//! # 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::token::{self, DelimToken, Token, TokenKind};
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_data_structures::sync::Lrc;
use rustc_macros::HashStable_Generic;
use rustc_span::{Span, DUMMY_SP};
use smallvec::{smallvec, SmallVec};
use std::{iter, mem};
/// 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, HashStable_Generic)]
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: DelimSpan, delim: DelimToken) -> TokenTree {
TokenTree::token(token::OpenDelim(delim), span.open)
}
/// Returns the closing delimiter as a token tree.
pub fn close_tt(span: DelimSpan, delim: DelimToken) -> TokenTree {
TokenTree::token(token::CloseDelim(delim), span.close)
}
}
impl<CTX> HashStable<CTX> for TokenStream
where
CTX: crate::HashStableContext,
{
fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
for sub_tt in self.trees() {
sub_tt.hash_stable(hcx, hasher);
}
}
}
/// 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, RustcEncodable, RustcDecodable)]
pub struct TokenStream(pub Lrc<Vec<TreeAndJoint>>);
pub type TreeAndJoint = (TokenTree, IsJoint);
// `TokenStream` is used a lot. Make sure it doesn't unintentionally get bigger.
#[cfg(target_arch = "x86_64")]
rustc_data_structures::static_assert_size!(TokenStream, 8);
#[derive(Clone, Copy, Debug, PartialEq, RustcEncodable, RustcDecodable)]
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<TokenTree> for TokenStream {
fn from(tree: TokenTree) -> TokenStream {
TokenStream::new(vec![(tree, NonJoint)])
}
}
impl From<TokenTree> for TreeAndJoint {
fn from(tree: TokenTree) -> TreeAndJoint {
(tree, NonJoint)
}
}
impl iter::FromIterator<TokenTree> for TokenStream {
fn from_iter<I: IntoIterator<Item = TokenTree>>(iter: I) -> Self {
TokenStream::new(iter.into_iter().map(Into::into).collect::<Vec<TreeAndJoint>>())
}
}
impl Eq for TokenStream {}
impl PartialEq<TokenStream> for TokenStream {
fn eq(&self, other: &TokenStream) -> bool {
self.trees().eq(other.trees())
}
}
impl TokenStream {
pub fn new(streams: Vec<TreeAndJoint>) -> TokenStream {
TokenStream(Lrc::new(streams))
}
pub fn is_empty(&self) -> bool {
self.0.is_empty()
}
pub fn len(&self) -> usize {
self.0.len()
}
pub fn span(&self) -> Option<Span> {
match &**self.0 {
[] => None,
[(tt, _)] => Some(tt.span()),
[(tt_start, _), .., (tt_end, _)] => Some(tt_start.span().to(tt_end.span())),
}
}
pub 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 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<F: FnMut(usize, TokenTree) -> 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<F: FnMut(TokenTree) -> 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<T: Into<TokenStream>>(&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<TokenTree> {
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<TreeAndJoint> {
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<TokenTree> {
self.stream.0[self.index..].get(n).map(|(tree, _)| tree.clone())
}
}
#[derive(Debug, Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable_Generic)]
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())
}
}