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//!
use crate::collections::{Map, Set};
use crate::grammar::repr::*;
use crate::lr1::build;
use crate::lr1::core::*;
use crate::lr1::first::FirstSets;
use crate::lr1::lane_table::lane::LaneTracer;
use crate::lr1::lane_table::table::context_set::OverlappingLookahead;
use crate::lr1::lane_table::table::{ConflictIndex, LaneTable};
use crate::lr1::lookahead::{Lookahead, TokenSet};
use crate::lr1::state_graph::StateGraph;
use ena::unify::InPlaceUnificationTable;
mod merge;
use self::merge::Merge;
mod state_set;
use self::state_set::StateSet;
pub struct LaneTableConstruct<'grammar> {
grammar: &'grammar Grammar,
first_sets: FirstSets,
start_nt: NonterminalString,
}
impl<'grammar> LaneTableConstruct<'grammar> {
pub fn new(grammar: &'grammar Grammar, start_nt: NonterminalString) -> Self {
let first_sets = FirstSets::new(grammar);
LaneTableConstruct {
grammar,
start_nt,
first_sets,
}
}
pub fn construct(self) -> Result<Vec<LR1State<'grammar>>, LR1TableConstructionError<'grammar>> {
let states = {
match build::build_lr0_states(self.grammar, self.start_nt.clone()) {
Ok(states) => {
// In this case, the grammar is actually
// LR(0). This is very rare -- it means that the
// grammar does not need lookahead to execute. In
// principle, we could stop here, except that if
// we do so, then the lookahead values that we get
// are very broad.
//
// Broad lookahead values will cause "eager"
// reduce at runtime -- i.e., if there is some
// scenario where the lookahead tells you we are
// in error, but we would have to reduce a few
// states before we see it. This, in turn, can
// cause infinite loops around error recovery
// (#240).
//
// Since we want to behave as a LR(1) parser
// would, we'll just go ahead and run the
// algorithm.
states
}
Err(TableConstructionError { states, .. }) => states,
}
};
// Convert the LR(0) states into LR(0-1) states.
let mut states = self.promote_lr0_states(states);
// For each inconsistent state, apply the lane-table algorithm to
// resolve it.
for i in 0.. {
if i >= states.len() {
break;
}
match self.resolve_inconsistencies(&mut states, StateIndex(i)) {
Ok(()) => {}
Err(_) => {
// We failed because of irreconcilable conflicts
// somewhere. Just compute the conflicts from the final set of
// states.
debug!(
"construct: failed to resolve inconsistencies in state {:#?}",
states[i]
);
let conflicts: Vec<Conflict<'grammar, TokenSet>> = states
.iter()
.flat_map(|s| Lookahead::conflicts(&s))
.collect();
return Err(TableConstructionError { states, conflicts });
}
}
}
Ok(states)
}
/// Given a set of LR0 states, returns LR1 states where the lookahead
/// is always `TokenSet::all()`. We refer to these states as LR(0-1)
/// states in the README.
fn promote_lr0_states(&self, lr0: Vec<LR0State<'grammar>>) -> Vec<LR1State<'grammar>> {
let all = TokenSet::all();
debug!("promote_lr0_states: all={:?}", all);
lr0.into_iter()
.map(|s| {
let items = s
.items
.vec
.iter()
.map(|item| Item {
production: item.production,
index: item.index,
lookahead: all.clone(),
})
.collect();
let reductions = s
.reductions
.into_iter()
.map(|(_, p)| (all.clone(), p))
.collect();
State {
index: s.index,
items: Items { vec: items },
shifts: s.shifts,
reductions,
gotos: s.gotos,
}
})
.collect()
}
fn resolve_inconsistencies(
&self,
states: &mut Vec<LR1State<'grammar>>,
inconsistent_state: StateIndex,
) -> Result<(), StateIndex> {
debug!(
"resolve_inconsistencies(inconsistent_state={:?}/{:#?}",
inconsistent_state, states[inconsistent_state.0]
);
let mut actions = super::conflicting_actions(&states[inconsistent_state.0]);
if actions.is_empty() {
// This can mean one of two things: only shifts, or a
// single reduction. We have to be careful about states
// with a single reduction: even though such a state is
// not inconsistent (there is only one possible course of
// action), we still want to run the lane table algorithm,
// because otherwise we get states with "complete"
// lookahead, which messes with error recovery.
//
// In particular, if there is too much lookahead, we will
// reduce even when it is inappropriate to do so.
actions = states[inconsistent_state.0]
.reductions
.iter()
.map(|&(_, prod)| Action::Reduce(prod))
.collect();
if actions.is_empty() {
return Ok(());
}
}
debug!("resolve_inconsistencies: conflicting_actions={:?}", actions);
let table = self.build_lane_table(states, inconsistent_state, &actions);
// Consider first the "LALR" case, where the lookaheads for each
// action are completely disjoint.
if self.attempt_lalr(&mut states[inconsistent_state.0], &table, &actions) {
return Ok(());
}
// Construct the initial states; each state will map to a
// context-set derived from its row in the lane-table. This is
// fallible, because a state may be internally inconstent.
//
// (To handle unification, we also map each state to a
// `StateSet` that is its entry in the `ena` table.)
let rows = table.rows()?;
let mut unify = InPlaceUnificationTable::<StateSet>::new();
let mut state_sets = Map::new();
for (&state_index, context_set) in &rows {
let state_set = unify.new_key(context_set.clone());
state_sets.insert(state_index, state_set);
debug!(
"resolve_inconsistencies: state_index={:?}, state_set={:?}",
state_index, state_set
);
}
// Now merge state-sets, cloning states where needed.
let mut merge = Merge::new(
&table,
&mut unify,
states,
&mut state_sets,
inconsistent_state,
);
let beachhead_states = table.beachhead_states();
for beachhead_state in beachhead_states {
match merge.start(beachhead_state) {
Ok(()) => {}
Err((source, _)) => {
debug!(
"resolve_inconsistencies: failed to merge, source={:?}",
source
);
return Err(source);
}
}
}
merge.patch_target_starts(&actions);
Ok(())
}
fn attempt_lalr(
&self,
state: &mut LR1State<'grammar>,
table: &LaneTable<'grammar>,
actions: &Set<Action<'grammar>>,
) -> bool {
match table.columns() {
Ok(columns) => {
debug!("attempt_lalr, columns={:#?}", columns);
columns.apply(state, actions);
debug!("attempt_lalr, state={:#?}", state);
true
}
Err(OverlappingLookahead) => {
debug!("attempt_lalr, OverlappingLookahead");
false
}
}
}
fn build_lane_table(
&self,
states: &[LR1State<'grammar>],
inconsistent_state: StateIndex,
actions: &Set<Action<'grammar>>,
) -> LaneTable<'grammar> {
let state_graph = StateGraph::new(states);
let mut tracer = LaneTracer::new(
self.grammar,
self.start_nt.clone(),
states,
&self.first_sets,
&state_graph,
actions.len(),
);
for (i, action) in actions.iter().enumerate() {
tracer.start_trace(inconsistent_state, ConflictIndex::new(i), action.clone());
}
tracer.into_table()
}
}