Merge pull request #1087 from jqno/kotlin-delegate

Support Kotlin delegates

Author: jqno

CHANGELOG.md

@@ -14,6 +14,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Support for Kotlin delegates. ([Issue 1083](https://github.com/jqno/equalsverifier/issues/1083))
+
 ## [4.0.1] - 2025-06-10
 
 ### Fixed

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

@@ -131,18 +131,22 @@ private List<FieldProbe> addFieldsFor(Class<?> c) {
         var statics = new ArrayList<FieldProbe>();
 
         for (Field field : c.getDeclaredFields()) {
-            if (!field.isSynthetic()
-                    && !"__cobertura_counters".equals(field.getName())
-                    && !field.getName().startsWith("bitmap$init$") // Generated by Scala 2.x's -Xcheckinit flag
-            ) {
-                FieldProbe probe = FieldProbe.of(field);
-                boolean isStatic = probe.isStatic();
-                if (isStatic && includeStatic) {
-                    statics.add(probe);
-                }
-                if (!isStatic) {
-                    fields.add(probe);
-                }
+            FieldProbe probe = FieldProbe.of(field);
+
+            if (field.isSynthetic() && !probe.isKotlinDelegate()) {
+                continue;
+            }
+            if (probe.getName().startsWith("bitmap$init$") // Generated by Scala 2.x's -Xcheckinit flag
+                    || probe.getName().equals("__cobertura_counters")) {
+                continue;
+            }
+
+            boolean isStatic = probe.isStatic();
+            if (isStatic && includeStatic) {
+                statics.add(probe);
+            }
+            if (!isStatic) {
+                fields.add(probe);
             }
         }
 

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

@@ -170,12 +170,21 @@ public boolean isAnnotatedNonnull(AnnotationCache annotationCache) {
      * @return Whether or not the field can be modified reflectively.
      */
     public boolean canBeModifiedReflectively() {
-        if (field.isSynthetic()) {
+        if (field.isSynthetic() && !isKotlinDelegate()) {
             return false;
         }
         if (isFinal() && isStatic()) {
             return false;
         }
         return true;
     }
+
+    /**
+     * Determines whether the field is a synthetic Kotlin delegate field.
+     *
+     * @return Whether or not the field is a synthetic Kotlin delegate field.
+     */
+    public boolean isKotlinDelegate() {
+        return field.isSynthetic() && field.getName().startsWith("$$delegate_");
+    }
 }

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

@@ -7,6 +7,8 @@
 
 import nl.jqno.equalsverifier.Mode;
 import nl.jqno.equalsverifier.Warning;
+import nl.jqno.equalsverifier.internal.reflection.FieldIterable;
+import nl.jqno.equalsverifier.internal.reflection.FieldProbe;
 import nl.jqno.equalsverifier.internal.reflection.TypeTag;
 import nl.jqno.equalsverifier.internal.reflection.annotations.*;
 
@@ -97,6 +99,14 @@ public static <T> Configuration<T> build(
                 fieldnameToGetter != null ? fieldnameToGetter : Configuration::defaulFieldNameToGetterConverter;
         boolean isKotlin = annotationCache.hasClassAnnotation(type, SupportedAnnotations.KOTLIN);
 
+        if (isKotlin) {
+            for (FieldProbe f : FieldIterable.ofKotlin(type)) {
+                if (f.isKotlinDelegate()) {
+                    nonnullFields.add(f.getName());
+                }
+            }
+        }
+
         return new Configuration<>(type,
                 typeTag,
                 ignoredFields,

equalsverifier-test-kotlin/src/test/kotlin/nl/jqno/equalsverifier/internal/reflection/KotlinFieldProbeTest.kt

@@ -0,0 +1,31 @@
+package nl.jqno.equalsverifier.internal.reflection
+
+import nl.jqno.equalsverifier.internal.reflection.FieldProbe
+import org.junit.jupiter.api.Test
+
+import org.assertj.core.api.Assertions.assertThat
+
+class KotlinFieldProbeTest {
+
+  @Test
+  fun isKotlinDelegate() {
+    var f = FooContainer::class.java.getDeclaredField("\$\$delegate_0")
+    var probe = FieldProbe.of(f)
+    assertThat(probe.isKotlinDelegate()).isTrue()
+  }
+
+  @Test
+  fun isNotKotlinDelegate() {
+    var f = FooContainer::class.java.getDeclaredField("bar")
+    var probe = FieldProbe.of(f)
+    assertThat(probe.isKotlinDelegate()).isFalse()
+  }
+
+  interface Foo {
+    val foo: Int
+  }
+
+  data class FooImpl(override val foo: Int): Foo
+
+  class FooContainer(fooValue: Int, val bar: Int): Foo by FooImpl(fooValue)
+}

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

@@ -0,0 +1,29 @@
+package nl.jqno.equalsverifier.kotlin
+
+import nl.jqno.equalsverifier.EqualsVerifier
+import org.junit.jupiter.api.Test
+
+class KotlinDelegationTest {
+
+  @Test
+  fun `succeed when class uses interface delegation`() {
+    EqualsVerifier.forClass(FooContainer::class.java).verify()
+  }
+
+  interface Foo {
+    val foo: Int
+  }
+
+  data class FooImpl(override val foo: Int): Foo
+
+  class FooContainer(fooValue: Int): Foo by FooImpl(fooValue) {
+
+    override fun equals(other: Any?): Boolean {
+      if (this === other) return true
+      if (other !is FooContainer) return false
+      return foo == other.foo
+    }
+
+    override fun hashCode(): Int = foo
+  }
+}