improvement: Use inlay hints for worksheets

Advantages:
- this would allow us to stop using a custom extension and support more editors such as Zed
- can reuse any new feature inlay hints add
- reevaluate on change? (or should we remove it?)

Disadvantages:
- no way to set color
- could mix with normal decorations

TODO:

- [ ] gather feedback
- [ ] fix tests
- [ ] check if we can remove other ways of publishing altogether

metals/src/main/scala/scala/meta/internal/metals/InlayHintResolveProvider.scala

@@ -23,11 +23,19 @@ final class InlayHintResolveProvider(
       token: CancelToken,
   ): Future[InlayHint] = {
     scala.util.Try {
-      val data = inlayHint.getData().asInstanceOf[JsonArray]
-      getLabelParts(inlayHint).zip(parseData(data))
+      Option(inlayHint.getData()) match {
+        case Some(data: JsonArray) =>
+          resolve(
+            inlayHint,
+            getLabelParts(inlayHint).zip(parseData(data)),
+            path,
+            token,
+          )
+
+        case _ => Future.successful(inlayHint)
+      }
     }.toEither match {
-      case Right(labelParts) =>
-        resolve(inlayHint, labelParts, path, token)
+      case Right(labelParts) => labelParts
       case Left(error) =>
         scribe.warn(s"Failed to resolve inlay hint: $error")
         rc.unsanitized.create(report(inlayHint, path, error), ifVerbose = true)

metals/src/main/scala/scala/meta/internal/metals/MetalsLspService.scala

@@ -421,6 +421,7 @@ abstract class MetalsLspService(
       new WorksheetProvider(
         folder,
         buffers,
+        trees,
         buildTargets,
         languageClient,
         () => userConfig,
@@ -430,7 +431,7 @@ abstract class MetalsLspService(
         worksheetPublisher,
         compilations,
         scalaVersionSelector,
-        clientConfig.initialConfig,
+        clientConfig,
       )
     )
   }
@@ -1015,7 +1016,11 @@ abstract class MetalsLspService(
           if (userConfig.areSyntheticsEnabled())
             compilers.inlayHints(params, token)
           else Future.successful(List.empty[l.InlayHint].asJava)
-      } yield hints
+        worksheet <- worksheetProvider.inlayHints(
+          params.getTextDocument().getUri().toAbsolutePath,
+          token,
+        )
+      } yield (hints.asScala ++ worksheet).asJava
     }
   }
 
@@ -1378,13 +1383,17 @@ abstract class MetalsLspService(
   def copyWorksheetOutput(
       worksheetPath: AbsolutePath
   ): CompletableFuture[Object] = {
-    val output = worksheetProvider.copyWorksheetOutput(worksheetPath)
-    if (output.nonEmpty) {
-      Future(output).asJavaObject
-    } else {
-      languageClient.showMessage(Messages.Worksheets.unableToExport)
-      Future.successful(()).asJavaObject
-    }
+    worksheetProvider
+      .copyWorksheetOutput(worksheetPath)
+      .map { output =>
+        if (output.nonEmpty) {
+          output
+        } else {
+          languageClient.showMessage(Messages.Worksheets.unableToExport)
+          ()
+        }
+      }
+      .asJavaObject
   }
 
   def analyzeStackTrace(content: String): Option[ExecuteCommandParams] =