.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn intern(string: &str) -> Term {
            Term(Symbol::intern(string))
        }

        /// Get a reference to the interned string.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn as_str(&self) -> &str {
            unsafe { &*(&*self.0.as_str() as *const str) }
        }
    }

    /// Whether an `Op` is either followed immediately by another `Op` or followed by whitespace.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub enum Spacing {
        /// e.g. `+` is `Alone` in `+ =`.
        Alone,
        /// e.g. `+` is `Joint` in `+=`.
        Joint,
    }

    /// A literal character (`'a'`), string (`"hello"`), or number (`2.3`).
    #[derive(Clone, Debug)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub struct Literal(token::Token);

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl fmt::Display for Literal {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            TokenTree { kind: TokenNode::Literal(self.clone()), span: Span(DUMMY_SP) }.fmt(f)
        }
    }

    macro_rules! int_literals {
        ($($int_kind:ident),*) => {$(
            /// Integer literal.
            #[unstable(feature = "proc_macro", issue = "38356")]
            pub fn $int_kind(n: $int_kind) -> Literal {
                Literal::typed_integer(n as i128, stringify!($int_kind))
            }
        )*}
    }

    impl Literal {
        /// Integer literal
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn integer(n: i128) -> Literal {
            Literal(token::Literal(token::Lit::Integer(Symbol::intern(&n.to_string())), None))
        }

        int_literals!(u8, i8, u16, i16, u32, i32, u64, i64, usize, isize);
        fn typed_integer(n: i128, kind: &'static str) -> Literal {
            Literal(token::Literal(token::Lit::Integer(Symbol::intern(&n.to_string())),
                                   Some(Symbol::intern(kind))))
        }

        /// Floating point literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn float(n: f64) -> Literal {
            if !n.is_finite() {
                panic!("Invalid float literal {}", n);
            }
            Literal(token::Literal(token::Lit::Float(Symbol::intern(&n.to_string())), None))
        }

        /// Floating point literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn f32(n: f32) -> Literal {
            if !n.is_finite() {
                panic!("Invalid f32 literal {}", n);
            }
            Literal(token::Literal(token::Lit::Float(Symbol::intern(&n.to_string())),
                                   Some(Symbol::intern("f32"))))
        }

        /// Floating point literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn f64(n: f64) -> Literal {
            if !n.is_finite() {
                panic!("Invalid f64 literal {}", n);
            }
            Literal(token::Literal(token::Lit::Float(Symbol::intern(&n.to_string())),
                                   Some(Symbol::intern("f64"))))
        }

        /// String literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn string(string: &str) -> Literal {
            let mut escaped = String::new();
            for ch in string.chars() {
                escaped.extend(ch.escape_unicode());
            }
            Literal(token::Literal(token::Lit::Str_(Symbol::intern(&escaped)), None))
        }

        /// Character literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn character(ch: char) -> Literal {
            let mut escaped = String::new();
            escaped.extend(ch.escape_unicode());
            Literal(token::Literal(token::Lit::Char(Symbol::intern(&escaped)), None))
        }

        /// Byte string literal.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn byte_string(bytes: &[u8]) -> Literal {
            let string = bytes.iter().cloned().flat_map(ascii::escape_default)
                .map(Into::<char>::into).collect::<String>();
            Literal(token::Literal(token::Lit::ByteStr(Symbol::intern(&string)), None))
        }
    }

    /// An iterator over `TokenTree`s.
    #[derive(Clone)]
    #[unstable(feature = "proc_macro", issue = "38356")]
    pub struct TokenTreeIter {
        cursor: tokenstream::Cursor,
        next: Option<tokenstream::TokenStream>,
    }

    #[unstable(feature = "proc_macro", issue = "38356")]
    impl Iterator for TokenTreeIter {
        type Item = TokenTree;

        fn next(&mut self) -> Option<TokenTree> {
            loop {
                let next =
                    unwrap_or!(self.next.take().or_else(|| self.cursor.next_as_stream()), return None);
                let tree = TokenTree::from_internal(next, &mut self.next);
                if tree.span.0 == DUMMY_SP {
                    if let TokenNode::Group(Delimiter::None, stream) = tree.kind {
                        self.cursor.insert(stream.0);
                        continue
                    }
                }
                return Some(tree);
            }
        }
    }

    impl Delimiter {
        fn from_internal(delim: token::DelimToken) -> Delimiter {
            match delim {
                token::Paren => Delimiter::Parenthesis,
                token::Brace => Delimiter::Brace,
                token::Bracket => Delimiter::Bracket,
                token::NoDelim => Delimiter::None,
            }
        }

        fn to_internal(self) -> token::DelimToken {
            match self {
                Delimiter::Parenthesis => token::Paren,
                Delimiter::Brace => token::Brace,
                Delimiter::Bracket => token::Bracket,
                Delimiter::None => token::NoDelim,
            }
        }
    }

    impl TokenTree {
        fn from_internal(stream: tokenstream::TokenStream, next: &mut Option<tokenstream::TokenStream>)
                    -> TokenTree {
            use syntax::parse::token::*;

            let (tree, is_joint) = stream.as_tree();
            let (mut span, token) = match tree {
                tokenstream::TokenTree::Token(span, token) => (span, token),
                tokenstream::TokenTree::Delimited(span, delimed) => {
                    let delimiter = Delimiter::from_internal(delimed.delim);
                    return TokenTree {
                        span: Span(span),
                        kind: TokenNode::Group(delimiter, TokenStream(delimed.tts.into())),
                    };
                }
            };

            let op_kind = if is_joint { Spacing::Joint } else { Spacing::Alone };
            macro_rules! op {
                ($op:expr) => { TokenNode::Op($op, op_kind) }
            }

            macro_rules! joint {
                ($first:expr, $rest:expr) => { joint($first, $rest, is_joint, &mut span, next) }
            }

            fn joint(first: char, rest: Token, is_joint: bool, span: &mut syntax_pos::Span,
                     next: &mut Option<tokenstream::TokenStream>)
                     -> TokenNode {
                let (first_span, rest_span) = (*span, *span);
                *span = first_span;
                let tree = tokenstream::TokenTree::Token(rest_span, rest);
                *next = Some(if is_joint { tree.joint() } else { tree.into() });
                TokenNode::Op(first, Spacing::Joint)
            }

            let kind = match token {
                Eq => op!('='),
                Lt => op!('<'),
                Le => joint!('<', Eq),
                EqEq => joint!('=', Eq),
                Ne => joint!('!', Eq),
                Ge => joint!('>', Eq),
                Gt => op!('>'),
                AndAnd => joint!('&', BinOp(And)),
                OrOr => joint!('|', BinOp(Or)),
                Not => op!('!'),
                Tilde => op!('~'),
                BinOp(Plus) => op!('+'),
                BinOp(Minus) => op!('-'),
                BinOp(Star) => op!('*'),
                BinOp(Slash) => op!('/'),
                BinOp(Percent) => op!('%'),
                BinOp(Caret) => op!('^'),
                BinOp(And) => op!('&'),
                BinOp(Or) => op!('|'),
                BinOp(Shl) => joint!('<', Lt),
                BinOp(Shr) => joint!('>', Gt),
                BinOpEq(Plus) => joint!('+', Eq),
                BinOpEq(Minus) => joint!('-', Eq),
                BinOpEq(Star) => joint!('*', Eq),
                BinOpEq(Slash) => joint!('/', Eq),
                BinOpEq(Percent) => joint!('%', Eq),
                BinOpEq(Caret) => joint!('^', Eq),
                BinOpEq(And) => joint!('&', Eq),
                BinOpEq(Or) => joint!('|', Eq),
                BinOpEq(Shl) => joint!('<', Le),
                BinOpEq(Shr) => joint!('>', Ge),
                At => op!('@'),
                Dot => op!('.'),
                DotDot => joint!('.', Dot),
                DotDotDot => joint!('.', DotDot),
                Comma => op!(','),
                Semi => op!(';'),
                Colon => op!(':'),
                ModSep => joint!(':', Colon),
                RArrow => joint!('-', Gt),
                LArrow => joint!('<', BinOp(Minus)),
                FatArrow => joint!('=', Gt),
                Pound => op!('#'),
                Dollar => op!('$'),
                Question => op!('?'),
                Underscore => op!('_'),

                Ident(ident) | Lifetime(ident) => TokenNode::Term(Term(ident.name)),
                Literal(..) | DocComment(..) => TokenNode::Literal(self::Literal(token)),

                Interpolated(ref nt) => {
                    // An `Interpolated` token means that we have a `Nonterminal`
                    // which is often a parsed AST item. At this point we now need
                    // to convert the parsed AST to an actual token stream, e.g.
                    // un-parse it basically.
                    //
                    // Unfortunately there's not really a great way to do that in a
                    // guaranteed lossless fashion right now. The fallback here is
                    // to just stringify the AST node and reparse it, but this loses
                    // all span information.
                    //
                    // As a result, some AST nodes are annotated with the token
                    // stream they came from. Attempt to extract these lossless
                    // token streams before we fall back to the stringification.
                    let mut tokens = None;

                    match nt.0 {
                        Nonterminal::NtItem(ref item) => {
                            tokens = prepend_attrs(&item.attrs, item.tokens.as_ref(), span);
                        }
                        Nonterminal::NtTraitItem(ref item) => {
                            tokens = prepend_attrs(&item.attrs, item.tokens.as_ref(), span);
                        }
                        Nonterminal::NtImplItem(ref item) => {
                            tokens = prepend_attrs(&item.attrs, item.tokens.as_ref(), span);
                        }
                        _ => {}
                    }

                    tokens.map(|tokens| {
                        TokenNode::Group(Delimiter::None,
                                         TokenStream(tokens.clone()))
                    }).unwrap_or_else(|| {
                        __internal::with_sess(|(sess, _)| {
                            TokenNode::Group(Delimiter::None, TokenStream(nt.1.force(|| {
                                // FIXME(jseyfried): Avoid this pretty-print + reparse hack
                                let name = "<macro expansion>".to_owned();
                                let source = pprust::token_to_string(&token);
                                parse_stream_from_source_str(name, source, sess, Some(span))
                            })))
                        })
                    })
                }

                OpenDelim(..) | CloseDelim(..) => unreachable!(),
                Whitespace | Comment | Shebang(..) | Eof => unreachable!(),
            };

            TokenTree { span: Span(span), kind: kind }
        }

        fn to_internal(self) -> tokenstream::TokenStream {
            use syntax::parse::token::*;
            use syntax::tokenstream::{TokenTree, Delimited};

            let (op, kind) = match self.kind {
                TokenNode::Op(op, kind) => (op, kind),
                TokenNode::Group(delimiter, tokens) => {
                    return TokenTree::Delimited(self.span.0, Delimited {
                        delim: delimiter.to_internal(),
                        tts: tokens.0.into(),
                    }).into();
                },
                TokenNode::Term(symbol) => {
                    let ident = ast::Ident { name: symbol.0, ctxt: self.span.0.ctxt };
                    let token =
                        if symbol.0.as_str().starts_with("'") { Lifetime(ident) } else { Ident(ident) };
                    return TokenTree::Token(self.span.0, token).into();
                }
                TokenNode::Literal(token) => return TokenTree::Token(self.span.0, token.0).into(),
            };

            let token = match op {
                '=' => Eq,
                '<' => Lt,
                '>' => Gt,
                '!' => Not,
                '~' => Tilde,
                '+' => BinOp(Plus),
                '-' => BinOp(Minus),
                '*' => BinOp(Star),
                '/' => BinOp(Slash),
                '%' => BinOp(Percent),
                '^' => BinOp(Caret),
                '&' => BinOp(And),
                '|' => BinOp(Or),
                '@' => At,
                '.' => Dot,
                ',' => Comma,
                ';' => Semi,
                ':' => Colon,
                '#' => Pound,
                '$' => Dollar,
                '?' => Question,
                '_' => Underscore,
                _ => panic!("unsupported character {}", op),
            };

            let tree = TokenTree::Token(self.span.0, token);
            match kind {
                Spacing::Alone => tree.into(),
                Spacing::Joint => tree.joint(),
            }
        }
    }

    fn prepend_attrs(attrs: &[ast::Attribute],
                     tokens: Option<&tokenstream::TokenStream>,
                     span: syntax_pos::Span)
        -> Option<tokenstream::TokenStream>
    {
        let tokens = match tokens {
            Some(tokens) => tokens,
            None => return None,
        };
        if attrs.len() == 0 {
            return Some(tokens.clone())
        }
        let mut builder = tokenstream::TokenStreamBuilder::new();
        for attr in attrs {
            assert_eq!(attr.style, ast::AttrStyle::Outer,
                       "inner attributes should prevent cached tokens from existing");
            let stream = __internal::with_sess(|(sess, _)| {
                // FIXME: Avoid this pretty-print + reparse hack as bove
                let name = "<macro expansion>".to_owned();
                let source = pprust::attr_to_string(attr);
                parse_stream_from_source_str(name, source, sess, Some(span))
            });
            builder.push(stream);
        }
        builder.push(tokens.clone());
        Some(builder.build())
    }

    /// 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 {
        pub use quote::{Quoter, __rt};

        use std::cell::Cell;

        use syntax::ast;
        use syntax::ext::base::ExtCtxt;
        use syntax::ext::hygiene::Mark;
        use syntax::ptr::P;
        use syntax::parse::{self, ParseSess};
        use syntax::parse::token::{self, Token};
        use syntax::tokenstream;
        use syntax_pos::DUMMY_SP;

        use super::{TokenStream, LexError};

        pub fn new_token_stream(item: P<ast::Item>) -> TokenStream {
            let token = Token::interpolated(token::NtItem(item));
            TokenStream(tokenstream::TokenTree::Token(DUMMY_SP, token).into())
        }

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

        pub fn token_stream_parse_items(stream: TokenStream) -> Result<Vec<P<ast::Item>>, LexError> {
            with_sess(move |(sess, _)| {
                let mut parser = parse::stream_to_parser(sess, stream.0);
                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::TokenStream {
            stream.0
        }

        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, Mark)> =
                Cell::new((0 as *const _, Mark::root()));
        }

        pub fn set_sess<F, R>(cx: &ExtCtxt, f: F) -> R
            where F: FnOnce() -> R
        {
            struct Reset { prev: (*const ParseSess, Mark) }

            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((cx.parse_sess, cx.current_expansion.mark));
                f()
            })
        }

        pub fn with_sess<F, R>(f: F) -> R
            where F: FnOnce((&ParseSess, Mark)) -> R
        {
            let p = CURRENT_SESS.with(|p| p.get());
            assert!(!p.0.is_null(), "proc_macro::__internal::with_sess() called \
                                     before set_parse_sess()!");
            f(unsafe { (&*p.0, p.1) })
        }
    }

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

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