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Fix false positive METHOD_RETURN_TYPE_CHANGED for covariant return type overrides (#522) #523

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Merged
siom79 merged 1 commit into from
May 27, 2026
Merged

Fix false positive METHOD_RETURN_TYPE_CHANGED for covariant return type overrides (#522) #523

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54 changes: 50 additions & 4 deletions japicmp/src/main/java/japicmp/compat/CompatibilityChanges.java
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
import japicmp.util.SignatureParser;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.NotFoundException;

import java.util.*;
Expand Down Expand Up @@ -448,10 +449,14 @@ private void checkIfMethodsHaveChangedIncompatible(JApiClass jApiClass, Map<Stri
private void checkIfReturnTypeChanged(JApiMethod method) {
// section 13.4.15 of "Java Language Specification" SE7 (Method Result Type)
if (method.getReturnType().getChangeStatus() == JApiChangeStatus.MODIFIED) {
JApiCompatibilityChange change = addCompatibilityChange(method, JApiCompatibilityChangeType.METHOD_RETURN_TYPE_CHANGED);
if (method.getAccessModifier().hasChangedToMoreVisible()) {
change.setSourceCompatible(true);
change.setBinaryCompatible(true);
if (isCovariantReturnTypeChange(method)) {
addCompatibilityChange(method, JApiCompatibilityChangeType.METHOD_RETURN_TYPE_COVARIANT_CHANGED);
} else {
JApiCompatibilityChange change = addCompatibilityChange(method, JApiCompatibilityChangeType.METHOD_RETURN_TYPE_CHANGED);
if (method.getAccessModifier().hasChangedToMoreVisible()) {
change.setSourceCompatible(true);
change.setBinaryCompatible(true);
}
}
}
if (method.getChangeStatus() == JApiChangeStatus.MODIFIED ||
Expand All @@ -462,6 +467,47 @@ private void checkIfReturnTypeChanged(JApiMethod method) {
}
}

private boolean isCovariantReturnTypeChange(JApiMethod method) {
if (!method.getOldMethod().isPresent() || !method.getNewMethod().isPresent()) {
return false;
}
// Check for a compiler-generated bridge method with the original return type in the new class
String methodName = method.getName();
String oldReturnType = method.getReturnType().getOldReturnType();
JApiClass jApiClass = method.getjApiClass();
boolean bridgeMethodFound = false;
for (JApiMethod candidate : jApiClass.getMethods()) {
if (candidate == method) {
continue;
}
if (!candidate.getName().equals(methodName)) {
continue;
}
Optional<BridgeModifier> newBridgeModifier = candidate.getBridgeModifier().getNewModifier();
if (!newBridgeModifier.isPresent() || newBridgeModifier.get() != BridgeModifier.BRIDGE) {
continue;
}
if (!candidate.getReturnType().getNewReturnType().equals(oldReturnType)) {
continue;
}
if (candidate.hasSameParameter(method)) {
bridgeMethodFound = true;
break;
}
}
if (!bridgeMethodFound) {
return false;
}
// Verify the new return type is a subtype of the old return type
try {
CtClass oldReturnCtClass = method.getOldMethod().get().getReturnType();
CtClass newReturnCtClass = method.getNewMethod().get().getReturnType();
return newReturnCtClass.subtypeOf(oldReturnCtClass);
} catch (NotFoundException e) {
return true; // trust the bridge method as the primary indicator
}
}

private void checkIfParametersGenericsChanged(JApiBehavior jApiBehavior) {
if (jApiBehavior.getChangeStatus() == JApiChangeStatus.MODIFIED ||
jApiBehavior.getChangeStatus() == JApiChangeStatus.UNCHANGED) {
Expand Down
1 change: 1 addition & 0 deletions japicmp/src/main/java/japicmp/model/JApiCompatibilityChangeType.java
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Expand Up @@ -31,6 +31,7 @@ public enum JApiCompatibilityChangeType {
METHOD_LESS_ACCESSIBLE_THAN_IN_SUPERCLASS(false, false, JApiSemanticVersionLevel.MAJOR),
METHOD_IS_STATIC_AND_OVERRIDES_NOT_STATIC(false, false, JApiSemanticVersionLevel.MAJOR),
METHOD_RETURN_TYPE_CHANGED(false, false, JApiSemanticVersionLevel.MAJOR),
METHOD_RETURN_TYPE_COVARIANT_CHANGED(true, true, JApiSemanticVersionLevel.MINOR),
METHOD_RETURN_TYPE_GENERICS_CHANGED(true, false, JApiSemanticVersionLevel.MINOR),
METHOD_PARAMETER_GENERICS_CHANGED(true, false, JApiSemanticVersionLevel.MINOR),
METHOD_NOW_ABSTRACT(false, false, JApiSemanticVersionLevel.MAJOR),
Expand Down
39 changes: 39 additions & 0 deletions japicmp/src/test/java/japicmp/compat/MethodCompatibilityTest.java
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Expand Up @@ -221,6 +221,45 @@ public List<CtClass> createNewClasses(ClassPool classPool) throws Exception {
assertThat(jApiMethod.isSourceCompatible(), is(true));
}

@Test
void testMethodReturnTypeCovariantChange() throws Exception {
JarArchiveComparatorOptions options = new JarArchiveComparatorOptions();
options.setIncludeSynthetic(true);
List<JApiClass> jApiClasses = ClassesHelper.compareClasses(options, new ClassesHelper.ClassesGenerator() {
@Override
public List<CtClass> createOldClasses(ClassPool classPool) throws Exception {
CtClass ctClass = CtClassBuilder.create().name("japicmp.Test").addToClassPool(classPool);
CtMethodBuilder.create().publicAccess().returnType(classPool.get("java.lang.Object")).name("getValue").body("return null;").addToClass(ctClass);
return Collections.singletonList(ctClass);
}

@Override
public List<CtClass> createNewClasses(ClassPool classPool) throws Exception {
CtClass ctClass = CtClassBuilder.create().name("japicmp.Test").addToClassPool(classPool);
// Covariant override — Integer is a subtype of Object
CtMethodBuilder.create().publicAccess().returnType(classPool.get("java.lang.Integer")).name("getValue").body("return Integer.valueOf(0);").addToClass(ctClass);
// Compiler-generated bridge method with original return type
CtMethodBuilder.create().publicAccess().bridgeModifier().syntheticModifier().returnType(classPool.get("java.lang.Object")).name("getValue").body("return null;").addToClass(ctClass);
return Collections.singletonList(ctClass);
}
});
JApiClass jApiClass = getJApiClass(jApiClasses, "japicmp.Test");
assertThat(jApiClass.getChangeStatus(), is(JApiChangeStatus.MODIFIED));
JApiMethod nonBridgeMethod = null;
for (JApiMethod m : jApiClass.getMethods()) {
if (m.getName().equals("getValue") &&
m.getBridgeModifier().getNewModifier().map(bm -> bm == BridgeModifier.NON_BRIDGE).orElse(false)) {
nonBridgeMethod = m;
break;
}
}
assertThat(nonBridgeMethod, is(notNullValue()));
assertThat(nonBridgeMethod.getCompatibilityChanges(), hasItem(new JApiCompatibilityChange(JApiCompatibilityChangeType.METHOD_RETURN_TYPE_COVARIANT_CHANGED)));
assertThat(nonBridgeMethod.getCompatibilityChanges(), not(hasItem(new JApiCompatibilityChange(JApiCompatibilityChangeType.METHOD_RETURN_TYPE_CHANGED))));
assertThat(nonBridgeMethod.isBinaryCompatible(), is(true));
assertThat(jApiClass.isBinaryCompatible(), is(true));
}

@Test
void testMethodNowAbstract() throws Exception {
JarArchiveComparatorOptions options = new JarArchiveComparatorOptions();
Expand Down
5 changes: 5 additions & 0 deletions japicmp/src/test/java/japicmp/util/CtMethodBuilder.java
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Expand Up @@ -39,6 +39,11 @@ public CtMethodBuilder syntheticModifier() {
return this;
}

public CtMethodBuilder bridgeModifier() {
this.modifier = this.modifier | ModifierHelper.ACC_BRIDGE;
return this;
}

public CtMethodBuilder parameters(CtClass[] parameters) {
return (CtMethodBuilder) super.parameters(parameters);
}
Expand Down
1 change: 1 addition & 0 deletions src/site/markdown/MavenPlugin.md
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Expand Up @@ -325,6 +325,7 @@ for each check. This allows you to customize the following verifications:
| METHOD_REMOVED | false | false | MAJOR |
| METHOD_REMOVED_IN_SUPERCLASS | false | false | MAJOR |
| METHOD_RETURN_TYPE_CHANGED | false | false | MAJOR |
| METHOD_RETURN_TYPE_COVARIANT_CHANGED | true | true | MINOR |
| METHOD_RETURN_TYPE_GENERICS_CHANGED | true | false | MINOR |
| METHOD_STATIC_IN_INTERFACE_NO_LONGER_STATIC | false | false | MAJOR |
| SUPERCLASS_ADDED | true | true | MINOR |
Expand Down
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