src/libsyntax/tokenstream.rs - third_party/rust - Git at Google

 // Copyright 2012-2016 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.

 //! # Token Streams
 //!
 //! `TokenStream`s represent syntactic objects before they are converted into ASTs.
 //! A `TokenStream` is, roughly speaking, a sequence (eg stream) of `TokenTree`s,
 //! which are themselves a single `Token` or a `Delimited` subsequence of tokens.
 //!
 //! ## Ownership
 //! `TokenStreams` are persistent data structures constructed as ropes with reference
 //! counted-children. In general, this means that calling an operation on a `TokenStream`
 //! (such as `slice`) produces an entirely new `TokenStream` from the borrowed reference to
 //! the original. This essentially coerces `TokenStream`s into 'views' of their subparts,
 //! and a borrowed `TokenStream` is sufficient to build an owned `TokenStream` without taking
 //! ownership of the original.

 use syntax_pos::{BytePos, Span, DUMMY_SP};
 use ext::base;
 use ext::tt::{macro_parser, quoted};
 use parse::Directory;
 use parse::token::{self, Token};
 use print::pprust;
 use serialize::{Decoder, Decodable, Encoder, Encodable};
 use util::RcSlice;

 use std::{fmt, iter, mem};
 use std::hash::{self, Hash};

 /// A delimited sequence of token trees
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct Delimited {
     /// The type of delimiter
     pub delim: token::DelimToken,
     /// The delimited sequence of token trees
     pub tts: ThinTokenStream,
 }

 impl Delimited {
     /// Returns the opening delimiter as a token.
     pub fn open_token(&self) -> token::Token {
         token::OpenDelim(self.delim)
     }

     /// Returns the closing delimiter as a token.
     pub fn close_token(&self) -> token::Token {
         token::CloseDelim(self.delim)
     }

     /// Returns the opening delimiter as a token tree.
     pub fn open_tt(&self, span: Span) -> TokenTree {
         let open_span = if span == DUMMY_SP {
             DUMMY_SP
         } else {
             span.with_hi(span.lo() + BytePos(self.delim.len() as u32))
         };
         TokenTree::Token(open_span, self.open_token())
     }

     /// Returns the closing delimiter as a token tree.
     pub fn close_tt(&self, span: Span) -> TokenTree {
         let close_span = if span == DUMMY_SP {
             DUMMY_SP
         } else {
             span.with_lo(span.hi() - BytePos(self.delim.len() as u32))
         };
         TokenTree::Token(close_span, self.close_token())
     }

     /// Returns the token trees inside the delimiters.
     pub fn stream(&self) -> TokenStream {
         self.tts.clone().into()
     }
 }

 /// When the main rust parser encounters a syntax-extension invocation, it
 /// parses the arguments to the invocation as a token-tree. This is a very
 /// loose structure, such that all sorts of different AST-fragments can
 /// be passed to syntax extensions using a uniform type.
 ///
 /// If the syntax extension is an MBE macro, it will attempt to match its
 /// LHS token tree against the provided token tree, and if it finds a
 /// match, will transcribe the RHS token tree, splicing in any captured
 /// `macro_parser::matched_nonterminals` into the `SubstNt`s it finds.
 ///
 /// The RHS of an MBE macro is the only place `SubstNt`s are substituted.
 /// Nothing special happens to misnamed or misplaced `SubstNt`s.
 #[derive(Debug, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
 pub enum TokenTree {
     /// A single token
     Token(Span, token::Token),
     /// A delimited sequence of token trees
     Delimited(Span, Delimited),
 }

 impl TokenTree {
     /// Use this token tree as a matcher to parse given tts.
     pub fn parse(cx: &base::ExtCtxt, mtch: &[quoted::TokenTree], tts: TokenStream)
                  -> macro_parser::NamedParseResult {
         // `None` is because we're not interpolating
         let directory = Directory {
             path: cx.current_expansion.module.directory.clone(),
             ownership: cx.current_expansion.directory_ownership,
         };
         macro_parser::parse(cx.parse_sess(), tts, mtch, Some(directory), true)
     }

     /// Check if this TokenTree is equal to the other, regardless of span information.
     pub fn eq_unspanned(&self, other: &TokenTree) -> bool {
         match (self, other) {
             (&TokenTree::Token(_, ref tk), &TokenTree::Token(_, ref tk2)) => tk == tk2,
             (&TokenTree::Delimited(_, ref dl), &TokenTree::Delimited(_, ref dl2)) => {
                 dl.delim == dl2.delim &&
                 dl.stream().trees().zip(dl2.stream().trees()).all(|(tt, tt2)| tt.eq_unspanned(&tt2))
             }
             (_, _) => false,
         }
     }

     /// Retrieve the TokenTree's span.
     pub fn span(&self) -> Span {
         match *self {
             TokenTree::Token(sp, _) | TokenTree::Delimited(sp, _) => sp,
         }
     }

     /// Modify the `TokenTree`'s span inplace.
     pub fn set_span(&mut self, span: Span) {
         match *self {
             TokenTree::Token(ref mut sp, _) | TokenTree::Delimited(ref mut sp, _) => {
                 *sp = span;
             }
         }
     }

     /// Indicates if the stream is a token that is equal to the provided token.
     pub fn eq_token(&self, t: Token) -> bool {
         match *self {
             TokenTree::Token(_, ref tk) => *tk == t,
             _ => false,
         }
     }

     pub fn joint(self) -> TokenStream {
         TokenStream { kind: TokenStreamKind::JointTree(self) }
     }
 }

 /// # Token Streams
 ///
 /// A `TokenStream` is an abstract sequence of tokens, organized into `TokenTree`s.
 /// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
 /// instead of a representation of the abstract syntax tree.
 /// Today's `TokenTree`s can still contain AST via `Token::Interpolated` for back-compat.
 #[derive(Clone, Debug)]
 pub struct TokenStream {
     kind: TokenStreamKind,
 }

 #[derive(Clone, Debug)]
 enum TokenStreamKind {
     Empty,
     Tree(TokenTree),
     JointTree(TokenTree),
     Stream(RcSlice<TokenStream>),
 }

 impl From<TokenTree> for TokenStream {
     fn from(tt: TokenTree) -> TokenStream {
         TokenStream { kind: TokenStreamKind::Tree(tt) }
     }
 }

 impl From<Token> for TokenStream {
     fn from(token: Token) -> TokenStream {
         TokenTree::Token(DUMMY_SP, token).into()
     }
 }

 impl<T: Into<TokenStream>> iter::FromIterator<T> for TokenStream {
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
         TokenStream::concat(iter.into_iter().map(Into::into).collect::<Vec<_>>())
     }
 }

 impl Eq for TokenStream {}

 impl PartialEq<TokenStream> for TokenStream {
     fn eq(&self, other: &TokenStream) -> bool {
         self.trees().eq(other.trees())
     }
 }

 impl TokenStream {
     pub fn len(&self) -> usize {
         if let TokenStreamKind::Stream(ref slice) = self.kind {
             slice.len()
         } else {
             0
         }
     }

     pub fn empty() -> TokenStream {
         TokenStream { kind: TokenStreamKind::Empty }
     }

     pub fn is_empty(&self) -> bool {
         match self.kind {
             TokenStreamKind::Empty => true,
             _ => false,
         }
     }

     pub fn concat(mut streams: Vec<TokenStream>) -> TokenStream {
         match streams.len() {
             0 => TokenStream::empty(),
             1 => streams.pop().unwrap(),
             _ => TokenStream::concat_rc_slice(RcSlice::new(streams)),
         }
     }

     fn concat_rc_slice(streams: RcSlice<TokenStream>) -> TokenStream {
         TokenStream { kind: TokenStreamKind::Stream(streams) }
     }

     pub fn trees(&self) -> Cursor {
         self.clone().into_trees()
     }

     pub fn into_trees(self) -> Cursor {
         Cursor::new(self)
     }

     /// Compares two TokenStreams, checking equality without regarding span information.
     pub fn eq_unspanned(&self, other: &TokenStream) -> bool {
         for (t1, t2) in self.trees().zip(other.trees()) {
             if !t1.eq_unspanned(&t2) {
                 return false;
             }
         }
         true
     }

     /// Precondition: `self` consists of a single token tree.
     /// Returns true if the token tree is a joint operation w.r.t. `proc_macro::TokenNode`.
     pub fn as_tree(self) -> (TokenTree, bool /* joint? */) {
         match self.kind {
             TokenStreamKind::Tree(tree) => (tree, false),
             TokenStreamKind::JointTree(tree) => (tree, true),
             _ => unreachable!(),
         }
     }

     pub fn map_enumerated<F: FnMut(usize, TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
         let mut trees = self.into_trees();
         let mut result = Vec::new();
         let mut i = 0;
         while let Some(stream) = trees.next_as_stream() {
             result.push(match stream.kind {
                 TokenStreamKind::Tree(tree) => f(i, tree).into(),
                 TokenStreamKind::JointTree(tree) => f(i, tree).joint(),
                 _ => unreachable!()
             });
             i += 1;
         }
         TokenStream::concat(result)
     }

     pub fn map<F: FnMut(TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
         let mut trees = self.into_trees();
         let mut result = Vec::new();
         while let Some(stream) = trees.next_as_stream() {
             result.push(match stream.kind {
                 TokenStreamKind::Tree(tree) => f(tree).into(),
                 TokenStreamKind::JointTree(tree) => f(tree).joint(),
                 _ => unreachable!()
             });
         }
         TokenStream::concat(result)
     }

     fn first_tree_and_joint(&self) -> Option<(TokenTree, bool)> {
         match self.kind {
             TokenStreamKind::Empty => None,
             TokenStreamKind::Tree(ref tree) => Some((tree.clone(), false)),
             TokenStreamKind::JointTree(ref tree) => Some((tree.clone(), true)),
             TokenStreamKind::Stream(ref stream) => stream.first().unwrap().first_tree_and_joint(),
         }
     }

     fn last_tree_if_joint(&self) -> Option<TokenTree> {
         match self.kind {
             TokenStreamKind::Empty | TokenStreamKind::Tree(..) => None,
             TokenStreamKind::JointTree(ref tree) => Some(tree.clone()),
             TokenStreamKind::Stream(ref stream) => stream.last().unwrap().last_tree_if_joint(),
         }
     }
 }

 pub struct TokenStreamBuilder(Vec<TokenStream>);

 impl TokenStreamBuilder {
     pub fn new() -> TokenStreamBuilder {
         TokenStreamBuilder(Vec::new())
     }

     pub fn push<T: Into<TokenStream>>(&mut self, stream: T) {
         let stream = stream.into();
         let last_tree_if_joint = self.0.last().and_then(TokenStream::last_tree_if_joint);
         if let Some(TokenTree::Token(last_span, last_tok)) = last_tree_if_joint {
             if let Some((TokenTree::Token(span, tok), is_joint)) = stream.first_tree_and_joint() {
                 if let Some(glued_tok) = last_tok.glue(tok) {
                     let last_stream = self.0.pop().unwrap();
                     self.push_all_but_last_tree(&last_stream);
                     let glued_span = last_span.to(span);
                     let glued_tt = TokenTree::Token(glued_span, glued_tok);
                     let glued_tokenstream = if is_joint {
                         glued_tt.joint()
                     } else {
                         glued_tt.into()
                     };
                     self.0.push(glued_tokenstream);
                     self.push_all_but_first_tree(&stream);
                     return
                 }
             }
         }
         self.0.push(stream);
     }

     pub fn add<T: Into<TokenStream>>(mut self, stream: T) -> Self {
         self.push(stream);
         self
     }

     pub fn build(self) -> TokenStream {
         TokenStream::concat(self.0)
     }

     fn push_all_but_last_tree(&mut self, stream: &TokenStream) {
         if let TokenStreamKind::Stream(ref streams) = stream.kind {
             let len = streams.len();
             match len {
                 1 => {}
                 2 => self.0.push(streams[0].clone().into()),
                 _ => self.0.push(TokenStream::concat_rc_slice(streams.sub_slice(0 .. len - 1))),
             }
             self.push_all_but_last_tree(&streams[len - 1])
         }
     }

     fn push_all_but_first_tree(&mut self, stream: &TokenStream) {
         if let TokenStreamKind::Stream(ref streams) = stream.kind {
             let len = streams.len();
             match len {
                 1 => {}
                 2 => self.0.push(streams[1].clone().into()),
                 _ => self.0.push(TokenStream::concat_rc_slice(streams.sub_slice(1 .. len))),
             }
             self.push_all_but_first_tree(&streams[0])
         }
     }
 }

 #[derive(Clone)]
 pub struct Cursor(CursorKind);

 #[derive(Clone)]
 enum CursorKind {
     Empty,
     Tree(TokenTree, bool /* consumed? */),
     JointTree(TokenTree, bool /* consumed? */),
     Stream(StreamCursor),
 }

 #[derive(Clone)]
 struct StreamCursor {
     stream: RcSlice<TokenStream>,
     index: usize,
     stack: Vec<(RcSlice<TokenStream>, usize)>,
 }

 impl StreamCursor {
     fn new(stream: RcSlice<TokenStream>) -> Self {
         StreamCursor { stream: stream, index: 0, stack: Vec::new() }
     }

     fn next_as_stream(&mut self) -> Option<TokenStream> {
         loop {
             if self.index < self.stream.len() {
                 self.index += 1;
                 let next = self.stream[self.index - 1].clone();
                 match next.kind {
                     TokenStreamKind::Tree(..) | TokenStreamKind::JointTree(..) => return Some(next),
                     TokenStreamKind::Stream(stream) => self.insert(stream),
                     TokenStreamKind::Empty => {}
                 }
             } else if let Some((stream, index)) = self.stack.pop() {
                 self.stream = stream;
                 self.index = index;
             } else {
                 return None;
             }
         }
     }

     fn insert(&mut self, stream: RcSlice<TokenStream>) {
         self.stack.push((mem::replace(&mut self.stream, stream),
                          mem::replace(&mut self.index, 0)));
     }
 }

 impl Iterator for Cursor {
     type Item = TokenTree;

     fn next(&mut self) -> Option<TokenTree> {
         self.next_as_stream().map(|stream| match stream.kind {
             TokenStreamKind::Tree(tree) | TokenStreamKind::JointTree(tree) => tree,
             _ => unreachable!()
         })
     }
 }

 impl Cursor {
     fn new(stream: TokenStream) -> Self {
         Cursor(match stream.kind {
             TokenStreamKind::Empty => CursorKind::Empty,
             TokenStreamKind::Tree(tree) => CursorKind::Tree(tree, false),
             TokenStreamKind::JointTree(tree) => CursorKind::JointTree(tree, false),
             TokenStreamKind::Stream(stream) => CursorKind::Stream(StreamCursor::new(stream)),
         })
     }

     pub fn next_as_stream(&mut self) -> Option<TokenStream> {
         let (stream, consumed) = match self.0 {
             CursorKind::Tree(ref tree, ref mut consumed @ false) =>
                 (tree.clone().into(), consumed),
             CursorKind::JointTree(ref tree, ref mut consumed @ false) =>
                 (tree.clone().joint(), consumed),
             CursorKind::Stream(ref mut cursor) => return cursor.next_as_stream(),
             _ => return None,
         };

         *consumed = true;
         Some(stream)
     }

     pub fn insert(&mut self, stream: TokenStream) {
         match self.0 {
             _ if stream.is_empty() => return,
             CursorKind::Empty => *self = stream.trees(),
             CursorKind::Tree(_, consumed) | CursorKind::JointTree(_, consumed) => {
                 *self = TokenStream::concat(vec![self.original_stream(), stream]).trees();
                 if consumed {
                     self.next();
                 }
             }
             CursorKind::Stream(ref mut cursor) => {
                 cursor.insert(ThinTokenStream::from(stream).0.unwrap());
             }
         }
     }

     pub fn original_stream(&self) -> TokenStream {
         match self.0 {
             CursorKind::Empty => TokenStream::empty(),
             CursorKind::Tree(ref tree, _) => tree.clone().into(),
             CursorKind::JointTree(ref tree, _) => tree.clone().joint(),
             CursorKind::Stream(ref cursor) => TokenStream::concat_rc_slice({
                 cursor.stack.get(0).cloned().map(|(stream, _)| stream)
                     .unwrap_or(cursor.stream.clone())
             }),
         }
     }

     pub fn look_ahead(&self, n: usize) -> Option<TokenTree> {
         fn look_ahead(streams: &[TokenStream], mut n: usize) -> Result<TokenTree, usize> {
             for stream in streams {
                 n = match stream.kind {
                     TokenStreamKind::Tree(ref tree) | TokenStreamKind::JointTree(ref tree)
                         if n == 0 => return Ok(tree.clone()),
                     TokenStreamKind::Tree(..) | TokenStreamKind::JointTree(..) => n - 1,
                     TokenStreamKind::Stream(ref stream) => match look_ahead(stream, n) {
                         Ok(tree) => return Ok(tree),
                         Err(n) => n,
                     },
                     _ => n,
                 };
             }
             Err(n)
         }

         match self.0 {
             CursorKind::Empty |
             CursorKind::Tree(_, true) |
             CursorKind::JointTree(_, true) => Err(n),
             CursorKind::Tree(ref tree, false) |
             CursorKind::JointTree(ref tree, false) => look_ahead(&[tree.clone().into()], n),
             CursorKind::Stream(ref cursor) => {
                 look_ahead(&cursor.stream[cursor.index ..], n).or_else(|mut n| {
                     for &(ref stream, index) in cursor.stack.iter().rev() {
                         n = match look_ahead(&stream[index..], n) {
                             Ok(tree) => return Ok(tree),
                             Err(n) => n,
                         }
                     }

                     Err(n)
                 })
             }
         }.ok()
     }
 }

 /// The `TokenStream` type is large enough to represent a single `TokenTree` without allocation.
 /// `ThinTokenStream` is smaller, but needs to allocate to represent a single `TokenTree`.
 /// We must use `ThinTokenStream` in `TokenTree::Delimited` to avoid infinite size due to recursion.
 #[derive(Debug, Clone)]
 pub struct ThinTokenStream(Option<RcSlice<TokenStream>>);

 impl From<TokenStream> for ThinTokenStream {
     fn from(stream: TokenStream) -> ThinTokenStream {
         ThinTokenStream(match stream.kind {
             TokenStreamKind::Empty => None,
             TokenStreamKind::Tree(tree) => Some(RcSlice::new(vec![tree.into()])),
             TokenStreamKind::JointTree(tree) => Some(RcSlice::new(vec![tree.joint()])),
             TokenStreamKind::Stream(stream) => Some(stream),
         })
     }
 }

 impl From<ThinTokenStream> for TokenStream {
     fn from(stream: ThinTokenStream) -> TokenStream {
         stream.0.map(TokenStream::concat_rc_slice).unwrap_or_else(TokenStream::empty)
     }
 }

 impl Eq for ThinTokenStream {}

 impl PartialEq<ThinTokenStream> for ThinTokenStream {
     fn eq(&self, other: &ThinTokenStream) -> bool {
         TokenStream::from(self.clone()) == TokenStream::from(other.clone())
     }
 }

 impl fmt::Display for TokenStream {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.write_str(&pprust::tokens_to_string(self.clone()))
     }
 }

 impl Encodable for TokenStream {
     fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), E::Error> {
         self.trees().collect::<Vec<_>>().encode(encoder)
     }
 }

 impl Decodable for TokenStream {
     fn decode<D: Decoder>(decoder: &mut D) -> Result<TokenStream, D::Error> {
         Vec::<TokenTree>::decode(decoder).map(|vec| vec.into_iter().collect())
     }
 }

 impl Hash for TokenStream {
     fn hash<H: hash::Hasher>(&self, state: &mut H) {
         for tree in self.trees() {
             tree.hash(state);
         }
     }
 }

 impl Encodable for ThinTokenStream {
     fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), E::Error> {
         TokenStream::from(self.clone()).encode(encoder)
     }
 }

 impl Decodable for ThinTokenStream {
     fn decode<D: Decoder>(decoder: &mut D) -> Result<ThinTokenStream, D::Error> {
         TokenStream::decode(decoder).map(Into::into)
     }
 }

 impl Hash for ThinTokenStream {
     fn hash<H: hash::Hasher>(&self, state: &mut H) {
         TokenStream::from(self.clone()).hash(state);
     }
 }


 #[cfg(test)]
 mod tests {
     use super::*;
     use syntax::ast::Ident;
     use syntax_pos::{Span, BytePos, NO_EXPANSION};
     use parse::token::Token;
     use util::parser_testing::string_to_stream;

     fn string_to_ts(string: &str) -> TokenStream {
         string_to_stream(string.to_owned())
     }

     fn sp(a: u32, b: u32) -> Span {
         Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
     }

     #[test]
     fn test_concat() {
         let test_res = string_to_ts("foo::bar::baz");
         let test_fst = string_to_ts("foo::bar");
         let test_snd = string_to_ts("::baz");
         let eq_res = TokenStream::concat(vec![test_fst, test_snd]);
         assert_eq!(test_res.trees().count(), 5);
         assert_eq!(eq_res.trees().count(), 5);
         assert_eq!(test_res.eq_unspanned(&eq_res), true);
     }

     #[test]
     fn test_to_from_bijection() {
         let test_start = string_to_ts("foo::bar(baz)");
         let test_end = test_start.trees().collect();
         assert_eq!(test_start, test_end)
     }

     #[test]
     fn test_eq_0() {
         let test_res = string_to_ts("foo");
         let test_eqs = string_to_ts("foo");
         assert_eq!(test_res, test_eqs)
     }

     #[test]
     fn test_eq_1() {
         let test_res = string_to_ts("::bar::baz");
         let test_eqs = string_to_ts("::bar::baz");
         assert_eq!(test_res, test_eqs)
     }

     #[test]
     fn test_eq_3() {
         let test_res = string_to_ts("");
         let test_eqs = string_to_ts("");
         assert_eq!(test_res, test_eqs)
     }

     #[test]
     fn test_diseq_0() {
         let test_res = string_to_ts("::bar::baz");
         let test_eqs = string_to_ts("bar::baz");
         assert_eq!(test_res == test_eqs, false)
     }

     #[test]
     fn test_diseq_1() {
         let test_res = string_to_ts("(bar,baz)");
         let test_eqs = string_to_ts("bar,baz");
         assert_eq!(test_res == test_eqs, false)
     }

     #[test]
     fn test_is_empty() {
         let test0: TokenStream = Vec::<TokenTree>::new().into_iter().collect();
         let test1: TokenStream =
             TokenTree::Token(sp(0, 1), Token::Ident(Ident::from_str("a"))).into();
         let test2 = string_to_ts("foo(bar::baz)");

         assert_eq!(test0.is_empty(), true);
         assert_eq!(test1.is_empty(), false);
         assert_eq!(test2.is_empty(), false);
     }

     #[test]
     fn test_dotdotdot() {
         let mut builder = TokenStreamBuilder::new();
         builder.push(TokenTree::Token(sp(0, 1), Token::Dot).joint());
         builder.push(TokenTree::Token(sp(1, 2), Token::Dot).joint());
         builder.push(TokenTree::Token(sp(2, 3), Token::Dot));
         let stream = builder.build();
         assert!(stream.eq_unspanned(&string_to_ts("...")));
         assert_eq!(stream.trees().count(), 1);
     }

 }
	// Copyright 2012-2016 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.

	//! # Token Streams
	//!
	//! `TokenStream`s represent syntactic objects before they are converted into ASTs.
	//! A `TokenStream` is, roughly speaking, a sequence (eg stream) of `TokenTree`s,
	//! which are themselves a single `Token` or a `Delimited` subsequence of tokens.
	//!
	//! ## Ownership
	//! `TokenStreams` are persistent data structures constructed as ropes with reference
	//! counted-children. In general, this means that calling an operation on a `TokenStream`
	//! (such as `slice`) produces an entirely new `TokenStream` from the borrowed reference to
	//! the original. This essentially coerces `TokenStream`s into 'views' of their subparts,
	//! and a borrowed `TokenStream` is sufficient to build an owned `TokenStream` without taking
	//! ownership of the original.

	use syntax_pos::{BytePos, Span, DUMMY_SP};
	use ext::base;
	use ext::tt::{macro_parser, quoted};
	use parse::Directory;
	use parse::token::{self, Token};
	use print::pprust;
	use serialize::{Decoder, Decodable, Encoder, Encodable};
	use util::RcSlice;

	use std::{fmt, iter, mem};
	use std::hash::{self, Hash};

	/// A delimited sequence of token trees
	#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
	pub struct Delimited {
	/// The type of delimiter
	pub delim: token::DelimToken,
	/// The delimited sequence of token trees
	pub tts: ThinTokenStream,
	}

	impl Delimited {
	/// Returns the opening delimiter as a token.
	pub fn open_token(&self) -> token::Token {
	token::OpenDelim(self.delim)
	}

	/// Returns the closing delimiter as a token.
	pub fn close_token(&self) -> token::Token {
	token::CloseDelim(self.delim)
	}

	/// Returns the opening delimiter as a token tree.
	pub fn open_tt(&self, span: Span) -> TokenTree {
	let open_span = if span == DUMMY_SP {
	DUMMY_SP
	} else {
	span.with_hi(span.lo() + BytePos(self.delim.len() as u32))
	};
	TokenTree::Token(open_span, self.open_token())
	}

	/// Returns the closing delimiter as a token tree.
	pub fn close_tt(&self, span: Span) -> TokenTree {
	let close_span = if span == DUMMY_SP {
	DUMMY_SP
	} else {
	span.with_lo(span.hi() - BytePos(self.delim.len() as u32))
	};
	TokenTree::Token(close_span, self.close_token())
	}

	/// Returns the token trees inside the delimiters.
	pub fn stream(&self) -> TokenStream {
	self.tts.clone().into()
	}
	}

	/// When the main rust parser encounters a syntax-extension invocation, it
	/// parses the arguments to the invocation as a token-tree. This is a very
	/// loose structure, such that all sorts of different AST-fragments can
	/// be passed to syntax extensions using a uniform type.
	///
	/// If the syntax extension is an MBE macro, it will attempt to match its
	/// LHS token tree against the provided token tree, and if it finds a
	/// match, will transcribe the RHS token tree, splicing in any captured
	/// `macro_parser::matched_nonterminals` into the `SubstNt`s it finds.
	///
	/// The RHS of an MBE macro is the only place `SubstNt`s are substituted.
	/// Nothing special happens to misnamed or misplaced `SubstNt`s.
	#[derive(Debug, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
	pub enum TokenTree {
	/// A single token
	Token(Span, token::Token),
	/// A delimited sequence of token trees
	Delimited(Span, Delimited),
	}

	impl TokenTree {
	/// Use this token tree as a matcher to parse given tts.
	pub fn parse(cx: &base::ExtCtxt, mtch: &[quoted::TokenTree], tts: TokenStream)
	-> macro_parser::NamedParseResult {
	// `None` is because we're not interpolating
	let directory = Directory {
	path: cx.current_expansion.module.directory.clone(),
	ownership: cx.current_expansion.directory_ownership,
	};
	macro_parser::parse(cx.parse_sess(), tts, mtch, Some(directory), true)
	}

	/// Check if this TokenTree is equal to the other, regardless of span information.
	pub fn eq_unspanned(&self, other: &TokenTree) -> bool {
	match (self, other) {
	(&TokenTree::Token(_, ref tk), &TokenTree::Token(_, ref tk2)) => tk == tk2,
	(&TokenTree::Delimited(_, ref dl), &TokenTree::Delimited(_, ref dl2)) => {
	dl.delim == dl2.delim &&
	dl.stream().trees().zip(dl2.stream().trees()).all(\|(tt, tt2)\| tt.eq_unspanned(&tt2))
	}
	(_, _) => false,
	}
	}

	/// Retrieve the TokenTree's span.
	pub fn span(&self) -> Span {
	match *self {
	TokenTree::Token(sp, _) \| TokenTree::Delimited(sp, _) => sp,
	}
	}

	/// Modify the `TokenTree`'s span inplace.
	pub fn set_span(&mut self, span: Span) {
	match *self {
	TokenTree::Token(ref mut sp, _) \| TokenTree::Delimited(ref mut sp, _) => {
	*sp = span;
	}
	}
	}

	/// Indicates if the stream is a token that is equal to the provided token.
	pub fn eq_token(&self, t: Token) -> bool {
	match *self {
	TokenTree::Token(_, ref tk) => *tk == t,
	_ => false,
	}
	}

	pub fn joint(self) -> TokenStream {
	TokenStream { kind: TokenStreamKind::JointTree(self) }
	}
	}

	/// # Token Streams
	///
	/// A `TokenStream` is an abstract sequence of tokens, organized into `TokenTree`s.
	/// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
	/// instead of a representation of the abstract syntax tree.
	/// Today's `TokenTree`s can still contain AST via `Token::Interpolated` for back-compat.
	#[derive(Clone, Debug)]
	pub struct TokenStream {
	kind: TokenStreamKind,
	}

	#[derive(Clone, Debug)]
	enum TokenStreamKind {
	Empty,
	Tree(TokenTree),
	JointTree(TokenTree),
	Stream(RcSlice<TokenStream>),
	}

	impl From<TokenTree> for TokenStream {
	fn from(tt: TokenTree) -> TokenStream {
	TokenStream { kind: TokenStreamKind::Tree(tt) }
	}
	}

	impl From<Token> for TokenStream {
	fn from(token: Token) -> TokenStream {
	TokenTree::Token(DUMMY_SP, token).into()
	}
	}

	impl<T: Into<TokenStream>> iter::FromIterator<T> for TokenStream {
	fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
	TokenStream::concat(iter.into_iter().map(Into::into).collect::<Vec<_>>())
	}
	}

	impl Eq for TokenStream {}

	impl PartialEq<TokenStream> for TokenStream {
	fn eq(&self, other: &TokenStream) -> bool {
	self.trees().eq(other.trees())
	}
	}

	impl TokenStream {
	pub fn len(&self) -> usize {
	if let TokenStreamKind::Stream(ref slice) = self.kind {
	slice.len()
	} else {
	0
	}
	}

	pub fn empty() -> TokenStream {
	TokenStream { kind: TokenStreamKind::Empty }
	}

	pub fn is_empty(&self) -> bool {
	match self.kind {
	TokenStreamKind::Empty => true,
	_ => false,
	}
	}

	pub fn concat(mut streams: Vec<TokenStream>) -> TokenStream {
	match streams.len() {
	0 => TokenStream::empty(),
	1 => streams.pop().unwrap(),
	_ => TokenStream::concat_rc_slice(RcSlice::new(streams)),
	}
	}

	fn concat_rc_slice(streams: RcSlice<TokenStream>) -> TokenStream {
	TokenStream { kind: TokenStreamKind::Stream(streams) }
	}

	pub fn trees(&self) -> Cursor {
	self.clone().into_trees()
	}

	pub fn into_trees(self) -> Cursor {
	Cursor::new(self)
	}

	/// Compares two TokenStreams, checking equality without regarding span information.
	pub fn eq_unspanned(&self, other: &TokenStream) -> bool {
	for (t1, t2) in self.trees().zip(other.trees()) {
	if !t1.eq_unspanned(&t2) {
	return false;
	}
	}
	true
	}

	/// Precondition: `self` consists of a single token tree.
	/// Returns true if the token tree is a joint operation w.r.t. `proc_macro::TokenNode`.
	pub fn as_tree(self) -> (TokenTree, bool /* joint? */) {
	match self.kind {
	TokenStreamKind::Tree(tree) => (tree, false),
	TokenStreamKind::JointTree(tree) => (tree, true),
	_ => unreachable!(),
	}
	}

	pub fn map_enumerated<F: FnMut(usize, TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
	let mut trees = self.into_trees();
	let mut result = Vec::new();
	let mut i = 0;
	while let Some(stream) = trees.next_as_stream() {
	result.push(match stream.kind {
	TokenStreamKind::Tree(tree) => f(i, tree).into(),
	TokenStreamKind::JointTree(tree) => f(i, tree).joint(),
	_ => unreachable!()
	});
	i += 1;
	}
	TokenStream::concat(result)
	}

	pub fn map<F: FnMut(TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
	let mut trees = self.into_trees();
	let mut result = Vec::new();
	while let Some(stream) = trees.next_as_stream() {
	result.push(match stream.kind {
	TokenStreamKind::Tree(tree) => f(tree).into(),
	TokenStreamKind::JointTree(tree) => f(tree).joint(),
	_ => unreachable!()
	});
	}
	TokenStream::concat(result)
	}

	fn first_tree_and_joint(&self) -> Option<(TokenTree, bool)> {
	match self.kind {
	TokenStreamKind::Empty => None,
	TokenStreamKind::Tree(ref tree) => Some((tree.clone(), false)),
	TokenStreamKind::JointTree(ref tree) => Some((tree.clone(), true)),
	TokenStreamKind::Stream(ref stream) => stream.first().unwrap().first_tree_and_joint(),
	}
	}

	fn last_tree_if_joint(&self) -> Option<TokenTree> {
	match self.kind {
	TokenStreamKind::Empty \| TokenStreamKind::Tree(..) => None,
	TokenStreamKind::JointTree(ref tree) => Some(tree.clone()),
	TokenStreamKind::Stream(ref stream) => stream.last().unwrap().last_tree_if_joint(),
	}
	}
	}

	pub struct TokenStreamBuilder(Vec<TokenStream>);

	impl TokenStreamBuilder {
	pub fn new() -> TokenStreamBuilder {
	TokenStreamBuilder(Vec::new())
	}

	pub fn push<T: Into<TokenStream>>(&mut self, stream: T) {
	let stream = stream.into();
	let last_tree_if_joint = self.0.last().and_then(TokenStream::last_tree_if_joint);
	if let Some(TokenTree::Token(last_span, last_tok)) = last_tree_if_joint {
	if let Some((TokenTree::Token(span, tok), is_joint)) = stream.first_tree_and_joint() {
	if let Some(glued_tok) = last_tok.glue(tok) {
	let last_stream = self.0.pop().unwrap();
	self.push_all_but_last_tree(&last_stream);
	let glued_span = last_span.to(span);
	let glued_tt = TokenTree::Token(glued_span, glued_tok);
	let glued_tokenstream = if is_joint {
	glued_tt.joint()
	} else {
	glued_tt.into()
	};
	self.0.push(glued_tokenstream);
	self.push_all_but_first_tree(&stream);
	return
	}
	}
	}
	self.0.push(stream);
	}

	pub fn add<T: Into<TokenStream>>(mut self, stream: T) -> Self {
	self.push(stream);
	self
	}

	pub fn build(self) -> TokenStream {
	TokenStream::concat(self.0)
	}

	fn push_all_but_last_tree(&mut self, stream: &TokenStream) {
	if let TokenStreamKind::Stream(ref streams) = stream.kind {
	let len = streams.len();
	match len {
	1 => {}
	2 => self.0.push(streams[0].clone().into()),
	_ => self.0.push(TokenStream::concat_rc_slice(streams.sub_slice(0 .. len - 1))),
	}
	self.push_all_but_last_tree(&streams[len - 1])
	}
	}

	fn push_all_but_first_tree(&mut self, stream: &TokenStream) {
	if let TokenStreamKind::Stream(ref streams) = stream.kind {
	let len = streams.len();
	match len {
	1 => {}
	2 => self.0.push(streams[1].clone().into()),
	_ => self.0.push(TokenStream::concat_rc_slice(streams.sub_slice(1 .. len))),
	}
	self.push_all_but_first_tree(&streams[0])
	}
	}
	}

	#[derive(Clone)]
	pub struct Cursor(CursorKind);

	#[derive(Clone)]
	enum CursorKind {
	Empty,
	Tree(TokenTree, bool /* consumed? */),
	JointTree(TokenTree, bool /* consumed? */),
	Stream(StreamCursor),
	}

	#[derive(Clone)]
	struct StreamCursor {
	stream: RcSlice<TokenStream>,
	index: usize,
	stack: Vec<(RcSlice<TokenStream>, usize)>,
	}

	impl StreamCursor {
	fn new(stream: RcSlice<TokenStream>) -> Self {
	StreamCursor { stream: stream, index: 0, stack: Vec::new() }
	}

	fn next_as_stream(&mut self) -> Option<TokenStream> {
	loop {
	if self.index < self.stream.len() {
	self.index += 1;
	let next = self.stream[self.index - 1].clone();
	match next.kind {
	TokenStreamKind::Tree(..) \| TokenStreamKind::JointTree(..) => return Some(next),
	TokenStreamKind::Stream(stream) => self.insert(stream),
	TokenStreamKind::Empty => {}
	}
	} else if let Some((stream, index)) = self.stack.pop() {
	self.stream = stream;
	self.index = index;
	} else {
	return None;
	}
	}
	}

	fn insert(&mut self, stream: RcSlice<TokenStream>) {
	self.stack.push((mem::replace(&mut self.stream, stream),
	mem::replace(&mut self.index, 0)));
	}
	}

	impl Iterator for Cursor {
	type Item = TokenTree;

	fn next(&mut self) -> Option<TokenTree> {
	self.next_as_stream().map(\|stream\| match stream.kind {
	TokenStreamKind::Tree(tree) \| TokenStreamKind::JointTree(tree) => tree,
	_ => unreachable!()
	})
	}
	}

	impl Cursor {
	fn new(stream: TokenStream) -> Self {
	Cursor(match stream.kind {
	TokenStreamKind::Empty => CursorKind::Empty,
	TokenStreamKind::Tree(tree) => CursorKind::Tree(tree, false),
	TokenStreamKind::JointTree(tree) => CursorKind::JointTree(tree, false),
	TokenStreamKind::Stream(stream) => CursorKind::Stream(StreamCursor::new(stream)),
	})
	}

	pub fn next_as_stream(&mut self) -> Option<TokenStream> {
	let (stream, consumed) = match self.0 {
	CursorKind::Tree(ref tree, ref mut consumed @ false) =>
	(tree.clone().into(), consumed),
	CursorKind::JointTree(ref tree, ref mut consumed @ false) =>
	(tree.clone().joint(), consumed),
	CursorKind::Stream(ref mut cursor) => return cursor.next_as_stream(),
	_ => return None,
	};

	*consumed = true;
	Some(stream)
	}

	pub fn insert(&mut self, stream: TokenStream) {
	match self.0 {
	_ if stream.is_empty() => return,
	CursorKind::Empty => *self = stream.trees(),
	CursorKind::Tree(_, consumed) \| CursorKind::JointTree(_, consumed) => {
	*self = TokenStream::concat(vec![self.original_stream(), stream]).trees();
	if consumed {
	self.next();
	}
	}
	CursorKind::Stream(ref mut cursor) => {
	cursor.insert(ThinTokenStream::from(stream).0.unwrap());
	}
	}
	}

	pub fn original_stream(&self) -> TokenStream {
	match self.0 {
	CursorKind::Empty => TokenStream::empty(),
	CursorKind::Tree(ref tree, _) => tree.clone().into(),
	CursorKind::JointTree(ref tree, _) => tree.clone().joint(),
	CursorKind::Stream(ref cursor) => TokenStream::concat_rc_slice({
	cursor.stack.get(0).cloned().map(\|(stream, _)\| stream)
	.unwrap_or(cursor.stream.clone())
	}),
	}
	}

	pub fn look_ahead(&self, n: usize) -> Option<TokenTree> {
	fn look_ahead(streams: &[TokenStream], mut n: usize) -> Result<TokenTree, usize> {
	for stream in streams {
	n = match stream.kind {
	TokenStreamKind::Tree(ref tree) \| TokenStreamKind::JointTree(ref tree)
	if n == 0 => return Ok(tree.clone()),
	TokenStreamKind::Tree(..) \| TokenStreamKind::JointTree(..) => n - 1,
	TokenStreamKind::Stream(ref stream) => match look_ahead(stream, n) {
	Ok(tree) => return Ok(tree),
	Err(n) => n,
	},
	_ => n,
	};
	}
	Err(n)
	}

	match self.0 {
	CursorKind::Empty \|
	CursorKind::Tree(_, true) \|
	CursorKind::JointTree(_, true) => Err(n),
	CursorKind::Tree(ref tree, false) \|
	CursorKind::JointTree(ref tree, false) => look_ahead(&[tree.clone().into()], n),
	CursorKind::Stream(ref cursor) => {
	look_ahead(&cursor.stream[cursor.index ..], n).or_else(\|mut n\| {
	for &(ref stream, index) in cursor.stack.iter().rev() {
	n = match look_ahead(&stream[index..], n) {
	Ok(tree) => return Ok(tree),
	Err(n) => n,
	}
	}

	Err(n)
	})
	}
	}.ok()
	}
	}

	/// The `TokenStream` type is large enough to represent a single `TokenTree` without allocation.
	/// `ThinTokenStream` is smaller, but needs to allocate to represent a single `TokenTree`.
	/// We must use `ThinTokenStream` in `TokenTree::Delimited` to avoid infinite size due to recursion.
	#[derive(Debug, Clone)]
	pub struct ThinTokenStream(Option<RcSlice<TokenStream>>);

	impl From<TokenStream> for ThinTokenStream {
	fn from(stream: TokenStream) -> ThinTokenStream {
	ThinTokenStream(match stream.kind {
	TokenStreamKind::Empty => None,
	TokenStreamKind::Tree(tree) => Some(RcSlice::new(vec![tree.into()])),
	TokenStreamKind::JointTree(tree) => Some(RcSlice::new(vec![tree.joint()])),
	TokenStreamKind::Stream(stream) => Some(stream),
	})
	}
	}

	impl From<ThinTokenStream> for TokenStream {
	fn from(stream: ThinTokenStream) -> TokenStream {
	stream.0.map(TokenStream::concat_rc_slice).unwrap_or_else(TokenStream::empty)
	}
	}

	impl Eq for ThinTokenStream {}

	impl PartialEq<ThinTokenStream> for ThinTokenStream {
	fn eq(&self, other: &ThinTokenStream) -> bool {
	TokenStream::from(self.clone()) == TokenStream::from(other.clone())
	}
	}

	impl fmt::Display for TokenStream {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	f.write_str(&pprust::tokens_to_string(self.clone()))
	}
	}

	impl Encodable for TokenStream {
	fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), E::Error> {
	self.trees().collect::<Vec<_>>().encode(encoder)
	}
	}

	impl Decodable for TokenStream {
	fn decode<D: Decoder>(decoder: &mut D) -> Result<TokenStream, D::Error> {
	Vec::<TokenTree>::decode(decoder).map(\|vec\| vec.into_iter().collect())
	}
	}

	impl Hash for TokenStream {
	fn hash<H: hash::Hasher>(&self, state: &mut H) {
	for tree in self.trees() {
	tree.hash(state);
	}
	}
	}

	impl Encodable for ThinTokenStream {
	fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), E::Error> {
	TokenStream::from(self.clone()).encode(encoder)
	}
	}

	impl Decodable for ThinTokenStream {
	fn decode<D: Decoder>(decoder: &mut D) -> Result<ThinTokenStream, D::Error> {
	TokenStream::decode(decoder).map(Into::into)
	}
	}

	impl Hash for ThinTokenStream {
	fn hash<H: hash::Hasher>(&self, state: &mut H) {
	TokenStream::from(self.clone()).hash(state);
	}
	}


	#[cfg(test)]
	mod tests {
	use super::*;
	use syntax::ast::Ident;
	use syntax_pos::{Span, BytePos, NO_EXPANSION};
	use parse::token::Token;
	use util::parser_testing::string_to_stream;

	fn string_to_ts(string: &str) -> TokenStream {
	string_to_stream(string.to_owned())
	}

	fn sp(a: u32, b: u32) -> Span {
	Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
	}

	#[test]
	fn test_concat() {
	let test_res = string_to_ts("foo::bar::baz");
	let test_fst = string_to_ts("foo::bar");
	let test_snd = string_to_ts("::baz");
	let eq_res = TokenStream::concat(vec![test_fst, test_snd]);
	assert_eq!(test_res.trees().count(), 5);
	assert_eq!(eq_res.trees().count(), 5);
	assert_eq!(test_res.eq_unspanned(&eq_res), true);
	}

	#[test]
	fn test_to_from_bijection() {
	let test_start = string_to_ts("foo::bar(baz)");
	let test_end = test_start.trees().collect();
	assert_eq!(test_start, test_end)
	}

	#[test]
	fn test_eq_0() {
	let test_res = string_to_ts("foo");
	let test_eqs = string_to_ts("foo");
	assert_eq!(test_res, test_eqs)
	}

	#[test]
	fn test_eq_1() {
	let test_res = string_to_ts("::bar::baz");
	let test_eqs = string_to_ts("::bar::baz");
	assert_eq!(test_res, test_eqs)
	}

	#[test]
	fn test_eq_3() {
	let test_res = string_to_ts("");
	let test_eqs = string_to_ts("");
	assert_eq!(test_res, test_eqs)
	}

	#[test]
	fn test_diseq_0() {
	let test_res = string_to_ts("::bar::baz");
	let test_eqs = string_to_ts("bar::baz");
	assert_eq!(test_res == test_eqs, false)
	}

	#[test]
	fn test_diseq_1() {
	let test_res = string_to_ts("(bar,baz)");
	let test_eqs = string_to_ts("bar,baz");
	assert_eq!(test_res == test_eqs, false)
	}

	#[test]
	fn test_is_empty() {
	let test0: TokenStream = Vec::<TokenTree>::new().into_iter().collect();
	let test1: TokenStream =
	TokenTree::Token(sp(0, 1), Token::Ident(Ident::from_str("a"))).into();
	let test2 = string_to_ts("foo(bar::baz)");

	assert_eq!(test0.is_empty(), true);
	assert_eq!(test1.is_empty(), false);
	assert_eq!(test2.is_empty(), false);
	}

	#[test]
	fn test_dotdotdot() {
	let mut builder = TokenStreamBuilder::new();
	builder.push(TokenTree::Token(sp(0, 1), Token::Dot).joint());
	builder.push(TokenTree::Token(sp(1, 2), Token::Dot).joint());
	builder.push(TokenTree::Token(sp(2, 3), Token::Dot));
	let stream = builder.build();
	assert!(stream.eq_unspanned(&string_to_ts("...")));
	assert_eq!(stream.trees().count(), 1);
	}

	}