Move faking errors to HideNonSensicalMessages

Because HideNonSensicalMessages looks at hasErrors, we need to narrow
the faking to just the isNonSensical call

Author: dwijnand

compiler/src/dotty/tools/dotc/reporting/HideNonSensicalMessages.scala

@@ -13,7 +13,18 @@ trait HideNonSensicalMessages extends Reporter {
    */
   override def isHidden(dia: Diagnostic)(using Context): Boolean =
     super.isHidden(dia) || {
-        dia.msg.isNonSensical &&
+        (if !errorsReported && dia.isInstanceOf[Diagnostic.Error] then
+          // Bump up errorCount so hasErrors is true while forcing the message.
+          // We use errorsReported as a predicate for broken code.
+          // So now any forcing won't cause, for instance,
+          // assertion errors and thus compiler crashes.
+          // Some messages, once forced, run more code
+          // to generate useful hints for the user.
+          try
+            _errorCount += 1
+            dia.msg.isNonSensical
+          finally _errorCount -= 1 // decrease rather than reset the value so we only ever decrease by 1
+        else dia.msg.isNonSensical) &&
         hasErrors && // if there are no errors yet, report even if diagnostic is non-sensical
         !ctx.settings.YshowSuppressedErrors.value
     }

compiler/src/dotty/tools/dotc/reporting/Reporter.scala

@@ -92,8 +92,8 @@ abstract class Reporter extends interfaces.ReporterResult {
 
   private def isIncompleteChecking = incompleteHandler ne defaultIncompleteHandler
 
-  private var _errorCount = 0
-  private var _warningCount = 0
+  protected var _errorCount = 0
+  protected var _warningCount = 0
 
   /** The number of errors reported by this reporter (ignoring outer reporters) */
   def errorCount: Int = _errorCount
@@ -154,20 +154,7 @@ abstract class Reporter extends interfaces.ReporterResult {
       val key = w.enablingOption.name
       addUnreported(key, 1)
     case _                                                  =>
-      val hide = if !errorsReported && dia.isInstanceOf[Error] then
-        // We bump up errorCount so errorsReported is true while executing isHidden.
-        // We use errorsReported as a predicate for broken code.
-        // So now any code `isHidden` runs won't cause, for instance,
-        // assertion errors and thus compiler crashes.
-        // This normally amounts to forcing the message, which might run more code
-        // to generate useful hints for the user.
-        try
-          _errorCount += 1
-          isHidden(dia)
-        finally
-          _errorCount -= 1 // decrease rather than set back to `oldErrorCount` so we only ever decrease by 1
-      else isHidden(dia)
-      if !hide then // avoid isHidden test for summarized warnings so that message is not forced
+      if !isHidden(dia) then // avoid isHidden test for summarized warnings so that message is not forced
         markReported(dia)
         withMode(Mode.Printing)(doReport(dia))
         dia match {