Line numbers in `package.mill` task body are off

[lihaoyi]

This error on line 331

lihaoyi mill$ git diff
diff --git a/website/package.mill b/website/package.mill
index 3184bc4112d..9393fe9a31f 100644
--- a/website/package.mill
+++ b/website/package.mill
@@ -328,6 +328,8 @@ object `package` extends mill.Module {
         if (crossValue3 == "dev") "dev-" + build.latestUnstableVersion()
         else crossValue3
 
+      ???
+
       val antoraVersion = if (crossValue4 == "dev") displayVersion else crossValue4
 
       val newWebsiteTask: Boolean = crossValue5

Results in a stack trace pointing at line 342

> ./mill 'website.oldDocs[dev,dev,dev,dev,true].oldDocSource'

...

[4/4, 1 failed] ========================= website.oldDocs[dev,dev,dev,dev,true].oldDocSource ======================== 30s
1 tasks failed
website.oldDocs[dev,dev,dev,dev,true].oldDocSource java.util.NoSuchElementException: None.get
    scala.None$.get(Option.scala:627)
    scala.None$.get(Option.scala:626)
    build_.website.package_$OldDocModule.oldDocSource$$anonfun$1$$anonfun$1(package.mill:342)
    mill.api.Task$Named.evaluate(Task.scala:328)
    mill.api.Task$Named.evaluate$(Task.scala:313)
    mill.api.Task$Computed.evaluate(Task.scala:339)

[lihaoyi]

Looks like this was broken in the Scala 3 upgrade #3369 which removed the line number plugin without replacement, and we didn't have any integration tests to catch it

[lihaoyi]

Ammonite and Scala-CLI update the line numbers by munging the bytecode https://github.com/com-lihaoyi/Ammonite/blob/main/amm/compiler/src/main/scala-3/ammonite/compiler/AsmPositionUpdater.scala