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Refactor isReassigned in PatternMatchingInstanceof to use the local field trick #6016

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Merged
copybara-service merged 1 commit into from
Aug 10, 2026
Merged

Refactor isReassigned in PatternMatchingInstanceof to use the local field trick #6016

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51 changes: 31 additions & 20 deletions core/src/main/java/com/google/errorprone/bugpatterns/PatternMatchingInstanceof.java
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Original file line number Diff line number Diff line change
Expand Up @@ -25,12 +25,12 @@
import static com.google.errorprone.util.ASTHelpers.getType;
import static com.google.errorprone.util.SourceVersion.supportsPatternMatchingInstanceof;
import static com.google.errorprone.util.TargetType.targetType;
import static java.lang.Boolean.TRUE;
import static java.util.Collections.nCopies;
import static java.util.stream.Collectors.joining;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.InstanceOfTreeMatcher;
Expand Down Expand Up @@ -345,38 +345,49 @@ private static boolean requiresParentheses(TreePath path) {
private static boolean isReassigned(VariableTree variableTree, List<Tree> trees) {
VarSymbol varSymbol = getSymbol(variableTree);

// TODO(kak): consider using the local field trick instead of the Boolean type param
var scanner =
new TreeScanner<Boolean, Void>() {
new TreeScanner<Void, Void>() {
private boolean reassigned = false;

@Override
public Boolean visitAssignment(AssignmentTree node, Void unused) {
return varSymbol.equals(getSymbol(node.getVariable()))
|| super.visitAssignment(node, null);
public Void scan(Tree tree, Void unused) {
return reassigned ? null : super.scan(tree, null);
}

@Override
public Boolean visitCompoundAssignment(CompoundAssignmentTree node, Void unused) {
return varSymbol.equals(getSymbol(node.getVariable()))
|| super.visitCompoundAssignment(node, null);
public Void visitAssignment(AssignmentTree node, Void unused) {
if (varSymbol.equals(getSymbol(node.getVariable()))) {
reassigned = true;
}
return super.visitAssignment(node, null);
}

@Override
public Boolean visitUnary(UnaryTree node, Void unused) {
return (switch (node.getKind()) {
case POSTFIX_INCREMENT, POSTFIX_DECREMENT, PREFIX_INCREMENT, PREFIX_DECREMENT ->
varSymbol.equals(getSymbol(node.getExpression()));
default -> false;
})
|| super.visitUnary(node, null);
public Void visitCompoundAssignment(CompoundAssignmentTree node, Void unused) {
if (varSymbol.equals(getSymbol(node.getVariable()))) {
reassigned = true;
}
return super.visitCompoundAssignment(node, null);
}

private static final ImmutableSet<Kind> INCREMENT_DECREMENT =
Sets.immutableEnumSet(
Kind.POSTFIX_INCREMENT,
Kind.POSTFIX_DECREMENT,
Kind.PREFIX_INCREMENT,
Kind.PREFIX_DECREMENT);

@Override
public Boolean reduce(Boolean left, Boolean right) {
// be careful because the parameters can be null!
return TRUE.equals(left) || TRUE.equals(right);
public Void visitUnary(UnaryTree node, Void unused) {
if (INCREMENT_DECREMENT.contains(node.getKind())
&& varSymbol.equals(getSymbol(node.getExpression()))) {
reassigned = true;
}
return super.visitUnary(node, null);
}
};
return scanner.scan(trees, null);
scanner.scan(trees, null);
return scanner.reassigned;
}

/**
Expand Down
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