Scala 3.6 new context bound syntax

[gvolpe]

Hi all, we've got the following trait being formatted as such:

trait BaseMultiStreamKinesisEventHandler[F[
    _
]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make}, Events <: Tuple]
    extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

Is there a way to achieve the following format with a .scalafmt configuration?

trait BaseMultiStreamKinesisEventHandler[
    F[_]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},
    Events <: Tuple
] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

If we manually write the code in the following way, then we get the desired format, but automated would be much better.

trait BaseMultiStreamKinesisEventHandler[
F[    _  ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make}, 
Events <: Tuple
]
    extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

scalafmt configuration

version = 3.8.6
runner.dialect = scala36
style = defaultWithAlign
maxColumn = 100
project {
  git = true
}
rewrite {
  scala3 {
    convertToNewSyntax = true
    removeOptionalBraces = true
    insertEndMarkerMinLines = 30
    removeEndMarkerMaxLines = 29
  }
  trailingCommas.style = never
}
fileOverride {
  "glob:**/build.sbt" {
    runner.dialect = scala213
  }
  "glob:**/project/**" {
    runner.dialect = scala213
  }
  "glob:**/modules/scalafix/rules/**" {
    runner.dialect = scala212
  }
  "glob:**/modules/scalafix/tests/**" {
    runner.dialect = scala212
  }
}
newlines.topLevelStatementBlankLines = [
  {
    minBreaks = 2
    blanks { before = 1 }
  }
]
newlines.beforeTypeBounds = keep
binPack.parentConstructors = Always
spaces.withinContextBoundBraces = Never

Reproduce via scala-cli

//> using scala "3.6.2"
//> using options "-Wunused:imports"
//> using options "-Werror"
//> using options "-Wvalue-discard"

trait Concurrent[F[_]]

object BaseKinesisEventHandler:
  trait Make[F[_]]

object KinesisProducer:
  trait Make[F[_]]

trait BaseHandler[F[_], E]

case class KinesisStreamEvent(name: String)

trait BaseMultiStreamKinesisEventHandler[F[
    _
]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make}, Events <: Tuple]
    extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

Willing to try out snapshots, etc, appreciate any help 🙏🏽

[kitbellew]

i'd try bracket versions of https://scalameta.org/scalafmt/docs/configuration.html#binpackbracketxxxsite and/or https://scalameta.org/scalafmt/docs/configuration.html#newlinesconfigstylexxxsite.

[kitbellew]

1. what do you mean by "non-deterministic with style"?
2. what do you mean by "in a completely different way"?
3. binPack.bracketDefnSite = oneline?

[gvolpe]

With (1) and (2) I mean the same, e.g. with this source code:

trait BaseMultiStreamKinesisEventHandler[    F[
        _
    ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},    Events <: Tuple] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

The result is the following:

trait BaseMultiStreamKinesisEventHandler[
    F[
        _
    ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},
    Events <: Tuple
] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

Whereas given this source:

trait BaseMultiStreamKinesisEventHandler[    F[        _    ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},    Events <: Tuple] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

The result is the desired one:

trait BaseMultiStreamKinesisEventHandler[
    F[_]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},
    Events <: Tuple
] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

Same thing happens with binPack.bracketDefnSite = oneline.

[gvolpe]

This is still better than what we currently have anyway, so we'll only need to put up some manual work to fix all places where we currently see similar code to the following:

trait Foo[F[
    _
  ]: { Bar: Baz }
]

So I'll mark this as the answer, appreciate your time 🙏🏽

[kitbellew]

trait BaseMultiStreamKinesisEventHandler[    F[
        _
    ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},    Events <: Tuple] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

The result is the following:

trait BaseMultiStreamKinesisEventHandler[
    F[
        _
    ]: {Concurrent, BaseKinesisEventHandler.Make, KinesisProducer.Make},
    Events <: Tuple
] extends BaseHandler[F, KinesisStreamEvent]:
  def foo: F[String] = ???

You have F[ <newline> something <newline> ], and for newlines.source={classic,keep} and newlines.configStyle.xxx.prefer = true that forces config style, by definition. so, use a different newlines.source or set configStyle...prefer = false.

[gvolpe]

The F[ <newline> <underscore> <newline> ] was an unfortunate product of previous scalafmt runs, not something we wrote consciously. Changing newlines.source=fold,unfold has undesired effects, sadly, and can't be used with newlines.beforeTypeBounds = keep.