InheritanceTypeChecking.java

/*
 * fb-contrib - Auxiliary detectors for Java programs
 * Copyright (C) 2005-2017 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.HashSet;
import java.util.Iterator;
import java.util.Set;

import org.apache.bcel.classfile.Code;

import com.mebigfatguy.fbcontrib.utils.OpcodeUtils;
import com.mebigfatguy.fbcontrib.utils.RegisterUtils;
import com.mebigfatguy.fbcontrib.utils.SignatureUtils;
import com.mebigfatguy.fbcontrib.utils.ToString;

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

/**
 * looks for if/else blocks where a series of them use instanceof on the same
 * variable to determine what do to. If these classes are related by
 * inheritance, this often is better handled through calling a single overridden
 * method.
 */
public class InheritanceTypeChecking extends BytecodeScanningDetector {
    private BugReporter bugReporter;
    private Set<IfStatement> ifStatements;

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

    /**
     * implements the visitor to allocate and clear the ifStatements set
     *
     * @param classContext
     *            the context object of the currently parsed class
     */
    @Override
    public void visitClassContext(ClassContext classContext) {
        try {
            ifStatements = new HashSet<IfStatement>();
            super.visitClassContext(classContext);
        } finally {
            ifStatements = null;
        }
    }

    /**
     * implements the visitor to clear the ifStatements set
     *
     * @param obj
     *            the context object of the currently parsed code block
     */
    @Override
    public void visitCode(Code obj) {
        ifStatements.clear();
        super.visitCode(obj);
    }

    /**
     * implements the visitor to find if/else code that checks types using
     * instanceof, and these types are related by inheritance.
     *
     * @param seen
     *            the opcode of the currently parsed instruction
     */
    @Override
    public void sawOpcode(int seen) {
        boolean processed = false;
        Iterator<IfStatement> isi = ifStatements.iterator();
        while (isi.hasNext()) {
            IfStatement.Action action = isi.next().processOpcode(this, bugReporter, seen);
            if (action == IfStatement.Action.REMOVE_ACTION)
                isi.remove();
            else if (action == IfStatement.Action.PROCESSED_ACTION)
                processed = true;
        }

        if (!processed && OpcodeUtils.isALoad(seen)) {
            IfStatement is = new IfStatement(this, seen);
            ifStatements.add(is);
        }
    }

    private static class IfStatement {
        enum Action {
            NO_ACTION, REMOVE_ACTION, PROCESSED_ACTION
        }

        enum State {
            SEEN_ALOAD, SEEN_INSTANCEOF, SEEN_IFEQ
        }

        private State state;
        private int reg;
        private int firstPC;
        private int branchTarget;
        private int matchCount;
        private Set<String> instanceOfTypes;

        public IfStatement(BytecodeScanningDetector bsd, int seen) {
            state = State.SEEN_ALOAD;
            reg = RegisterUtils.getALoadReg(bsd, seen);
            matchCount = 0;
            firstPC = bsd.getPC();
        }

        public IfStatement.Action processOpcode(BytecodeScanningDetector bsd, BugReporter bugReporter, int seen) {
            switch (state) {
            case SEEN_ALOAD:
                if (seen == INSTANCEOF) {
                    if (instanceOfTypes == null)
                        instanceOfTypes = new HashSet<String>();
                    instanceOfTypes.add(bsd.getClassConstantOperand());
                    state = State.SEEN_INSTANCEOF;
                    return IfStatement.Action.PROCESSED_ACTION;
                }
                break;

            case SEEN_INSTANCEOF:
                if (seen == IFEQ) {
                    branchTarget = bsd.getBranchTarget();
                    state = State.SEEN_IFEQ;
                    matchCount++;
                    return IfStatement.Action.PROCESSED_ACTION;
                }
                break;

            case SEEN_IFEQ:
                if (bsd.getPC() == branchTarget) {
                    if (OpcodeUtils.isALoad(seen) && (reg == RegisterUtils.getALoadReg(bsd, seen))) {
                        state = State.SEEN_ALOAD;
                        return IfStatement.Action.PROCESSED_ACTION;
                    }
                    if (matchCount > 1) {
                        String clsName = bsd.getClassName();
                        int priority = NORMAL_PRIORITY;
                        for (String type : instanceOfTypes) {
                            if (!SignatureUtils.similarPackages(clsName, type, 2)) {
                                priority = LOW_PRIORITY;
                                break;
                            }
                        }

                        bugReporter.reportBug(
                                new BugInstance(bsd, "ITC_INHERITANCE_TYPE_CHECKING", priority).addClass(bsd).addMethod(bsd).addSourceLine(bsd, firstPC));
                        return IfStatement.Action.REMOVE_ACTION;
                    }
                }
                return IfStatement.Action.NO_ACTION;
            }

            return IfStatement.Action.REMOVE_ACTION;
        }

        @Override
        public String toString() {
            return ToString.build(this);
        }
    }
}