Java tutorial
/* * Copyright 2017 Google Inc. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.errorprone.bugpatterns; import static com.google.common.base.MoreObjects.firstNonNull; import static com.google.errorprone.BugPattern.Category.JDK; import static com.google.errorprone.BugPattern.SeverityLevel.ERROR; import static com.google.errorprone.matchers.Description.NO_MATCH; import com.google.common.base.Joiner; import com.google.common.collect.ImmutableList; import com.google.common.collect.ImmutableSet; import com.google.errorprone.BugPattern; import com.google.errorprone.VisitorState; import com.google.errorprone.bugpatterns.BugChecker.DoWhileLoopTreeMatcher; import com.google.errorprone.bugpatterns.BugChecker.ForLoopTreeMatcher; import com.google.errorprone.bugpatterns.BugChecker.WhileLoopTreeMatcher; import com.google.errorprone.matchers.Description; import com.google.errorprone.util.ASTHelpers; import com.sun.source.tree.AssignmentTree; import com.sun.source.tree.BinaryTree; import com.sun.source.tree.CompoundAssignmentTree; import com.sun.source.tree.DoWhileLoopTree; import com.sun.source.tree.ExpressionTree; import com.sun.source.tree.ForLoopTree; import com.sun.source.tree.IdentifierTree; import com.sun.source.tree.LiteralTree; import com.sun.source.tree.MethodInvocationTree; import com.sun.source.tree.Tree; import com.sun.source.tree.UnaryTree; import com.sun.source.tree.WhileLoopTree; import com.sun.source.util.SimpleTreeVisitor; import com.sun.source.util.TreeScanner; import com.sun.tools.javac.code.Symbol; /** @author cushon@google.com (Liam Miller-Cushon) */ @BugPattern(name = "LoopConditionChecker", category = JDK, summary = "Loop condition is never modified in loop body.", severity = ERROR) public class LoopConditionChecker extends BugChecker implements ForLoopTreeMatcher, DoWhileLoopTreeMatcher, WhileLoopTreeMatcher { @Override public Description matchDoWhileLoop(DoWhileLoopTree tree, VisitorState state) { return check(tree.getCondition(), ImmutableList.of(tree.getCondition(), tree.getStatement())); } @Override public Description matchForLoop(ForLoopTree tree, VisitorState state) { if (tree.getCondition() == null) { return NO_MATCH; } return check(tree.getCondition(), ImmutableList.<Tree>builder().add(tree.getCondition()) .add(tree.getStatement()).addAll(tree.getUpdate()).build()); } @Override public Description matchWhileLoop(WhileLoopTree tree, VisitorState state) { return check(tree.getCondition(), ImmutableList.of(tree.getCondition(), tree.getStatement())); } private Description check(ExpressionTree condition, ImmutableList<Tree> loopBodyTrees) { ImmutableSet<Symbol.VarSymbol> conditionVars = LoopConditionVisitor.scan(condition); if (conditionVars.isEmpty()) { return NO_MATCH; } for (Tree tree : loopBodyTrees) { if (UpdateScanner.scan(tree, conditionVars)) { return NO_MATCH; } } return buildDescription(condition) .setMessage(String.format("condition variable(s) never modified in loop body: %s", Joiner.on(", ").join(conditionVars))) .build(); } /** Scan for loop conditions that are determined entirely by the state of local variables. */ private static class LoopConditionVisitor extends SimpleTreeVisitor<Boolean, Void> { static ImmutableSet<Symbol.VarSymbol> scan(Tree tree) { ImmutableSet.Builder<Symbol.VarSymbol> conditionVars = ImmutableSet.builder(); if (!firstNonNull(tree.accept(new LoopConditionVisitor(conditionVars), null), false)) { return ImmutableSet.of(); } return conditionVars.build(); } private final ImmutableSet.Builder<Symbol.VarSymbol> conditionVars; public LoopConditionVisitor(ImmutableSet.Builder<Symbol.VarSymbol> conditionVars) { this.conditionVars = conditionVars; } @Override public Boolean visitIdentifier(IdentifierTree tree, Void unused) { Symbol sym = ASTHelpers.getSymbol(tree); if (sym instanceof Symbol.VarSymbol) { switch (sym.getKind()) { case LOCAL_VARIABLE: case PARAMETER: conditionVars.add((Symbol.VarSymbol) sym); return true; default: // fall out } } return false; } @Override public Boolean visitLiteral(LiteralTree tree, Void unused) { return true; } @Override public Boolean visitUnary(UnaryTree node, Void aVoid) { return node.getExpression().accept(this, null); } @Override public Boolean visitBinary(BinaryTree node, Void aVoid) { return firstNonNull(node.getLeftOperand().accept(this, null), false) && firstNonNull(node.getRightOperand().accept(this, null), false); } } /** Scan for updates to the given variables. */ private static class UpdateScanner extends TreeScanner<Void, Void> { public static boolean scan(Tree tree, ImmutableSet<Symbol.VarSymbol> variables) { UpdateScanner scanner = new UpdateScanner(variables); tree.accept(scanner, null); return scanner.modified; } private boolean modified = false; private final ImmutableSet<Symbol.VarSymbol> variables; public UpdateScanner(ImmutableSet<Symbol.VarSymbol> variables) { this.variables = variables; } @Override public Void visitUnary(UnaryTree tree, Void unused) { switch (tree.getKind()) { case POSTFIX_INCREMENT: case PREFIX_INCREMENT: case POSTFIX_DECREMENT: case PREFIX_DECREMENT: check(tree.getExpression()); break; default: // fall out } return super.visitUnary(tree, unused); } @Override public Void visitMethodInvocation(MethodInvocationTree tree, Void unused) { check(ASTHelpers.getReceiver(tree)); return super.visitMethodInvocation(tree, unused); } @Override public Void visitAssignment(AssignmentTree tree, Void unused) { check(tree.getVariable()); return super.visitAssignment(tree, unused); } @Override public Void visitCompoundAssignment(CompoundAssignmentTree tree, Void unused) { check(tree.getVariable()); return super.visitCompoundAssignment(tree, unused); } private void check(ExpressionTree expression) { Symbol sym = ASTHelpers.getSymbol(expression); modified |= variables.contains(sym); } } }