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Worry about generics in PatternMatchingInstanceof.
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PiperOrigin-RevId: 698929262
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@graememorgan
graememorgan authored and Error Prone Team committed Nov 22, 2024
1 parent 1046226 commit 25b61e3
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6 changes: 6 additions & 0 deletions check_api/src/main/java/com/google/errorprone/fixes/SuggestedFix.java
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Expand Up @@ -35,6 +35,7 @@
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collector;
import org.jspecify.annotations.Nullable;

/**
Expand Down Expand Up @@ -168,6 +169,11 @@ public static SuggestedFix merge(SuggestedFix first, SuggestedFix second, Sugges
return builder.build();
}

public static Collector<SuggestedFix, ?, SuggestedFix> mergeFixes() {
return Collector.of(
SuggestedFix::builder, Builder::merge, Builder::merge, SuggestedFix.Builder::build);
}

public static Builder builder() {
return new Builder();
}
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143 changes: 96 additions & 47 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 @@ -17,6 +17,7 @@
package com.google.errorprone.bugpatterns;

import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.fixes.SuggestedFix.mergeFixes;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import static com.google.errorprone.util.ASTHelpers.getType;
Expand All @@ -25,96 +26,144 @@
import com.google.common.collect.ImmutableSet;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.IfTreeMatcher;
import com.google.errorprone.bugpatterns.BugChecker.InstanceOfTreeMatcher;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.sun.source.tree.BinaryTree;
import com.sun.source.tree.BlockTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IfTree;
import com.sun.source.tree.InstanceOfTree;
import com.sun.source.tree.ParenthesizedTree;
import com.sun.source.tree.Tree.Kind;
import com.sun.source.tree.StatementTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.TypeCastTree;
import com.sun.source.tree.VariableTree;
import com.sun.source.util.SimpleTreeVisitor;
import com.sun.source.util.TreePath;
import com.sun.source.util.TreePathScanner;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Type;
import org.jspecify.annotations.Nullable;

/** A BugPattern; see the summary. */
@BugPattern(
severity = WARNING,
summary = "This code can be simplified to use a pattern-matching instanceof.")
public final class PatternMatchingInstanceof extends BugChecker implements IfTreeMatcher {
public final class PatternMatchingInstanceof extends BugChecker implements InstanceOfTreeMatcher {

@Override
public Description matchIf(IfTree tree, VisitorState state) {
public Description matchInstanceOf(InstanceOfTree instanceOfTree, VisitorState state) {
if (!supportsPatternMatchingInstanceof(state.context)) {
return NO_MATCH;
}
ImmutableSet<InstanceOfTree> instanceofChecks = scanForInstanceOf(tree.getCondition());
if (instanceofChecks.isEmpty()) {
return NO_MATCH;
var enclosingIf = findEnclosingIf(instanceOfTree, state);
if (enclosingIf != null) {
var replaceExistingVariable = checkForImmediateVariable(instanceOfTree, state, enclosingIf);
if (replaceExistingVariable != NO_MATCH) {
return replaceExistingVariable;
}
if (getSymbol(instanceOfTree.getExpression()) instanceof VarSymbol varSymbol) {
Type targetType = getType(instanceOfTree.getType());
var allCasts = findAllCasts(varSymbol, enclosingIf.getThenStatement(), targetType, state);
if (!allCasts.isEmpty()) {
// This is a gamble as to an appropriate name. We could make sure it doesn't clash with
// anything in scope, but that's effort.
var name = lowerFirstLetter(targetType.tsym.getSimpleName().toString());
return describeMatch(
instanceOfTree,
SuggestedFix.builder()
.postfixWith(instanceOfTree, " " + name)
.merge(
allCasts.stream()
.map(c -> SuggestedFix.replace(c, name))
.collect(mergeFixes()))
.build());
}
}
}
var body = tree.getThenStatement();
if (!(body instanceof BlockTree)) {
// TODO(ghm): Handle things other than just ifs. It'd be great to refactor `foo instanceof Bar
// && ((Bar) foo).baz()`.
return NO_MATCH;
}

private Description checkForImmediateVariable(
InstanceOfTree instanceOfTree, VisitorState state, IfTree enclosingIf) {
var body = enclosingIf.getThenStatement();
if (!(body instanceof BlockTree block)) {
return NO_MATCH;
}
var block = (BlockTree) body;
if (block.getStatements().isEmpty()) {
return NO_MATCH;
}
var firstStatement = block.getStatements().get(0);
if (!(firstStatement instanceof VariableTree)) {
if (!(firstStatement instanceof VariableTree variableTree)) {
return NO_MATCH;
}
var variableTree = (VariableTree) firstStatement;
if (!(variableTree.getInitializer() instanceof TypeCastTree)) {
if (!(variableTree.getInitializer() instanceof TypeCastTree typeCast)) {
return NO_MATCH;
}
var typeCast = (TypeCastTree) variableTree.getInitializer();
var matchingInstanceof =
instanceofChecks.stream()
.filter(
i ->
state.getTypes().isSameType(getType(i.getType()), getType(typeCast.getType()))
&& getSymbol(i.getExpression()) instanceof VarSymbol
&& getSymbol(i.getExpression()).equals(getSymbol(typeCast.getExpression())))
.findFirst()
.orElse(null);
if (matchingInstanceof == null) {
// TODO(ghm): Relax the requirement of this being an exact same symbol. Handle expressions?
if (!(state
.getTypes()
.isSubtype(getType(instanceOfTree.getType()), getType(variableTree.getType()))
&& getSymbol(instanceOfTree.getExpression()) instanceof VarSymbol varSymbol
&& varSymbol.equals(getSymbol(typeCast.getExpression())))) {
return NO_MATCH;
}
return describeMatch(
firstStatement,
SuggestedFix.builder()
.delete(variableTree)
.postfixWith(matchingInstanceof, " " + variableTree.getName().toString())
.postfixWith(instanceOfTree, " " + variableTree.getName().toString())
.build());
}

private ImmutableSet<InstanceOfTree> scanForInstanceOf(ExpressionTree condition) {
ImmutableSet.Builder<InstanceOfTree> instanceOfs = ImmutableSet.builder();
new SimpleTreeVisitor<Void, Void>() {
@Override
public Void visitParenthesized(ParenthesizedTree tree, Void unused) {
return visit(tree.getExpression(), null);
}

@Override
public Void visitBinary(BinaryTree tree, Void unused) {
if (tree.getKind() != Kind.CONDITIONAL_AND) {
/**
* Finds the enclosing IfTree if the provided {@code instanceof} is guaranteed to imply the then
* branch.
*/
// TODO(ghm): handle _inverted_ ifs.
private static @Nullable IfTree findEnclosingIf(InstanceOfTree tree, VisitorState state) {
Tree last = tree;
for (Tree parent : state.getPath().getParentPath()) {
switch (parent.getKind()) {
case CONDITIONAL_AND, PARENTHESIZED -> {}
case IF -> {
if (((IfTree) parent).getCondition() == last) {
return (IfTree) parent;
} else {
return null;
}
}
default -> {
return null;
}
visit(tree.getLeftOperand(), null);
visit(tree.getRightOperand(), null);
return null;
}
last = parent;
}
return null;
}

/** Finds all casts of {@code symbol} which are cast to {@code targetType} within {@code tree}. */
private static ImmutableSet<Tree> findAllCasts(
VarSymbol symbol, StatementTree tree, Type targetType, VisitorState state) {
ImmutableSet.Builder<Tree> usages = ImmutableSet.builder();
new TreePathScanner<Void, Void>() {
@Override
public Void visitInstanceOf(InstanceOfTree tree, Void unused) {
instanceOfs.add(tree);
return null;
public Void visitTypeCast(TypeCastTree node, Void unused) {
if (getSymbol(node.getExpression()) instanceof VarSymbol v) {
if (v.equals(symbol) && state.getTypes().isSubtype(targetType, getType(node.getType()))) {
usages.add(
getCurrentPath().getParentPath().getLeaf() instanceof ParenthesizedTree p
? p
: node);
}
}
return super.visitTypeCast(node, null);
}
}.visit(condition, null);
return instanceOfs.build();
}.scan(new TreePath(new TreePath(state.getPath().getCompilationUnit()), tree), null);
return usages.build();
}

private static String lowerFirstLetter(String description) {
return Character.toLowerCase(description.charAt(0)) + description.substring(1);
}
}
38 changes: 33 additions & 5 deletions core/src/test/java/com/google/errorprone/bugpatterns/PatternMatchingInstanceofTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -186,9 +186,38 @@ void test(Object x, String k) {
.doTest();
}

@Test
public void notImmediatelyAssignedToVariable() {
helper
.addInputLines(
"Test.java",
"""
class Test {
void test(Object o) {
if (o instanceof Test) {
test((Test) o);
test(((Test) o).hashCode());
}
}
}
""")
.addOutputLines(
"Test.java",
"""
class Test {
void test(Object o) {
if (o instanceof Test test) {
test(test);
test(test.hashCode());
}
}
}
""")
.doTest();
}

@Test
public void genericWithUpperBoundedWildcard() {
assume().that(Runtime.version().feature()).isAtLeast(21);
helper
.addInputLines(
"Test.java",
Expand All @@ -199,13 +228,11 @@ class Test {
void test(Object object) {
if (object instanceof List) {
@SuppressWarnings("unchecked")
List<? extends CharSequence> list = (List) object;
System.err.println(list.get(0));
List<? extends CharSequence> xs = (List) object;
}
}
}
""")
// TODO: b/380054832 - this shouldn't get re-written
.addOutputLines(
"Test.java",
"""
Expand All @@ -214,7 +241,8 @@ void test(Object object) {
class Test {
void test(Object object) {
if (object instanceof List list) {
System.err.println(list.get(0));
@SuppressWarnings("unchecked")
List<? extends CharSequence> xs = list;
}
}
}
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