Add test for #19842 (#19866)

Add test for #19842 
Doesn't close it.

Author: nicolasstucki

tests/neg-macros/i19842.check

@@ -0,0 +1,32 @@
+-- Error: tests/neg-macros/i19842/Test.scala:9:50 ----------------------------------------------------------------------
+9 |@main def Test = summon[Serializer[ValidationCls]] // error
+  |                                                  ^
+  |Malformed tree was found while expanding macro with -Xcheck-macros.
+  |The tree does not conform to the compiler's tree invariants.
+  |
+  |Macro was:
+  |scala.quoted.runtime.Expr.splice[Serializer[ValidationCls]](((contextual$2: scala.quoted.Quotes) ?=> Macros.makeSerializer[ValidationCls](scala.quoted.Type.of[ValidationCls](contextual$2), contextual$2)))
+  |
+  |The macro returned:
+  |{
+  |  object objectSerializer$macro$1 extends Serializer[ValidationCls] { this: objectSerializer$macro$1.type =>
+  |    
+  |  }
+  |  objectSerializer$macro$1
+  |}
+  |
+  |Error:
+  |assertion failed: Parents of class symbol differs from the parents in the tree for object objectSerializer$macro$1
+  |
+  |Parents in symbol: [class Object, trait Serializer]
+  |Parents in tree: [trait Serializer]
+  |
+  |
+  |stacktrace available when compiling with `-Ydebug`
+  |---------------------------------------------------------------------------------------------------------------------
+  |Inline stack trace
+  |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+  |This location contains code that was inlined from Test.scala:5
+5 |    implicit inline def implicitMakeSerializer[T]: Serializer[T] = ${ Macros.makeSerializer[T] }
+  |                                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   ---------------------------------------------------------------------------------------------------------------------

tests/neg-macros/i19842/Macro.scala

@@ -0,0 +1,29 @@
+
+import scala.annotation.{experimental, targetName}
+import scala.quoted.*
+import scala.util.Try
+
+object Macros {
+  def makeSerializer[T: Type](using Quotes): Expr[Serializer[T]] = {
+    import quotes.reflect.*
+
+    val tpe: TypeRepr = TypeRepr.of[T]
+    val name: String = Symbol.freshName("objectSerializer")
+
+    val modSym: Symbol = Symbol.newModule(
+      Symbol.spliceOwner,
+      name,
+      Flags.Implicit,
+      Flags.EmptyFlags,
+      // Without TypeRep.of[Object] it would fail with java.lang.AssertionError: assertion failed: First parent must be a class
+      List(TypeRepr.of[Object], TypeRepr.of[Serializer[T]]),
+      _ => Nil,
+      Symbol.noSymbol
+    )
+
+    val (modValDef: ValDef, modClassDef: ClassDef) =
+      ClassDef.module(modSym, List(TypeTree.of[Serializer[T]]), Nil)
+
+    Block(List(modValDef, modClassDef), Ref(modSym)).asExprOf[Serializer[T]]
+  }
+}

tests/neg-macros/i19842/Test.scala

@@ -0,0 +1,9 @@
+
+trait Serializer[@specialized T]
+
+object Serializer:
+    implicit inline def implicitMakeSerializer[T]: Serializer[T] = ${ Macros.makeSerializer[T] }
+
+case class ValidationCls(string: String)
+
+@main def Test = summon[Serializer[ValidationCls]] // error