//! # 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 //! //! `TokenStream`s 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 crate::parse::token::{self, DelimToken, Token, TokenKind}; use syntax_pos::{BytePos, Span, DUMMY_SP}; #[cfg(target_arch = "x86_64")] use rustc_data_structures::static_assert_size; use rustc_data_structures::sync::Lrc; use rustc_serialize::{Decoder, Decodable, Encoder, Encodable}; use smallvec::{SmallVec, smallvec}; use std::{iter, mem}; #[cfg(test)] mod tests; /// 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, RustcEncodable, RustcDecodable)] pub enum TokenTree { /// A single token Token(Token), /// A delimited sequence of token trees Delimited(DelimSpan, DelimToken, TokenStream), } // Ensure all fields of `TokenTree` is `Send` and `Sync`. #[cfg(parallel_compiler)] fn _dummy() where Token: Send + Sync, DelimSpan: Send + Sync, DelimToken: Send + Sync, TokenStream: Send + Sync, {} impl TokenTree { /// Checks 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(token), TokenTree::Token(token2)) => token.kind == token2.kind, (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => { delim == delim2 && tts.eq_unspanned(&tts2) } _ => false, } } // See comments in `Nonterminal::to_tokenstream` for why we care about // *probably* equal here rather than actual equality // // This is otherwise the same as `eq_unspanned`, only recursing with a // different method. pub fn probably_equal_for_proc_macro(&self, other: &TokenTree) -> bool { match (self, other) { (TokenTree::Token(token), TokenTree::Token(token2)) => { token.probably_equal_for_proc_macro(token2) } (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => { delim == delim2 && tts.probably_equal_for_proc_macro(&tts2) } _ => false, } } /// Retrieves the TokenTree's span. pub fn span(&self) -> Span { match self { TokenTree::Token(token) => token.span, TokenTree::Delimited(sp, ..) => sp.entire(), } } /// Modify the `TokenTree`'s span in-place. pub fn set_span(&mut self, span: Span) { match self { TokenTree::Token(token) => token.span = span, TokenTree::Delimited(dspan, ..) => *dspan = DelimSpan::from_single(span), } } pub fn joint(self) -> TokenStream { TokenStream::new(vec![(self, Joint)]) } pub fn token(kind: TokenKind, span: Span) -> TokenTree { TokenTree::Token(Token::new(kind, span)) } /// Returns the opening delimiter as a token tree. pub fn open_tt(span: Span, delim: DelimToken) -> TokenTree { let open_span = if span.is_dummy() { span } else { span.with_hi(span.lo() + BytePos(delim.len() as u32)) }; TokenTree::token(token::OpenDelim(delim), open_span) } /// Returns the closing delimiter as a token tree. pub fn close_tt(span: Span, delim: DelimToken) -> TokenTree { let close_span = if span.is_dummy() { span } else { span.with_lo(span.hi() - BytePos(delim.len() as u32)) }; TokenTree::token(token::CloseDelim(delim), close_span) } } /// 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, Default)] pub struct TokenStream(pub Lrc>); pub type TreeAndJoint = (TokenTree, IsJoint); // `TokenStream` is used a lot. Make sure it doesn't unintentionally get bigger. #[cfg(target_arch = "x86_64")] static_assert_size!(TokenStream, 8); #[derive(Clone, Copy, Debug, PartialEq)] pub enum IsJoint { Joint, NonJoint } use IsJoint::*; impl TokenStream { /// Given a `TokenStream` with a `Stream` of only two arguments, return a new `TokenStream` /// separating the two arguments with a comma for diagnostic suggestions. pub fn add_comma(&self) -> Option<(TokenStream, Span)> { // Used to suggest if a user writes `foo!(a b);` let mut suggestion = None; let mut iter = self.0.iter().enumerate().peekable(); while let Some((pos, ts)) = iter.next() { if let Some((_, next)) = iter.peek() { let sp = match (&ts, &next) { (_, (TokenTree::Token(Token { kind: token::Comma, .. }), _)) => continue, ((TokenTree::Token(token_left), NonJoint), (TokenTree::Token(token_right), _)) if ((token_left.is_ident() && !token_left.is_reserved_ident()) || token_left.is_lit()) && ((token_right.is_ident() && !token_right.is_reserved_ident()) || token_right.is_lit()) => token_left.span, ((TokenTree::Delimited(sp, ..), NonJoint), _) => sp.entire(), _ => continue, }; let sp = sp.shrink_to_hi(); let comma = (TokenTree::token(token::Comma, sp), NonJoint); suggestion = Some((pos, comma, sp)); } } if let Some((pos, comma, sp)) = suggestion { let mut new_stream = vec![]; let parts = self.0.split_at(pos + 1); new_stream.extend_from_slice(parts.0); new_stream.push(comma); new_stream.extend_from_slice(parts.1); return Some((TokenStream::new(new_stream), sp)); } None } } impl From for TokenStream { fn from(tree: TokenTree) -> TokenStream { TokenStream::new(vec![(tree, NonJoint)]) } } impl From for TreeAndJoint { fn from(tree: TokenTree) -> TreeAndJoint { (tree, NonJoint) } } impl> iter::FromIterator for TokenStream { fn from_iter>(iter: I) -> Self { TokenStream::from_streams(iter.into_iter().map(Into::into).collect::>()) } } impl Eq for TokenStream {} impl PartialEq for TokenStream { fn eq(&self, other: &TokenStream) -> bool { self.trees().eq(other.trees()) } } impl TokenStream { pub fn new(streams: Vec) -> TokenStream { TokenStream(Lrc::new(streams)) } pub fn is_empty(&self) -> bool { self.0.is_empty() } pub fn len(&self) -> usize { self.0.len() } pub(crate) fn from_streams(mut streams: SmallVec<[TokenStream; 2]>) -> TokenStream { match streams.len() { 0 => TokenStream::default(), 1 => streams.pop().unwrap(), _ => { // We are going to extend the first stream in `streams` with // the elements from the subsequent streams. This requires // using `make_mut()` on the first stream, and in practice this // doesn't cause cloning 99.9% of the time. // // One very common use case is when `streams` has two elements, // where the first stream has any number of elements within // (often 1, but sometimes many more) and the second stream has // a single element within. // Determine how much the first stream will be extended. // Needed to avoid quadratic blow up from on-the-fly // reallocations (#57735). let num_appends = streams.iter() .skip(1) .map(|ts| ts.len()) .sum(); // Get the first stream. If it's `None`, create an empty // stream. let mut iter = streams.drain(); let mut first_stream_lrc = iter.next().unwrap().0; // Append the elements to the first stream, after reserving // space for them. let first_vec_mut = Lrc::make_mut(&mut first_stream_lrc); first_vec_mut.reserve(num_appends); for stream in iter { first_vec_mut.extend(stream.0.iter().cloned()); } // Create the final `TokenStream`. TokenStream(first_stream_lrc) } } } pub fn append_to_tree_and_joint_vec(self, vec: &mut Vec) { vec.extend(self.0.iter().cloned()); } pub fn trees(&self) -> Cursor { self.clone().into_trees() } pub fn into_trees(self) -> Cursor { Cursor::new(self) } /// Compares two `TokenStream`s, checking equality without regarding span information. pub fn eq_unspanned(&self, other: &TokenStream) -> bool { let mut t1 = self.trees(); let mut t2 = other.trees(); for (t1, t2) in t1.by_ref().zip(t2.by_ref()) { if !t1.eq_unspanned(&t2) { return false; } } t1.next().is_none() && t2.next().is_none() } // See comments in `Nonterminal::to_tokenstream` for why we care about // *probably* equal here rather than actual equality // // This is otherwise the same as `eq_unspanned`, only recursing with a // different method. pub fn probably_equal_for_proc_macro(&self, other: &TokenStream) -> bool { // When checking for `probably_eq`, we ignore certain tokens that aren't // preserved in the AST. Because they are not preserved, the pretty // printer arbitrarily adds or removes them when printing as token // streams, making a comparison between a token stream generated from an // AST and a token stream which was parsed into an AST more reliable. fn semantic_tree(tree: &TokenTree) -> bool { if let TokenTree::Token(token) = tree { if let // The pretty printer tends to add trailing commas to // everything, and in particular, after struct fields. | token::Comma // The pretty printer emits `NoDelim` as whitespace. | token::OpenDelim(DelimToken::NoDelim) | token::CloseDelim(DelimToken::NoDelim) // The pretty printer collapses many semicolons into one. | token::Semi // The pretty printer collapses whitespace arbitrarily and can // introduce whitespace from `NoDelim`. | token::Whitespace // The pretty printer can turn `$crate` into `::crate_name` | token::ModSep = token.kind { return false; } } true } let mut t1 = self.trees().filter(semantic_tree); let mut t2 = other.trees().filter(semantic_tree); for (t1, t2) in t1.by_ref().zip(t2.by_ref()) { if !t1.probably_equal_for_proc_macro(&t2) { return false; } } t1.next().is_none() && t2.next().is_none() } pub fn map_enumerated TokenTree>(self, mut f: F) -> TokenStream { TokenStream(Lrc::new( self.0 .iter() .enumerate() .map(|(i, (tree, is_joint))| (f(i, tree.clone()), *is_joint)) .collect() )) } pub fn map TokenTree>(self, mut f: F) -> TokenStream { TokenStream(Lrc::new( self.0 .iter() .map(|(tree, is_joint)| (f(tree.clone()), *is_joint)) .collect() )) } } // 99.5%+ of the time we have 1 or 2 elements in this vector. #[derive(Clone)] pub struct TokenStreamBuilder(SmallVec<[TokenStream; 2]>); impl TokenStreamBuilder { pub fn new() -> TokenStreamBuilder { TokenStreamBuilder(SmallVec::new()) } pub fn push>(&mut self, stream: T) { let mut stream = stream.into(); // If `self` is not empty and the last tree within the last stream is a // token tree marked with `Joint`... if let Some(TokenStream(ref mut last_stream_lrc)) = self.0.last_mut() { if let Some((TokenTree::Token(last_token), Joint)) = last_stream_lrc.last() { // ...and `stream` is not empty and the first tree within it is // a token tree... let TokenStream(ref mut stream_lrc) = stream; if let Some((TokenTree::Token(token), is_joint)) = stream_lrc.first() { // ...and the two tokens can be glued together... if let Some(glued_tok) = last_token.glue(&token) { // ...then do so, by overwriting the last token // tree in `self` and removing the first token tree // from `stream`. This requires using `make_mut()` // on the last stream in `self` and on `stream`, // and in practice this doesn't cause cloning 99.9% // of the time. // Overwrite the last token tree with the merged // token. let last_vec_mut = Lrc::make_mut(last_stream_lrc); *last_vec_mut.last_mut().unwrap() = (TokenTree::Token(glued_tok), *is_joint); // Remove the first token tree from `stream`. (This // is almost always the only tree in `stream`.) let stream_vec_mut = Lrc::make_mut(stream_lrc); stream_vec_mut.remove(0); // Don't push `stream` if it's empty -- that could // block subsequent token gluing, by getting // between two token trees that should be glued // together. if !stream.is_empty() { self.0.push(stream); } return; } } } } self.0.push(stream); } pub fn build(self) -> TokenStream { TokenStream::from_streams(self.0) } } #[derive(Clone)] pub struct Cursor { pub stream: TokenStream, index: usize, } impl Iterator for Cursor { type Item = TokenTree; fn next(&mut self) -> Option { self.next_with_joint().map(|(tree, _)| tree) } } impl Cursor { fn new(stream: TokenStream) -> Self { Cursor { stream, index: 0 } } pub fn next_with_joint(&mut self) -> Option { if self.index < self.stream.len() { self.index += 1; Some(self.stream.0[self.index - 1].clone()) } else { None } } pub fn append(&mut self, new_stream: TokenStream) { if new_stream.is_empty() { return; } let index = self.index; let stream = mem::take(&mut self.stream); *self = TokenStream::from_streams(smallvec![stream, new_stream]).into_trees(); self.index = index; } pub fn look_ahead(&self, n: usize) -> Option { self.stream.0[self.index ..].get(n).map(|(tree, _)| tree.clone()) } } impl Encodable for TokenStream { fn encode(&self, encoder: &mut E) -> Result<(), E::Error> { self.trees().collect::>().encode(encoder) } } impl Decodable for TokenStream { fn decode(decoder: &mut D) -> Result { Vec::::decode(decoder).map(|vec| vec.into_iter().collect()) } } #[derive(Debug, Copy, Clone, PartialEq, RustcEncodable, RustcDecodable)] pub struct DelimSpan { pub open: Span, pub close: Span, } impl DelimSpan { pub fn from_single(sp: Span) -> Self { DelimSpan { open: sp, close: sp, } } pub fn from_pair(open: Span, close: Span) -> Self { DelimSpan { open, close } } pub fn dummy() -> Self { Self::from_single(DUMMY_SP) } pub fn entire(self) -> Span { self.open.with_hi(self.close.hi()) } }