Improve line number information

[retronym]

Ensure that standard line number information is kept when inlining from the same file, eliminated otherwise. Write tests.

Next step: add support for JSR-45 debugging info, which allows

• line numbers of multiple source files within one classfile
• full (project-relative?) path of source file, not only the file name, should help debuggers in when not using Java's package/directory convention for sources

[lrytz]

also https://issues.scala-lang.org/browse/SI-7518

[fommil]

Would this be appropriate for a scala center proposal?

[fommil]

btw, we already (in ensime) handle the source file lookup issue in ensime using our indexer.

Does this JSR-45 support include information such as expanding line numbers to source ranges? The problem faced when writing a debugger is that we only get line number info, but we want to highlight the block of code (rangepos) that is being evaluated.

Of course, stacktrace demangling is another issue...

[som-snytt]

Relatedly https://issues.scala-lang.org/browse/SI-8526 for macro API.

[fommil]

This has gone a bit cold, could somebody please help me with technical input to write a proposal?

[fommil]

GSoC needs a mentor, which would be hard for this. We also have a debugging proposal already :-)

Scala Center is ideal for this if Lightbend's customers aren't prepared to directly fund it, because it really needs somebody working closely with EPFL or core scala team.

[fommil]

I've put together a draft SC proposal here if anybody has any comments: https://gist.github.com/fommil/1867119e7f184d36342bd5e4b34c7bfe

[SethTisue]

Scala Center proposals in this area:

• SCP-011 was accepted in 2017, but never really happened
• SCP-022 proposes resuming work on it (and targeting Scala 3 as well)

[SethTisue]

further on SCP-022: https://contributors.scala-lang.org/t/improving-the-scala-debugging-experience/4264

cc @errikos, who might not know about this ticket

[dwijnand]

@errikos does your work on JSR 45 (scala/scala#9121) cover this as well, do you think?