Overhaul 2.9 Migration and Highlight docs

[mkurz]

Skim through the 2.9.0 release draft and check if there are notheworty things that are not yet mentioned (I think there were some things that should have made it into Highlights or Migration guide)

I think it would also be a good idea to give a forecast for the next release:
E.g. I think it's a good idea to finally drop a lot of deprecations in Play code, I think there are api's deprecated since Play 2.5 which sometimes makes live a bit hard for adding new features.

I will keep following lists updated until the releasee:

Highlights

Beta Give feedback

1. Drop Java 8
2. Java 17 is supported (also run the tests against Java 20, if the pass it's likely it wiill work with Java 21 LTS)
3. Require sbt 1.9
4. Drop sbt 0.13 #9936
   +0
5. Support ["*"] when configuring play.filters.cors.allowedOrigins #10146
   +0
6. Add Result attributes #10228
   +0
7. Support custom name of play_evolutions(_lock) table #10039
   +0
8. Add HttpErrorInfo request attribute to track origins of errors #10270
   +0
9. Allow file uploads with empty body or empty filenames #10236
   +0
10. Config to set Caffeine's internal executor #10224
    +0
11. Caffeine's internal executor should use Play's default dispatcher #10282
    +0
12. Drop Scala 2.12 and sbt 1.3 (and 0.13.x leftovers) #10956
    +0
13. Infrastructe: Switched to GitHub actions (from TravisCI), release by tag
14. akka-http 10.2.x
15. akka-http and netty backend use PhaseServiceRequestsDone to drain requests #11758
    +0
16. Add UUID PathBindableExtractor #10699
    +0
17. Support setting of hikari keepaliveTime #11805
    +0
18. Upgrade sbt-web and sbt-js-engine #11811
    +0
19. Introduce play.http.actionComposition.includeWebSocketActions #11933
    +0

Migration Guide

Beta Give feedback

1. Remove dependency from play-jdbc-api to play #10997
   +0
2. Mention the jnotify and java flags from the 2.8.15 release: https://github.com/playframework/playframework/releases/tag/2.8.15
3. Remove play omnidoc from main plugin #9905
   +0
4. Rename HttpExecution[Context] to ClassLoaderExecution[Context] #10225
   +0
5. Handle incorrect percent-encoded query chars #11671
   +0
6. Deprecate TypedMap symbols and replace with named functions #11672
   +0
7. Disable https port by default in tests + use random port #11833
   +0
8. Switch to Jakarta JPA #11079
   +0
9. org.fluentlenium -> io.fluentlenium package
10. Remove Jetty ALPN Agent / sbt-javaagent #10734
    +0
11. AnyContent body parser should correctly handle empty bodies #11920
    +0

Forecast for next release

Beta Give feedback

1. Dropping API's that are marked as deprecated as of Play 2.8 and older
2. 2.10 roadmap
3. More infrastructure improvements (Play release procedure with one click + deployment of docs, transfer domain to opencollective)
4. Recommend switching to Java 17
5. akka/akka-http replacement
6. Remove Play app global state #9263
   type:deprecated-feature +1
7. Play applications should by default run tests in parallel #8569
   topic:sbt type:improvement +2
8. Switch to Java 17? Would make live easier again
9. change groupId to org.playframework or com.playframework? (also we still use "package com.typesafe.play.docs")
10. if we switch to Java 17 + groupId change + remove global state + remove akka would make sense to call it Play 3.0 (?)
11. Pekko

Scala 3

TODO:

• Go through the scala3 label and see what else should be mentioned here.
• Come up with better wording for onLoadMessage in PlayAkkaHttpServer related to Scala 3, see Work around missing akka-http Scala 3 artifacts for tests #11738 (comment)
• Need to document AkkaHttpServer fails to run on scala 3 with 2.9 milestones #11846
• Need to mention Make Play compatible with akka 2.8+ / akka-http 10.5+ when using Scala 3 #11883
• Scala3 migration guide #11739 (comment)
• Mention

libraryDependencies += clusterSharding
libraryDependencies += ("com.typesafe.akka" %% "akka-cluster-sharding-typed" % "2.6.20").cross(CrossVersion.for3Use2_13)
excludeDependencies += sbt.ExclusionRule("com.typesafe.akka", "akka-cluster-sharding-typed_3")

because it is not possible to override / replace the clusterSharding dependency from the akka-http sbt plugin.

[mkurz]

• Update Java 11+ requirement in https://github.com/playframework/playframework/blob/main/documentation/manual/gettingStarted/Requirements.md (see Show latest version of java supported in 2.8 in Requirements.md #11055)
• Same in https://github.com/playframework/playframework/blob/main/documentation/manual/gettingStarted/Installing.md see openjdk version "1.8.0_222"

[mkurz]

So, I am just working on this docs now anymore. Let's ship this finally.