tiny fix for type rendering to include variance. It caused unhelpful errors because variance mismatches in duckdb map values

Author: Jolanrensen

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/Rendering.kt

@@ -16,6 +16,7 @@ import java.net.URL
 import java.time.LocalDateTime
 import java.time.LocalTime
 import kotlin.reflect.KType
+import kotlin.reflect.KVariance
 import kotlin.reflect.full.isSubtypeOf
 import kotlin.reflect.jvm.jvmErasure
 import kotlin.reflect.typeOf
@@ -89,7 +90,12 @@ internal fun renderType(type: KType?): String {
                 append(name)
                 if (type.arguments.isNotEmpty()) {
                     val arguments = type.arguments.joinToString {
-                        renderType(it.type)
+                        when (it.variance) {
+                            null -> "*"
+                            KVariance.INVARIANT -> renderType(it.type)
+                            KVariance.IN -> "in ${renderType(it.type)}"
+                            KVariance.OUT -> "out ${renderType(it.type)}"
+                        }
                     }
                     append("<$arguments>")
                 }

dataframe-jdbc/src/main/kotlin/org/jetbrains/kotlinx/dataframe/io/db/DuckDb.kt

@@ -132,7 +132,7 @@ public object DuckDb : DbType("duckdb") {
                 Map::class.createType(
                     listOf(
                         KTypeProjection.invariant(key.toKType(false)),
-                        KTypeProjection.covariant(value.toKType(true)),
+                        KTypeProjection.invariant(value.toKType(true)),
                     ),
                 )
             }
@@ -141,7 +141,7 @@ public object DuckDb : DbType("duckdb") {
                 // TODO requires #1266 and #1273 for specific types
                 //   val listType = parseListType(sqlTypeName)
                 //   Array::class.createType(
-                //       listOf(KTypeProjection.covariant(listType.toKType(true))),
+                //       listOf(KTypeProjection.invariant(listType.toKType(true))),
                 //   )
                 typeOf<Array>()
             }