Added support for readonly immutable fields

src/Uno.CodeGen.Tests/Given_ImmutableEntity.Fields.cs

@@ -0,0 +1,35 @@
+// ******************************************************************
+// Copyright <20> 2015-2018 nventive inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// ******************************************************************
+using System.Collections.Generic;
+
+namespace Uno.CodeGen.Tests
+{
+	[GeneratedImmutable]
+	internal partial class MyEntityWithFields
+	{
+		private readonly IReadOnlyDictionary<string, string> _readonlyField;
+
+		public MyEntityWithFields(IReadOnlyDictionary<string, string> readonlyField)
+		{
+			_readonlyField = readonlyField;
+		}
+	}
+
+	partial class Given_ImmutableEntity
+	{
+	}
+}

src/Uno.CodeGen/ImmutableGenerator.cs

@@ -951,10 +951,17 @@ $@"public sealed class {symbolName}BuilderJsonConverterTo{symbolName}{genericArg
 
 				if (!field.IsStatic)
 				{
-					Error(
-						builder,
-						$"Immutable type {symbolNames.SymbolNameWithGenerics} cannot "
-						+ $"have the non-static field {field.Name}. You must remove it for immutable generation or make it static.");
+					if (field.IsReadOnly)
+					{
+						CheckTypeImmutable(field.Type, $"Field {field.Name}");
+					}
+					else
+					{
+						Error(
+							builder,
+							$"Immutable type {symbolNames.SymbolNameWithGenerics} cannot "
+							+ $"have the non-static field {field.Name}. You must either remove it, make it readonly or static to allow for immutable generation.");
+					}
 				}
 			}
 		}