Fixed: do not report AV1562 on parameters typed as ref struct.

Author: bkoelman

src/CSharpGuidelinesAnalyzer/CSharpGuidelinesAnalyzer.Test/Specs/Maintainability/DoNotDeclareRefOrOutParameterSpecs.cs

@@ -113,6 +113,27 @@ static void Test()
             VerifyGuidelineDiagnostic(source);
         }
 
+        [Fact]
+        internal void When_method_parameter_has_ref_modifier_to_ref_struct_it_must_be_skipped()
+        {
+            // Arrange
+            ParsedSourceCode source = new TypeSourceCodeBuilder()
+                .InGlobalScope(@"
+                    ref struct S
+                    {
+                    }
+
+                    class C
+                    {
+                        void M(ref S s) => throw null;
+                    }
+                ")
+                .Build();
+
+            // Act and assert
+            VerifyGuidelineDiagnostic(source);
+        }
+
         [Fact]
         internal void When_constructor_parameter_has_no_modifier_it_must_be_skipped()
         {

src/CSharpGuidelinesAnalyzer/CSharpGuidelinesAnalyzer/Rules/Maintainability/DoNotDeclareRefOrOutParameterAnalyzer.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Immutable;
+using System.Reflection;
 using CSharpGuidelinesAnalyzer.Extensions;
 using JetBrains.Annotations;
 using Microsoft.CodeAnalysis;
@@ -24,6 +25,9 @@ public sealed class DoNotDeclareRefOrOutParameterAnalyzer : DiagnosticAnalyzer
         private static readonly DiagnosticDescriptor Rule = new DiagnosticDescriptor(DiagnosticId, Title, MessageFormat, Category.DisplayName,
             DiagnosticSeverity.Warning, true, Description, Category.GetHelpLinkUri(DiagnosticId));
 
+        [CanBeNull]
+        private static readonly PropertyInfo IsRefLikeTypeProperty = typeof(ITypeSymbol).GetRuntimeProperty("IsRefLikeType");
+
         [NotNull]
         private static readonly Action<SyntaxNodeAnalysisContext> AnalyzeParameterAction = context => context.SkipEmptyName(AnalyzeParameter);
 
@@ -68,12 +72,22 @@ private static bool IsOutParameterInTryMethod([NotNull] IParameterSymbol paramet
 
         private static void AnalyzeRefParameter([NotNull] IParameterSymbol parameter, SymbolAnalysisContext context)
         {
+            if (IsRefStruct(parameter.Type))
+            {
+                return;
+            }
+
             ISymbol containingMember = parameter.ContainingSymbol;
 
             if (!containingMember.IsOverride && !containingMember.HidesBaseMember(context.CancellationToken) && !parameter.IsInterfaceImplementation())
             {
                 context.ReportDiagnostic(Diagnostic.Create(Rule, parameter.Locations[0], parameter.Name));
             }
         }
+
+        private static bool IsRefStruct([NotNull] ITypeSymbol type)
+        {
+            return IsRefLikeTypeProperty != null && type.TypeKind == TypeKind.Struct && (bool)IsRefLikeTypeProperty.GetValue(type);
+        }
     }
 }