Help wanted: unexpected failures of binary checking when updating to Scala 2.13.9

[danicheg]

Can you please help to check whether those failures in various libraries when updating Scala to 2.13.9 are expected or if there is an issue in the Mima tool? Thanks!
#1

[error] log4cats-core: Failed binary compatibility check against org.typelevel:log4cats-core_sjs1_2.13:2.5.0 (e:info.versionScheme=early-semver)! Found 2 potential problems
[error]  * extension static method productIterator$extension(java.lang.String)scala.collection.Iterator in class org.typelevel.log4cats.LoggerName does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("org.typelevel.log4cats.LoggerName.productIterator$extension")

#2

[error] monoids: Failed binary compatibility check against org.typelevel:monoids_2.13:0.2.0 (e:info.versionScheme=early-semver)! Found 28 potential problems
[error]  * extension static method productIterator$extension(Boolean)scala.collection.Iterator in class org.typelevel.monoids.All does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("org.typelevel.monoids.All.productIterator$extension")
[error]  * extension method productIterator$extension(Boolean)scala.collection.Iterator in object org.typelevel.monoids.All does not have a correspondent in current version

[SethTisue]

The relevant PR is scala/scala#10002

[SethTisue]

@som-snytt @lrytz I haven't had time yet to ponder this. Is there any scenario in which the no-longer-generated methods could be called from code generated by an older compiler?

[som-snytt]

A case class extending AnyVal had product methods:

  public static java.lang.String productElementName$extension(java.lang.String, int);
  public static scala.collection.Iterator<java.lang.Object> productIterator$extension(java.lang.String);
  public static java.lang.Object productElement$extension(java.lang.String, int);
  public static int productArity$extension(java.lang.String);
  public static java.lang.String productPrefix$extension(java.lang.String);
  public scala.collection.Iterator<java.lang.String> productElementNames();
  public java.lang.String productPrefix();
  public int productArity();
  public java.lang.Object productElement(int);
  public scala.collection.Iterator<java.lang.Object> productIterator();
  public java.lang.String productElementName(int);

where productElementNames lacks an extension method and would therefore always box.

Now productIterator also lacks an $extension method for some reason. (Presumably, the reason is that methods inherited from a trait don't get the value class treatment.)

Product extends Any is a universal trait.

This is clearly a problem.

[SethTisue]

I'm also wondering about a meta-issue here: why didn't this crop up in scala/scala itself, which uses MiMa? (If not when the PR landed, then at least when 2.13.9 became the reference compiler?)

[som-snytt]

How many case classes extend AnyVal? [Edited, thanks.]

[SethTisue]

How many case classes extend Any?

This is about extends AnyVal, iiuc — as in, value classes. (By default, case classes extend AnyRef.)

[danicheg]

How many case classes extend AnyVal?

If you're asking me, well, that pattern is used quite frequently. https://github.com/search?l=Scala&q=extends+AnyVal&type=Code

[SethTisue]

Let's continue at scala/bug#12650 , since it appears that MiMa is functioning as expected, here.

[SethTisue]

We will be releasing Scala 2.13.10 soon with a fix for the regression; you can follow progress on the release at https://contributors.scala-lang.org/t/scala-2-13-10-release-planning/5943

[danicheg]

Good to hear that. Thank you!