SemanticDB options on an sbt dotty project are wrong

[adpi2]

Describe the bug

The sbt-metals plugin generates wrong SemanticDB options on the Test configuration of a Dotty project.

To Reproduce

Steps to reproduce the behavior:

1. Create an sbt dotty project

// project/plugin.sbt
addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.4.4")
addSbtPlugin("org.scalameta" % "sbt-metals" % "0.9.5-SNAPSHOT")

// build.sbt
scalaVersion := "0.27.0-RC1"

2. Run show Test / scalacOptions in an sbt shell

sbt:example> show Test / scalacOptions
[info] * -Ysemanticdb
[info] * -semanticdb-target
[info] * /example/target/scala-0.27/meta
[info] * /example/target/scala-0.27/test-meta

3. Run Test / compile in an sbt shell

sbt:example> Test / compile
[info] compiling 4 Scala sources to /example/target/scala-0.27/test-classes ...
[error] expected file, received directory '/example/target/scala-0.27/test-meta'
[error] one error found
[error] (Test / compileIncremental) Compilation failed
[error] Total time: 0 s, completed Nov 3, 2020, 9:19:14 PM

Expected behavior

The scalacOptions of the Test configuration should be:

sbt:example> show Test / scalacOptions
[info] * -Ysemanticdb
[info] * -semanticdb-target
[info] * /example/target/scala-0.27/test-meta

Installation:

• Operating system: Linux
• Metals version: v0.9.5-SNAPSHOT

Search terms

SemanticDB, compiler options, dotty, scala 3, sbt-metals

[adpi2]

This lines of code in sbt/sbt could help to fix this issue:

https://github.com/sbt/sbt/blob/c00196abf0c0b60d301e9516b8513b498359f987/main/src/main/scala/sbt/plugins/SemanticdbPlugin.scala#L68-L76

As you can see, the target root coming from the Compile configuration is removed before we add the Test target root.

[adpi2]

Maybe it is even easier to just do semanticdbEnabled := true in sbt-metals. It should add the required -Ysemanticdb and the correct -semanticdb-target options.

[tgodzik]

Thanks for reporting! Good catch! I can confirm it's an issue. Should be easy to fix in the plugin.

[ckipp01]

Thanks for the report @adpi2! I should have it fixed in #2139

Maybe it is even easier to just do semanticdbEnabled := true in sbt-metals. It should add the required -Ysemanticdb and the correct -semanticdb-target options.

That was originally brought up in #2049, but there seemed to be concern about ensuring that the user has a supported Scala version. So we don't want to just check check the sbt version and enable it based off that which could cause issues from my understanding.