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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.misc;

import org.antlr.v4.runtime.Dependents;
import org.antlr.v4.runtime.RuleDependencies;
import org.antlr.v4.runtime.RuleDependency;
import org.antlr.v4.runtime.RuleVersion;
import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNDeserializer;
import org.antlr.v4.runtime.atn.ATNSimulator;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.RuleTransition;
import org.antlr.v4.runtime.atn.Transition;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.AnnotationValue;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.MirroredTypeException;
import javax.lang.model.type.TypeMirror;
import javax.tools.Diagnostic;

import java.lang.annotation.AnnotationTypeMismatchException;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * A compile-time validator for rule dependencies.
 *
 * @see RuleDependency
 * @see RuleDependencies
 * @author Sam Harwell
 */
@SupportedAnnotationTypes({RuleDependencyProcessor.RuleDependencyClassName, RuleDependencyProcessor.RuleDependenciesClassName, RuleDependencyProcessor.RuleVersionClassName})
public class RuleDependencyProcessor extends AbstractProcessor {
	public static final String RuleDependencyClassName = "org.antlr.v4.runtime.RuleDependency";
	public static final String RuleDependenciesClassName = "org.antlr.v4.runtime.RuleDependencies";
	public static final String RuleVersionClassName = "org.antlr.v4.runtime.RuleVersion";

	public RuleDependencyProcessor() {
	}

	@Override
	public SourceVersion getSupportedSourceVersion() {
		SourceVersion latestSupported = SourceVersion.latestSupported();

		if (latestSupported.ordinal() <= 6) {
			return SourceVersion.RELEASE_6;
		}
		else if (latestSupported.ordinal() <= 8) {
			return latestSupported;
		}
		else {
			// this annotation processor is tested through Java 8
			return SourceVersion.values()[8];
		}
	}

	@Override
	public boolean process(Set annotations, RoundEnvironment roundEnv) {
		if (!checkClassNameConstants()) {
			return true;
		}

		List> dependencies = getDependencies(roundEnv);
		Map>> recognizerDependencies
			= new HashMap>>();
		for (Tuple2 dependency : dependencies) {
			TypeMirror recognizerType = getRecognizerType(dependency.getItem1());
			List> list = recognizerDependencies.get(recognizerType);
			if (list == null) {
				list = new ArrayList>();
				recognizerDependencies.put(recognizerType, list);
			}

			list.add(dependency);
		}

		for (Map.Entry>> entry : recognizerDependencies.entrySet()) {
			processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, String.format("ANTLR 4: Validating %d dependencies on rules in %s.", entry.getValue().size(), entry.getKey().toString()));
			checkDependencies(entry.getValue(), entry.getKey());
		}

		return true;
	}

	private boolean checkClassNameConstants() {
		boolean success = checkClassNameConstant(RuleDependencyClassName, RuleDependency.class);
		success &= checkClassNameConstant(RuleDependenciesClassName, RuleDependencies.class);
		success &= checkClassNameConstant(RuleVersionClassName, RuleVersion.class);
		return success;
	}

	private boolean checkClassNameConstant(String className, Class clazz) {
		Args.notNull("className", className);
		Args.notNull("clazz", clazz);
		if (!className.equals(clazz.getCanonicalName())) {
			processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("Unable to process rule dependencies due to class name mismatch: %s != %s", className, clazz.getCanonicalName()));
			return false;
		}

		return true;
	}

	private static TypeMirror getRecognizerType(RuleDependency dependency) {
		try {
			dependency.recognizer();
			String message = String.format("Expected %s to get the %s.", MirroredTypeException.class.getSimpleName(), TypeMirror.class.getSimpleName());
			throw new UnsupportedOperationException(message);
		}
		catch (MirroredTypeException ex) {
			return ex.getTypeMirror();
		}
	}

	private void checkDependencies(List> dependencies, TypeMirror recognizerType) {
		String[] ruleNames = getRuleNames(recognizerType);
		int[] ruleVersions = getRuleVersions(recognizerType, ruleNames);
		RuleRelations relations = extractRuleRelations(recognizerType);

		for (Tuple2 dependency : dependencies) {
			try {
				if (!processingEnv.getTypeUtils().isAssignable(getRecognizerType(dependency.getItem1()), recognizerType)) {
					continue;
				}

				// this is the rule in the dependency set with the highest version number
				int effectiveRule = dependency.getItem1().rule();
				if (effectiveRule < 0 || effectiveRule >= ruleVersions.length) {
					Tuple2 ruleReferenceElement = findRuleDependencyProperty(dependency, RuleDependencyProperty.RULE);
					String message = String.format("Rule dependency on unknown rule %d@%d in %s",
												   dependency.getItem1().rule(),
												   dependency.getItem1().version(),
												   getRecognizerType(dependency.getItem1()).toString());

					if (ruleReferenceElement != null) {
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
													  dependency.getItem2(), ruleReferenceElement.getItem1(), ruleReferenceElement.getItem2());
					}
					else {
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
													  dependency.getItem2());
					}

					continue;
				}

				EnumSet dependents = EnumSet.of(Dependents.SELF, dependency.getItem1().dependents());
				reportUnimplementedDependents(dependency, dependents);

				BitSet checked = new BitSet();

				int highestRequiredDependency = checkDependencyVersion(dependency, ruleNames, ruleVersions, effectiveRule, null);

				if (dependents.contains(Dependents.PARENTS)) {
					BitSet parents = relations.parents[dependency.getItem1().rule()];
					for (int parent = parents.nextSetBit(0); parent >= 0; parent = parents.nextSetBit(parent + 1)) {
						if (parent < 0 || parent >= ruleVersions.length || checked.get(parent)) {
							continue;
						}

						checked.set(parent);
						int required = checkDependencyVersion(dependency, ruleNames, ruleVersions, parent, "parent");
						highestRequiredDependency = Math.max(highestRequiredDependency, required);
					}
				}

				if (dependents.contains(Dependents.CHILDREN)) {
					BitSet children = relations.children[dependency.getItem1().rule()];
					for (int child = children.nextSetBit(0); child >= 0; child = children.nextSetBit(child + 1)) {
						if (child < 0 || child >= ruleVersions.length || checked.get(child)) {
							continue;
						}

						checked.set(child);
						int required = checkDependencyVersion(dependency, ruleNames, ruleVersions, child, "child");
						highestRequiredDependency = Math.max(highestRequiredDependency, required);
					}
				}

				if (dependents.contains(Dependents.ANCESTORS)) {
					BitSet ancestors = relations.getAncestors(dependency.getItem1().rule());
					for (int ancestor = ancestors.nextSetBit(0); ancestor >= 0; ancestor = ancestors.nextSetBit(ancestor + 1)) {
						if (ancestor < 0 || ancestor >= ruleVersions.length || checked.get(ancestor)) {
							continue;
						}

						checked.set(ancestor);
						int required = checkDependencyVersion(dependency, ruleNames, ruleVersions, ancestor, "ancestor");
						highestRequiredDependency = Math.max(highestRequiredDependency, required);
					}
				}

				if (dependents.contains(Dependents.DESCENDANTS)) {
					BitSet descendants = relations.getDescendants(dependency.getItem1().rule());
					for (int descendant = descendants.nextSetBit(0); descendant >= 0; descendant = descendants.nextSetBit(descendant + 1)) {
						if (descendant < 0 || descendant >= ruleVersions.length || checked.get(descendant)) {
							continue;
						}

						checked.set(descendant);
						int required = checkDependencyVersion(dependency, ruleNames, ruleVersions, descendant, "descendant");
						highestRequiredDependency = Math.max(highestRequiredDependency, required);
					}
				}

				int declaredVersion = dependency.getItem1().version();
				if (declaredVersion > highestRequiredDependency) {
					Tuple2 versionElement = findRuleDependencyProperty(dependency, RuleDependencyProperty.VERSION);
					String message = String.format("Rule dependency version mismatch: %s has maximum dependency version %d (expected %d) in %s",
												   ruleNames[dependency.getItem1().rule()],
												   highestRequiredDependency,
												   declaredVersion,
												   getRecognizerType(dependency.getItem1()).toString());

					if (versionElement != null) {
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
														  dependency.getItem2(), versionElement.getItem1(), versionElement.getItem2());
					}
					else {
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
														  dependency.getItem2());
					}
				}
			}
			catch (AnnotationTypeMismatchException ex) {
				processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, String.format("Could not validate rule dependencies for element %s", dependency.getItem2().toString()),
														 dependency.getItem2());
			}
		}
	}

	private static final Set IMPLEMENTED_DEPENDENTS = EnumSet.of(Dependents.SELF, Dependents.PARENTS, Dependents.CHILDREN, Dependents.ANCESTORS, Dependents.DESCENDANTS);

	private void reportUnimplementedDependents(Tuple2 dependency, EnumSet dependents) {
		EnumSet unimplemented = dependents.clone();
		unimplemented.removeAll(IMPLEMENTED_DEPENDENTS);
		if (!unimplemented.isEmpty()) {
			Tuple2 dependentsElement = findRuleDependencyProperty(dependency, RuleDependencyProperty.DEPENDENTS);
			if (dependentsElement == null) {
				dependentsElement = findRuleDependencyProperty(dependency, RuleDependencyProperty.RULE);
			}

			String message = String.format("Cannot validate the following dependents of rule %d: %s",
										   dependency.getItem1().rule(),
										   unimplemented);

			if (dependentsElement != null) {
				processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, message,
											  dependency.getItem2(), dependentsElement.getItem1(), dependentsElement.getItem2());
			}
			else {
				processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, message,
											  dependency.getItem2());
			}
		}
	}

	private int checkDependencyVersion(Tuple2 dependency, String[] ruleNames, int[] ruleVersions, int relatedRule, String relation) {
		String ruleName = ruleNames[dependency.getItem1().rule()];
		String path;
		if (relation == null) {
			path = ruleName;
		}
		else {
			String mismatchedRuleName = ruleNames[relatedRule];
			path = String.format("rule %s (%s of %s)", mismatchedRuleName, relation, ruleName);
		}

		int declaredVersion = dependency.getItem1().version();
		int actualVersion = ruleVersions[relatedRule];
		if (actualVersion > declaredVersion) {
			Tuple2 versionElement = findRuleDependencyProperty(dependency, RuleDependencyProperty.VERSION);
			String message = String.format("Rule dependency version mismatch: %s has version %d (expected <= %d) in %s",
										   path,
										   actualVersion,
										   declaredVersion,
										   getRecognizerType(dependency.getItem1()).toString());

			if (versionElement != null) {
				processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
												  dependency.getItem2(), versionElement.getItem1(), versionElement.getItem2());
			}
			else {
				processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message,
												  dependency.getItem2());
			}
		}

		return actualVersion;
	}

	private int[] getRuleVersions(TypeMirror recognizerClass, String[] ruleNames) {
		int[] versions = new int[ruleNames.length];

		List elements = processingEnv.getElementUtils().getAllMembers((TypeElement)processingEnv.getTypeUtils().asElement(recognizerClass));
		for (Element element : elements) {
			if (element.getKind() != ElementKind.FIELD) {
				continue;
			}

			VariableElement field = (VariableElement)element;
			boolean isStatic = element.getModifiers().contains(Modifier.STATIC);
			Object constantValue = field.getConstantValue();
			boolean isInteger = constantValue instanceof Integer;
			String name = field.getSimpleName().toString();
			if (isStatic && isInteger && name.startsWith("RULE_")) {
				try {
					name = name.substring("RULE_".length());
					if (name.isEmpty() || !Character.isLowerCase(name.charAt(0))) {
						continue;
					}

					int index = (Integer)constantValue;
					if (index < 0 || index >= versions.length) {
						String message = String.format("Rule index %d for rule '%s' out of bounds for recognizer %s.", index, name, recognizerClass.toString());
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message, element);
						continue;
					}

					if (name.indexOf(ATNSimulator.RULE_VARIANT_DELIMITER) >= 0) {
						// ignore left-factored pseudo-rules
						continue;
					}

					ExecutableElement ruleMethod = getRuleMethod(recognizerClass, name);
					if (ruleMethod == null) {
						String message = String.format("Could not find rule method for rule '%s' in recognizer %s.", name, recognizerClass.toString());
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, message, element);
						continue;
					}

					RuleVersion ruleVersion = ruleMethod.getAnnotation(RuleVersion.class);
					int version = ruleVersion != null ? ruleVersion.value() : 0;
					versions[index] = version;
				} catch (IllegalArgumentException ex) {
					processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "Exception occurred while validating rule dependencies.", element);
				}
			}
		}

		return versions;
	}

	private ExecutableElement getRuleMethod(TypeMirror recognizerClass, String name) {
		List elements = processingEnv.getElementUtils().getAllMembers((TypeElement)processingEnv.getTypeUtils().asElement(recognizerClass));
		for (Element element : elements) {
			if (element.getKind() != ElementKind.METHOD) {
				continue;
			}

			ExecutableElement method = (ExecutableElement)element;
			if (method.getSimpleName().contentEquals(name) && hasRuleVersionAnnotation(method)) {
				return method;
			}
		}

		return null;
	}

	private boolean hasRuleVersionAnnotation(ExecutableElement method) {
		TypeElement ruleVersionAnnotationElement = processingEnv.getElementUtils().getTypeElement(RuleVersionClassName);
		if (ruleVersionAnnotationElement == null) {
			return false;
		}

		for (AnnotationMirror annotation : method.getAnnotationMirrors()) {
			if (processingEnv.getTypeUtils().isSameType(annotation.getAnnotationType(), ruleVersionAnnotationElement.asType())) {
				return true;
			}
		}

		return false;
	}

	private String[] getRuleNames(TypeMirror recognizerClass) {
		List result = new ArrayList();

		List elements = processingEnv.getElementUtils().getAllMembers((TypeElement)processingEnv.getTypeUtils().asElement(recognizerClass));
		for (Element element : elements) {
			if (element.getKind() != ElementKind.FIELD) {
				continue;
			}

			VariableElement field = (VariableElement)element;
			boolean isStatic = element.getModifiers().contains(Modifier.STATIC);
			Object constantValue = field.getConstantValue();
			boolean isInteger = constantValue instanceof Integer;
			String name = field.getSimpleName().toString();
			if (isStatic && isInteger && name.startsWith("RULE_")) {
				try {
					name = name.substring("RULE_".length());
					if (name.isEmpty() || !Character.isLowerCase(name.charAt(0))) {
						continue;
					}

					int index = (Integer)constantValue;
					if (index < 0) {
						continue;
					}

					while (result.size() <= index) {
						result.add("");
					}

					result.set(index, name);
				} catch (IllegalArgumentException ex) {
					processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "Exception occurred while validating rule dependencies.", element);
				}
			}
		}

		return result.toArray(new String[result.size()]);
	}

	public static List> getDependencies(RoundEnvironment roundEnv) {
		List> result = new ArrayList>();
		Set elements = roundEnv.getElementsAnnotatedWith(RuleDependency.class);
		for (Element element : elements) {
			RuleDependency dependency = element.getAnnotation(RuleDependency.class);
			if (dependency == null) {
				continue;
			}

			result.add(Tuple.create(dependency, element));
		}

		elements = roundEnv.getElementsAnnotatedWith(RuleDependencies.class);
		for (Element element : elements) {
			RuleDependencies dependencies = element.getAnnotation(RuleDependencies.class);
			if (dependencies == null || dependencies.value() == null) {
				continue;
			}

			for (RuleDependency dependency : dependencies.value()) {
				result.add(Tuple.create(dependency, element));
			}
		}

		return result;
	}

	public enum RuleDependencyProperty {
		RECOGNIZER,
		RULE,
		VERSION,
		DEPENDENTS,
	}

	@Nullable
	private Tuple2 findRuleDependencyProperty(@NotNull Tuple2 dependency, @NotNull RuleDependencyProperty property) {
		TypeElement ruleDependencyTypeElement = processingEnv.getElementUtils().getTypeElement(RuleDependencyClassName);
		TypeElement ruleDependenciesTypeElement = processingEnv.getElementUtils().getTypeElement(RuleDependenciesClassName);
		List mirrors = dependency.getItem2().getAnnotationMirrors();
		for (AnnotationMirror annotationMirror : mirrors) {
			if (processingEnv.getTypeUtils().isSameType(ruleDependencyTypeElement.asType(), annotationMirror.getAnnotationType())) {
				AnnotationValue element = findRuleDependencyProperty(dependency, annotationMirror, property);
				if (element != null) {
					return Tuple.create(annotationMirror, element);
				}
			}
			else if (processingEnv.getTypeUtils().isSameType(ruleDependenciesTypeElement.asType(), annotationMirror.getAnnotationType())) {
				Map values = annotationMirror.getElementValues();
				for (Map.Entry value : values.entrySet()) {
					if ("value()".equals(value.getKey().toString())) {
						AnnotationValue annotationValue = value.getValue();
						if (!(annotationValue.getValue() instanceof List)) {
							processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Expected array of RuleDependency annotations for annotation property 'value()'.", dependency.getItem2(), annotationMirror, annotationValue);
							break;
						}

						List annotationValueList = (List)annotationValue.getValue();
						for (Object obj : annotationValueList) {
							if (!(obj instanceof AnnotationMirror)) {
								processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Expected RuleDependency annotation mirror for element of property 'value()'.", dependency.getItem2(), annotationMirror, annotationValue);
								break;
							}

							AnnotationValue element = findRuleDependencyProperty(dependency, (AnnotationMirror)obj, property);
							if (element != null) {
								return Tuple.create((AnnotationMirror)obj, element);
							}
						}
					}
					else {
						processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("Unexpected annotation property %s.", value.getKey().toString()), dependency.getItem2(), annotationMirror, value.getValue());
					}
				}
			}
		}

		return null;
	}

	@Nullable
	private AnnotationValue findRuleDependencyProperty(@NotNull Tuple2 dependency, @NotNull AnnotationMirror annotationMirror, @NotNull RuleDependencyProperty property) {
		AnnotationValue recognizerValue = null;
		AnnotationValue ruleValue = null;
		AnnotationValue versionValue = null;
		AnnotationValue dependentsValue = null;

		Map values = annotationMirror.getElementValues();
		for (Map.Entry value : values.entrySet()) {
			AnnotationValue annotationValue = value.getValue();
			if ("rule()".equals(value.getKey().toString())) {
				ruleValue = annotationValue;
				if (!(annotationValue.getValue() instanceof Integer)) {
					processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Expected int constant for annotation property 'rule()'.", dependency.getItem2(), annotationMirror, annotationValue);
					return null;
				}

				if ((Integer)annotationValue.getValue() != dependency.getItem1().rule()) {
					// this is a valid dependency annotation, but not the one we're looking for
					return null;
				}
			}
			else if ("recognizer()".equals(value.getKey().toString())) {
				recognizerValue = annotationValue;
				if (!(annotationValue.getValue() instanceof TypeMirror)) {
					processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Expected Class constant for annotation property 'recognizer()'.", dependency.getItem2(), annotationMirror, annotationValue);
					return null;
				}

				TypeMirror annotationRecognizer = (TypeMirror)annotationValue.getValue();
				TypeMirror expectedRecognizer = getRecognizerType(dependency.getItem1());
				if (!processingEnv.getTypeUtils().isSameType(expectedRecognizer, annotationRecognizer)) {
					// this is a valid dependency annotation, but not the one we're looking for
					return null;
				}
			}
			else if ("version()".equals(value.getKey().toString())) {
				versionValue = annotationValue;
				if (!(annotationValue.getValue() instanceof Integer)) {
					processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Expected int constant for annotation property 'version()'.", dependency.getItem2(), annotationMirror, annotationValue);
					return null;
				}

				if ((Integer)annotationValue.getValue() != dependency.getItem1().version()) {
					// this is a valid dependency annotation, but not the one we're looking for
					return null;
				}
			}
		}

		if (recognizerValue != null) {
			if (property == RuleDependencyProperty.RECOGNIZER) {
				return recognizerValue;
			}
			else if (ruleValue != null) {
				if (property == RuleDependencyProperty.RULE) {
					return ruleValue;
				}
				else if (versionValue != null) {
					if (property == RuleDependencyProperty.VERSION) {
						return versionValue;
					}
					else if (property == RuleDependencyProperty.DEPENDENTS) {
						return dependentsValue;
					}
				}
			}
		}

		if (recognizerValue == null) {
			processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Could not find 'recognizer()' element in annotation.", dependency.getItem2(), annotationMirror);
		}

		if (property == RuleDependencyProperty.RECOGNIZER) {
			return null;
		}

		if (ruleValue == null) {
			processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Could not find 'rule()' element in annotation.", dependency.getItem2(), annotationMirror);
		}

		if (property == RuleDependencyProperty.RULE) {
			return null;
		}

		if (versionValue == null) {
			processingEnv.getMessager().printMessage(Diagnostic.Kind.WARNING, "Could not find 'version()' element in annotation.", dependency.getItem2(), annotationMirror);
		}

		return null;
	}

	private RuleRelations extractRuleRelations(TypeMirror recognizer) {
		String serializedATN = getSerializedATN(recognizer);
		if (serializedATN == null) {
			return null;
		}

		ATN atn = new ATNDeserializer().deserialize(serializedATN.toCharArray());
		RuleRelations relations = new RuleRelations(atn.ruleToStartState.length);
		for (ATNState state : atn.states) {
			if (!state.epsilonOnlyTransitions) {
				continue;
			}

			for (Transition transition : state.getTransitions()) {
				if (transition.getSerializationType() != Transition.RULE) {
					continue;
				}

				RuleTransition ruleTransition = (RuleTransition)transition;
				relations.addRuleInvocation(state.ruleIndex, ruleTransition.target.ruleIndex);
			}
		}

		return relations;
	}

	private String getSerializedATN(TypeMirror recognizerClass) {
		List elements = processingEnv.getElementUtils().getAllMembers((TypeElement)processingEnv.getTypeUtils().asElement(recognizerClass));
		for (Element element : elements) {
			if (element.getKind() != ElementKind.FIELD) {
				continue;
			}

			VariableElement field = (VariableElement)element;
			boolean isStatic = element.getModifiers().contains(Modifier.STATIC);
			Object constantValue = field.getConstantValue();
			boolean isString = constantValue instanceof String;
			String name = field.getSimpleName().toString();
			if (isStatic && isString && name.equals("_serializedATN")) {
				return (String)constantValue;
			}
		}

		processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "Could not retrieve serialized ATN from grammar.");
		return null;
	}

	private static final class RuleRelations {
		private final BitSet[] parents;
		private final BitSet[] children;

		public RuleRelations(int ruleCount) {
			parents = new BitSet[ruleCount];
			for (int i = 0; i < ruleCount; i++) {
				parents[i] = new BitSet();
			}

			children = new BitSet[ruleCount];
			for (int i = 0; i < ruleCount; i++) {
				children[i] = new BitSet();
			}
		}

		public boolean addRuleInvocation(int caller, int callee) {
			if (caller < 0) {
				// tokens rule
				return false;
			}

			if (children[caller].get(callee)) {
				// already added
				return false;
			}

			children[caller].set(callee);
			parents[callee].set(caller);
			return true;
		}

		public BitSet getAncestors(int rule) {
			BitSet ancestors = new BitSet();
			ancestors.or(parents[rule]);
			while (true) {
				int cardinality = ancestors.cardinality();
				for (int i = ancestors.nextSetBit(0); i >= 0; i = ancestors.nextSetBit(i + 1)) {
					ancestors.or(parents[i]);
				}

				if (ancestors.cardinality() == cardinality) {
					// nothing changed
					break;
				}
			}

			return ancestors;
		}

		public BitSet getDescendants(int rule) {
			BitSet descendants = new BitSet();
			descendants.or(children[rule]);
			while (true) {
				int cardinality = descendants.cardinality();
				for (int i = descendants.nextSetBit(0); i >= 0; i = descendants.nextSetBit(i + 1)) {
					descendants.or(children[i]);
				}

				if (descendants.cardinality() == cardinality) {
					// nothing changed
					break;
				}
			}

			return descendants;
		}
	}
}