endless compilation (more than 500 seconds) for simple program with -Xprint-types

[rssh]

Minimized code

2 files:
X.scala:

package x

import scala.quoted._

trait CB[T]

trait M[F[_]]

object MCB extends M[CB]

given M[CB] = MCB

object Y {

 inline def foundMF1[F[_],A](inline x: A)(using M[F]) : Boolean = ${
   foundMFImpl1('x)
 }

 def foundMFImpl1[F[_]:Type,A:Type](f:Expr[A])(using qctx: QuoteContext):Expr[Boolean] = {
    Expr( Expr.summon[M[F]].isDefined )
 }

}

and Main.scala

package x

object Main {

 def main(args:Array[String]):Unit =
   println(Y.foundMF1[CB,Any]({ case 1 => 10 }))
 
}

Output

rssh@rssh4 endless-compile % sbt clean compile   
[info] welcome to sbt 1.3.13 (N/A Java 14.0.1)
[info] loading settings for project endless-compile-build from plugins.sbt ...
[info] loading project definition from /Users/rssh/tests/dotty/endless-compile/project
Fetching latest Dotty nightly version...
Latest Dotty nightly build version: 0.27.0-bin-20200807-dfcc0b1-NIGHTLY
[info] loading settings for project root from build.sbt ...
[info] set current project to test (in build file:/Users/rssh/tests/dotty/endless-compile/)
[info] Executing in batch mode. For better performance use sbt's shell
[success] Total time: 0 s, completed 8 Aug 2020, 11:32:08
[info] Compiling 2 Scala sources to /Users/rssh/tests/dotty/endless-compile/target/scala-0.27/classes ...






  | => root / Compile / compileIncremental 541s

Expectation

will compiles.

[rssh]

Hmm, looks like this depends from compiler flags: -Xprint-types.

-Xprint-types: endless

without --- show error.

[rssh]

endless-compile.tar.gz

(full sbt project)

[rssh]

Hmm, looks like without implicit search - the same,
Minimized variant:

package x

import scala.quoted._
object Y {

 inline def foundMF1[F[_],A](inline x: A): Boolean = ${
   foundMFImpl1('x)
 }

 def foundMFImpl1[F[_]:Type,A:Type](f:Expr[A])(using qctx: QuoteContext):Expr[Boolean] = {
    Expr( true )
 }

}

and main the same:

package x


object Main {

 def main(args:Array[String]):Unit =
   println(Y.foundMF1[CB,Any]({ case 1 => 10 }))

}

[nicolasstucki]

Minimized to a single file

package x

trait CB[T]

trait M[F[_]]

object MCB extends M[CB]

given M[CB] = MCB

object Y {
 def foundMF1[F[_],A](x: A)(using M[F]) : Boolean = true
}

object Main {

 def main(args:Array[String]):Unit =
   println(Y.foundMF1[CB,Any]({ case 1 => 10 }))

}

[smarter]

Really not sure, but might be related to #9504
EDIT: looks like it isn't

[nicolasstucki]

Minimal

def test():Unit = foo({ case 1 => 10 })
def foo(x: Any): Boolean = true

[nicolasstucki]

It looks like we get here with an anonymous instance of Type for tp3

https://github.com/lampepfl/dotty/blob/7c4fa0c6412677651fd319e892c4c3f633be1517/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala#L699