Compiler crash in 2.11 when inheriting from a trait with a JS module

trait Foo {
  object jsObj extends js.Object
}

class Bar extends Foo

Expected: Compiles

Actual:

[info] compiling 1 Scala source to /home/tos/gh/scala-js/examples/helloworld/.2.11/target/scala-2.11/classes ...
[error] Error while emitting HelloWorld.scala
[error] assertion failed: 
[error]   object Foo$jsObj at source-/home/tos/gh/scala-js/examples/helloworld/src/main/scala/helloworld/HelloWorld.scala,line-15,offset=200: jsClassValue.isDefined = false but isInnerNonNativeJSClass = true
[error]      while compiling: /home/tos/gh/scala-js/examples/helloworld/src/main/scala/helloworld/HelloWorld.scala
[error]         during phase: jscode
[error]      library version: version 2.11.12
[error]     compiler version: version 2.11.12
[error]   reconstructed args: -encoding utf8 -deprecation -feature -Xplugin:/home/tos/gh/scala-js/compiler/.2.11/target/scala-2.11/scalajs-compiler_2.11.12-1.12.1-SNAPSHOT.jar -classpath /home/tos/gh/scala-js/examples/helloworld/.2.11/target/scala-2.11/classes:/home/tos/gh/scala-js/library/.2.11/target/scala-2.11/scalajs-library_2.11-1.12.1-SNAPSHOT.jar:/home/tos/gh/scala-js/javalib-public/target/classes:/home/tos/gh/scala-js/javalib-public/target/scalajs-javalib-1.12.1-SNAPSHOT.jar -bootclasspath /home/tos/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.11.12/scala-library-2.11.12.jar -Xfatal-warnings -unchecked
[error] 
[error]   last tree to typer: term jsObj$module
[error]        tree position: line 12 of /home/tos/gh/scala-js/examples/helloworld/src/main/scala/helloworld/HelloWorld.scala
[error]             tree tpe: <notype>
[error]               symbol: variable jsObj$module in object Foo$class
[error]    symbol definition: var jsObj$module: helloworld.Foo$jsObj.type (a TermSymbol)
[error]       symbol package: helloworld
[error]        symbol owners: variable jsObj$module -> object Foo$class
[error]            call site: object Foo$jsObj in package helloworld in package helloworld
[error] 
[error] == Source file context for tree position ==
[error] 
[error]      9 
[error]     10 trait Foo {
[error]     11   object jsObj extends js.Object
[error]     12 }
[error]     13 
[error]     14 class Bar extends Foo
[error] one error found
[error] (helloworld2_11 / Compile / compileIncremental) Compilation failed
[error] Total time: 1 s, completed Dec 4, 2022, 12:05:44 PM

[gzm0]

Makes me want to drop 2.11 😕

[sjrd]

Er, that seems pretty bad. 😦

Trait mixin was indeed completely redone in 2.12. I guess in 2.11, for module accessors, mixin discards the previous getter/constructor and recreates a new one in the subclass. So the transformation done by xplicitlocaljs gets erased.

In theory we could re-intercept the $lzycompute method for module accessor mixins in the back-end, and regenerate them entirely.

But perhaps, as you say, it might be the straw that breaks the 2.11 camel’s back. In that case we should create an RFC issue to drop Scala 2.11 and publicize it to get feedback. Would you like to create the issue?