Make BSP 1st class citizen

[joan38]

This is a proposal, and if agreed, road map to make BSP 1st class citizen of Mill.

Why?

From an Intellij user perspective the current default way of importing a Mill project in our IDE is to run mill mill.scalalib.GenIdea/idea and then open the generated project.
That is very much the way SBT started to get into Idea and then benefited of an official support from the Intellij Scala plugin.
Now it seems SBT is going down the path of using BSP exclusively.

The current limitations with this approche are:

• The user needs to first run a mill command to generate the Idea project
• Does not work for other IDEs than Intellij
• The Intellij support burden is on mill's side

How?

List of things that needs to happen before we could even consider this proposal:

• Support cross compiled modules BSP: Not really working when used with Cross and CrossScalaModule #864
• Fix cross compiled modules in Idea BSP: Fix cross modules JetBrains/intellij-scala#534 SCL-17551
• Fix compile and clean BSP: Compile not working #893
• Automatically import Mill projects in Idea (no need to run a mill command first) Automatically import Mill project with BSP JetBrains/intellij-scala#536
• Support for $file imports BSP: Import build related deps for IDE support in build.sc files #863
• Move from contrib to scalalib so that there is no need to add import $ivy.com.lihaoyi::mill-contrib-bsp:$MILL_VERSION
• Any other features GenIdea not supported by BSP? (Please comment with your points)

Thanks

[sequencer]

I have a question that App from Intellij seems to be 2x slower than console execuation. Is that a limitation from Intellij?

[lefou]

When working via GenIdea, editing build.sc and other included ammonite script work almost out of the box, whereas via BSP, everything is red and IDEA has no idea how to handle it.

[joan38]

The only red thing I have on my side is when we use the $file notation.
I solve that by setting Preferences... > Language & Framework > Worksheet > Treat .sc files as: to Always Ammonite.
This step is automatically set by GenIdea and I was unable to make the Scala Intellij plugin to do that automatically. cc @jastice

@lefou do you have more red than that?

[lefou]

@lefou do you have more red than that?

Yes, almost everthing that's imported, e.g the mill API. It's interesting that things coming from explicit $ivy imports are properly resolved, e.g. extra mill plugins.

[joan38]

I just tried 0.8.0-30-656310 and it works.
Ah I just noticed I'm using a locally built version of JetBrains/intellij-scala#572. This PR is built against Idea idea203.x but I backported it locally to idea202.x since idea203.x is not yet released. Very bleeding edge 😄
The current release of the Scala Idea plugin does not support #969

[lefou]

I also tried to open the same project in vscode with the newest Metals plugin, switched to mill BSP. It seems, that it is only seeing ScalaModules. All other modules (JavaModule, JavaModule with AspectJModule, ...) are not recognized.

[joan38]

VSCode definitely need more work but on the server side (Mill side) I don't see any outstanding task/improvement pending.

[lefou]

Have you seen the latest issues opened by @ckipp01?

• [BSP] - Support for workspace/reload #986
• [BSP] - Diagnostics not being cleared after successful compilation #987
• [BSP] - Missing build/taskFinish #988
• [BSP] - Incorrect Range in Diagnostic. #989

[joan38]

Ah. Ok there seem to be work to do then.

[lefou]

More BSP issues:

• The classpath for BSP when using the mill dev.launcher is too long #962 - issues with dev.launcher classpath
• Piggyback on ammonite's BSP implementation for build files  #971 - build.sc editing experience
• BSP: Incorrect range end position in problem reporter #1011 - incorrect problem range end column

[lefou]

BSP is now a first class citizen. ;-)

There are some open issues, though. Any help is appreciated!