ParameterAssignmentCheck.java
///////////////////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
// Copyright (C) 2001-2022 the original author or authors.
//
// 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.puppycrawl.tools.checkstyle.checks.coding;
import java.util.ArrayDeque;
import java.util.Collections;
import java.util.Deque;
import java.util.HashSet;
import java.util.Set;
import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
/**
* <p>
* Disallows assignment of parameters.
* </p>
* <p>
* Rationale:
* Parameter assignment is often considered poor
* programming practice. Forcing developers to declare
* parameters as final is often onerous. Having a check
* ensure that parameters are never assigned would give
* the best of both worlds.
* </p>
* <p>
* To configure the check:
* </p>
* <pre>
* <module name="ParameterAssignment"/>
* </pre>
* <p>
* Example:
* </p>
* <pre>
* class MyClass {
* int methodOne(int parameter) {
* if (parameter <= 0 ) {
* throw new IllegalArgumentException("A positive value is expected");
* }
* parameter -= 2; // violation
* return parameter;
* }
*
* int methodTwo(int parameter) {
* if (parameter <= 0 ) {
* throw new IllegalArgumentException("A positive value is expected");
* }
* int local = parameter;
* local -= 2; // OK
* return local;
* }
*
* IntPredicate obj = a -> ++a == 12; // violation
* IntBinaryOperator obj2 = (int a, int b) -> {
* a++; // violation
* b += 12; // violation
* return a + b;
* };
* IntPredicate obj3 = a -> {
* int b = a; // ok
* return ++b == 12;
* };
* }
* </pre>
* <p>
* Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
* </p>
* <p>
* Violation Message Keys:
* </p>
* <ul>
* <li>
* {@code parameter.assignment}
* </li>
* </ul>
*
* @since 3.2
*/
@FileStatefulCheck
public final class ParameterAssignmentCheck extends AbstractCheck {
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_KEY = "parameter.assignment";
/** Stack of methods' parameters. */
private final Deque<Set<String>> parameterNamesStack = new ArrayDeque<>();
/** Current set of parameters. */
private Set<String> parameterNames;
@Override
public int[] getDefaultTokens() {
return getRequiredTokens();
}
@Override
public int[] getRequiredTokens() {
return new int[] {
TokenTypes.CTOR_DEF,
TokenTypes.METHOD_DEF,
TokenTypes.ASSIGN,
TokenTypes.PLUS_ASSIGN,
TokenTypes.MINUS_ASSIGN,
TokenTypes.STAR_ASSIGN,
TokenTypes.DIV_ASSIGN,
TokenTypes.MOD_ASSIGN,
TokenTypes.SR_ASSIGN,
TokenTypes.BSR_ASSIGN,
TokenTypes.SL_ASSIGN,
TokenTypes.BAND_ASSIGN,
TokenTypes.BXOR_ASSIGN,
TokenTypes.BOR_ASSIGN,
TokenTypes.INC,
TokenTypes.POST_INC,
TokenTypes.DEC,
TokenTypes.POST_DEC,
TokenTypes.LAMBDA,
};
}
@Override
public int[] getAcceptableTokens() {
return getRequiredTokens();
}
@Override
public void beginTree(DetailAST rootAST) {
// clear data
parameterNamesStack.clear();
parameterNames = Collections.emptySet();
}
@Override
public void visitToken(DetailAST ast) {
final int type = ast.getType();
if (TokenUtil.isOfType(type, TokenTypes.CTOR_DEF, TokenTypes.METHOD_DEF)) {
visitMethodDef(ast);
}
else if (type == TokenTypes.LAMBDA) {
if (ast.getParent().getType() != TokenTypes.SWITCH_RULE) {
visitLambda(ast);
}
}
else {
checkNestedIdent(ast);
}
}
@Override
public void leaveToken(DetailAST ast) {
final int type = ast.getType();
if (TokenUtil.isOfType(type, TokenTypes.CTOR_DEF, TokenTypes.METHOD_DEF)
|| type == TokenTypes.LAMBDA
&& ast.getParent().getType() != TokenTypes.SWITCH_RULE) {
parameterNames = parameterNamesStack.pop();
}
}
/**
* Check if nested ident is parameter.
*
* @param ast parent of node of ident
*/
private void checkNestedIdent(DetailAST ast) {
final DetailAST identAST = ast.getFirstChild();
if (identAST != null
&& identAST.getType() == TokenTypes.IDENT
&& parameterNames.contains(identAST.getText())) {
log(ast, MSG_KEY, identAST.getText());
}
}
/**
* Creates new set of parameters and store old one in stack.
*
* @param ast a method to process.
*/
private void visitMethodDef(DetailAST ast) {
parameterNamesStack.push(parameterNames);
parameterNames = new HashSet<>();
visitMethodParameters(ast.findFirstToken(TokenTypes.PARAMETERS));
}
/**
* Creates new set of parameters and store old one in stack.
*
* @param lambdaAst node of type {@link TokenTypes#LAMBDA}.
*/
private void visitLambda(DetailAST lambdaAst) {
parameterNamesStack.push(parameterNames);
parameterNames = new HashSet<>();
DetailAST parameterAst = lambdaAst.findFirstToken(TokenTypes.PARAMETERS);
if (parameterAst == null) {
parameterAst = lambdaAst.getFirstChild();
}
visitLambdaParameters(parameterAst);
}
/**
* Creates new parameter set for given method.
*
* @param ast a method for process.
*/
private void visitMethodParameters(DetailAST ast) {
visitParameters(ast);
}
/**
* Creates new parameter set for given lambda expression.
*
* @param ast a lambda expression parameter to process
*/
private void visitLambdaParameters(DetailAST ast) {
if (ast.getType() == TokenTypes.IDENT) {
parameterNames.add(ast.getText());
}
else {
visitParameters(ast);
}
}
/**
* Visits parameter list and adds parameter names to the set.
*
* @param parametersAst ast node of type {@link TokenTypes#PARAMETERS}.
*/
private void visitParameters(DetailAST parametersAst) {
DetailAST parameterDefAST =
parametersAst.findFirstToken(TokenTypes.PARAMETER_DEF);
while (parameterDefAST != null) {
if (parameterDefAST.getType() == TokenTypes.PARAMETER_DEF
&& !CheckUtil.isReceiverParameter(parameterDefAST)) {
final DetailAST param =
parameterDefAST.findFirstToken(TokenTypes.IDENT);
parameterNames.add(param.getText());
}
parameterDefAST = parameterDefAST.getNextSibling();
}
}
}