Asking @SethTisue @lrytz @som-snytt @sjrd @smarter for advice.

Just yesterday I made Play build with with 3.3.2:

• Upgrade to latest scala versions #12401

Now I run into a problem which IMHO is caused by

• scala/scala3@a10a271
• (which is cherry-picked from Fix overcompilation due to unstable context bound desugaring scala/scala3#18280)

How to reproduce:

1. Checkout Play locally with current main (3ace273)
2. Build Play locally: sbt +publishLocal
3. Clone the play-samples repo: https://github.com/playframework/play-samples/

   git clone [email protected]:playframework/play-samples.git
   # Make sure you are on the 3.0.x branch (default anyway)
   

4. Within the samples repo:

   cd play-java-chatroom-example
   

5. Make sure to apply the local Play snapshot:

   --- a/play-java-chatroom-example/project/plugins.sbt
   +++ b/play-java-chatroom-example/project/plugins.sbt
   @@ -1,2 +1,2 @@
    // The Play plugin
   -addSbtPlugin("org.playframework" % "sbt-plugin" % "3.0.1")
   +addSbtPlugin("org.playframework" % "sbt-plugin" % "3.1.0-SNAPSHOT")

6. Currently, the sample project is using Scala 3.3.1 (but Play is now build with 3.3.2). Now try to compile the project:

   $ sbt ++3.x compile
   [info] welcome to sbt 1.9.8 (Eclipse Adoptium Java 11.0.22)
   ...
   [info] Version 3.1.0-SNAPSHOT running Java 11.0.22
   ...
   [info] Setting Scala version to 3.3.1 on 1 projects.
   ...
   [info] compiling 5 Scala sources and 3 Java sources to ./play-samples/play-java-chatroom-example/target/scala-3.3.1/classes ...
   [error] error while loading PathBindableMacros,
   [error] class file play/api/mvc/PathBindableMacros.class is broken, reading aborted with class java.util.NoSuchElementException
   [error] contextual$
   [error] one error found
   [error] (Compile / compileIncremental) Compilation failed
   [error] Total time: 2 s, completed Feb 27, 2024, 4:10:59 PM
   

7. Changing the Scala version of the project to 3.3.2 makes compiliation work however (in build.sbt: crossScalaVersions := Seq("2.13.12", "3.3.2"),)

So this is the file which this problem is about: https://github.com/playframework/playframework/blob/main/core/play/src/main/scala-3/play/api/mvc/PathBindableMacros.scala

If I build Play with Scala 3.3.1 by reverting yesterdays commit (git revert -m 1 552f5a0ae1876804b06114a94b619712a22c46c4), I can run the samples project again with Scala 3.3.1 set in the project.

Now what I found out is that the tasty files generated by Play with Scala 3.3.1 vs Scala 3.3.2 differ:

• The file ./core/play/target/scala-3.3.1/classes/play/api/mvc/PathBindableMacros.tasty contains evidence$
• The file ./core/play/target/scala-3.3.2/classes/play/api/mvc/PathBindableMacros.tasty replaced evidence$ with contextual$

I also inspected the class files

• ./core/play/target/scala-3.3.1/classes/play/api/mvc/PathBindableMacros.class
• ./core/play/target/scala-3.3.2/classes/play/api/mvc/PathBindableMacros.class

with javap -v and it looks like they are identical (except some bytes in the tasty part):

--- /tmp/3.3.1_javap	2024-02-27 16:43:43.766644833 +0100
+++ /tmp/3.3.2_javap	2024-02-27 16:43:47.259650233 +0100
@@ -1,5 +1,5 @@
-Classfile ./core/play/target/scala-3.3.1/classes/play/api/mvc/PathBindableMacros.class
+Classfile ./core/play/target/scala-3.3.2/classes/play/api/mvc/PathBindableMacros.class
   Last modified Feb 27, 2024; size 175 bytes
-  MD5 checksum 604088e2d12cc976c4f58b7d109da0e7
+  MD5 checksum 144a574029f956604ac0ae298c323c5f
   Compiled from "PathBindableMacros.scala"
 public interface play.api.mvc.PathBindableMacros
@@ -23,5 +23,5 @@
 SourceFile: "PathBindableMacros.scala"
   TASTY: length = 0x10 (unknown attribute)
-   00 98 FE E0 E7 74 F5 C5 00 66 D7 56 61 0B CB 19
+   00 B6 6E 0F BB C2 58 C5 00 66 D7 56 61 0B CB 19
 
   Scala: length = 0x0 (unknown attribute)