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Simplify exit of Delimited submatchers.

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Currently, we detect an exit from a `Delimited` submatcher when `idx`
exceeds the bounds of the current submatcher *and* there is a `stack`
entry.

This commit changes it to something simpler: just look for a
`CloseDelim` token.
This commit is contained in:
Nicholas Nethercote 2022-03-30 11:21:32 +11:00
parent c5cf08d37b
commit 21699c41af
1 changed files with 12 additions and 18 deletions
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30
compiler/rustc_expand/src/mbe/macro_parser.rs
View file

@ -75,7 +75,7 @@ crate use ParseResult::*;
use crate::mbe::{self, SequenceRepetition, TokenTree};
use rustc_ast::token::{self, DocComment, Nonterminal, Token};
use rustc_ast::token::{self, DocComment, Nonterminal, Token, TokenKind};
use rustc_parse::parser::{NtOrTt, Parser};
use rustc_session::parse::ParseSess;
use rustc_span::symbol::MacroRulesNormalizedIdent;
@ -454,18 +454,6 @@ impl<'tt> TtParser<'tt> {
let mut eof_mps = EofMatcherPositions::None;
while let Some(mut mp) = self.cur_mps.pop() {
// Backtrack out of delimited submatcher when necessary. When backtracking out again,
// we need to advance the "dot" past the delimiters in the parent matcher(s).
while mp.idx >= mp.tts.len() {
match mp.stack.pop() {
Some(MatcherPosFrame { tts, idx }) => {
mp.tts = tts;
mp.idx = idx + 1;
}
None => break,
}
}
// Get the current position of the "dot" (`idx`) in `mp` and the number of token
// trees in the matcher (`len`).
let idx = mp.idx;
@ -516,11 +504,10 @@ impl<'tt> TtParser<'tt> {
TokenTree::Delimited(_, delimited) => {
// To descend into a delimited submatcher, we push the current matcher onto
// a stack and push a new mp containing the submatcher onto `cur_mps`.
//
// At the beginning of the loop, if we reach the end of the delimited
// submatcher, we pop the stack to backtrack out of the descent. Note that
// we use `all_tts` to include the open and close delimiter tokens.
// a stack and push a new mp containing the submatcher onto `cur_mps`. When
// we reach the closing delimiter, we will pop the stack to backtrack out
// of the descent. Note that we use `all_tts` to include the open and close
// delimiter tokens.
let tts = mem::replace(&mut mp.tts, &delimited.all_tts);
let idx = mp.idx;
mp.stack.push(MatcherPosFrame { tts, idx });
@ -542,6 +529,13 @@ impl<'tt> TtParser<'tt> {
mp.idx += 1;
self.cur_mps.push(mp);
} else if token_name_eq(&t, token) {
if let TokenKind::CloseDelim(_) = token.kind {
// Ascend out of the delimited submatcher.
debug_assert_eq!(idx, len - 1);
let frame = mp.stack.pop().unwrap();
mp.tts = frame.tts;
mp.idx = frame.idx;
}
mp.idx += 1;
self.next_mps.push(mp);
}