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

import com.mebigfatguy.fbcontrib.utils.BugType;
import com.mebigfatguy.fbcontrib.utils.SignatureUtils;
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.internalAnnotations.SlashedClassName;

/**
 * looks for methods that call a method to retrieve a reference to an object, to
 * use to load a constant. It is simpler and more performant to access the
 * static variable directly from the class itself.
 */
public class NeedlessInstanceRetrieval extends BytecodeScanningDetector {
    enum State {
        SEEN_NOTHING, SEEN_INVOKE, SEEN_POP
    }

    private final BugReporter bugReporter;
    private LineNumberTable lnTable;
    private State state;
    private int invokePC;
    private @SlashedClassName String returnType;

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

    /**
     * overrides the interface to collect the line number table, and reset state
     *
     * @param obj the content object of the currently parsed code
     */
    @Override
    public void visitCode(Code obj) {
        try {
            lnTable = obj.getLineNumberTable();
            if (lnTable != null) {
                state = State.SEEN_NOTHING;
                invokePC = -1;
                returnType = null;
                super.visitCode(obj);
            }
        } finally {
            lnTable = null;
        }
    }

    /**
     * overrides the interface to find accesses of static variables off of an
     * instance immediately fetched from a method call.
     *
     * @param seen the opcode of the currently visited instruction
     */
    @Override
    public void sawOpcode(int seen) {
        switch (state) {
        case SEEN_NOTHING:
            if ((seen == Const.INVOKEINTERFACE) || (seen == Const.INVOKEVIRTUAL)) {
                String sig = getSigConstantOperand();
                String returnSig = SignatureUtils.getReturnSignature(sig);
                if (returnSig.startsWith(Values.SIG_QUALIFIED_CLASS_PREFIX)) {
                    String clsName = getClassConstantOperand();
                    if (!Values.SLASHED_JAVA_LANG_OBJECT.equals(clsName)
                            && !Values.SLASHED_JAVA_LANG_CLASS.equals(clsName)) {
                        returnType = SignatureUtils.trimSignature(returnSig);
                        invokePC = getPC();
                        state = State.SEEN_INVOKE;
                    }
                }
            }
            break;

        case SEEN_INVOKE:
            if (seen == Const.POP) {
                state = State.SEEN_POP;
            } else {
                state = State.SEEN_NOTHING;
                returnType = null;
            }
            break;

        case SEEN_POP:
            if (((seen >= Const.ACONST_NULL) && (seen <= Const.DCONST_1)) || (seen == Const.GETFIELD)) {
                state = State.SEEN_POP;
            } else if ((seen == Const.INVOKESTATIC) || (seen == Const.GETSTATIC)) {
                if (getClassConstantOperand().equals(returnType)
                        && (lnTable.getSourceLine(invokePC) == lnTable.getSourceLine(getPC()))) {
                    bugReporter.reportBug(
                            new BugInstance(this, BugType.NIR_NEEDLESS_INSTANCE_RETRIEVAL.name(), NORMAL_PRIORITY)
                                    .addClass(this).addMethod(this).addSourceLine(this));
                }
                state = State.SEEN_NOTHING;
                returnType = null;
            } else {
                state = State.SEEN_NOTHING;
                returnType = null;
            }
            break;

        default:
            state = State.SEEN_NOTHING;
            returnType = null;
            break;
        }
    }
}