Properly handle by-name function types in repl

Fixes scala#18756

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/ElimByName.scala

@@ -60,7 +60,7 @@ class ElimByName extends MiniPhase, InfoTransformer:
   override def description: String = ElimByName.description
 
   override def runsAfterGroupsOf: Set[String] = Set(ExpandSAMs.name, ElimRepeated.name, RefChecks.name)
-    // - ExpanSAMs applied to partial functions creates methods that need
+    // - ExpandSAMs applied to partial functions creates methods that need
     //   to be fully defined before converting. Test case is pos/i9391.scala.
     // - ElimByName needs to run in a group after ElimRepeated since ElimRepeated
     //   works on simple arguments but not converted closures, and it sees the arguments
@@ -131,7 +131,6 @@ class ElimByName extends MiniPhase, InfoTransformer:
 
   override def transformApply(tree: Apply)(using Context): Tree =
     trace(s"transforming ${tree.show} at phase ${ctx.phase}", show = true) {
-
       def transformArg(arg: Tree, formal: Type): Tree = formal match
         case defn.ByNameFunction(formalResult) =>
           def stripTyped(t: Tree): Tree = t match
@@ -147,7 +146,8 @@ class ElimByName extends MiniPhase, InfoTransformer:
         case _ =>
           arg
 
-      val mt @ MethodType(_) = tree.fun.tpe.widen: @unchecked
+      val mt0 @ MethodType(_) = tree.fun.tpe.widen: @unchecked
+      val mt @ MethodType(_) =transformInfo(mt0, tree.fun.symbol): @unchecked
       val args1 = tree.args.zipWithConserve(mt.paramInfos)(transformArg)
       cpy.Apply(tree)(tree.fun, args1)
     }

compiler/src/dotty/tools/dotc/transform/SpecializeFunctions.scala

@@ -71,7 +71,10 @@ class SpecializeFunctions extends MiniPhase {
   override def transformApply(tree: Apply)(using Context) =
     tree match {
       case Apply(fun: NameTree, args) if fun.name == nme.apply && args.size <= 3 && fun.symbol.maybeOwner.isType =>
-        val argTypes = fun.tpe.widen.firstParamTypes.map(_.widenSingleton.dealias)
+        val argTypes = fun.tpe.widen.firstParamTypes.map(_.widenSingleton.dealias).map {
+          case ExprType(resType) => defn.FunctionOf(Nil, resType, isContextual = true)
+          case arg => arg
+        }
         val retType  = tree.tpe.widenSingleton.dealias
         val isSpecializable =
           defn.isSpecializableFunction(

compiler/test-resources/repl/i18756

@@ -0,0 +1,5 @@
+scala> def f: ( => Int) => Int = i => i ; f(1)
+def f: (=> Int) => Int
+val res0: Int = 1
+scala> f(1)
+val res1: Int = 1