Regression: betterFors doesn't remove trailing map #23409
Description
Compiler version
3.7.0, 3.7.1-RC1, 3.7.2-RC1
Minimized example
//> using scala "3.7.2-RC1" //> using options "-preview", "-Vprint:typer" @main def main = println: for a <- List(1) b <- List(a) yield bFor comparison, the same code with older compiler version:
//> using scala "3.6.4" //> using options "-language:experimental.betterFors", "-Vprint:typer" @main def main = println: for a <- List(1) b <- List(a) yield bOutput
In 3.7.0, 3.7.1-RC1, 3.7.2-RC1 the trailing map is not removed:
@main def main: Unit = println( List.apply[Int]([1 : Int]*).flatMap[Int]((a: Int) => List.apply[Int]([a : Int]*).map[Int]((b: Int) => b)) )In 3.6.4 the trailing map is removed:
@main def main: Unit = println( List.apply[Int]([1 : Int]*).flatMap[Int]((a: Int) => List.apply[Int]([a : Int]*)) )Expectation
Have the trailing map removed.
Here is more complex case. The lack of trailing map removal causes 20% lower scores in this microbenchmark suite. Applies to all effect systems.