Note if a nowarn was superseded

Author: som-snytt

compiler/src/dotty/tools/dotc/Run.scala

@@ -92,14 +92,21 @@ extends ImplicitRunInfo, ConstraintRunInfo, cc.CaptureRunInfo {
       mySuspendedMessages.getOrElseUpdate(warning.pos.source, mutable.LinkedHashSet.empty) += warning
 
     def nowarnAction(dia: Diagnostic): Action.Warning.type | Action.Verbose.type | Action.Silent.type =
-      mySuppressions.getOrElse(dia.pos.source, Nil).find(_.matches(dia)) match {
-        case Some(s) =>
+      mySuppressions.get(dia.pos.source) match
+      case Some(suppressions) =>
+        val matching = suppressions.iterator.filter(_.matches(dia))
+        if matching.hasNext then
+          val s = matching.next()
+          for other <- matching do
+            if !other.used then
+              other.markSuperseded() // superseded unless marked used later
           s.markUsed()
-          if (s.verbose) Action.Verbose
+          if s.verbose then Action.Verbose
           else Action.Silent
-        case _ =>
+        else
           Action.Warning
-      }
+      case none =>
+        Action.Warning
 
     def registerNowarn(annotPos: SourcePosition, range: Span)(conf: String, pos: SrcPos)(using Context): Unit =
       var verbose = false
@@ -132,7 +139,8 @@ extends ImplicitRunInfo, ConstraintRunInfo, cc.CaptureRunInfo {
       mySuspendedMessages.remove(source).foreach(_.foreach(ctx.reporter.issueIfNotSuppressed))
     }
 
-    def runFinished(hasErrors: Boolean): Unit =
+    def runFinished()(using Context): Unit =
+      val hasErrors = ctx.reporter.hasErrors
       // report suspended messages (in case the run finished before typer)
       mySuspendedMessages.keysIterator.toList.foreach(reportSuspendedMessages)
       // report unused nowarns only if all all phases are done
@@ -147,7 +155,9 @@ extends ImplicitRunInfo, ConstraintRunInfo, cc.CaptureRunInfo {
             && !suppressions.exists(s => s.ne(sup) && s.used && s.annotPos == sup.annotPos) // duplicate
             && sup.filters != List(MessageFilter.None) // invalid suppression, don't report as unused
             then
-              report.warning("@nowarn annotation does not suppress any warnings", sup.annotPos)
+              val more = if sup.superseded then " but matches a diagnostic" else ""
+              report.warning("@nowarn annotation does not suppress any warnings"+more, sup.annotPos)
+  end suppressions
 
   /** The compilation units currently being compiled, this may return different
    *  results over time.
@@ -413,7 +423,7 @@ extends ImplicitRunInfo, ConstraintRunInfo, cc.CaptureRunInfo {
     ctx.reporter.finalizeReporting()
     if (!ctx.reporter.hasErrors)
       Rewrites.writeBack()
-    suppressions.runFinished(hasErrors = ctx.reporter.hasErrors)
+    suppressions.runFinished()
     while (finalizeActions.nonEmpty && canProgress()) {
       val action = finalizeActions.remove(0)
       action()

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

@@ -138,10 +138,16 @@ object WConf:
       else Right(WConf(configs))
 
 class Suppression(val annotPos: SourcePosition, val filters: List[MessageFilter], val start: Int, val end: Int, val verbose: Boolean):
-  private var _used = false
-  def used: Boolean = _used
+  inline def unusedState = 0
+  inline def usedState = 1
+  inline def supersededState = 2
+  private var _used = unusedState
+  def used: Boolean = _used == usedState
+  def superseded: Boolean = _used == supersededState
   def markUsed(): Unit =
-    _used = true
+    _used = usedState
+  def markSuperseded(): Unit =
+    _used = supersededState
   def matches(dia: Diagnostic): Boolean =
     val pos = dia.pos
     pos.exists && start <= pos.start && pos.end <= end && filters.forall(_.matches(dia))

tests/warn/i23651.scala

@@ -8,18 +8,20 @@ class A
 @deprecated
 class B
 
+@nowarn("msg=trait C is deprecated") // warn
+  // @nowarn annotation does not suppress any warnings
 @nowarn("msg=class A is deprecated")
-@nowarn("cat=deprecation&msg=class A is deprecated") // warn @nowarn annotation does not suppress any warnings
+@nowarn("cat=deprecation&msg=class A is deprecated") // warn
+  // @nowarn annotation does not suppress any warnings but matches a diagnostic
 @nowarn("cat=deprecation&msg=class B is deprecated")
-trait C1 {
+trait C1:
   def a: A
   def b: B
-}
 
 @nowarn("cat=deprecation&msg=class B is deprecated")
-@nowarn("cat=deprecation&msg=class B is deprecated") // warn @nowarn annotation does not suppress any warnings
+@nowarn("cat=deprecation&msg=class B is deprecated") // warn
+  // @nowarn annotation does not suppress any warnings but matches a diagnostic
 @nowarn("cat=deprecation&msg=class A is deprecated")
-trait C2 {
+trait C2:
   def a: A
   def b: B
-}