Optimize FunctionNOf.unapply

[Cherry-picked bbd8d81]

Author: nicolasstucki

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

@@ -1138,13 +1138,10 @@ class Definitions {
     /** Matches a (possibly aliased) `FunctionN[...]` or `ContextFunctionN[...]`.
      *  Extracts the list of function argument types, the result type and whether function is contextual.
      */
-    def unapply(tpe: Type)(using Context): Option[(List[Type], Type, Boolean)] = {
-      val tsym = tpe.typeSymbol
-      if isFunctionSymbol(tsym) && tpe.isRef(tsym) then
-        val targs = tpe.argInfos
-        if (targs.isEmpty) None
-        else Some(targs.init, targs.last, tsym.name.isContextFunction)
-      else None
+    def unapply(tpe: AppliedType)(using Context): Option[(List[Type], Type, Boolean)] = {
+      val targs = tpe.args
+      if targs.isEmpty || !isFunctionNType(tpe) then None
+      else Some(targs.init, targs.last, tpe.typeSymbol.name.isContextFunction)
     }
   }