adjust for Java 8 and fix doc test

[Cherry-picked d1a150a]

Author: kasiaMarek

presentation-compiler/src/main/dotty/tools/pc/ScalaPresentationCompiler.scala

@@ -98,15 +98,14 @@ case class ScalaPresentationCompiler(
          params match {
            case range: RangeParams =>
              extractMethod(range, extractionPos)
-           case _ =>
-             CompletableFuture.failedFuture(
-               new IllegalArgumentException(s"Expected range parameters")
-             )
+           case _ => failedFuture(new IllegalArgumentException(s"Expected range parameters"))
          }
-       case (id, _) =>
-         CompletableFuture.failedFuture(
-           new IllegalArgumentException(s"Unsupported action id $id")
-         )
+       case (id, _) => failedFuture(new IllegalArgumentException(s"Unsupported action id $id"))
+
+  private def failedFuture[T](e: Throwable): CompletableFuture[T] =
+    val f = new CompletableFuture[T]()
+    f.completeExceptionally(e)
+    f
 
   override def withCompletionItemPriority(
     priority: CompletionItemPriority

presentation-compiler/test/dotty/tools/pc/tests/hover/HoverNamedArgSuite.scala

@@ -29,7 +29,6 @@ class HoverNamedArgSuite extends BaseHoverSuite:
       """|```scala
          |named: Int
          |```
-         |Found documentation for a/b.foo().(named)
          |""".stripMargin
     )