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Rewrite Parser::collect_tokens
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The previous implementation did not work when called on an opening
delimiter, or when called re-entrantly from the same `TokenCursor` stack
depth.
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@Aaron1011
Aaron1011 committed May 22, 2020
1 parent 148c125 commit 52bb09a
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Showing 3 changed files with 115 additions and 75 deletions.
186 changes: 113 additions & 73 deletions src/librustc_parse/parser/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -118,6 +118,8 @@ impl<'a> Drop for Parser<'a> {
struct TokenCursor {
frame: TokenCursorFrame,
stack: Vec<TokenCursorFrame>,
cur_token: Option<TreeAndJoint>,
collecting: Option<Collecting>,
}

#[derive(Clone)]
Expand All @@ -127,30 +129,24 @@ struct TokenCursorFrame {
open_delim: bool,
tree_cursor: tokenstream::Cursor,
close_delim: bool,
last_token: LastToken,
}

/// This is used in `TokenCursorFrame` above to track tokens that are consumed
/// by the parser, and then that's transitively used to record the tokens that
/// each parse AST item is created with.
///
/// Right now this has two states, either collecting tokens or not collecting
/// tokens. If we're collecting tokens we just save everything off into a local
/// `Vec`. This should eventually though likely save tokens from the original
/// token stream and just use slicing of token streams to avoid creation of a
/// whole new vector.
///
/// The second state is where we're passively not recording tokens, but the last
/// token is still tracked for when we want to start recording tokens. This
/// "last token" means that when we start recording tokens we'll want to ensure
/// that this, the first token, is included in the output.
///
/// You can find some more example usage of this in the `collect_tokens` method
/// on the parser.
#[derive(Clone)]
enum LastToken {
Collecting(Vec<TreeAndJoint>),
Was(Option<TreeAndJoint>),
/// Used to track additional state needed by `collect_tokens`
#[derive(Clone, Debug)]
struct Collecting {
/// Holds the current tokens captured during the most
/// recent call to `collect_tokens`
buf: Vec<TreeAndJoint>,
/// The depth of the `TokenCursor` stack at the time
/// collection was started. When we encounter a `TokenTree::Delimited`,
/// we want to record the `TokenTree::Delimited` itself,
/// but *not* any of the inner tokens while we are inside
/// the new frame (this would cause us to record duplicate tokens).
///
/// This `depth` fields tracks stack depth we are recording tokens.
/// Only tokens encountered at this depth will be recorded. See
/// `TokenCursor::next` for more details.
depth: usize,
}

impl TokenCursorFrame {
Expand All @@ -161,7 +157,6 @@ impl TokenCursorFrame {
open_delim: delim == token::NoDelim,
tree_cursor: tts.clone().into_trees(),
close_delim: delim == token::NoDelim,
last_token: LastToken::Was(None),
}
}
}
Expand All @@ -171,25 +166,38 @@ impl TokenCursor {
loop {
let tree = if !self.frame.open_delim {
self.frame.open_delim = true;
TokenTree::open_tt(self.frame.span, self.frame.delim)
} else if let Some(tree) = self.frame.tree_cursor.next() {
TokenTree::open_tt(self.frame.span, self.frame.delim).into()
} else if let Some(tree) = self.frame.tree_cursor.next_with_joint() {
tree
} else if !self.frame.close_delim {
self.frame.close_delim = true;
TokenTree::close_tt(self.frame.span, self.frame.delim)
TokenTree::close_tt(self.frame.span, self.frame.delim).into()
} else if let Some(frame) = self.stack.pop() {
self.frame = frame;
continue;
} else {
return Token::new(token::Eof, DUMMY_SP);
};

match self.frame.last_token {
LastToken::Collecting(ref mut v) => v.push(tree.clone().into()),
LastToken::Was(ref mut t) => *t = Some(tree.clone().into()),
// Don't set an open delimiter as our current token - we want
// to leave it as the full `TokenTree::Delimited` from the previous
// iteration of this loop
if !matches!(tree.0, TokenTree::Token(Token { kind: TokenKind::OpenDelim(_), .. })) {
self.cur_token = Some(tree.clone());
}

if let Some(collecting) = &mut self.collecting {
if collecting.depth == self.stack.len() {
debug!(
"TokenCursor::next(): collected {:?} at depth {:?}",
tree,
self.stack.len()
);
collecting.buf.push(tree.clone().into())
}
}

match tree {
match tree.0 {
TokenTree::Token(token) => return token,
TokenTree::Delimited(sp, delim, tts) => {
let frame = TokenCursorFrame::new(sp, delim, &tts);
Expand Down Expand Up @@ -350,6 +358,8 @@ impl<'a> Parser<'a> {
token_cursor: TokenCursor {
frame: TokenCursorFrame::new(DelimSpan::dummy(), token::NoDelim, &tokens),
stack: Vec::new(),
cur_token: None,
collecting: None,
},
desugar_doc_comments,
unmatched_angle_bracket_count: 0,
Expand Down Expand Up @@ -1105,65 +1115,95 @@ impl<'a> Parser<'a> {
}
}

/// Records all tokens consumed by the provided callback,
/// including the current token. These tokens are collected
/// into a `TokenStream`, and returned along with the result
/// of the callback.
///
/// Note: If your callback consumes an opening delimiter
/// (including the case where you call `collect_tokens`
/// when the current token is an opening delimeter),
/// you must also consume the corresponding closing delimiter.
///
/// That is, you can consume
/// `something ([{ }])` or `([{}])`, but not `([{}]`
///
/// This restriction shouldn't be an issue in practice,
/// since this function is used to record the tokens for
/// a parsed AST item, which always has matching delimiters.
fn collect_tokens<R>(
&mut self,
f: impl FnOnce(&mut Self) -> PResult<'a, R>,
) -> PResult<'a, (R, TokenStream)> {
// Record all tokens we parse when parsing this item.
let mut tokens = Vec::new();
let prev_collecting = match self.token_cursor.frame.last_token {
LastToken::Collecting(ref mut list) => Some(mem::take(list)),
LastToken::Was(ref mut last) => {
tokens.extend(last.take());
None
}
};
self.token_cursor.frame.last_token = LastToken::Collecting(tokens);
let prev = self.token_cursor.stack.len();
let tokens: Vec<TreeAndJoint> = self.token_cursor.cur_token.clone().into_iter().collect();
debug!("collect_tokens: starting with {:?}", tokens);

// We need special handling for the case where `collect_tokens` is called
// on an opening delimeter (e.g. '('). At this point, we have already pushed
// a new frame - however, we want to record the original `TokenTree::Delimited`,
// for consistency with the case where we start recording one token earlier.
// See `TokenCursor::next` to see how `cur_token` is set up.
let prev_depth =
if matches!(self.token_cursor.cur_token, Some((TokenTree::Delimited(..), _))) {
if self.token_cursor.stack.is_empty() {
// There is nothing below us in the stack that
// the function could consume, so the only thing it can legally
// capture is the entire contents of the current frame.
return Ok((f(self)?, TokenStream::new(tokens)));
}
// We have already recorded the full `TokenTree::Delimited` when we created
// our `tokens` vector at the start of this function. We are now inside
// a new frame corresponding to the `TokenTree::Delimited` we already recoreded.
// We don't want to record any of the tokens inside this frame, since they
// will be duplicates of the tokens nested inside the `TokenTree::Delimited`.
// Therefore, we set our recording depth to the *previous* frame. This allows
// us to record a sequence like: `(foo).bar()`: the `(foo)` will be recored
// as our initial `cur_token`, while the `.bar()` will be recored after we
// pop the `(foo)` frame.
self.token_cursor.stack.len() - 1
} else {
self.token_cursor.stack.len()
};
let prev_collecting =
self.token_cursor.collecting.replace(Collecting { buf: tokens, depth: prev_depth });

let ret = f(self);
let last_token = if self.token_cursor.stack.len() == prev {
&mut self.token_cursor.frame.last_token
} else if self.token_cursor.stack.get(prev).is_none() {
// This can happen due to a bad interaction of two unrelated recovery mechanisms with
// mismatched delimiters *and* recovery lookahead on the likely typo `pub ident(`
// (#62881).
return Ok((ret?, TokenStream::default()));

let mut collected_tokens = if let Some(collecting) = self.token_cursor.collecting.take() {
collecting.buf
} else {
&mut self.token_cursor.stack[prev].last_token
let msg = format!("our vector went away?");
debug!("collect_tokens: {}", msg);
self.sess.span_diagnostic.delay_span_bug(self.token.span, &msg);
// This can happen due to a bad interaction of two unrelated recovery mechanisms
// with mismatched delimiters *and* recovery lookahead on the likely typo
// `pub ident(` (#62895, different but similar to the case above).
return Ok((ret?, TokenStream::default()));
};

// Pull out the tokens that we've collected from the call to `f` above.
let mut collected_tokens = match *last_token {
LastToken::Collecting(ref mut v) => mem::take(v),
LastToken::Was(ref was) => {
let msg = format!("our vector went away? - found Was({:?})", was);
debug!("collect_tokens: {}", msg);
self.sess.span_diagnostic.delay_span_bug(self.token.span, &msg);
// This can happen due to a bad interaction of two unrelated recovery mechanisms
// with mismatched delimiters *and* recovery lookahead on the likely typo
// `pub ident(` (#62895, different but similar to the case above).
return Ok((ret?, TokenStream::default()));
}
};
debug!("collect_tokens: got raw tokens {:?}", collected_tokens);

// If we're not at EOF our current token wasn't actually consumed by
// `f`, but it'll still be in our list that we pulled out. In that case
// put it back.
let extra_token = if self.token != token::Eof { collected_tokens.pop() } else { None };

// If we were previously collecting tokens, then this was a recursive
// call. In that case we need to record all the tokens we collected in
// our parent list as well. To do that we push a clone of our stream
// onto the previous list.
match prev_collecting {
Some(mut list) => {
list.extend(collected_tokens.iter().cloned());
list.extend(extra_token);
*last_token = LastToken::Collecting(list);
}
None => {
*last_token = LastToken::Was(extra_token);
if let Some(mut collecting) = prev_collecting {
// If we were previously collecting at the same depth,
// then the previous call to `collect_tokens` needs to see
// the tokens we just recorded.
//
// If we were previously recording at an lower `depth`,
// then the previous `collect_tokens` call already recorded
// this entire frame in the form of a `TokenTree::Delimited`,
// so there is nothing else for us to do.
if collecting.depth == prev_depth {
collecting.buf.extend(collected_tokens.iter().cloned());
collecting.buf.extend(extra_token);
debug!("collect_tokens: updating previous buf to {:?}", collecting);
}
self.token_cursor.collecting = Some(collecting)
}

Ok((ret?, TokenStream::new(collected_tokens)))
Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/ast-json/ast-json-noexpand-output.stdout
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2 changes: 1 addition & 1 deletion src/test/ui/ast-json/ast-json-output.stdout
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@@ -1 +1 @@
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