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An auxiliary findbugs.sourceforge.net plugin for java bug detectors that fall outside the narrow scope of detectors to be packaged with the product itself.
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/*
 * fb-contrib - Auxiliary detectors for Java programs
 * Copyright (C) 2005-2019 Dave Brosius
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package com.mebigfatguy.fbcontrib.detect;

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

import org.apache.bcel.Const;
import org.apache.bcel.classfile.Code;

import com.mebigfatguy.fbcontrib.collect.ImmutabilityType;
import com.mebigfatguy.fbcontrib.collect.MethodInfo;
import com.mebigfatguy.fbcontrib.collect.Statistics;
import com.mebigfatguy.fbcontrib.utils.BugType;
import com.mebigfatguy.fbcontrib.utils.CollectionUtils;
import com.mebigfatguy.fbcontrib.utils.QMethod;
import com.mebigfatguy.fbcontrib.utils.SignatureBuilder;
import com.mebigfatguy.fbcontrib.utils.StopOpcodeParsingException;
import com.mebigfatguy.fbcontrib.utils.Values;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.OpcodeStack;
import edu.umd.cs.findbugs.OpcodeStack.CustomUserValue;
import edu.umd.cs.findbugs.ba.ClassContext;

/**
 * looks for code that attempts to modify a collection that is or may be defined
 * as immutable. Doing so will cause exceptions at runtime.
 */
@CustomUserValue
public class ModifyingUnmodifiableCollection extends BytecodeScanningDetector {

    private static final Map MODIFYING_METHODS;

    static {
        Map mm = new HashMap<>();
        mm.put(new QMethod("add", SignatureBuilder.SIG_OBJECT_TO_BOOLEAN), Values.ONE);
        mm.put(new QMethod("remove", SignatureBuilder.SIG_OBJECT_TO_BOOLEAN), Values.ONE);
        mm.put(new QMethod("addAll", SignatureBuilder.SIG_COLLECTION_TO_PRIMITIVE_BOOLEAN), Values.ONE);
        mm.put(new QMethod("retainAll", SignatureBuilder.SIG_COLLECTION_TO_PRIMITIVE_BOOLEAN), Values.ONE);
        mm.put(new QMethod("removeAll", SignatureBuilder.SIG_COLLECTION_TO_PRIMITIVE_BOOLEAN), Values.ONE);
        mm.put(new QMethod("put", SignatureBuilder.SIG_TWO_OBJECTS_TO_OBJECT), Values.TWO);
        mm.put(new QMethod("remove", SignatureBuilder.SIG_OBJECT_TO_OBJECT), Values.ONE);
        mm.put(new QMethod("putAll", new SignatureBuilder().withParamTypes(Values.SLASHED_JAVA_UTIL_MAP).toString()),
                Values.ONE);
        MODIFYING_METHODS = Collections.unmodifiableMap(mm);
    }

    private final BugReporter bugReporter;
    private OpcodeStack stack;
    private ImmutabilityType reportedType;

    /**
     * constructs a MUC detector given the reporter to report bugs on
     *
     * @param reporter the sync of bug reports
     */
    public ModifyingUnmodifiableCollection(BugReporter reporter) {
        bugReporter = reporter;
    }

    /**
     * overrides the visitor to setup and tear down the opcode stack
     *
     * @param context the context object of the currently parse java class
     */
    @Override
    public void visitClassContext(ClassContext context) {
        try {
            stack = new OpcodeStack();
            super.visitClassContext(context);
        } finally {
            stack = null;
        }
    }

    /**
     * overrides the visitor to reset the opcode stack, and reset the reported
     * immutability of the method
     *
     * @param obj the context object of the currently parse code block
     */
    @Override
    public void visitCode(Code obj) {
        try {
            stack.resetForMethodEntry(this);
            reportedType = ImmutabilityType.UNKNOWN;
            super.visitCode(obj);
        } catch (StopOpcodeParsingException e) {
            // report type is immutable
        }
    }

    /**
     * overrides the visitor to find method mutations on collections that have
     * previously been determined to have been created as immutable collections
     *
     * @param seen the currently parsed opcode
     */
    @Override
    public void sawOpcode(int seen) {
        ImmutabilityType imType = null;

        try {
            stack.precomputation(this);

            switch (seen) {
            case Const.INVOKESTATIC:
            case Const.INVOKEINTERFACE:
            case Const.INVOKESPECIAL:
            case Const.INVOKEVIRTUAL: {
                String className = getClassConstantOperand();
                String methodName = getNameConstantOperand();
                String signature = getSigConstantOperand();

                MethodInfo mi = Statistics.getStatistics().getMethodStatistics(className, methodName, signature);
                imType = mi.getImmutabilityType();

                if (seen == Const.INVOKEINTERFACE) {
                    Integer collectionOffset = MODIFYING_METHODS.get(new QMethod(methodName, signature));
                    if ((collectionOffset != null) && CollectionUtils.isListSetMap(className)
                            && (stack.getStackDepth() > collectionOffset.intValue())) {
                        OpcodeStack.Item item = stack.getStackItem(collectionOffset.intValue());
                        ImmutabilityType type = (ImmutabilityType) item.getUserValue();

                        if ((type == ImmutabilityType.IMMUTABLE) || ((type == ImmutabilityType.POSSIBLY_IMMUTABLE)
                                && (reportedType != ImmutabilityType.POSSIBLY_IMMUTABLE))) {
                            bugReporter.reportBug(
                                    new BugInstance(this, BugType.MUC_MODIFYING_UNMODIFIABLE_COLLECTION.name(),
                                            (type == ImmutabilityType.IMMUTABLE) ? HIGH_PRIORITY : NORMAL_PRIORITY)
                                                    .addClass(this).addMethod(this).addSourceLine(this));
                            if (type == ImmutabilityType.IMMUTABLE) {
                                throw new StopOpcodeParsingException();
                            }

                            reportedType = type;
                        }
                    }
                }
            }
                break;
            default:
                break;
            }
        } catch (ClassNotFoundException cnfe) {
            bugReporter.reportMissingClass(cnfe);
        } finally {
            stack.sawOpcode(this, seen);
            if ((imType != null) && (stack.getStackDepth() > 0)) {
                OpcodeStack.Item item = stack.getStackItem(0);
                item.setUserValue(imType);
            }

        }
    }
}