Add Scala.js source map compiler flag

[Quafadas]

My attempt to fix #431

I haven't been able to test this at all. I think the solution is "spiritually" correct, but getting upickle to build in my environment, is not a trivial undertaking. I'll try it on a home computer once I get the chance. I'm also not sure, if this should be a very different place in upickle or mill itself - making it a bit of a shot in the dark to debug through CI right now.

The idea is stolen from here;
https://github.com/raquo/Laminar/blob/739cc0dbab319c685f28be30a1592b7d04347842/build.sbt#L78

[Quafadas]

This now compiles locally for me, so I guess it would have some chance of working.

If it was possible to let it run through the CI, it may (?) to test, whether this change worked or not ...

[lolgab]

Hi @Quafadas and thank you for your contribution! Having proper sourceMap links is a great addition to the com-lihaoyi ecosystem.
There are some problems in the PR. publishVersion and scalaVersion are targets and you can't simply call toString on them, but you need to call apply, and be in another Task to do so.
I suggest you to call this command to check what is the result:

mill -w show upickle.js[2.13.10,1.10.1].scalacOptions 

Also checking sbt-typelevel they don't do anything specific for Scala 2.12 and 2.11 so you can just check if it's scala3 or not.
I checked cats-effect core scalacOptions and this is what it outputs:

-P:scalajs:mapSourceURI:file:/Users/lorenzo/scala/cats-effect/->https://raw.githubusercontent.com/typelevel/cats-effect/73d63c8f301df317efe39dcc7d12b79914aa9455/

So this lacks a trailing / after the path.
Also the path should be the base directory of the project (T.workspace), not the millSourcePath
It would look like something like this:

  private def sourceMapOption = T.task {
    val remoteSourcesPath = s"https://raw.githubusercontent.com/com-lihaoyi/upickle/${publishVersion()}/"
    val sourcesOptionName = if(isScala3(crossScalaVersion)) "-scalajs-mapSourceURI" else "-P:scalajs:mapSourceURI"
    s"$sourcesOptionName:${T.workspace}/->$remoteSourcesPath"
  }
  override def scalacOptions = super.scalacOptions() ++ Seq(sourceMapOption())

which outputs this:

"-P:scalajs:mapSourceURI:/Users/lorenzo/scala/upickle/->https://raw.githubusercontent.com/com-lihaoyi/upickle/3.0.0-M1-4-48f229-DIRTYa58c6001/"

Now, if you wanna be fancy and have some code that is portable to other repositories as well, you can derive the URL from pomSettings() (after fixing it, since it still points to the old URL (github.com/lihaoyi/upickle):

  private def sourceMapOption = T.task {
    val baseUrl = pomSettings().url.replace("github.com", "raw.githubusercontent.com")
    val sourcesOptionName = if(isScala3(crossScalaVersion)) "-scalajs-mapSourceURI" else "-P:scalajs:mapSourceURI"
    s"$sourcesOptionName:${T.workspace}/->$baseUrl/${publishVersion()}/"
  }
  override def scalacOptions = super.scalacOptions() ++ Seq(sourceMapOption())

This is the final draft.

[Quafadas]

@lolgab Oh wow - that is amazing feedback! Thankyou for taking the time - wonderfully educational too.

As soon as I get a chance, I'll be taking another look...

[Quafadas]

@lefou @lolgab would it be possible to trigger CI again? It runs green on my fork now.

One day I'll look at adding this to a mill plugin as practise for making a mill plugin, if it is not already done by then. But it will not be soon, sadly :-( ...

Thankyou again so much for your help.

[lefou]

@lolgab Is this good to merge?

[lolgab]

@lefou There were some problems that I fixed in the last commits. Let's wait for the CI and then I think we can merge.

[Quafadas]

@lolgab Thankyou so much again for your time.

[lefou]

@lefou There were some problems that I fixed in the last commits. Let's wait for the CI and then I think we can merge.

Very nice, thank you! It would be great to test this manually once we tagged and released 3.0.0-M2.

[Quafadas]

I would be very happy to pick up the manual test once the release is out and will report back here.

[Quafadas]

@lefou @lolgab I think this can be left safely closed. I added upickle 3.0.0-M2 to a toy app and did two checks;

1. In testvite.Main$.js.map which is a source map generated by vite, I found links like this;
   "https://raw.githubusercontent.com/lihaoyi/upickle/3.0.0-M2/ujson/src/ujson/Readable.scala"
   Which click through to the sources for upickle.

2. I generated an exception inside a upickle read block, which left a stack trace in the browser console, which looked like this;
   

That "Api.scala", is from upickle, and clicks right through to the sources on GitHub.

So I conclude this works great - thank you both for your time!

[lefou]

@Quafadas Thanks for reporting back!