Adds assertion on min/max of fields in case class

Author: lukaszlenart

core/src/main/scala/magnolia1/magnolia.scala

@@ -127,6 +127,22 @@ object Magnolia {
     val SubtypeTpe = typeOf[Subtype[Any, Any]].typeConstructor
     val TypeNameObj = reify(magnolia1.TypeName).tree
 
+    def assertFieldsLimits(caseClassSym: TypeSymbol): Unit = {
+      val minLimit = config.map(_.minFields).getOrElse(-1)
+      val maxLimit = config.map(_.maxFields).getOrElse(Int.MaxValue)
+      val fieldsNumber = caseClassSym.info.members.size
+
+      if (minLimit > -1 && fieldsNumber < minLimit) {
+        error(s"Case class ${caseClassSym.name} has $fieldsNumber fields which is less than required minimum: $minLimit")
+      }
+
+      if (fieldsNumber > maxLimit) {
+        error(s"Case class ${caseClassSym.name} has $fieldsNumber fields which is above the required maximum: $maxLimit")
+      }
+    }
+
+    assertFieldsLimits(CaseClassSym)
+
     val debug = c.macroApplication.symbol.annotations
       .find(_.tree.tpe <:< DebugTpe)
       .flatMap(_.tree.children.tail.collectFirst {