CORDA-2318 resolve type variables recursively (#4414)

* Resolve type variables recursively

* Clarify test

* Formatting

serialization/src/main/kotlin/net/corda/serialization/internal/model/TypeIdentifier.kt

@@ -225,7 +225,10 @@ internal fun Type.resolveAgainst(context: Type): Type = when (this) {
     is WildcardType -> this.upperBound
     is ReconstitutedParameterizedType -> this
     is ParameterizedType,
-    is TypeVariable<*> -> TypeToken.of(context).resolveType(this).type.upperBound
+    is TypeVariable<*> -> {
+        val resolved = TypeToken.of(context).resolveType(this).type.upperBound
+        if (resolved !is TypeVariable<*> || resolved == this) resolved else resolved.resolveAgainst(context)
+    }
     else -> this
 }
 

serialization/src/test/kotlin/net/corda/serialization/internal/amqp/RoundTripTests.kt

@@ -163,4 +163,26 @@ class RoundTripTests {
         val deserialized = DeserializationInput(factory).deserialize(bytes)
         assertEquals(mapOf("foo" to "bar"), deserialized.changedMembership.state.data.metadata)
     }
+
+    interface I2<T> {
+        val t: T
+    }
+
+    data class C<A, B : A>(override val t: B) : I2<B>
+
+    @Test
+    fun recursiveTypeVariableResolution() {
+        val factory = testDefaultFactoryNoEvolution()
+        val instance = C<Collection<String>, List<String>>(emptyList())
+
+        val bytes = SerializationOutput(factory).serialize(instance)
+        DeserializationInput(factory).deserialize(bytes)
+
+        assertEquals(
+                """
+                C (erased)(t: *): I2<*>
+                  t: *
+                """.trimIndent(),
+                factory.getTypeInformation(instance::class.java).prettyPrint())
+    }
 }