Ongoing Scala 3 migration effort

[jrudolph]

Projects can already use Akka HTTP with Scala 3 by using CrossVersion.for3Use2_13, but for libraries that is not a good solution. This PR is about providing 'native' Scala 3 artifacts for Akka HTTP.

Commits are supposed to stay, so let's try to use reasonable commits. Changes can be PR'd against this branch.

Here are some guidelines about what we want to achieve:

• Scala 3 support for all modules
• No significant code forks (version-dependent directories) of general purpose code. We can maintain some forks (e.g. in parsers if not possible otherwise) but in general we cannot maintain significant forks for Scala 3 compatibility. I.e. for now we need to find solutions that work for all of Scala 2.12, 2.13, and 3. If Scala 2.12 support is too big a burden, we might consider targeting Akka HTTP 10.3.0 where we might want to drop Scala 2.12 support (and Akka 2.5).
• Only Akka 2.6 is supported, so I changed the default Akka version. Since we still build against Akka 2.5 by default we will have to find a solution for publishing the Scala 3 version against 2.6.
• Please add a comment when working on a task item to avoid stepping on each other's toes.

Tasks:

• Port parboiled2 to our private fork
• akka-http-core
  • Make main sources compile without parsers
  • Gradually make parsers compile for Scala 3 scala3: compile akka-http-core and pass all its tests #4097
  • Incrementally move tests back from scala-2 to scala directory, fixing issues in the process scala3: compile akka-http-core and pass all its tests #4097
  • Setup Scala 3 compiler plugin to elide methods marked with @pre213 annotation (or wait until Scala 2.12 is dropped) Scala 3: edit sources on-the-fly in sbt to support @pre213 methods in shared source code #4113
• akka-http2-support (only has tests)
• akka-http
  • Enable akka-http module for Scala 3 (currently disabled in Scala 3) and make main code compile @jchyb
• akka-http-testkit @jrudolph Enable Scala 3 for testkit + caching #4101
• akka-http-tests http-tests: allow to compile with Scala 3 with 3.0-migration option #4107
  • Make tests compile http-tests: allow to compile with Scala 3 with 3.0-migration option #4107
  • Make tests pass http-tests: allow to compile with Scala 3 with 3.0-migration option #4107
• Enable akka-caching @jrudolph Enable Scala 3 for testkit + caching #4101
• Enable akka-http-spray-json http-tests: allow to compile with Scala 3 with 3.0-migration option #4107
• Enable akka-http-scala-xml http-tests: allow to compile with Scala 3 with 3.0-migration option #4107
• Enable akka-http-jackson scala 3: compile and test marshalling, JMH and docs subprojects #4126
• akka-http-bench-jmh
  • Run some benchmarks to find most obvious issues
• docs module scala 3: compile and test marshalling, JMH and docs subprojects #4126
• Make compilation work without 3.0-migration compiler option Scala 3: Remove 3.0-migration compiler option from all modules #4114
• Backport non-intrusive changes to main (or whatever we call the 10.2.x branch) so we minimize the diff between 10.2.x and 10.3.x for easier backporting later on

For now start sbt with sbt -Dakka.build.akkaVersion=2.6.18 ++3.1.1 shell

[jrudolph]

If all parser sources are enabled, Scala 3 still gets into an unlimited loop. A relatively simple (though, nested) Parser that shows this behavior is IpAddressParsing.

[jchyb]

Hello, I started working on the "Enable akka-http module for Scala 3 (currently disabled in Scala 3) and make main code compile" task, or at least as much as can be done without all of the akka-http-core parsers. Good luck everyone!

[jrudolph]

Hello, I started working on the "Enable akka-http module for Scala 3 (currently disabled in Scala 3) and make main code compile" task, or at least as much as can be done without all of the akka-http-core parsers. Good luck everyone!

Great, thanks!

[prolativ]

I started working on the parsers. At least for now I have found out that that there's no infinite loop but the compilation time grows very quickly when a rule gets just slightly more complicated

[hughsimpson]

I've been noodling around with akka-http-core and found that if there were more than two non-literal subrules in a parser chained with ~ it basically takes forever to compile, unless you force right-associativity with parentheses (i.e. `ip-number` ~ ('.' ~ (`ip-number` ~ ('.' ~ `ip-number`))) compiles fast enough, but `ip-number` ~ '.' ~ `ip-number` ~ '.' ~ `ip-number` basically takes forever). That trick allows pretty much all the rules to compile before one dies of old age, except for a couple of the top-level date parsers where it's still taking about 10 mins on my machine, and the UriParser stuff, which I didn't look at yet. Might be able to tidy up and pr some of that this week if all goes well. Not sure what the underlying cause for that slowdown is, though...

[lightbend-cla-validator]

Hi @jrudolph, @raboof, @jchyb, @hughsimpson,

Thank you for your contribution! We really value the time you've taken to put this together.

We see that you have signed the Lightbend Contributors License Agreement before, however, the CLA has changed since you last signed it.
Please review the new CLA and sign it before we proceed with reviewing this pull request:

https://www.lightbend.com/contribute/cla

[lightbend-cla-validator]

Hi @jrudolph, @raboof, @jchyb,

Thank you for your contribution! We really value the time you've taken to put this together.

We see that you have signed the Lightbend Contributors License Agreement before, however, the CLA has changed since you last signed it.
Please review the new CLA and sign it before we proceed with reviewing this pull request:

https://www.lightbend.com/contribute/cla

[mushtaq]

@jrudolph Any way of trying out akka-http snapshot artifacts for scala-3?

[lightbend-cla-validator]

Hi @jrudolph, @raboof, @jchyb,

Thank you for your contribution! We really value the time you've taken to put this together.

We see that you have signed the Lightbend Contributors License Agreement before, however, the CLA has changed since you last signed it.
Please review the new CLA and sign it before we proceed with reviewing this pull request:

https://www.lightbend.com/contribute/cla

[johanandren]

Not yet, for now you would have to build your own snapshot out of this branch.

[johanandren]

Manually verified that jchyb has signed the CLA (and obviously jrudolph and raboof had since they were on the team)

The other failure is Fossa, ignoring that and merging.

[mkurz]

Is there any chance this gets backported to 10.2.x?

[johanandren]

No, we will only address critical security updates and critical bugs in the 10.2 series (as announced by Jonas here: https://discuss.lightbend.com/t/2-6-x-maintenance-proposal/9949/2 )

[mushtaq]

@johanandren I remember that there used to be a maven repository containing akka nightly build jars. Google is not helping me right now, but I have used that once in the past.

[raboof]

I remember that there used to be a maven repository containing akka nightly build jars. Google is not helping me right now, but I have used that once in the past.

Those are at https://oss.sonatype.org/content/repositories/snapshots/com/typesafe/akka/ (further documented at https://doc.akka.io/docs/akka-http/current/contributing.html#snapshots)

[mushtaq]

thanks @raboof !

[johanandren]

@mushtaq now out in a first milestone release on maven central 10.5.0-M1

[mushtaq]

@mushtaq now out in a first milestone release on maven central 10.5.0-M1

Awesome, thank you!

[mushtaq]

@johanandren I tried the milestone, but this single crashed the compiler!

$ echo demo.sc
//> using scala "3.2.1"
//> using lib "com.typesafe.akka::akka-http:10.5.0-M1"

println(akka.http.scaladsl.model.HttpEntity)

$ scala-cli compile demo.sc
Compiling project (Scala 3.2.1, JVM)
exception occurred while compiling /Users/mushtaqahmed/projects/scala3/scripts/.scala-build/project_0676cca331-7fb9ff8688/src_generated/main/akka-http-compiler-crash.scala
Error compiling project (Scala 3.2.1, JVM)
Error: Unexpected error when compiling project_0676cca331-7fb9ff8688: 'assertion failed'
Compilation failed

Should I open an issue?

[johanandren]

Please do, it's nothing we were aware of.

[mushtaq]

Done #4194