Inline FunctionOf in FunctionTypeOfMethod and optimize

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1117,10 +1117,14 @@ class Definitions {
         case RefinedType(parent, nme.apply, mt: MethodOrPoly)
         if parent.derivesFrom(defn.PolyFunctionClass) || isFunctionNType(parent) =>
           Some(mt)
-        case FunctionOf(argTypes, resultType, isContextual) =>
-          val methodType = if isContextual then ContextualMethodType else MethodType
-          Some(methodType(argTypes, resultType))
-        case _ => None
+        case _ =>
+          val tsym = ft.typeSymbol
+          val targs = ft.argInfos
+          if targs.nonEmpty && isFunctionSymbol(tsym) && ft.isRef(tsym) then
+            val isContextual = tsym.name.isContextFunction
+            val methodType = if isContextual then ContextualMethodType else MethodType
+            Some(methodType(targs.init, targs.last))
+          else None
     }
   }