Rudimentary readonly struct support

src/PublicApiGenerator/ApiGenerator.cs

@@ -209,18 +209,32 @@ static CodeTypeDeclaration CreateTypeDeclaration(TypeDefinition publicType, stri
             // correct C#, but it's good enough for our API outline
             var name = publicType.Name;
 
+            var isStruct = publicType.IsValueType && !publicType.IsPrimitive && !publicType.IsEnum;
+
+            var @readonly = isStruct && publicType.CustomAttributes.Any(a =>
+                                 a.AttributeType.FullName == "System.Runtime.CompilerServices.IsReadOnlyAttribute");
+
             var index = name.IndexOf('`');
             if (index != -1)
                 name = name.Substring(0, index);
-            var declaration = new CodeTypeDeclaration(@static ? "static " + name : name)
+
+            var declarationName = string.Empty;
+            if (@readonly)
+                declarationName += "readonly ";
+            if (@static)
+                declarationName += "static ";
+
+            declarationName += name;
+
+            var declaration = new CodeTypeDeclaration(declarationName)
             {
                 CustomAttributes = CreateCustomAttributes(publicType, excludeAttributes),
                 // TypeAttributes must be specified before the IsXXX as they manipulate TypeAttributes!
                 TypeAttributes = attributes,
                 IsClass = publicType.IsClass,
                 IsEnum = publicType.IsEnum,
                 IsInterface = publicType.IsInterface,
-                IsStruct = publicType.IsValueType && !publicType.IsPrimitive && !publicType.IsEnum,
+                IsStruct = isStruct,
             };
 
             if (declaration.IsInterface && publicType.BaseType != null)
@@ -417,6 +431,7 @@ static string ConvertAttributeToCode(Func<CodeTypeReference, CodeTypeReference>
             "System.Runtime.CompilerServices.ExtensionAttribute",
             "System.Runtime.CompilerServices.RuntimeCompatibilityAttribute",
             "System.Runtime.CompilerServices.IteratorStateMachineAttribute",
+            "System.Runtime.CompilerServices.IsReadOnlyAttribute",
             "System.Reflection.DefaultMemberAttribute",
             "System.Diagnostics.DebuggableAttribute",
             "System.Diagnostics.DebuggerNonUserCodeAttribute",

src/PublicApiGeneratorTests/PublicApiGeneratorTests.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netcoreapp2.1;net452</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0067</NoWarn>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/PublicApiGeneratorTests/Struct_readonly.cs

@@ -0,0 +1,28 @@
+using System;
+using PublicApiGeneratorTests.Examples;
+using Xunit;
+
+namespace PublicApiGeneratorTests
+{
+    public class Struct_readonly : ApiGeneratorTestsBase
+    {
+        [Fact]
+        public void Should_output()
+        {
+            AssertPublicApi<ReadonlyStruct>(
+@"namespace PublicApiGeneratorTests.Examples
+{
+    public struct readonly ReadonlyStruct { }
+}");
+        }
+    }
+
+    // ReSharper disable ClassNeverInstantiated.Global
+    namespace Examples
+    {
+        public readonly struct ReadonlyStruct
+        {
+        }
+    }
+    // ReSharper restore ClassNeverInstantiated.Global
+}