Map ReportDiagnostic.Default and Suppress to null instead of the default DiagnosticSeverity

src/Compilers/Core/Portable/Diagnostic/Diagnostic.cs

@@ -182,7 +182,7 @@ public abstract partial class Diagnostic : IEquatable<Diagnostic>, IFormattable
             var warningLevel = GetDefaultWarningLevel(effectiveSeverity, descriptor.DefaultSeverity);
             return SimpleDiagnostic.Create(
                 descriptor,
-                severity: effectiveSeverity.ToDiagnosticSeverity(descriptor.DefaultSeverity),
+                severity: effectiveSeverity.ToDiagnosticSeverity() ?? descriptor.DefaultSeverity,
                 warningLevel: warningLevel,
                 location: location ?? Location.None,
                 additionalLocations: additionalLocations,

src/Compilers/Core/Portable/Diagnostic/ReportDiagnosticExtensions.cs

@@ -6,7 +6,7 @@ namespace Microsoft.CodeAnalysis
 {
     public static class ReportDiagnosticExtensions
     {
-        public static DiagnosticSeverity ToDiagnosticSeverity(this ReportDiagnostic reportDiagnostic, DiagnosticSeverity defaultSeverity)
+        public static DiagnosticSeverity? ToDiagnosticSeverity(this ReportDiagnostic reportDiagnostic)
         {
             switch (reportDiagnostic)
             {
@@ -24,7 +24,7 @@ public static DiagnosticSeverity ToDiagnosticSeverity(this ReportDiagnostic repo
 
             case ReportDiagnostic.Suppress:
             case ReportDiagnostic.Default:
-                return defaultSeverity;
+                return null;
 
             default:
                 throw ExceptionUtilities.UnexpectedValue(reportDiagnostic);

src/Compilers/Core/Portable/PublicAPI.Unshipped.txt

@@ -7,5 +7,5 @@ Microsoft.CodeAnalysis.ReportDiagnosticExtensions
 abstract Microsoft.CodeAnalysis.Compilation.ClassifyCommonConversion(Microsoft.CodeAnalysis.ITypeSymbol source, Microsoft.CodeAnalysis.ITypeSymbol destination) -> Microsoft.CodeAnalysis.Operations.CommonConversion
 static Microsoft.CodeAnalysis.Diagnostic.Create(Microsoft.CodeAnalysis.DiagnosticDescriptor descriptor, Microsoft.CodeAnalysis.Location location, Microsoft.CodeAnalysis.ReportDiagnostic effectiveSeverity, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.Location> additionalLocations, System.Collections.Immutable.ImmutableDictionary<string, string> properties, params object[] messageArgs) -> Microsoft.CodeAnalysis.Diagnostic
 static Microsoft.CodeAnalysis.DiagnosticSeverityExtensions.ToReportDiagnostic(this Microsoft.CodeAnalysis.DiagnosticSeverity diagnosticSeverity) -> Microsoft.CodeAnalysis.ReportDiagnostic
-static Microsoft.CodeAnalysis.ReportDiagnosticExtensions.ToDiagnosticSeverity(this Microsoft.CodeAnalysis.ReportDiagnostic reportDiagnostic, Microsoft.CodeAnalysis.DiagnosticSeverity defaultSeverity) -> Microsoft.CodeAnalysis.DiagnosticSeverity
+static Microsoft.CodeAnalysis.ReportDiagnosticExtensions.ToDiagnosticSeverity(this Microsoft.CodeAnalysis.ReportDiagnostic reportDiagnostic) -> Microsoft.CodeAnalysis.DiagnosticSeverity?
 static Microsoft.CodeAnalysis.ReportDiagnosticExtensions.WithDefaultSeverity(this Microsoft.CodeAnalysis.ReportDiagnostic reportDiagnostic, Microsoft.CodeAnalysis.DiagnosticSeverity defaultSeverity) -> Microsoft.CodeAnalysis.ReportDiagnostic

src/Workspaces/Core/Portable/CodeStyle/CodeStyleOption.cs

@@ -49,7 +49,7 @@ public CodeStyleOption(T value, NotificationOption notification)
                 new XAttribute(nameof(SerializationVersion), SerializationVersion),
                 new XAttribute("Type", GetTypeNameForSerialization()),
                 new XAttribute(nameof(Value), GetValueForSerialization()),
-                new XAttribute(nameof(DiagnosticSeverity), Notification.Severity.ToDiagnosticSeverity(DiagnosticSeverity.Hidden)));
+                new XAttribute(nameof(DiagnosticSeverity), Notification.Severity.ToDiagnosticSeverity() ?? DiagnosticSeverity.Hidden));
 
         private object GetValueForSerialization()
         {

src/Workspaces/Core/Portable/CodeStyle/NotificationOption.cs

@@ -25,7 +25,7 @@ public ReportDiagnostic Severity
         [Obsolete("Use " + nameof(Severity) + " instead.")]
         public DiagnosticSeverity Value
         {
-            get => Severity.ToDiagnosticSeverity(DiagnosticSeverity.Hidden);
+            get => Severity.ToDiagnosticSeverity() ?? DiagnosticSeverity.Hidden;
             set => Severity = value.ToReportDiagnostic();
         }
 

src/Workspaces/Core/Portable/NamingStyles/Serialization/SerializableNamingRule.cs

@@ -24,7 +24,7 @@ internal XElement CreateXElement()
             var element = new XElement(nameof(SerializableNamingRule),
                 new XAttribute(nameof(SymbolSpecificationID), SymbolSpecificationID),
                 new XAttribute(nameof(NamingStyleID), NamingStyleID),
-                new XAttribute(nameof(EnforcementLevel), EnforcementLevel.ToDiagnosticSeverity(DiagnosticSeverity.Hidden)));
+                new XAttribute(nameof(EnforcementLevel), EnforcementLevel.ToDiagnosticSeverity() ?? DiagnosticSeverity.Hidden));
 
             return element;
         }