show void keyword in completion after readonly in struct

src/EditorFeatures/CSharpTest2/Recommendations/VoidKeywordRecommenderTests.cs

@@ -772,5 +772,25 @@ class C
 {
     delegate*$$");
         }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
+        [WorkItem(43295, "https://github.com/dotnet/roslyn/issues/43295")]
+        public async Task TestAfterReadonlyInStruct()
+        {
+            await VerifyKeywordAsync(@"
+struct S
+{
+    public readonly $$");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.KeywordRecommending)]
+        [WorkItem(43295, "https://github.com/dotnet/roslyn/issues/43295")]
+        public async Task TestNotAfterReadonlyInClass()
+        {
+            await VerifyAbsenceAsync(@"
+class C
+{
+    public readonly $$");
+        }
     }
 }

src/Features/CSharp/Portable/Completion/KeywordRecommenders/VoidKeywordRecommender.cs

@@ -12,7 +12,7 @@ namespace Microsoft.CodeAnalysis.CSharp.Completion.KeywordRecommenders
 {
     internal class VoidKeywordRecommender : AbstractSyntacticSingleKeywordRecommender
     {
-        private static readonly ISet<SyntaxKind> s_validModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
+        private static readonly ISet<SyntaxKind> s_validClassInterfaceRecordModifiers = new HashSet<SyntaxKind>(SyntaxFacts.EqualityComparer)
         {
             SyntaxKind.NewKeyword,
             SyntaxKind.PublicKeyword,
@@ -29,6 +29,11 @@ internal class VoidKeywordRecommender : AbstractSyntacticSingleKeywordRecommende
             SyntaxKind.AsyncKeyword
         };
 
+        private static readonly ISet<SyntaxKind> s_validStructModifiers = new HashSet<SyntaxKind>(s_validClassInterfaceRecordModifiers, SyntaxFacts.EqualityComparer)
+        {
+            SyntaxKind.ReadOnlyKeyword,
+        };
+
         public VoidKeywordRecommender()
             : base(SyntaxKind.VoidKeyword)
         {
@@ -101,15 +106,8 @@ private static bool IsUnsafeLocalVariableDeclarationContext(CSharpSyntaxContext
         }
 
         private static bool IsMemberReturnTypeContext(int position, CSharpSyntaxContext context, CancellationToken cancellationToken)
-        {
-            var syntaxTree = context.SyntaxTree;
-            return
-                syntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
-                context.IsMemberDeclarationContext(
-                    validModifiers: s_validModifiers,
-                    validTypeDeclarations: SyntaxKindSet.ClassInterfaceStructRecordTypeDeclarations,
-                    canBePartial: true,
-                    cancellationToken: cancellationToken);
-        }
+            => context.SyntaxTree.IsGlobalMemberDeclarationContext(position, SyntaxKindSet.AllGlobalMemberModifiers, cancellationToken) ||
+                context.IsMemberDeclarationContext(validModifiers: s_validClassInterfaceRecordModifiers, validTypeDeclarations: SyntaxKindSet.ClassInterfaceRecordTypeDeclarations, canBePartial: true, cancellationToken) ||
+                context.IsMemberDeclarationContext(validModifiers: s_validStructModifiers, validTypeDeclarations: SyntaxKindSet.StructOnlyTypeDeclarations, canBePartial: false, cancellationToken);
     }
 }