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This project contains a parser for the Checker Framework's stub files: https://checkerframework.org/manual/#stub . It is a fork of the JavaParser project.
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/*
 * Copyright (C) 2015-2016 Federico Tomassetti
 * Copyright (C) 2017-2024 The JavaParser Team.
 *
 * This file is part of JavaParser.
 *
 * JavaParser can be used either under the terms of
 * a) the GNU Lesser General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 * b) the terms of the Apache License
 *
 * You should have received a copy of both licenses in LICENCE.LGPL and
 * LICENCE.APACHE. Please refer to those files for details.
 *
 * JavaParser is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 */
package com.github.javaparser.resolution.logic;

import com.github.javaparser.resolution.TypeSolver;
import com.github.javaparser.resolution.declarations.ResolvedReferenceTypeDeclaration;
import com.github.javaparser.resolution.declarations.ResolvedTypeParameterDeclaration;
import com.github.javaparser.resolution.model.typesystem.ReferenceTypeImpl;
import com.github.javaparser.resolution.types.*;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @author Federico Tomassetti
 */
public class InferenceContext {

    private int nextInferenceVariableId = 0;

    private TypeSolver typeSolver;

    private List inferenceVariableTypes = new ArrayList<>();

    private Map inferenceVariableTypeMap = new HashMap<>();

    public InferenceContext(TypeSolver typeSolver) {
        this.typeSolver = typeSolver;
    }

    private InferenceVariableType inferenceVariableTypeForTp(ResolvedTypeParameterDeclaration tp) {
        if (!inferenceVariableTypeMap.containsKey(tp.getName())) {
            InferenceVariableType inferenceVariableType =
                    new InferenceVariableType(nextInferenceVariableId++, typeSolver);
            inferenceVariableTypes.add(inferenceVariableType);
            inferenceVariableType.setCorrespondingTp(tp);
            inferenceVariableTypeMap.put(tp.getName(), inferenceVariableType);
        }
        return inferenceVariableTypeMap.get(tp.getName());
    }

    /**
     * @return the actual with the inference variable inserted
     */
    public ResolvedType addPair(ResolvedType target, ResolvedType actual) {
        target = placeInferenceVariables(target);
        actual = placeInferenceVariables(actual);
        registerCorrespondance(target, actual);
        return target;
    }

    public ResolvedType addSingle(ResolvedType actual) {
        return placeInferenceVariables(actual);
    }

    private void registerCorrespondance(ResolvedType formalType, ResolvedType actualType) {
        if (formalType.isReferenceType() && actualType.isReferenceType()) {
            ResolvedReferenceType formalTypeAsReference = formalType.asReferenceType();
            ResolvedReferenceType actualTypeAsReference = actualType.asReferenceType();
            if (!formalTypeAsReference.getQualifiedName().equals(actualTypeAsReference.getQualifiedName())) {
                List ancestors = actualTypeAsReference.getAllAncestors();
                final String formalParamTypeQName = formalTypeAsReference.getQualifiedName();
                // Interfaces do not extend the class Object,
                // which means that if the formal parameter is of type Object,
                // all types can match including the actual type.
                List correspondingFormalType = "java.lang.Object".equals(formalParamTypeQName)
                        ? Stream.concat(
                                        new ArrayList(Arrays.asList(actualType)).stream(),
                                        ancestors.stream()
                                                .map(ancestor -> ancestor.asReferenceType())
                                                .collect(Collectors.toList())
                                                .stream())
                                .collect(Collectors.toList())
                        : ancestors.stream()
                                .filter((a) -> a.getQualifiedName().equals(formalParamTypeQName))
                                .collect(Collectors.toList());
                if (correspondingFormalType.isEmpty()) {
                    ancestors = formalTypeAsReference.getAllAncestors();
                    final String actualParamTypeQname = actualTypeAsReference.getQualifiedName();
                    List correspondingActualType = ancestors.stream()
                            .filter(a -> a.getQualifiedName().equals(actualParamTypeQname))
                            .collect(Collectors.toList());
                    if (correspondingActualType.isEmpty()) {
                        throw new ConflictingGenericTypesException(formalType, actualType);
                    }
                    correspondingFormalType = correspondingActualType;
                }
                actualTypeAsReference = correspondingFormalType.get(0).asReferenceType();
            }
            if (formalTypeAsReference.getQualifiedName().equals(actualTypeAsReference.getQualifiedName())) {
                if (!formalTypeAsReference.typeParametersValues().isEmpty()) {
                    if (actualTypeAsReference.isRawType()) {
                        // nothing to do
                    } else {
                        int i = 0;
                        for (ResolvedType formalTypeParameter : formalTypeAsReference.typeParametersValues()) {
                            registerCorrespondance(
                                    formalTypeParameter,
                                    actualTypeAsReference.typeParametersValues().get(i));
                            i++;
                        }
                    }
                }
            }
        } else if (formalType instanceof InferenceVariableType && !actualType.isPrimitive()) {
            ((InferenceVariableType) formalType).registerEquivalentType(actualType);
            if (actualType instanceof InferenceVariableType) {
                ((InferenceVariableType) actualType).registerEquivalentType(formalType);
            }
        } else if (actualType.isNull()) {
            // nothing to do
        } else if (actualType.equals(formalType)) {
            // nothing to do
        } else if (actualType.isArray() && formalType.isArray()) {
            registerCorrespondance(
                    formalType.asArrayType().getComponentType(),
                    actualType.asArrayType().getComponentType());
        } else if (formalType.isWildcard()) {
            // nothing to do
            if ((actualType instanceof InferenceVariableType)
                    && formalType.asWildcard().isBounded()) {
                ((InferenceVariableType) actualType)
                        .registerEquivalentType(formalType.asWildcard().getBoundedType());
                if (formalType.asWildcard().getBoundedType() instanceof InferenceVariableType) {
                    ((InferenceVariableType) formalType.asWildcard().getBoundedType())
                            .registerEquivalentType(actualType);
                }
            }
            if (actualType.isWildcard()) {
                ResolvedWildcard formalWildcard = formalType.asWildcard();
                ResolvedWildcard actualWildcard = actualType.asWildcard();
                if (formalWildcard.isBounded() && formalWildcard.getBoundedType() instanceof InferenceVariableType) {
                    if (formalWildcard.isSuper() && actualWildcard.isSuper()) {
                        ((InferenceVariableType) formalType.asWildcard().getBoundedType())
                                .registerEquivalentType(actualWildcard.getBoundedType());
                    } else if (formalWildcard.isExtends() && actualWildcard.isExtends()) {
                        ((InferenceVariableType) formalType.asWildcard().getBoundedType())
                                .registerEquivalentType(actualWildcard.getBoundedType());
                    }
                }
            }
            if (actualType.isReferenceType()) {
                if (formalType.asWildcard().isBounded()) {
                    registerCorrespondance(formalType.asWildcard().getBoundedType(), actualType);
                }
            }
        } else if (actualType instanceof InferenceVariableType) {
            if (formalType instanceof ResolvedReferenceType) {
                ((InferenceVariableType) actualType).registerEquivalentType(formalType);
            } else if (formalType instanceof InferenceVariableType) {
                ((InferenceVariableType) actualType).registerEquivalentType(formalType);
            }
        } else if (actualType.isConstraint()) {
            ResolvedLambdaConstraintType constraintType = actualType.asConstraintType();
            if (constraintType.getBound() instanceof InferenceVariableType) {
                ((InferenceVariableType) constraintType.getBound()).registerEquivalentType(formalType);
            }
        } else if (actualType.isPrimitive()) {
            if (formalType.isPrimitive()) {
                // nothing to do
            } else {
                ResolvedReferenceTypeDeclaration resolvedTypedeclaration =
                        typeSolver.solveType(actualType.asPrimitive().getBoxTypeQName());
                registerCorrespondance(formalType, new ReferenceTypeImpl(resolvedTypedeclaration));
            }
        } else if (actualType.isReferenceType()) {
            if (formalType.isPrimitive()) {
                if (formalType.asPrimitive().getBoxTypeQName().equals(actualType.describe())) {
                    ResolvedReferenceTypeDeclaration resolvedTypedeclaration =
                            typeSolver.solveType(formalType.asPrimitive().getBoxTypeQName());
                    registerCorrespondance(new ReferenceTypeImpl(resolvedTypedeclaration), actualType);
                } else {
                    // nothing to do
                }
            } else {
                // nothing to do
            }
        } else if (formalType.isReferenceType()) {
            ResolvedReferenceType formalTypeAsReference = formalType.asReferenceType();
            if (formalTypeAsReference.isJavaLangObject()) {
                // nothing to do
            } else {
                throw new UnsupportedOperationException(formalType.describe() + " " + actualType.describe());
            }
        } else {
            throw new UnsupportedOperationException(formalType.describe() + " " + actualType.describe());
        }
    }

    private ResolvedType placeInferenceVariables(ResolvedType type) {
        if (type.isWildcard()) {
            if (type.asWildcard().isExtends()) {
                return ResolvedWildcard.extendsBound(
                        placeInferenceVariables(type.asWildcard().getBoundedType()));
            }
            if (type.asWildcard().isSuper()) {
                return ResolvedWildcard.superBound(
                        placeInferenceVariables(type.asWildcard().getBoundedType()));
            }
            return type;
        }
        if (type.isTypeVariable()) {
            return inferenceVariableTypeForTp(type.asTypeParameter());
        }
        if (type.isReferenceType()) {
            return type.asReferenceType().transformTypeParameters(tp -> placeInferenceVariables(tp));
        }
        if (type.isArray()) {
            return new ResolvedArrayType(
                    placeInferenceVariables(type.asArrayType().getComponentType()));
        }
        if (type.isNull() || type.isPrimitive() || type.isVoid()) {
            return type;
        }
        if (type.isConstraint()) {
            return ResolvedLambdaConstraintType.bound(
                    placeInferenceVariables(type.asConstraintType().getBound()));
        }
        if (type instanceof InferenceVariableType) {
            return type;
        }
        throw new UnsupportedOperationException(type.describe());
    }

    public ResolvedType resolve(ResolvedType type) {
        if (type instanceof InferenceVariableType) {
            InferenceVariableType inferenceVariableType = (InferenceVariableType) type;
            return inferenceVariableType.equivalentType();
        }
        if (type.isReferenceType()) {
            return type.asReferenceType().transformTypeParameters(tp -> resolve(tp));
        }
        if (type.isNull() || type.isPrimitive() || type.isVoid()) {
            return type;
        }
        if (type.isArray()) {
            return new ResolvedArrayType(resolve(type.asArrayType().getComponentType()));
        }
        if (type.isWildcard()) {
            if (type.asWildcard().isExtends()) {
                return ResolvedWildcard.extendsBound(resolve(type.asWildcard().getBoundedType()));
            }
            if (type.asWildcard().isSuper()) {
                return ResolvedWildcard.superBound(resolve(type.asWildcard().getBoundedType()));
            }
            return type;
        }
        throw new UnsupportedOperationException(type.describe());
    }
}