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shift conflicts do not need to be traced

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This commit is contained in:
Niko Matsakis 2016-03-06 06:05:09 -05:00
parent ed089c27fd
commit e72378d2bc
1 changed files with 20 additions and 1 deletions
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21
lalrpop/src/lr1/lane_table/lane/mod.rs
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@ -41,7 +41,26 @@ impl<'trace, 'grammar> LaneTracer<'trace, 'grammar> {
conflict: ConflictIndex,
item: LR0Item<'grammar>) {
let mut visited_set = Set::default();
self.continue_trace(state, conflict, item, &mut visited_set);
// if the conflict item is a "shift" item, then the context
// is always the termianl to shift (and conflicts only arise
// around shifting terminal, so it must be a terminal)
match item.shift_symbol() {
Some((Symbol::Terminal(term), _)) => {
let mut token_set = TokenSet::new(self.grammar);
token_set.insert(self.grammar, Token::Terminal(term));
self.table.add_lookahead(state, conflict, &token_set);
}
Some((Symbol::Nonterminal(_), _)) => {
panic!("invalid conflict item `{:?}`: shifts nonterminal",
item);
}
None => {
self.continue_trace(state, conflict, item, &mut visited_set);
}
}
}
fn continue_trace(&mut self,