Fix more warnings

[Cherry-picked f879e64]

Author: noti0na1

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -353,8 +353,8 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
     import summaryReport._
 
-    protected final val realStdout = System.out
-    protected final val realStderr = System.err
+    protected final val realStdout: PrintStream = System.out
+    protected final val realStderr: PrintStream = System.err
 
     /** A runnable that logs its contents in a buffer */
     trait LoggedRunnable extends Runnable {

presentation-compiler/test/dotty/tools/pc/base/BasePCSuite.scala

@@ -25,7 +25,7 @@ import org.junit.runner.RunWith
 import scala.meta.pc.CompletionItemPriority
 
 object TestResources:
-  val classpath = BuildInfo.ideTestsDependencyClasspath.map(_.toPath).toSeq
+  val classpath: Seq[Path] = BuildInfo.ideTestsDependencyClasspath.map(_.toPath).toSeq
   val classpathSearch =
     ClasspathSearch.fromClasspath(classpath, ExcludedPackagesHandler.default)
 
@@ -34,7 +34,7 @@ abstract class BasePCSuite extends PcAssertions:
   val completionItemPriority: CompletionItemPriority = (_: String) => 0
   private val isDebug = ManagementFactory.getRuntimeMXBean.getInputArguments.toString.contains("-agentlib:jdwp")
 
-  val tmp = Files.createTempDirectory("stable-pc-tests")
+  val tmp: Path = Files.createTempDirectory("stable-pc-tests")
   val executorService: ScheduledExecutorService =
     Executors.newSingleThreadScheduledExecutor()
   val testingWorkspaceSearch = TestingWorkspaceSearch(

presentation-compiler/test/dotty/tools/pc/utils/MockSymbolSearch.scala

@@ -66,7 +66,7 @@ class MockSymbolSearch(
   override def documentation(
       symbol: String,
       parents: ParentSymbols
-  ) = documentation(symbol, parents, ContentType.MARKDOWN)
+  ): Optional[SymbolDocumentation] = documentation(symbol, parents, ContentType.MARKDOWN)
 
   override def documentation(
       symbol: String,