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VoidUsed: flag Void variables being _used_, where they can simply…
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… be replaced with a literal `null`.

Findings here (unknown commit) before I fixed the bug with assignments.

PiperOrigin-RevId: 627676095
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graememorgan authored and Error Prone Team committed Apr 24, 2024
1 parent 3ee6f41 commit f289d9e
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76 changes: 76 additions & 0 deletions core/src/main/java/com/google/errorprone/bugpatterns/VoidUsed.java
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/*
* Copyright 2024 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.Sets.immutableEnumSet;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.suppliers.Suppliers.JAVA_LANG_VOID_TYPE;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import static com.google.errorprone.util.ASTHelpers.isSameType;
import static javax.lang.model.element.ElementKind.FIELD;
import static javax.lang.model.element.ElementKind.LOCAL_VARIABLE;
import static javax.lang.model.element.ElementKind.PARAMETER;

import com.google.common.collect.ImmutableSet;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.IdentifierTreeMatcher;
import com.google.errorprone.bugpatterns.BugChecker.MemberSelectTreeMatcher;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.sun.source.tree.AssignmentTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.Tree;
import javax.lang.model.element.ElementKind;

/** A BugPattern; see the summary. */
@BugPattern(
summary =
"Using a Void-typed variable is potentially confusing, and can be replaced with a literal"
+ " `null`.",
severity = WARNING)
public final class VoidUsed extends BugChecker
implements IdentifierTreeMatcher, MemberSelectTreeMatcher {
@Override
public Description matchIdentifier(IdentifierTree tree, VisitorState state) {
return handle(tree, state);
}

@Override
public Description matchMemberSelect(MemberSelectTree tree, VisitorState state) {
return handle(tree, state);
}

private Description handle(Tree tree, VisitorState state) {
var parent = state.getPath().getParentPath().getLeaf();
if (parent instanceof AssignmentTree && ((AssignmentTree) parent).getVariable().equals(tree)) {
return NO_MATCH;
}
var symbol = getSymbol(tree);
if (symbol == null
|| !KINDS.contains(symbol.getKind())
|| !isSameType(symbol.type, JAVA_LANG_VOID_TYPE.get(state), state)) {
return NO_MATCH;
}
return describeMatch(tree, SuggestedFix.replace(tree, "null"));
}

private static final ImmutableSet<ElementKind> KINDS =
immutableEnumSet(PARAMETER, LOCAL_VARIABLE, FIELD);
}
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Expand Up @@ -434,6 +434,7 @@
import com.google.errorprone.bugpatterns.VarTypeName;
import com.google.errorprone.bugpatterns.VariableNameSameAsType;
import com.google.errorprone.bugpatterns.Varifier;
import com.google.errorprone.bugpatterns.VoidUsed;
import com.google.errorprone.bugpatterns.WaitNotInLoop;
import com.google.errorprone.bugpatterns.WildcardImport;
import com.google.errorprone.bugpatterns.WithSignatureDiscouraged;
Expand Down Expand Up @@ -1094,6 +1095,7 @@ public static ScannerSupplier warningChecks() {
UnusedVariable.class,
UseBinds.class,
VariableNameSameAsType.class,
VoidUsed.class,
WaitNotInLoop.class,
WakelockReleasedDangerously.class,
WithSignatureDiscouraged.class
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/*
* Copyright 2024 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.CompilationTestHelper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

@RunWith(JUnit4.class)
public final class VoidUsedTest {
private final CompilationTestHelper helper =
CompilationTestHelper.newInstance(VoidUsed.class, getClass());

@Test
public void positive() {
helper
.addSourceLines(
"Test.java", //
"class Test {",
" void test(Void v) {",
" // BUG: Diagnostic contains: null",
" System.out.println(v);",
" }",
"}")
.doTest();
}

@Test
public void notVoid_noFinding() {
helper
.addSourceLines(
"Test.java", //
"class Test {",
" void test(Integer v) {",
" System.out.println(v);",
" }",
"}")
.doTest();
}

@Test
public void assignedTo_noFinding() {
helper
.addSourceLines(
"Test.java", //
"class Test {",
" void test(Void v) {",
" v = null;",
" }",
"}")
.doTest();
}
}

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