| // Copyright 2017 The Bazel Authors. 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.devtools.skylark.skylint; |
| |
| import com.google.devtools.build.lib.syntax.BuildFileAST; |
| import com.google.devtools.build.lib.syntax.Expression; |
| import com.google.devtools.build.lib.syntax.ExpressionStatement; |
| import com.google.devtools.build.lib.syntax.FuncallExpression; |
| import com.google.devtools.build.lib.syntax.FunctionDefStatement; |
| import com.google.devtools.build.lib.syntax.ListComprehension; |
| import com.google.devtools.build.lib.syntax.Statement; |
| import com.google.devtools.build.lib.syntax.SyntaxTreeVisitor; |
| import com.google.devtools.skylark.common.DocstringUtils; |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| /** Checks for statements that have no effect. */ |
| public class StatementWithoutEffectChecker extends SyntaxTreeVisitor { |
| private static final String NO_EFFECT_CATEGORY = "no-effect"; |
| |
| private final List<Issue> issues = new ArrayList<>(); |
| private boolean hasEffect = false; |
| private boolean topLevel = true; |
| |
| public static List<Issue> check(BuildFileAST ast) { |
| StatementWithoutEffectChecker checker = new StatementWithoutEffectChecker(); |
| checker.visit(ast); |
| return checker.issues; |
| } |
| |
| @Override |
| public void visit(BuildFileAST ast) { |
| checkStatementsExceptDocstrings(ast.getStatements(), /*allowVariableDocstrings=*/ true); |
| } |
| |
| @Override |
| public void visit(FunctionDefStatement node) { |
| topLevel = false; |
| checkStatementsExceptDocstrings(node.getStatements(), /*allowVariableDocstrings=*/ false); |
| topLevel = true; |
| } |
| |
| private void checkStatementsExceptDocstrings( |
| List<Statement> stmts, boolean allowVariableDocstrings) { |
| Statement prev = null; |
| for (Statement cur : stmts) { |
| boolean isStringLiteral = DocstringUtils.getStringLiteral(cur) != null; |
| boolean isVariableDocstring = |
| allowVariableDocstrings |
| && isStringLiteral |
| && DocstringUtils.getAssignedVariableName(prev) != null; |
| boolean isDocstringAtTop = isStringLiteral && prev == null; |
| if (!isVariableDocstring && !isDocstringAtTop) { |
| visit(cur); |
| } |
| prev = cur; |
| } |
| } |
| |
| @Override |
| public void visit(ExpressionStatement node) { |
| hasEffect = false; |
| super.visit(node); |
| Expression expr = node.getExpression(); |
| if (expr instanceof FuncallExpression) { |
| return; // function calls can have an effect |
| } |
| if (expr instanceof ListComprehension && topLevel && hasEffect) { |
| // allow list comprehensions at the top level if they have an effect, e.g. [print(x) for x in |
| // list] |
| return; |
| } |
| String message = "expression result not used"; |
| if (expr instanceof ListComprehension && !topLevel) { |
| message += ". Use a for-loop instead of a list comprehension."; |
| } |
| issues.add(Issue.create(NO_EFFECT_CATEGORY, message, node.getLocation())); |
| } |
| |
| @Override |
| public void visit(FuncallExpression node) { |
| hasEffect = true; |
| } |
| } |