feat: Make accessible the original descriptor when nullable (#2631)

Kotlin · Apr 17, 2024 · 5d22d74 · 5d22d74
1 parent 84f5e8a
commit 5d22d74
Show file tree

Hide file tree

Showing 3 changed files with 35 additions and 0 deletions.
diff --git a/core/api/kotlinx-serialization-core.api b/core/api/kotlinx-serialization-core.api
@@ -309,6 +309,7 @@ public final class kotlinx/serialization/descriptors/SerialDescriptorsKt {
 	public static final fun buildSerialDescriptor (Ljava/lang/String;Lkotlinx/serialization/descriptors/SerialKind;[Lkotlinx/serialization/descriptors/SerialDescriptor;Lkotlin/jvm/functions/Function1;)Lkotlinx/serialization/descriptors/SerialDescriptor;
 	public static synthetic fun buildSerialDescriptor$default (Ljava/lang/String;Lkotlinx/serialization/descriptors/SerialKind;[Lkotlinx/serialization/descriptors/SerialDescriptor;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)Lkotlinx/serialization/descriptors/SerialDescriptor;
 	public static final fun getNullable (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public static final fun getUnwrapNullable (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/descriptors/SerialDescriptor;
 	public static final fun listSerialDescriptor (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/descriptors/SerialDescriptor;
 	public static final fun mapSerialDescriptor (Lkotlinx/serialization/descriptors/SerialDescriptor;Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/descriptors/SerialDescriptor;
 	public static final fun serialDescriptor (Lkotlin/reflect/KType;)Lkotlinx/serialization/descriptors/SerialDescriptor;

diff --git a/core/commonMain/src/kotlinx/serialization/descriptors/SerialDescriptors.kt b/core/commonMain/src/kotlinx/serialization/descriptors/SerialDescriptors.kt
@@ -223,6 +223,20 @@ public val SerialDescriptor.nullable: SerialDescriptor
         return SerialDescriptorForNullable(this)
     }
 
+/**
+ * Returns non-nullable serial descriptor for the type, if [this] is a nullable descriptor created automatically or
+ * with `.nullable` extensions on a descriptor or serializer. Otherwise, returns [this].
+ *
+ * @see SerialDescriptor.nullable
+ * @see KSerializer.nullable
+ */
+@ExperimentalSerializationApi
+public val SerialDescriptor.unwrapNullable: SerialDescriptor
+    get() = when (this) {
+        is SerialDescriptorForNullable -> original
+        else -> this
+    }
+
 /**
  * Builder for [SerialDescriptor] for user-defined serializers.
  *

diff --git a/core/commonTest/src/kotlinx/serialization/SerialDescriptorBuilderTest.kt b/core/commonTest/src/kotlinx/serialization/SerialDescriptorBuilderTest.kt
@@ -94,4 +94,24 @@ class SerialDescriptorBuilderTest {
         assertTrue(descriptor.isNullable)
         assertEquals("my.Simple?", descriptor.serialName)
     }
+
+    @Test
+    fun testUnwrapNullable() {
+        listOf(
+            buildClassSerialDescriptor("my.Simple") {},
+            Boolean.serializer().descriptor,
+            String.serializer().descriptor,
+            ListSerializer(Int.serializer()).descriptor,
+        ).forEach { originalDescriptor ->
+            // Unwrapping nullable when it is not nullable should return the same descriptor (no-op operation)
+            assertSame(originalDescriptor.unwrapNullable, originalDescriptor)
+
+            // Unwrapping nullable when it is nullable should return the original descriptor
+            assertSame(originalDescriptor.nullable.unwrapNullable, originalDescriptor)
+        }
+
+        @Serializable class Type(val field: String?)
+        // Unwrapping nullable of a nullable field should return the original non-null descriptor
+        assertSame(Type.serializer().descriptor.getElementDescriptor(0).unwrapNullable, String.serializer().descriptor)
+    }
 }