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Add a check for unnecessary usages of
StringBuilder
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core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilder.java
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| /* | ||
| * Copyright 2023 The Error Prone Authors. | ||
| * | ||
| * 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.collect.Iterables.getOnlyElement; | ||
| import static com.google.errorprone.matchers.Description.NO_MATCH; | ||
| import static com.google.errorprone.matchers.method.MethodMatchers.constructor; | ||
| import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod; | ||
| import static com.google.errorprone.util.ASTHelpers.getSymbol; | ||
| import static com.google.errorprone.util.ASTHelpers.getType; | ||
| import static com.google.errorprone.util.ASTHelpers.isSubtype; | ||
| import static com.google.errorprone.util.ASTHelpers.requiresParentheses; | ||
| import static com.google.errorprone.util.ASTHelpers.targetType; | ||
| import static java.util.stream.Collectors.joining; | ||
|
|
||
| import com.google.errorprone.BugPattern; | ||
| import com.google.errorprone.VisitorState; | ||
| import com.google.errorprone.bugpatterns.BugChecker.NewClassTreeMatcher; | ||
| import com.google.errorprone.fixes.SuggestedFix; | ||
| import com.google.errorprone.matchers.Description; | ||
| import com.google.errorprone.matchers.Matcher; | ||
| import com.google.errorprone.suppliers.Supplier; | ||
| import com.google.errorprone.util.ASTHelpers; | ||
| import com.google.errorprone.util.ASTHelpers.TargetType; | ||
| import com.sun.source.tree.ExpressionTree; | ||
| import com.sun.source.tree.IdentifierTree; | ||
| import com.sun.source.tree.MemberSelectTree; | ||
| import com.sun.source.tree.MethodInvocationTree; | ||
| import com.sun.source.tree.NewClassTree; | ||
| import com.sun.source.tree.Tree; | ||
| import com.sun.source.tree.VariableTree; | ||
| import com.sun.source.util.TreePath; | ||
| import com.sun.source.util.TreePathScanner; | ||
| import com.sun.tools.javac.code.Symbol; | ||
| import com.sun.tools.javac.code.Type; | ||
| import java.util.ArrayList; | ||
| import java.util.List; | ||
| import javax.lang.model.element.ElementKind; | ||
|
|
||
| /** A {@link BugChecker}; see the associated {@link BugPattern} annotation for details. */ | ||
| @BugPattern( | ||
| summary = | ||
| "Prefer string concatenation over explicitly using `StringBuilder#append`, since `+` reads" | ||
| + " better and has equivalent or better performance.", | ||
| severity = BugPattern.SeverityLevel.WARNING) | ||
| public class UnnecessaryStringBuilder extends BugChecker implements NewClassTreeMatcher { | ||
| private static final Matcher<ExpressionTree> MATCHER = | ||
| constructor().forClass("java.lang.StringBuilder"); | ||
|
|
||
| private static final Matcher<ExpressionTree> APPEND = | ||
| instanceMethod().onExactClass("java.lang.StringBuilder").named("append"); | ||
|
|
||
| private static final Matcher<ExpressionTree> TO_STRING = | ||
| instanceMethod().onExactClass("java.lang.StringBuilder").named("toString"); | ||
|
|
||
| @Override | ||
| public Description matchNewClass(NewClassTree tree, VisitorState state) { | ||
| if (!MATCHER.matches(tree, state)) { | ||
| return NO_MATCH; | ||
| } | ||
| List<ExpressionTree> parts = new ArrayList<>(); | ||
| switch (tree.getArguments().size()) { | ||
| case 0: | ||
| break; | ||
| case 1: | ||
| ExpressionTree argument = getOnlyElement(tree.getArguments()); | ||
| if (isSubtype(getType(argument), JAVA_LANG_CHARSEQUENCE.get(state), state)) { | ||
| parts.add(argument); | ||
| } | ||
| break; | ||
| default: | ||
| return NO_MATCH; | ||
| } | ||
| TreePath path = state.getPath(); | ||
| while (true) { | ||
| TreePath parentPath = path.getParentPath(); | ||
| if (!(parentPath.getLeaf() instanceof MemberSelectTree)) { | ||
| break; | ||
| } | ||
| TreePath grandParent = parentPath.getParentPath(); | ||
| if (!(grandParent.getLeaf() instanceof MethodInvocationTree)) { | ||
| break; | ||
| } | ||
| MethodInvocationTree methodInvocationTree = (MethodInvocationTree) grandParent.getLeaf(); | ||
| if (!methodInvocationTree.getMethodSelect().equals(parentPath.getLeaf())) { | ||
| break; | ||
| } | ||
| if (APPEND.matches(methodInvocationTree, state)) { | ||
| if (methodInvocationTree.getArguments().size() != 1) { | ||
| // an append method that doesn't transliterate to concat | ||
| return NO_MATCH; | ||
| } | ||
| parts.add(getOnlyElement(methodInvocationTree.getArguments())); | ||
| path = parentPath.getParentPath(); | ||
| } else if (TO_STRING.matches(methodInvocationTree, state)) { | ||
| return describeMatch( | ||
| methodInvocationTree, | ||
| SuggestedFix.replace(methodInvocationTree, replacement(state, parts))); | ||
| } else { | ||
| // another instance method on StringBuilder | ||
| return NO_MATCH; | ||
| } | ||
| } | ||
| ASTHelpers.TargetType target = ASTHelpers.targetType(state.withPath(path)); | ||
| if (!isUsedAsStringBuilder(state, target)) { | ||
| return describeMatch( | ||
| path.getLeaf(), SuggestedFix.replace(path.getLeaf(), replacement(state, parts))); | ||
| } | ||
| Tree leaf = target.path().getLeaf(); | ||
| if (leaf instanceof VariableTree) { | ||
| VariableTree variableTree = (VariableTree) leaf; | ||
| if (isRewritableVariable(variableTree, state)) { | ||
| return describeMatch( | ||
| variableTree, | ||
| SuggestedFix.builder() | ||
| .replace(variableTree.getType(), "String") | ||
| .replace(variableTree.getInitializer(), replacement(state, parts)) | ||
| .build()); | ||
| } | ||
| } | ||
| return NO_MATCH; | ||
| } | ||
|
|
||
| /** | ||
| * Returns true if the StringBuilder is assigned to a variable, and the type of the variable can | ||
| * safely be refactored to be a String. | ||
| */ | ||
| boolean isRewritableVariable(VariableTree variableTree, VisitorState state) { | ||
| Symbol sym = getSymbol(variableTree); | ||
| if (!sym.getKind().equals(ElementKind.LOCAL_VARIABLE)) { | ||
| return false; | ||
| } | ||
| boolean[] ok = {true}; | ||
| new TreePathScanner<Void, Void>() { | ||
| @Override | ||
| public Void visitIdentifier(IdentifierTree tree, Void unused) { | ||
| if (sym.equals(getSymbol(tree))) { | ||
| TargetType target = targetType(state.withPath(getCurrentPath())); | ||
| if (isUsedAsStringBuilder(state, target)) { | ||
| ok[0] = false; | ||
| } | ||
| } | ||
| return super.visitIdentifier(tree, unused); | ||
| } | ||
| }.scan(state.getPath().getCompilationUnit(), null); | ||
| return ok[0]; | ||
| } | ||
|
|
||
| private static boolean isUsedAsStringBuilder(VisitorState state, TargetType target) { | ||
| if (target.path().getLeaf().getKind().equals(Tree.Kind.MEMBER_REFERENCE)) { | ||
| // e.g. sb::append | ||
| return true; | ||
| } | ||
| return ASTHelpers.isSubtype(target.type(), JAVA_LANG_APPENDABLE.get(state), state); | ||
| } | ||
|
|
||
| private static String replacement(VisitorState state, List<ExpressionTree> parts) { | ||
| if (parts.isEmpty()) { | ||
| return "\"\""; | ||
| } | ||
| return parts.stream() | ||
| .map( | ||
| x -> { | ||
| String source = state.getSourceForNode(x); | ||
| if (requiresParentheses(x, state)) { | ||
| source = String.format("(%s)", source); | ||
| } | ||
| return source; | ||
| }) | ||
| .collect(joining(" + ")); | ||
| } | ||
|
|
||
| private static final Supplier<Type> JAVA_LANG_APPENDABLE = | ||
| VisitorState.memoize(state -> state.getTypeFromString("java.lang.Appendable")); | ||
|
|
||
| private static final Supplier<Type> JAVA_LANG_CHARSEQUENCE = | ||
| VisitorState.memoize(state -> state.getTypeFromString("java.lang.CharSequence")); | ||
| } |
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145 changes: 145 additions & 0 deletions
145
core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilderTest.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,145 @@ | ||
| /* | ||
| * Copyright 2023 The Error Prone Authors. | ||
| * | ||
| * 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 com.google.errorprone.BugCheckerRefactoringTestHelper; | ||
| import com.google.errorprone.CompilationTestHelper; | ||
| import org.junit.Test; | ||
| import org.junit.runner.RunWith; | ||
| import org.junit.runners.JUnit4; | ||
|
|
||
| @RunWith(JUnit4.class) | ||
| public class UnnecessaryStringBuilderTest { | ||
| private final BugCheckerRefactoringTestHelper refactoringHelper = | ||
| BugCheckerRefactoringTestHelper.newInstance(UnnecessaryStringBuilder.class, getClass()); | ||
| private final CompilationTestHelper testHelper = | ||
| CompilationTestHelper.newInstance(UnnecessaryStringBuilder.class, getClass()); | ||
|
|
||
| @Test | ||
| public void positive() { | ||
| refactoringHelper | ||
| .addInputLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(String hello) {", | ||
| " System.err.println(new StringBuilder().append(hello).append(\"world\"));", | ||
| " System.err.println(new StringBuilder(hello).append(\"world\"));", | ||
| " System.err.println(new StringBuilder(10).append(hello).append(\"world\"));", | ||
| " System.err.println(new StringBuilder(hello).append(\"world\").toString());", | ||
| " System.err.println(new StringBuilder().toString());", | ||
| " }", | ||
| "}") | ||
| .addOutputLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(String hello) {", | ||
| " System.err.println(hello + \"world\");", | ||
| " System.err.println(hello + \"world\");", | ||
| " System.err.println(hello + \"world\");", | ||
| " System.err.println(hello + \"world\");", | ||
| " System.err.println(\"\");", | ||
| " }", | ||
| "}") | ||
| .doTest(); | ||
| } | ||
|
|
||
| @Test | ||
| public void variable() { | ||
| refactoringHelper | ||
| .addInputLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(String hello) {", | ||
| " String a = new StringBuilder().append(hello).append(\"world\").toString();", | ||
| " StringBuilder b = new StringBuilder().append(hello).append(\"world\");", | ||
| " StringBuilder c = new StringBuilder().append(hello).append(\"world\");", | ||
| " System.err.println(b);", | ||
| " System.err.println(b + \"\");", | ||
| " System.err.println(c);", | ||
| " c.append(\"goodbye\");", | ||
| " }", | ||
| "}") | ||
| .addOutputLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(String hello) {", | ||
| " String a = hello + \"world\";", | ||
| " String b = hello + \"world\";", | ||
| " StringBuilder c = new StringBuilder().append(hello).append(\"world\");", | ||
| " System.err.println(b);", | ||
| " System.err.println(b + \"\");", | ||
| " System.err.println(c);", | ||
| " c.append(\"goodbye\");", | ||
| " }", | ||
| "}") | ||
| .doTest(); | ||
| } | ||
|
|
||
| @Test | ||
| public void negative() { | ||
| testHelper | ||
| .addSourceLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(Iterable<String> xs) {", | ||
| " StringBuilder sb = new StringBuilder();", | ||
| " for (String s : xs) {", | ||
| " sb.append(s);", | ||
| " }", | ||
| " System.err.println(sb);", | ||
| " }", | ||
| "}") | ||
| .doTest(); | ||
| } | ||
|
|
||
| @Test | ||
| public void negativeMethodReference() { | ||
| testHelper | ||
| .addSourceLines( | ||
| "Test.java", | ||
| "class Test {", | ||
| " void f(Iterable<String> xs) {", | ||
| " StringBuilder sb = new StringBuilder();", | ||
| " xs.forEach(sb::append);", | ||
| " System.err.println(sb);", | ||
| " }", | ||
| "}") | ||
| .doTest(); | ||
| } | ||
|
|
||
| @Test | ||
| public void needsParens() { | ||
| refactoringHelper | ||
| .addInputLines( | ||
| "Test.java", | ||
| "abstract class Test {", | ||
| " abstract void g(String x);", | ||
| " void f(boolean b, String hello) {", | ||
| " g(new StringBuilder().append(b ? hello : \"\").append(\"world\").toString());", | ||
| " }", | ||
| "}") | ||
| .addOutputLines( | ||
| "Test.java", | ||
| "abstract class Test {", | ||
| " abstract void g(String x);", | ||
| " void f(boolean b, String hello) {", | ||
| " g((b ? hello : \"\") + \"world\");", | ||
| " }", | ||
| "}") | ||
| .doTest(); | ||
| } | ||
| } |