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Merge pull request #1159 from sogilis/improve-kotlin-data-class-support
Ignore properties not declared in the primary constructor of Kotlin data classes
2 parents ae6ab2f + 81c58ee commit b175147

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‎.tool-versions‎

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java temurin-25.0.1+8.0.LTS

‎docs/_manual/16-kotlin.md‎

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@@ -15,6 +15,20 @@ EqualsVerifier.forClass(Foo::class.java)
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For most simple classes and data classes, that's enough.
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## Data classes
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Since data class equality is based on primary constructor parameters, EqualsVerifier ignores other properties in such classes.
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For instance, in following code, `isEmpty` property is ignored:
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```kotlin
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data class MyDataclass(val value: String) {
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val isEmpty = value.isEmpty()
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}
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```
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This behavior requires `org.jetbrains.kotlin:kotlin-reflect` library to be available, otherwise data classes are treated like any other class.
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## Delegates
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Kotlin supports various forms of delegate fields. In a Kotlin class definition, delegates may look like this:

‎equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/checkers/fieldchecks/SignificantFieldCheck.java‎

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import nl.jqno.equalsverifier.internal.reflection.FieldProbe;
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import nl.jqno.equalsverifier.internal.reflection.annotations.AnnotationCache;
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import nl.jqno.equalsverifier.internal.reflection.annotations.SupportedAnnotations;
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import nl.jqno.equalsverifier.internal.util.*;
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import nl.jqno.equalsverifier.internal.reflection.kotlin.KotlinScreen;
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import nl.jqno.equalsverifier.internal.util.CachedHashCodeInitializer;
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import nl.jqno.equalsverifier.internal.util.Configuration;
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import nl.jqno.equalsverifier.internal.util.Context;
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import nl.jqno.equalsverifier.internal.util.Formatter;
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import nl.jqno.equalsverifier.internal.util.PrimitiveMappers;
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import nl.jqno.equalsverifier.internal.valueproviders.SubjectCreator;
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public class SignificantFieldCheck<T> implements FieldCheck<T> {
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Significant fields: equals does not use %%, or it is stateless.
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Suppress Warning.SURROGATE_KEY if you want to use only the @Id or @EmbeddedId field(s).""";
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}
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else if (KotlinScreen.isKotlin(type)) {
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message =
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"""
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Significant fields: equals does not use %%, or it is stateless.
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Note: This is a Kotlin class. Import kotlin reflect in the classpath to use the adapted equalsverifier implementation.
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""";
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}
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else {
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message = "Significant fields: equals does not use %%, or it is stateless.";
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}

‎equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/kotlin/KotlinProbe.java‎

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Assert.fail(Formatter.of(msg));
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}
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}
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public static boolean isDeclaredInPrimaryConstructor(Field field) {
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Class<?> declaringClass = field.getDeclaringClass();
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KClass<?> kType = JvmClassMappingKt.getKotlinClass(declaringClass);
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if (kType.getConstructors().isEmpty()) {
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return false;
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}
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KFunction<?> constructor = KClasses.getPrimaryConstructor(kType);
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return constructor.getParameters().stream().anyMatch(p -> p.getName().equals(field.getName()));
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}
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public static <T> boolean isDataClass(Class<T> type) {
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return JvmClassMappingKt.getKotlinClass(type).isData();
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}
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}

‎equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/util/Configuration.java‎

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import nl.jqno.equalsverifier.internal.reflection.FieldProbe;
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import nl.jqno.equalsverifier.internal.reflection.TypeTag;
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import nl.jqno.equalsverifier.internal.reflection.annotations.*;
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import nl.jqno.equalsverifier.internal.reflection.kotlin.KotlinProbe;
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import nl.jqno.equalsverifier.internal.reflection.kotlin.KotlinScreen;
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// CHECKSTYLE OFF: ParameterNumber
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if (isKotlin) {
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for (FieldProbe f : FieldIterable.ofKotlin(type)) {
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if (KotlinScreen.canProbe()
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&& KotlinProbe.isDataClass(type)
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&& !KotlinProbe.isDeclaredInPrimaryConstructor(f.getField())) {
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ignoredFields.add(f.getName());
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}
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if (KotlinScreen.isSyntheticKotlinDelegate(f.getField())) {
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nonnullFields.add(f.getName());
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}

‎equalsverifier-test-kotlin-noreflect/src/test/kotlin/nl/jqno/equalsverifier/kotlin/KotlinDataClassTest.kt‎

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package nl.jqno.equalsverifier.kotlin
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import nl.jqno.equalsverifier.EqualsVerifier
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import org.assertj.core.api.Assertions.assertThatThrownBy
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import org.junit.jupiter.api.Test
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class KotlinDataClassTest {
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data class DataClassWithComputedProperty(val value: String) {
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val isEmpty = value.isEmpty()
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}
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@Test
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fun `properties not declared in primary constructor of data classes are ignored`() {
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assertThatThrownBy {
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EqualsVerifier.forClass(DataClassWithComputedProperty::class.java)
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.verify()
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}.isInstanceOf(AssertionError::class.java)
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.hasMessageContaining("Significant fields: equals does not use isEmpty, or it is stateless.")
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.hasMessageContaining("Note: This is a Kotlin class. Import kotlin reflect in the classpath to use the adapted equalsverifier implementation.")
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}
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data class DataClassWithSecondaryConstructor(val value: String) {
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constructor(prefix: String, isEmpty: Boolean) : this(prefix)
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val isEmpty = value.isEmpty()
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}
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@Test
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fun `properties declared in secondary constructor of data classes are ignored`() {
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assertThatThrownBy {
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EqualsVerifier.forClass(DataClassWithSecondaryConstructor::class.java)
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.verify()
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}.isInstanceOf(AssertionError::class.java)
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.hasMessageContaining("Significant fields: equals does not use isEmpty, or it is stateless.")
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.hasMessageContaining("Note: This is a Kotlin class. Import kotlin reflect in the classpath to use the adapted equalsverifier implementation.")
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}
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}

‎equalsverifier-test-kotlin/src/test/kotlin/nl/jqno/equalsverifier/kotlin/KotlinDataClassTest.kt‎

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package nl.jqno.equalsverifier.kotlin
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import nl.jqno.equalsverifier.EqualsVerifier
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import org.junit.jupiter.api.Test
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class KotlinDataClassTest {
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data class DataClassWithComputedProperty(val value: String) {
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val isEmpty = value.isEmpty()
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}
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@Test
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fun `properties not declared in primary constructor of data classes are ignored`() {
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EqualsVerifier.forClass(DataClassWithComputedProperty::class.java)
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.verify()
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}
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data class DataClassWithSecondaryConstructor(val value: String) {
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constructor(prefix: String, isEmpty: Boolean) : this(prefix)
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val isEmpty = value.isEmpty()
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}
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@Test
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fun `properties declared in secondary constructor of data classes are ignored`() {
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EqualsVerifier.forClass(DataClassWithSecondaryConstructor::class.java)
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.verify()
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}
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}

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