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With inspiration from other libraries
/*
* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
package org.antlr.v4.runtime.atn;
import org.antlr.v4.runtime.RuleContext;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.misc.IntervalSet;
import java.util.BitSet;
import java.util.HashSet;
import java.util.Set;
public class LL1Analyzer {
/** Special value added to the lookahead sets to indicate that we hit
* a predicate during analysis if {@code seeThruPreds==false}.
*/
public static final int HIT_PRED = Token.INVALID_TYPE;
public final ATN atn;
public LL1Analyzer(ATN atn) { this.atn = atn; }
/**
* Calculates the SLL(1) expected lookahead set for each outgoing transition
* of an {@link ATNState}. The returned array has one element for each
* outgoing transition in {@code s}. If the closure from transition
* i leads to a semantic predicate before matching a symbol, the
* element at index i of the result will be {@code null}.
*
* @param s the ATN state
* @return the expected symbols for each outgoing transition of {@code s}.
*/
public IntervalSet[] getDecisionLookahead(ATNState s) {
// System.out.println("LOOK("+s.stateNumber+")");
if ( s==null ) {
return null;
}
IntervalSet[] look = new IntervalSet[s.getNumberOfTransitions()];
for (int alt = 0; alt < s.getNumberOfTransitions(); alt++) {
look[alt] = new IntervalSet();
Set lookBusy = new HashSet();
boolean seeThruPreds = false; // fail to get lookahead upon pred
_LOOK(s.transition(alt).target, null, PredictionContext.EMPTY,
look[alt], lookBusy, new BitSet(), seeThruPreds, false);
// Wipe out lookahead for this alternative if we found nothing
// or we had a predicate when we !seeThruPreds
if ( look[alt].size()==0 || look[alt].contains(HIT_PRED) ) {
look[alt] = null;
}
}
return look;
}
/**
* Compute set of tokens that can follow {@code s} in the ATN in the
* specified {@code ctx}.
*
* If {@code ctx} is {@code null} and the end of the rule containing
* {@code s} is reached, {@link Token#EPSILON} is added to the result set.
* If {@code ctx} is not {@code null} and the end of the outermost rule is
* reached, {@link Token#EOF} is added to the result set.
*
* @param s the ATN state
* @param ctx the complete parser context, or {@code null} if the context
* should be ignored
*
* @return The set of tokens that can follow {@code s} in the ATN in the
* specified {@code ctx}.
*/
public IntervalSet LOOK(ATNState s, RuleContext ctx) {
return LOOK(s, null, ctx);
}
/**
* Compute set of tokens that can follow {@code s} in the ATN in the
* specified {@code ctx}.
*
* If {@code ctx} is {@code null} and the end of the rule containing
* {@code s} is reached, {@link Token#EPSILON} is added to the result set.
* If {@code ctx} is not {@code null} and the end of the outermost rule is
* reached, {@link Token#EOF} is added to the result set.
*
* @param s the ATN state
* @param stopState the ATN state to stop at. This can be a
* {@link BlockEndState} to detect epsilon paths through a closure.
* @param ctx the complete parser context, or {@code null} if the context
* should be ignored
*
* @return The set of tokens that can follow {@code s} in the ATN in the
* specified {@code ctx}.
*/
public IntervalSet LOOK(ATNState s, ATNState stopState, RuleContext ctx) {
IntervalSet r = new IntervalSet();
boolean seeThruPreds = true; // ignore preds; get all lookahead
PredictionContext lookContext = ctx != null ? PredictionContext.fromRuleContext(s.atn, ctx) : null;
_LOOK(s, stopState, lookContext,
r, new HashSet(), new BitSet(), seeThruPreds, true);
return r;
}
/**
* Compute set of tokens that can follow {@code s} in the ATN in the
* specified {@code ctx}.
*
* If {@code ctx} is {@code null} and {@code stopState} or the end of the
* rule containing {@code s} is reached, {@link Token#EPSILON} is added to
* the result set. If {@code ctx} is not {@code null} and {@code addEOF} is
* {@code true} and {@code stopState} or the end of the outermost rule is
* reached, {@link Token#EOF} is added to the result set.
*
* @param s the ATN state.
* @param stopState the ATN state to stop at. This can be a
* {@link BlockEndState} to detect epsilon paths through a closure.
* @param ctx The outer context, or {@code null} if the outer context should
* not be used.
* @param look The result lookahead set.
* @param lookBusy A set used for preventing epsilon closures in the ATN
* from causing a stack overflow. Outside code should pass
* {@code new HashSet} for this argument.
* @param calledRuleStack A set used for preventing left recursion in the
* ATN from causing a stack overflow. Outside code should pass
* {@code new BitSet()} for this argument.
* @param seeThruPreds {@code true} to true semantic predicates as
* implicitly {@code true} and "see through them", otherwise {@code false}
* to treat semantic predicates as opaque and add {@link #HIT_PRED} to the
* result if one is encountered.
* @param addEOF Add {@link Token#EOF} to the result if the end of the
* outermost context is reached. This parameter has no effect if {@code ctx}
* is {@code null}.
*/
protected void _LOOK(ATNState s,
ATNState stopState,
PredictionContext ctx,
IntervalSet look,
Set lookBusy,
BitSet calledRuleStack,
boolean seeThruPreds, boolean addEOF)
{
// System.out.println("_LOOK("+s.stateNumber+", ctx="+ctx);
ATNConfig c = new ATNConfig(s, 0, ctx);
if ( !lookBusy.add(c) ) return;
if (s == stopState) {
if (ctx == null) {
look.add(Token.EPSILON);
return;
}
else if (ctx.isEmpty() && addEOF) {
look.add(Token.EOF);
return;
}
}
if ( s instanceof RuleStopState ) {
if ( ctx==null ) {
look.add(Token.EPSILON);
return;
}
else if (ctx.isEmpty() && addEOF) {
look.add(Token.EOF);
return;
}
if ( ctx != PredictionContext.EMPTY ) {
// run thru all possible stack tops in ctx
boolean removed = calledRuleStack.get(s.ruleIndex);
try {
calledRuleStack.clear(s.ruleIndex);
for (int i = 0; i < ctx.size(); i++) {
ATNState returnState = atn.states.get(ctx.getReturnState(i));
// System.out.println("popping back to "+retState);
_LOOK(returnState, stopState, ctx.getParent(i), look, lookBusy, calledRuleStack, seeThruPreds, addEOF);
}
}
finally {
if (removed) {
calledRuleStack.set(s.ruleIndex);
}
}
return;
}
}
int n = s.getNumberOfTransitions();
for (int i=0; i