Fix synthesizing tupled functions

We spread the erasedness of tupled functions to all the parameters.

Author: natsukagami

compiler/src/dotty/tools/dotc/typer/Synthesizer.scala

@@ -109,8 +109,11 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
       case AppliedType(_, funArgs @ fun :: tupled :: Nil) =>
         def functionTypeEqual(baseFun: Type, actualArgs: List[Type],
             actualRet: Type, expected: Type) =
+          val efp = defn.erasedFunctionParameters(baseFun)
+          assert(efp.size == 1)
+          val erasedParams = actualArgs.map(_ => efp(0))
           expected =:= defn.FunctionOf(actualArgs, actualRet,
-            defn.isContextFunctionType(baseFun), defn.erasedFunctionParameters(baseFun))
+            defn.isContextFunctionType(baseFun), erasedParams)
         val arity: Int =
           if defn.isErasedFunctionType(fun) || defn.isErasedFunctionType(fun) then -1 // TODO support?
           else if defn.isFunctionType(fun) then