Remove redundant mapOver in fixThisTypeModuleClassReferences

We should only have mapOver in the default branch or on the returned
type not both as that redundant and causes exponential growth in
compilation time.

fixes: #25362

Author: eejbyfeldt

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -607,12 +607,11 @@ object Inlines:
         TreeTypeMap(
           typeMap = new TypeMap:
             override def stopAt = StopAt.Package
-            def apply(t: Type) = mapOver {
+            def apply(t: Type) =
               t match
                 case ThisType(tref @ TypeRef(prefix, _)) if tref.symbol.flags.is(Module) && !owners.contains(tref.symbol) =>
                   TermRef(apply(prefix), tref.symbol.companionModule)
                 case _ => mapOver(t)
-            }
         ).typeMap(tpe)
 
       if !hasOpaqueProxies && !hasOpaquesInResultFromCallWithTransparentContext then inlined

tests/pos/i25362/Macro_1.scala

@@ -0,0 +1,15 @@
+package example
+import scala.deriving.Mirror
+import scala.quoted.*
+
+class TC[A] {
+  type Out
+}
+
+object TC {
+  transparent inline def derived[Left: Mirror.ProductOf as m]: TC[Left] =
+    ${ derivedImpl[Left, m.MirroredElemTypes] }
+
+  private def derivedImpl[Left: Type, LeftTypes: Type](using Quotes): Expr[TC[Left]] =
+    '{ new TC[Left] { type Out = LeftTypes } }
+}

tests/pos/i25362/Test_2.scala

@@ -0,0 +1,14 @@
+package example
+
+opaque type BigTuple <: Repr = Repr
+final case class Repr(
+  f1: Int, f2: Int, f3: Int, f4: Int, f5: Int,
+  f6: Int, f7: Int, f8: Int, f9: Int, f10: Int,
+  f11: Int, f12: Int, f13: Int, f14: Int, f15: Int,
+  f16: Int, f17: Int, f18: Int, f19: Int, f20: Int,
+  f21: Int, f22: Int, f23: Int, f24: Int, f25: Int,
+)
+
+class test {
+  val merger = TC.derived[BigTuple]
+}