Clean up compilation error message at attempt to derive codec for class that has a transient field without default value

Author: plokhotnyuk

jsoniter-scala-macros/shared/src/main/scala-2/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMaker.scala

@@ -924,8 +924,10 @@ object JsonCodecMaker {
             val symbol = p.asTerm
             val name = decodeName(symbol)
             val annotationOption = annotations.get(name)
-            if (annotationOption.exists(_.transient)) None
-            else {
+            if (annotationOption.exists(_.transient)) {
+              if (symbol.isParamWithDefault) None
+              else fail(s"Transient field '$name' in class '$tpe' should have default value.")
+            } else {
               val mappedName = annotationOption.flatMap(_.partiallyMappedName)
                 .getOrElse(cfg.fieldNameMapper.lift(name).getOrElse(name))
               val tmpName = TermName(s"_${symbol.name}")

jsoniter-scala-macros/shared/src/main/scala-3/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMaker.scala

@@ -2145,7 +2145,7 @@ private class JsonCodecMakerInstance(cfg: CodecMakerConfig)(using Quotes) {
     val construct = typeInfo.genNew(typeInfo.paramLists.map(_.foldLeft(new mutable.ListBuffer[Term]) { (params, fieldInfo) =>
       params.addOne(if (fieldInfo.isTransient) {
         fieldInfo.defaultValue
-          .getOrElse(fail(s"Transient field ${fieldInfo.symbol.name} in class ${tpe.show} have no default value"))
+          .getOrElse(fail(s"Transient field '${fieldInfo.symbol.name}' in class '${tpe.show}' should have default value."))
       } else {
         nonTransientFieldIndex += 1
         Ref(readVars(nonTransientFieldIndex).symbol)

jsoniter-scala-macros/shared/src/test/scala/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMakerSpec.scala

@@ -3252,6 +3252,15 @@ class JsonCodecMakerSpec extends VerifyingSpec {
         else "No implicit 'com.github.plokhotnyuk.jsoniter_scala.core.JsonValueCodec[_ >: scala.Nothing <: scala.Any]' defined for '_root_.java.util.Date'."
       })
     }
+    "don't generate codecs for classes with transient field without default value" in {
+      assert(intercept[TestFailedException](assertCompiles {
+        """case class TransientFieldWithoutDefaultValue(@transient x: Int)
+          |
+          |JsonCodecMaker.make[TransientFieldWithoutDefaultValue]""".stripMargin
+      }).getMessage.contains {
+        "Transient field 'x' in class 'TransientFieldWithoutDefaultValue' should have default value."
+      })
+    }
   }
   "deserialize using the nullValue of codecs that are injected by implicits" in {
     import test._