Adds assertion on min/max of fields in case class

Author: lukaszlenart

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

@@ -127,6 +127,20 @@ object Magnolia {
     val SubtypeTpe = typeOf[Subtype[Any, Any]].typeConstructor
     val TypeNameObj = reify(magnolia1.TypeName).tree
 
+    def assertFieldsLimits(caseClassParameters: List[TermSymbol]): Unit = {
+      val minLimit = config.map(_.minFields).getOrElse(-1)
+      val maxLimit = config.map(_.maxFields).getOrElse(-1)
+      val fieldsNumber = caseClassParameters.size
+
+      if (minLimit > -1 && fieldsNumber < minLimit) {
+        error(s"Case class ${genericSymbol.name} has $fieldsNumber fields which is less than required minimum: $minLimit")
+      }
+
+      if (maxLimit > -1 && fieldsNumber > maxLimit) {
+        error(s"Case class ${genericSymbol.name} has $fieldsNumber fields which is above the required maximum: $maxLimit")
+      }
+    }
+
     val debug = c.macroApplication.symbol.annotations
       .find(_.tree.tpe <:< DebugTpe)
       .flatMap(_.tree.children.tail.collectFirst {
@@ -426,6 +440,8 @@ object Magnolia {
           }
         )
 
+        assertFieldsLimits(caseClassParameters)
+
         val (factoryObject, factoryMethod) = {
           if (isReadOnly && isValueClass) ReadOnlyParamObj -> TermName("valueParam")
           else if (isReadOnly) ReadOnlyParamObj -> TermName("apply")

examples/src/main/scala/magnolia1/examples/csv.scala

@@ -1,6 +1,6 @@
 package magnolia1.examples
 
-import magnolia1.{CaseClass, Config, Magnolia, SealedTrait}
+import magnolia1._
 
 import scala.language.experimental.macros
 
@@ -12,9 +12,9 @@ object CsvConfig extends Config {
   type Proxy = Csv.type
   type Ignore = transient
   final val readOnly = true
-  final val minFields = 0
+  final val minFields = -1
   final val maxFields = -1
-  final val minCases = 0
+  final val minCases = -1
   final val maxCases = -1
 }