akka/akka-core

Scala 3 type inference issue with ActorSystemSetups#get

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#29,990 opened on Feb 1, 2021

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1 - triagedhelp wantedt:coret:scala-3

Description

Investigate and see if it surfaces in user code or just some curiosity in the tests/interaction with Scalatest.

Needing that extra type ascription is curious, but only about some weirdness with Scalatest === in Scala 3 right?

(The signature of get is ActorSystemSetups#get[T <: Setup: ClassTag]: Option[T] and we explicitly give it the T, so get here returns Option[DummySetup] and setup is DummySetup so Some(setup) should be Some[DummySetup] which extends Option[DummySetup])

Originally posted by @johanandren in https://github.com/akka/akka/pull/29956#discussion_r565905744

Contributor guide

Tech stack
None
Domain
backend
Issue type
research
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
Scala 3 type systemAkka core basicsScalatest
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate if the type inference issue is specific to Scalatest's `===` operator or appears in general user code. Refer to the discussion in PR #29956 (https://github.com/akka/akka/pull/29956) for context. Check the source file for ActorSystemSetups#get to understand the generic type constraints. Reproduce the issue in a simple Scala 3 project with and without Scalatest to determine the scope.
Scala 3 type inference issue with ActorSystemSetups#get · akka/akka-core#29990 | Good First Issue