Fix diagnostic suppressor feature for compiler warnings in presence o…

…f /warnaserror

Follow up to dotnet#36067
Fixes dotnet#36215

src/Compilers/CSharp/Test/CommandLine/CommandLineTests.cs

@@ -10790,7 +10790,7 @@ public void InvalidPathCharacterInPdbPath()
         }
 
         [WorkItem(20242, "https://github.com/dotnet/roslyn/issues/20242")]
-        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/36215")]
+        [Fact]
         public void TestSuppression_CompilerParserWarningAsError()
         {
             string source = @"

src/Compilers/Core/Portable/CommandLine/CommonCompiler.cs

@@ -560,7 +560,7 @@ internal bool ReportDiagnostics(IEnumerable<DiagnosticInfo> diagnostics, TextWri
             => ReportDiagnostics(diagnostics.Select(info => Diagnostic.Create(info)), consoleOutput, errorLoggerOpt);
 
         /// <summary>
-        /// Returns true if there are any diagnostics in the bag which have error severity and are
+        /// Returns true if there are any diagnostics in the bag which have default severity error and are
         /// not marked "suppressed". Note: does NOT do filtering, so it may return false if a
         /// non-error diagnostic were later elevated to an error through filtering (e.g., through
         /// warn-as-error). This is meant to be a check if there are any "real" errors, in the bag
@@ -571,22 +571,14 @@ internal static bool HasUnsuppressedErrors(DiagnosticBag diagnostics)
         {
             foreach (var diag in diagnostics.AsEnumerable())
             {
-                if (IsReportedError(diag))
+                if (diag.DefaultSeverity == DiagnosticSeverity.Error && !diag.IsSuppressed)
                 {
                     return true;
                 }
             }
             return false;
         }
 
-        /// <summary>
-        /// Returns true if the diagnostic is an error that should be reported.
-        /// </summary>
-        private static bool IsReportedError(Diagnostic diagnostic)
-        {
-            return (diagnostic.Severity == DiagnosticSeverity.Error) && !diagnostic.IsSuppressed;
-        }
-
         protected virtual void PrintError(Diagnostic diagnostic, TextWriter consoleOutput)
         {
             consoleOutput.WriteLine(DiagnosticFormatter.Format(diagnostic, Culture));

src/Compilers/Core/Portable/Compilation/Compilation.cs

@@ -1347,7 +1347,7 @@ internal void CompleteCompilationEventQueue_NoLock()
         /// </summary>
         /// <param name="accumulator">Bag to which filtered diagnostics will be added.</param>
         /// <param name="incoming">Diagnostics to be filtered.</param>
-        /// <returns>True if there were no errors or warnings-as-errors.</returns>
+        /// <returns>True if there were no errors.</returns>
         internal bool FilterAndAppendAndFreeDiagnostics(DiagnosticBag accumulator, ref DiagnosticBag incoming)
         {
             bool result = FilterAndAppendDiagnostics(accumulator, incoming.AsEnumerableWithoutResolution(), exclude: null);
@@ -1378,7 +1378,7 @@ internal bool FilterAndAppendDiagnostics(DiagnosticBag accumulator, IEnumerable<
                 {
                     continue;
                 }
-                else if (filtered.Severity == DiagnosticSeverity.Error &&
+                else if (filtered.DefaultSeverity == DiagnosticSeverity.Error &&
                     !filtered.IsSuppressed)
                 {
                     hasError = true;

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

@@ -51,7 +51,8 @@ public bool IsEmptyWithoutResolution
         }
 
         /// <summary>
-        /// Returns true if the bag has any diagnostics with Severity=Error. Does not consider warnings or informationals.
+        /// Returns true if the bag has any diagnostics with DefaultSeverity=Error. Does not consider warnings or informationals
+        /// or warnings promoted to error via /warnaserror.
         /// </summary>
         /// <remarks>
         /// Resolves any lazy diagnostics in the bag.
@@ -68,7 +69,7 @@ public bool HasAnyErrors()
 
             foreach (Diagnostic diagnostic in Bag)
             {
-                if (diagnostic.Severity == DiagnosticSeverity.Error)
+                if (diagnostic.DefaultSeverity == DiagnosticSeverity.Error)
                 {
                     return true;
                 }
@@ -78,7 +79,8 @@ public bool HasAnyErrors()
         }
 
         /// <summary>
-        /// Returns true if the bag has any non-lazy diagnostics with Severity=Error.
+        /// Returns true if the bag has any non-lazy diagnostics with DefaultSeverity=Error. Does not consider warnings or informationals
+        /// or warnings promoted to error via /warnaserror.
         /// </summary>
         /// <remarks>
         /// Does not resolve any lazy diagnostics in the bag.
@@ -95,7 +97,7 @@ internal bool HasAnyResolvedErrors()
 
             foreach (Diagnostic diagnostic in Bag)
             {
-                if ((diagnostic as DiagnosticWithInfo)?.HasLazyInfo != true && diagnostic.Severity == DiagnosticSeverity.Error)
+                if ((diagnostic as DiagnosticWithInfo)?.HasLazyInfo != true && diagnostic.DefaultSeverity == DiagnosticSeverity.Error)
                 {
                     return true;
                 }

src/Compilers/VisualBasic/Test/CommandLine/CommandLineTests.vb

@@ -9386,7 +9386,7 @@ End Class"
         End Sub
 
         <WorkItem(20242, "https://github.com/dotnet/roslyn/issues/20242")>
-        <Fact(Skip:="https://github.com/dotnet/roslyn/issues/36215")>
+        <Fact>
         Public Sub TestSuppression_CompilerWarningAsError()
             ' warning BC40008 : 'C' is obsolete
             Dim source = "