-nowarn is -Wconf:any:s

src/compiler/scala/tools/nsc/Reporting.scala

@@ -66,9 +66,12 @@ trait Reporting extends internal.Reporting { self: ast.Positions with Compilatio
             conf.copy(filters = user ::: fixed)
           }
           else conf
-        val Migration = MessageFilter.Category(WarningCategory.Scala3Migration)
-        val boost = (settings.isScala3: @nowarn) && !conf.filters.exists(_._1.exists(_ == Migration))
-        if (boost) adjusted.copy(filters = adjusted.filters :+ (Migration :: Nil, Action.Error)) else adjusted
+        def Migration = MessageFilter.Category(WarningCategory.Scala3Migration)
+        if (settings.nowarn.value)
+          adjusted.copy(filters = adjusted.filters :+ (MessageFilter.Any :: Nil, Action.Silent))
+        else if ((settings.isScala3: @nowarn) && !conf.filters.exists(_._1.exists(_ == Migration)))
+          adjusted.copy(filters = adjusted.filters :+ (Migration :: Nil, Action.Error))
+        else adjusted
     }
 
     private lazy val quickfixFilters = {
@@ -397,7 +400,7 @@ trait Reporting extends internal.Reporting { self: ast.Positions with Compilatio
     var seenMacroExpansionsFallingBack = false
 
     // i.e., summarize warnings
-    def summarizeErrors(): Unit = if (!reporter.hasErrors && !settings.nowarn.value) {
+    def summarizeErrors(): Unit = if (!reporter.hasErrors) {
       for (c <- summarizedWarnings.keys.toList.sortBy(_.name))
         summarize(Action.WarningSummary, c)
       for (c <- summarizedInfos.keys.toList.sortBy(_.name))

src/compiler/scala/tools/nsc/reporters/ConsoleReporter.scala

@@ -26,7 +26,7 @@ class ConsoleReporter(val settings: Settings, val reader: BufferedReader, val wr
 
   override def finish(): Unit = {
     import reflect.internal.util.StringOps.countElementsAsString
-    if (!settings.nowarn.value && hasWarnings)
+    if (hasWarnings)
       writer.println(countElementsAsString(warningCount, WARNING.toString.toLowerCase))
     if (hasErrors)
       writer.println(countElementsAsString(errorCount, ERROR.toString.toLowerCase))

src/compiler/scala/tools/nsc/settings/StandardScalaSettings.scala

@@ -45,7 +45,7 @@ trait StandardScalaSettings { _: MutableSettings =>
   }
   val g =               ChoiceSetting ("-g", "level", "Set level of generated debugging info.", List("none", "source", "line", "vars", "notailcalls"), "vars")
   val help =           BooleanSetting ("-help", "Print a synopsis of standard options") withAbbreviation "--help" withAbbreviation("-h")
-  val nowarn =         BooleanSetting ("-nowarn", "Generate no warnings.") withAbbreviation "--no-warnings" withPostSetHook { s => if (s.value) maxwarns.value = 0 }
+  val nowarn =         BooleanSetting ("-nowarn", "Silence warnings. (-Wconf:any:s)") withAbbreviation "--no-warnings"
   val optimise:        BooleanSetting // depends on post hook which mutates other settings
   val print =          BooleanSetting ("-print", "Print program with Scala-specific features removed.") withAbbreviation "--print"
   val quickfix =       MultiStringSetting(

test/files/neg/t12664.check

@@ -0,0 +1,4 @@
+warning: 1 lint warning; change -Wconf for cat=lint to display individual messages
+error: No warnings can be incurred under -Werror.
+1 warning
+1 error

test/files/neg/t12664.scala

@@ -0,0 +1,14 @@
+//> using options -nowarn -Wconf:cat=lint-missing-interpolator:ws -Werror -Xlint -Xsource:3
+//> xusing options -Wconf:cat=lint-missing-interpolator:ws -Werror -Xlint -Xsource:3
+
+trait T {
+  def g[A]: Option[A]
+}
+
+class C extends T {
+  def f: Unit = 42 // suppressed other warning for expr, lint for parens
+
+  override def g[A] = None // suppressed migration warning, not boosted to error under --no-warnings
+
+  def oops = "$f" // summarized lint
+}