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The ANTLR 4 grammar compiler.
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/*
 * Copyright (c) 2012 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.ParserErrorListener;
import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.misc.NotNull;

import java.util.BitSet;

/**
 * This class represents profiling event information for an ambiguity.
 * Ambiguities are decisions where a particular input resulted in an SLL
 * conflict, followed by LL prediction also reaching a conflict state
 * (indicating a true ambiguity in the grammar).
 *
 * 
 * This event may be reported during SLL prediction in cases where the
 * conflicting SLL configuration set provides sufficient information to
 * determine that the SLL conflict is truly an ambiguity. For example, if none
 * of the ATN configurations in the conflicting SLL configuration set have
 * traversed a global follow transition (i.e.
 * {@link ATNConfig#getReachesIntoOuterContext} is {@code false} for all
 * configurations), then the result of SLL prediction for that input is known to
 * be equivalent to the result of LL prediction for that input.
 *
 * 
 * In some cases, the minimum represented alternative in the conflicting LL
 * configuration set is not equal to the minimum represented alternative in the
 * conflicting SLL configuration set. Grammars and inputs which result in this
 * scenario are unable to use {@link PredictionMode#SLL}, which in turn means
 * they cannot use the two-stage parsing strategy to improve parsing performance
 * for that input.
 *
 * @see ParserATNSimulator#reportAmbiguity
 * @see ParserErrorListener#reportAmbiguity
 *
 * @since 4.3
 */
public class AmbiguityInfo extends DecisionEventInfo {
	/** The set of alternative numbers for this decision event that lead to a valid parse. */
	@NotNull
	private final BitSet ambigAlts;

	/**
	 * Constructs a new instance of the {@link AmbiguityInfo} class with the
	 * specified detailed ambiguity information.
	 *
	 * @param decision The decision number
	 * @param state The final simulator state identifying the ambiguous
	 * alternatives for the current input
	 * @param ambigAlts The set of alternatives in the decision that lead to a valid parse.
	 *                  The predicted alt is the min(ambigAlts)
	 * @param input The input token stream
	 * @param startIndex The start index for the current prediction
	 * @param stopIndex The index at which the ambiguity was identified during
	 * prediction
	 */
	public AmbiguityInfo(int decision,
						 @NotNull SimulatorState state,
						 @NotNull BitSet ambigAlts,
						 @NotNull TokenStream input, int startIndex, int stopIndex)
	{
		super(decision, state, input, startIndex, stopIndex, state.useContext);
		this.ambigAlts = ambigAlts;
	}

	/**
	 * Gets the set of alternatives in the decision that lead to a valid parse.
	 *
	 * @since 4.5
	 */
	@NotNull
	public BitSet getAmbiguousAlternatives() {
		return ambigAlts;
	}
}