withFilter required for irrefutable for comprehension pattern

[Swoorup]

Tuple decomposition seems to have regressed in some cases. The following works fine under 3.1.3

Compiler version

3.2.0-RC1

Minimized code

//> using scala "3.2.0-RC1"
//> using option "-source:future"
//> using option "-Ykind-projector"
//> using lib "org.typelevel::cats-effect::3.3.13"

import cats.Monad
import cats.effect.Temporal
import cats.syntax.all.*

trait ProjectionStore[F[_], State, Output]:
  def loadRecent: F[(Int, Option[State])]

def test[F[_]: Temporal](store: ProjectionStore[F, Int, Int]) = 
  for (x, y) <- store.loadRecent
  yield println(s"x: $x, y: $y")

Output

[error] ./t.scala:14:17: value withFilter is not a member of F[(Int, Option[Int])]
[error]
[error] where:    F is a type in method test with bounds <: [_] =>> Any
[error]   for (x, y) <- store.loadRecent
[error]                 ^^^^^^^^^^^^^^^^
Error compiling project (Scala 3.2.0-RC1, JVM)
Compilation failed

Expectation

Compilation passes

[armanbilge]

Minification:

//> using scala "3.nightly"
//> using option "-source:future"

trait Foo[A]:
  def map[B](f: A => B): Foo[B] = ???

def baz: Foo[(Int, String)] = ???

@main def main =
  for (x, y) <- baz
  yield ()

Compiling project (Scala 3.2.1-RC1-bin-20220703-cde3d13-NIGHTLY, JVM)
[error] ./test.scala:10:17: value withFilter is not a member of Foo[(Int, String)]
[error]   for (x, y) <- baz
[error]                 ^^^
Error compiling project (Scala 3.2.1-RC1-bin-20220703-cde3d13-NIGHTLY, JVM)
Compilation failed

[bishabosha]

Minification:

//> using scala "3.nightly"
//> using option "-source:future"

trait Foo[A]:
  def map[B](f: A => B): Foo[B] = ???

def baz: Foo[(Int, String)] = ???

@main def main =
  for (x, y) <- baz
  yield ()

Compiling project (Scala 3.2.1-RC1-bin-20220703-cde3d13-NIGHTLY, JVM)
[error] ./test.scala:10:17: value withFilter is not a member of Foo[(Int, String)]
[error]   for (x, y) <- baz
[error]                 ^^^
Error compiling project (Scala 3.2.1-RC1-bin-20220703-cde3d13-NIGHTLY, JVM)
Compilation failed

This code has failed the same way since 3.0.0

[armanbilge]

Are you sure?
This one compiles for me.

//> using scala "3.1.3"
//> using option "-source:future"

trait Foo[A]:
  def map[B](f: A => B): Foo[B] = ???

def baz: Foo[(Int, String)] = ???

@main def main =
  for (x, y) <- baz
  yield ()

$ scala-cli compile test.scala 
Compiling project (Scala 3.1.3, JVM)
Compiled project (Scala 3.1.3, JVM)

Apologies if I did something dumb here :)

Edit: even works in 3.0.0.

$ scala-cli compile test.scala 
Downloading Scala 3.0.0 compiler
Compiling project (Scala 3.0.0, JVM)
Compiled project (Scala 3.0.0, JVM)

[bishabosha]

when I tried in the repl:

~/workspace/scripts » scala
Welcome to Scala 3.1.3 (17.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                             
scala> trait Foo[A]:
     |   def map[B](f: A => B): Foo[B] = ???
     | 
     | def baz: Foo[(Int, String)] = ???
     | 
     | @main def main =
     |   for (x, y) <- baz
     |   yield ()
     | 
-- [E008] Not Found Error: -----------------------------------------------------
7 |  for (x, y) <- baz
  |                ^^^
  |                value withFilter is not a member of Foo[(Int, String)]
1 error found
                                                                                                                             
scala> 

Edit: ok sorry, I did not see you used the -source:future option:

[bishabosha]

so it seems that (x, y) is not considered irrefutable anymore?

[bishabosha]

same issue with a non-tuple pattern:

//> using scala "3.2.0-RC1"
trait Foo[A]:
  def map[B](f: A => B): Foo[B] = ???

final case class Bar[A, B](a: A, b: B)

def baz: Foo[Bar[Int, String]] = ???

@main def main =
  for Bar(x, y) <- baz
  yield ()

-- [E008] Not Found Error: -----------------------------------------------------
9 |  for Bar(x, y) <- baz
  |                   ^^^
  |                 value withFilter is not a member of Foo[Bar[Int, String]]

[prolativ]

Should we classify this issue as a regression then? On the one hand this stopped working, on the other the semantics of -source:future is theoretically different when one changes the minor version but still this should not break in this case.

[bishabosha]

I think the issue is that these patterns should not be considered refutable

[griggt]

😳

PR: #15593

Thanks for testing the RC and catching this!