[BUG]: Metals glitch when implementing a trait wrong in a layer

[markehammons]

Version

v1.0-RC1

Scala Version

3.8.3

Expected Behavior

Metals should be able to present an error when a class is missing members

Actual Behavior

2026.05.04 16:50:25 WARN Invalid text document uri received from build server: file:///home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala
2026.05.04 16:50:25 ERROR /home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala: error overriding method y in trait B of type => Unit < kyo.Sync;
method y of type => Int < kyo.Sync has incompatible type

Steps to Reproduce

The following code triggers the issues for metals:

trait A:
  def x: Unit < Sync

object A:
  def layer = Layer:
    new A:
      def x: Unit < Any = ???

trait B:
  def y: Unit < Sync

object B:
  def layer = Layer.from: (a: A) =>
    for _ <- a.x
    yield new B:
      def y: Int < Sync = ???

Current Workaround

Defining the implementation class outside of the layer definition results in normal errors.

[johnhungerford]

I don't see the issue here. The class (B) is not missing any members. You have provided an implementation for y, but with the wrong type: Int < Sync instead of Unit < Sync. This is what the error message indicates.

[markehammons]

The problem is that metals is not able to render the error. I don't know if this is caused by how Kyo is built or not, but I've only ever seen an error like this with kyo:

2026.05.04 16:50:25 WARN Invalid text document uri received from build server: file:///home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala

The above path does not exist in my code at all, but seems to correspond to Kyo's structure somehow.

due to this invalid text document URI, metals shows no errors at all in the project, but there's quite clearly an error due to the wrong type signature as you noted.

[markehammons]

I'll also note that this behavior only appears (so far) with the usage of Layer.from, and only when I'm creating an anonymous instance of the trait within Layer.from. If I create a private subclass and use that inside the Layer.from invocation, I have appropriate errors and no invalid text document uri warning.

[johnhungerford]

I can see the error in the output you included under "Actual Behavior", after the metals error. Or did you not mean to include that?

[markehammons]

I meant to include that. I'll show a screenshot to make the issue clearer:

When using metals with the following code, no error is shown through normal views. I can find the error in the output tab showing raw metals server output, where it logs

2026.05.12 15:21:26 WARN  Invalid text document uri received from build server: file:///home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala
2026.05.12 15:21:26 ERROR /home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala: error overriding method y in trait B of type => Unit < kyo.Sync;
  method y of type => Int < kyo.Sync has incompatible type

but the error is not highlighted, and worse, the error causes all other errors in the project to not be reported. I believe this is due to metals messing up from the first line:

2026.05.12 15:21:26 WARN  Invalid text document uri received from build server: file:///home/mhammons/Projects/Haven/kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala

The SBT BSP is reporting that there is a kyo-kernel/shared/src/main/scala/kyo/kernel/Pending.scala in my project folder. There is no kyo-kernel folder in my project at all, so clearly this is wrong, and it triggers the warning you see.

This may not be a bug in Kyo, but this is the first time I'm seeing behavior like this from metals. This lack of error reporting has happened previously for me when I triggered compiler crashes, but this is not the case here. Likewise, I'm only seeing this behavior with the pattern shown above (so far). It doesn't happen with the other Layer methods I've used, it doesn't happen with non-anonymous instances of B, etc.

[markehammons]

For reference, my error/warning indicators look like this with the properly implemented B:

I have a good deal of warnings to deal with 😆

This is a particularly annoying issue because changing the source trait stops giving error/warning feedback if I do the typical thing and use an anonymous instance of the trait.

[johnhungerford]

I suspect it's the fact that the scala compiler is erroneously locating the error in Pending.scala that is leading to the metals error and the strange behavior in your IDE. It makes sense, e.g., that there would be no error highlighting in your file, since the compiler is reporting that the error is somewhere else. I can confirm that this happens in IntelliJ too.

I'll open an issue in the scala3 repo when I have a chance, unless you want to do so now.

[markehammons]

I could do, but I doubt that I have the appropriate insights into how Kyo works at present to get this fixed. I'd suspect the compiler devs would want a further minimized test case than what I've provided here.