Compilation never stops with an upper bounded type param using a union type with 3 types

Compiler version

3.1.1

Minimized code

This code compiles (although it takes a little bit, aka more than usual for so little code)

import squants.energy.{Energy, KilowattHours}
import squants.time.{Minutes, Time}
import squants.thermal.{Temperature, Kelvin}
import squants.{Quantity, UnitOfMeasure, Dimensionless, Each}

case class Price[Q <: Quantity[Q] & (Energy | Time)](amount: Double, per: UnitOfMeasure[Q])
Price(5.5, KilowattHours)
Price(5.5, Minutes)
//Price(5.5, Kelvin) // This line correctly fails to compile

Changing Price to

case class Price[Q <: Quantity[Q] & (Energy | Time | Dimensionless)](amount: Double, per: UnitOfMeasure[Q])

Causes the compiler to never stop compiling.

Output

Scastie times out after 30 seconds. Ran locally for 300 seconds then killed it.

Expectation

With a union type of 2 types it works, but with 3 types it fails. This suggests a explosion of combinations to big to handle in a reasonable time. There must be a limit to this explosion of combinations, however I was expecting it to be much higher: in the tens or even in the hundreds not 3.

[odersky]

I could find the culprit that caused the exponential explosion, and it looks like this case can be fixed, after all.

[Lasering]

Squants defines Quantity with a f-bound, and since I want to have a UnitOfMeasure I’m forced to also have an f-bound. Otherwise it would be much simpler to do:

class Price[Q <: (Energy | Time | Dimensionless)](amount: Double, per: UnitOfMeasure[Q])

Which in an ideal world would compile since Energy, Time, and Dimensionless are all subclasses of Quantity[Q] however the compiler says: Type argument Q does not conform to upper bound squants.Quantity[Q]

It would be interesting to see how to solve problems the f-bounds solve without using them.