Supply proper equals(), hashCode(), and toString() for SerialDescriptor() wrapper.

Fixes #2941

Author: sandwwraith

core/commonMain/src/kotlinx/serialization/descriptors/SerialDescriptors.kt

@@ -121,7 +121,25 @@ public fun SerialDescriptor(serialName: String, original: SerialDescriptor): Ser
     return WrappedSerialDescriptor(serialName, original)
 }
 
-internal class WrappedSerialDescriptor(override val serialName: String, original: SerialDescriptor) : SerialDescriptor by original
+internal class WrappedSerialDescriptor(override val serialName: String, private val original: SerialDescriptor) :
+    SerialDescriptor by original {
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is WrappedSerialDescriptor) return false
+
+        return serialName == other.serialName && original == other.original
+    }
+
+    override fun hashCode(): Int {
+        var result = serialName.hashCode()
+        result = 31 * result + original.hashCode()
+        return result
+    }
+
+    override fun toString(): String = toStringImpl()
+
+}
 
 /**
  * An unsafe alternative to [buildClassSerialDescriptor] that supports an arbitrary [SerialKind].
@@ -370,10 +388,5 @@ internal class SerialDescriptorImpl(
 
     override fun hashCode(): Int = _hashCode
 
-    override fun toString(): String {
-        return (0 until elementsCount).joinToString(", ", prefix = "$serialName(", postfix = ")") {
-            getElementName(it) + ": " + getElementDescriptor(it).serialName
-        }
-    }
+    override fun toString(): String = toStringImpl()
 }
-

core/commonMain/src/kotlinx/serialization/internal/PluginGeneratedSerialDescriptor.kt

@@ -96,11 +96,7 @@ internal open class PluginGeneratedSerialDescriptor(
 
     override fun hashCode(): Int = _hashCode
 
-    override fun toString(): String {
-        return (0 until elementsCount).joinToString(", ", "$serialName(", ")") { i ->
-            getElementName(i) + ": " + getElementDescriptor(i).serialName
-        }
-    }
+    override fun toString(): String = toStringImpl()
 }
 
 @OptIn(ExperimentalSerializationApi::class)
@@ -131,3 +127,7 @@ internal fun SerialDescriptor.hashCodeImpl(typeParams: Array<SerialDescriptor>):
     result = 31 * result + kindHash
     return result
 }
+
+internal fun SerialDescriptor.toStringImpl(): String = (0 until elementsCount).joinToString(", ", "$serialName(", ")") { i ->
+    getElementName(i) + ": " + getElementDescriptor(i).serialName
+}

core/commonTest/src/kotlinx/serialization/WrappedSerialDescriptorTest.kt

@@ -75,4 +75,14 @@ class WrappedSerialDescriptorTest {
         }
         assertFails { SerialDescriptor("kotlin.Int", Int.serializer().descriptor) }
     }
+
+    @Test
+    fun testWrappedEqHc() {
+        val a = SerialDescriptor("SimpleTypeWrapper", SimpleType.serializer().descriptor)
+        val b = SerialDescriptor("SimpleTypeWrapper", SimpleType.serializer().descriptor)
+        assertEquals(a, b)
+        assertEquals(a.hashCode(), b.hashCode())
+        assertNotEquals(a, SimpleType.serializer().descriptor)
+        assertEquals(a.toString(), "SimpleTypeWrapper(int: kotlin.Int, float: kotlin.Float)")
+    }
 }