javassist/src/main/java/javassist/bytecode/analysis/MultiType.java

/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */
package javassist.bytecode.analysis;

import java.util.HashMap;
import java.util.Map;

import javassist.CtClass;

/**
 * MultiType represents an unresolved type. Whenever two {@code Type}
 * instances are merged, if they share more than one super type (either an
 * interface or a superclass), then a {@code MultiType} is used to
 * represent the possible super types. The goal of a {@code MultiType}
 * is to reduce the set of possible types down to a single resolved type. This
 * is done by eliminating non-assignable types from the typeset when the
 * {@code MultiType} is passed as an argument to
 * {@link Type#isAssignableFrom(Type)}, as well as removing non-intersecting
 * types during a merge.
 *
 * Note: Currently the {@code MultiType} instance is reused as much
 * as possible so that updates are visible from all frames. In addition, all
 * {@code MultiType} merge paths are also updated. This is somewhat
 * hackish, but it appears to handle most scenarios.
 *
 * @author Jason T. Greene
 */

/* TODO - A better, but more involved, approach would be to track the instruction
 * offset that resulted in the creation of this type, and
 * whenever the typeset changes, to force a merge on that position. This
 * would require creating a new MultiType instance every time the typeset
 * changes, and somehow communicating assignment changes to the Analyzer
 */
public class MultiType extends Type {
    private Map<String,CtClass> interfaces;
    private Type resolved;
    private Type potentialClass;
    private MultiType mergeSource;
    private boolean changed = false;

    public MultiType(Map<String,CtClass> interfaces) {
        this(interfaces, null);
    }

    public MultiType(Map<String,CtClass> interfaces, Type potentialClass) {
        super(null);
        this.interfaces = interfaces;
        this.potentialClass = potentialClass;
    }

    /**
     * Gets the class that corresponds with this type. If this information
     * is not yet known, java.lang.Object will be returned.
     */
    @Override
    public CtClass getCtClass() {
        if (resolved != null)
            return resolved.getCtClass();

        return Type.OBJECT.getCtClass();
    }

    /**
     * Always returns null since this type is never used for an array.
     */
    @Override
    public Type getComponent() {
        return null;
    }

    /**
     * Always returns 1, since this type is a reference.
     */
    @Override
    public int getSize() {
        return 1;
    }

    /**
     * Always reutnrs false since this type is never used for an array
     */
    @Override
    public boolean isArray() {
        return false;
    }

    /**
     * Returns true if the internal state has changed.
     */
    @Override
    boolean popChanged() {
        boolean changed = this.changed;
        this.changed = false;
        return changed;
    }

    @Override
    public boolean isAssignableFrom(Type type) {
        throw new UnsupportedOperationException("Not implemented");
    }

    public boolean isAssignableTo(Type type) {
        if (resolved != null)
            return type.isAssignableFrom(resolved);

        if (Type.OBJECT.equals(type))
            return true;

        if (potentialClass != null && !type.isAssignableFrom(potentialClass))
            potentialClass = null;

        Map<String,CtClass> map = mergeMultiAndSingle(this, type);

        if (map.size() == 1 && potentialClass == null) {
            // Update previous merge paths to the same resolved type
            resolved = Type.get(map.values().iterator().next());
            propogateResolved();

            return true;
        }

        // Keep all previous merge paths up to date
        if (map.size() >= 1) {
            interfaces = map;
            propogateState();

            return true;
        }

        if (potentialClass != null) {
            resolved = potentialClass;
            propogateResolved();

            return true;
        }

        return false;
    }

    private void propogateState() {
        MultiType source = mergeSource;
        while (source != null) {
            source.interfaces = interfaces;
            source.potentialClass = potentialClass;
            source = source.mergeSource;
        }
    }

    private void propogateResolved() {
        MultiType source = mergeSource;
        while (source != null) {
            source.resolved = resolved;
            source = source.mergeSource;
        }
    }

    /**
     * Always returns true, since this type is always a reference.
     *
     * @return true
     */
    @Override
    public boolean isReference() {
       return true;
    }

    private Map<String,CtClass> getAllMultiInterfaces(MultiType type) {
        Map<String,CtClass> map = new HashMap<String,CtClass>();

        for (CtClass intf:type.interfaces.values()) {
            map.put(intf.getName(), intf);
            getAllInterfaces(intf, map);
        }

        return map;
    }


    private Map<String,CtClass> mergeMultiInterfaces(MultiType type1, MultiType type2) {
        Map<String,CtClass> map1 = getAllMultiInterfaces(type1);
        Map<String,CtClass> map2 = getAllMultiInterfaces(type2);

        return findCommonInterfaces(map1, map2);
    }

    private Map<String,CtClass> mergeMultiAndSingle(MultiType multi, Type single) {
        Map<String,CtClass> map1 = getAllMultiInterfaces(multi);
        Map<String,CtClass> map2 = getAllInterfaces(single.getCtClass(), null);

        return findCommonInterfaces(map1, map2);
    }

    private boolean inMergeSource(MultiType source) {
        while (source != null) {
            if (source == this)
                return true;

            source = source.mergeSource;
        }

        return false;
    }

    @Override
    public Type merge(Type type) {
        if (this == type)
            return this;

        if (type == UNINIT)
            return this;

        if (type == BOGUS)
            return BOGUS;

        if (type == null)
            return this;

        if (resolved != null)
            return resolved.merge(type);

        if (potentialClass != null) {
            Type mergePotential = potentialClass.merge(type);
            if (! mergePotential.equals(potentialClass) || mergePotential.popChanged()) {
                potentialClass = Type.OBJECT.equals(mergePotential) ? null : mergePotential;
                changed = true;
            }
        }

        Map<String,CtClass> merged;

        if (type instanceof MultiType) {
            MultiType multi = (MultiType)type;

            if (multi.resolved != null) {
                merged = mergeMultiAndSingle(this, multi.resolved);
            } else {
                merged = mergeMultiInterfaces(multi, this);
                if (! inMergeSource(multi))
                    mergeSource = multi;
            }
        } else {
            merged = mergeMultiAndSingle(this, type);
        }

        // Keep all previous merge paths up to date
        if (merged.size() > 1 || (merged.size() == 1 && potentialClass != null)) {
            // Check for changes
            if (merged.size() != interfaces.size())
                changed = true;
            else if (changed == false)
                for (String key:merged.keySet())
                    if (!interfaces.containsKey(key))
                        changed = true;


            interfaces = merged;
            propogateState();

            return this;
        }

        if (merged.size() == 1)
            resolved = Type.get(merged.values().iterator().next());
        else if (potentialClass != null)
            resolved = potentialClass;
        else
            resolved = OBJECT;

        propogateResolved();

        return resolved;
    }

    @Override
    public int hashCode() {
        if (resolved != null)
            return resolved.hashCode();

        return interfaces.keySet().hashCode();
    }

    @Override
    public boolean equals(Object o) {
        if (! (o instanceof MultiType))
            return false;

        MultiType multi = (MultiType) o;
        if (resolved != null)
            return resolved.equals(multi.resolved);
        else if (multi.resolved != null)
            return false;

        return interfaces.keySet().equals(multi.interfaces.keySet());
    }

    @Override
    public String toString() {
        if (resolved != null)
            return resolved.toString();

        StringBuilder buffer = new StringBuilder();
        buffer.append('{');
        for (String key:interfaces.keySet())
            buffer.append(key).append(", ");
        if (potentialClass != null)
            buffer.append('*').append(potentialClass.toString());
        else
            buffer.setLength(buffer.length() - 2);
        buffer.append('}');
        return buffer.toString();
    }
}