org.sonar.java.se.checks.RedundantAssignmentsCheck.java Source code

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Here is the source code for org.sonar.java.se.checks.RedundantAssignmentsCheck.java

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/*
 * SonarQube Java
 * Copyright (C) 2012-2019 SonarSource SA
 * mailto:info AT sonarsource DOT com
 *
 * This program 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 3 of the License, or (at your option) any later version.
 *
 * This program 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 program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */
package org.sonar.java.se.checks;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Multimap;

import org.sonar.check.Rule;
import org.sonar.java.cfg.CFG;
import org.sonar.java.se.CheckerContext;
import org.sonar.java.se.ExplodedGraph;
import org.sonar.java.se.Flow;
import org.sonar.java.se.FlowComputation;
import org.sonar.java.se.ProgramState;
import org.sonar.java.se.ProgramState.SymbolicValueSymbol;
import org.sonar.java.se.symbolicvalues.SymbolicValue;
import org.sonar.plugins.java.api.JavaFileScannerContext;
import org.sonar.plugins.java.api.semantic.Symbol;
import org.sonar.plugins.java.api.tree.AssignmentExpressionTree;
import org.sonar.plugins.java.api.tree.MethodTree;
import org.sonar.plugins.java.api.tree.Tree;

import javax.annotation.Nullable;

import java.util.Collection;
import java.util.Collections;
import java.util.Deque;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

@Rule(key = "S4165")
public class RedundantAssignmentsCheck extends SECheck {

    private static final Set<String> STREAM_TYPES = ImmutableSet.of("java.util.stream.Stream",
            "java.util.stream.IntStream", "java.util.stream.LongStream", "java.util.stream.DoubleStream");
    private final Deque<Multimap<AssignmentExpressionTree, AssignmentDataHolder>> assignmentsByMethod = new LinkedList<>();

    @Override
    public void scanFile(JavaFileScannerContext context) {
        assignmentsByMethod.clear();
        super.scanFile(context);
    }

    @Override
    public void init(MethodTree methodTree, CFG cfg) {
        assignmentsByMethod.push(ArrayListMultimap.create());
    }

    @Override
    public ProgramState checkPostStatement(CheckerContext context, Tree syntaxNode) {
        if (syntaxNode.is(Tree.Kind.ASSIGNMENT)) {
            handleAssignment(context, (AssignmentExpressionTree) syntaxNode);
        }
        return super.checkPostStatement(context, syntaxNode);
    }

    private void handleAssignment(CheckerContext context, AssignmentExpressionTree assignmentExpressionTree) {
        SymbolicValueSymbol assignedVariable = context.getState().peekValueSymbol();
        Symbol assignedSymbol = assignedVariable.symbol();
        if (assignedSymbol == null
                // Rule S3959 returns the same SV after each intermediate operations,
                // meaning that 'stream = stream.map(...);' would be detected as redundant assignment if not explicitly excluded
                || STREAM_TYPES.stream().anyMatch(assignedSymbol.type()::is)) {
            return;
        }
        ExplodedGraph.Node node = context.getNode();
        ProgramState previousState = node.programState;
        SymbolicValue oldValue = previousState.getValue(assignedSymbol);
        SymbolicValue newValue = assignedVariable.symbolicValue();
        Symbol fromSymbol = previousState.peekValueSymbol().symbol();
        assignmentsByMethod.peek().put(assignmentExpressionTree,
                new AssignmentDataHolder(assignedSymbol, oldValue, newValue, fromSymbol, node));
    }

    @Override
    public void interruptedExecution(CheckerContext context) {
        this.assignmentsByMethod.pop();
    }

    @Override
    public void checkEndOfExecution(CheckerContext context) {
        for (Map.Entry<AssignmentExpressionTree, Collection<AssignmentDataHolder>> assignmentForTree : assignmentsByMethod
                .pop().asMap().entrySet()) {
            Collection<AssignmentDataHolder> allAssignments = assignmentForTree.getValue();
            if (allAssignments.stream().allMatch(AssignmentDataHolder::isRedundant)) {
                Set<Flow> flows = allAssignments.stream().map(AssignmentDataHolder::flows).flatMap(Set::stream)
                        .collect(Collectors.toSet());
                reportIssue(assignmentForTree.getKey(), String.format(
                        "Remove this useless assignment; \"%s\" already holds the assigned value along all execution paths.",
                        Iterables.getFirst(allAssignments, null).assignedSymbol.name()), flows);
            }
        }
    }

    private static class AssignmentDataHolder {

        private final Symbol assignedSymbol;
        @Nullable
        private final Symbol fromSymbol;
        private final SymbolicValue oldValue;
        private final SymbolicValue newValue;
        private final ExplodedGraph.Node node;

        public AssignmentDataHolder(Symbol assignedSymbol, @Nullable SymbolicValue oldValue, SymbolicValue newValue,
                @Nullable Symbol fromSymbol, ExplodedGraph.Node node) {
            this.assignedSymbol = assignedSymbol;
            this.fromSymbol = fromSymbol;
            this.oldValue = oldValue;
            this.newValue = newValue;
            this.node = node;
        }

        public boolean isRedundant() {
            return oldValue == newValue;
        }

        public Set<Flow> flows() {
            return FlowComputation.flow(node, newValue, Collections.emptyList(), fromSymbol);
        }
    }

}