Regression in asflierl/sglicko2 - type inference

[WojciechMazur]

Reproducer of failure found in Open Community Build for project asflierl/sglicko2 - build logs

Compiler version

Since 3.4.0-RC1-bin-20231113-0dfe593-NIGHTLY

Bisect points to a196167
Related issue #19001 - bisect points to the same commit, but I don't think we give any guarantees about type inference, though I've decided to create seperate issue

Minimized code

trait Player[+P]()
trait RatingPeriod[P]:
  def games: Map[P, Vector[ScoreVsPlayer[P]]]

trait ScoreVsPlayer[+P]

def updated[P](playerID: P, matchResults: IndexedSeq[ScoreVsPlayer[P]], lookup: P => Option[Player[P]]): Player[P] = ???

trait Leaderboard[P]:
  def  playersByIdInNoParticularOrder: Map[P, Player[P]]

  def after[P2 >: P](ratingPeriod: RatingPeriod[? <: P]): Leaderboard[P2] =
    val competingPlayers = ratingPeriod.games.iterator.map { (id, matchResults) => 
      updated(id, matchResults, playersByIdInNoParticularOrder.get) // error
      // workaround: 
      updated[P](id, matchResults, playersByIdInNoParticularOrder.get) 
    }
    ???

Output

-- [E007] Type Mismatch Error: /Users/wmazur/projects/sandbox/main.scala:14:32 -
14 |      updated(id, matchResults, playersByIdInNoParticularOrder.get) // error
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |           Found:    Option[Player[P]]
   |           Required: Option[Player[ratingPeriod.P²]]
   |
   |           where:    P  is a type in trait Leaderboard with bounds <: P2
   |                     P² is a type in trait RatingPeriod
   |
   | longer explanation available when compiling with `-explain`
1 error found

Expectation

Should compile

[WojciechMazur]

Another reproducer based on joernio/joern build logs. Again it only related to type inference

object NodeOrdering:
  def postOrderNumbering[NodeType](
    cfgEntry: NodeType,
    expand: NodeType => Iterator[NodeType]
  ): Map[NodeType, Int]  = ???

trait CfgNode
trait Method extends CfgNode

def postOrder = {
  def method: Method = ???
  def expand(x: CfgNode): Iterator[CfgNode] = ???
  NodeOrdering.postOrderNumbering(method, expand)
}

error:

-- [E007] Type Mismatch Error: /Users/wmazur/projects/dotty/bisect/main.scala:13:42 
13 |  NodeOrdering.postOrderNumbering(method, expand)
   |                                          ^^^^^^
   |                                          Found:    Iterator[CfgNode]
   |                                          Required: Iterator[Method]
   |

[WojciechMazur]

Another one based on earogov/ordset - build logs

trait Bound[+E]

trait SegmentT[E, +S]
object SegmentT:
  trait WithPrev[E, +S] extends SegmentT[E, S]

trait SegmentSeqT[E, +S]:
  def getSegmentForBound(bound: Bound[E]): SegmentT[E, S] with S

abstract class AbstractSegmentSeq[E, +S] extends SegmentSeqT[E, S]

trait MappedSegmentBase[E, S]

type MappedSegment[E, S] = AbstractMappedSegmentSeq.MappedSegment[E, S]

object AbstractMappedSegmentSeq:
  type MappedSegment[E, S] = SegmentT[E, MappedSegmentBase[E, S]] with MappedSegmentBase[E, S]

abstract class AbstractMappedSegmentSeq[E, S]
    extends AbstractSegmentSeq[E, MappedSegmentBase[E, S]]:
  def originalSeq: SegmentSeqT[E, S]

  final override def getSegmentForBound(bound: Bound[E]): MappedSegment[E, S] =
    searchFrontMapper(frontMapperGeneral, originalSeq.getSegmentForBound(bound))

  protected final def frontMapperGeneral(original: SegmentT[E, S]): MappedSegment[E, S] = ???

  protected def searchFrontMapper[Seg >: SegmentT.WithPrev[E, S] <: SegmentT[E, S], R](
      mapper: Seg => R,
      original: Seg
  ): R = ???

error:

-- [E007] Type Mismatch Error: /Users/wmazur/projects/sandbox/main.scala:26:72 -
26 |    searchFrontMapper(frontMapperGeneral, originalSeq.getSegmentForBound(bound))
   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                                       Found:    SegmentT[E, S] & S
   |                                       Required: SegmentT.WithPrev[E, S]
   |