Added [KnownAsImmutable] assembly attribute

doc/Immutable Generation.md

@@ -361,3 +361,17 @@ public class MyImmutable
 > (`[GeneratedImmutable(GenerateEquality = false)]`)
 > won't have any effect in inherited class if the generation is active on the
 > base class.
+
+## I want to reference external classes from my entities.
+
+I'm getting this error:
+
+``` csharp
+#error: 'ImmutableGenerator: Property MyClass.SomeField type ExternalClass.SuperClass is not immutable. It cannot be used in an immutable entity.'
+```
+
+To fix this, put this attribute on your assembly:
+
+``` csharp
+[assembly: Uno.KnownAsImmutable(typeof(ExternalClass.SuperClass))]
+```

src/Uno.CodeGen.Tests/Given_ImmutableEntity.KnownAsImmutable.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.Net.Mail;
+using Uno;
+
+[assembly: KnownAsImmutable(typeof(SmtpException))]
+
+namespace Uno.CodeGen.Tests
+{
+	partial class Given_ImmutableEntity
+	{
+		internal static readonly MyImmutableWithExternalKnownAsImmutable KnownAsImmutable =
+			MyImmutableWithExternalKnownAsImmutable.Default;
+	}
+
+	[GeneratedImmutable]
+	internal partial class MyImmutableWithExternalKnownAsImmutable
+	{
+		private SmtpException Exception { get; }
+	}
+}

src/Uno.CodeGen/Helpers/TypeSymbolExtensions.cs

@@ -60,7 +60,7 @@ namespace Uno.Helpers
 		private static ImmutableDictionary<(ITypeSymbol, bool), bool> _isImmutable =
 			ImmutableDictionary<(ITypeSymbol, bool), bool>.Empty;
 
-		public static bool IsImmutable(this ITypeSymbol type, bool treatArrayAsImmutable)
+		public static bool IsImmutable(this ITypeSymbol type, bool treatArrayAsImmutable, IReadOnlyList<ITypeSymbol> knownAsImmutable)
 		{
 			bool GetIsImmutable((ITypeSymbol type, bool treatArrayAsImmutable) x)
 			{
@@ -92,7 +92,7 @@ namespace Uno.Helpers
 
 				if (t is IArrayTypeSymbol arrayType)
 				{
-					return arrayType.ElementType?.IsImmutable(asImmutable) ?? false;
+					return arrayType.ElementType?.IsImmutable(asImmutable, knownAsImmutable) ?? false;
 				}
 
 				var definitionType = t.GetDefinitionType();
@@ -127,7 +127,7 @@ namespace Uno.Helpers
 					case "System.Collections.Immutable.ImmutableStack<T>":
 						{
 							var argumentParameter = (t as INamedTypeSymbol)?.TypeArguments.FirstOrDefault();
-							return argumentParameter == null || argumentParameter.IsImmutable(asImmutable);
+							return argumentParameter == null || argumentParameter.IsImmutable(asImmutable, knownAsImmutable);
 						}
 					case "System.Collections.Immutable.IImmutableDictionary<TKey, TValue>":
 					case "System.Collections.Immutable.ImmutableDictionary<TKey, TValue>":
@@ -135,11 +135,16 @@ namespace Uno.Helpers
 						{
 							var keyTypeParameter = (t as INamedTypeSymbol)?.TypeArguments.FirstOrDefault();
 							var valueTypeParameter = (t as INamedTypeSymbol)?.TypeArguments.Skip(1).FirstOrDefault();
-							return (keyTypeParameter == null || keyTypeParameter.IsImmutable(asImmutable))
-								&& (valueTypeParameter == null || valueTypeParameter.IsImmutable(asImmutable));
+							return (keyTypeParameter == null || keyTypeParameter.IsImmutable(asImmutable, knownAsImmutable))
+								&& (valueTypeParameter == null || valueTypeParameter.IsImmutable(asImmutable, knownAsImmutable));
 						}
 				}
 
+				if (knownAsImmutable.Contains(definitionType))
+				{
+					return true;
+				}
+
 				switch (definitionType.GetType().Name)
 				{
 					case "TupleTypeSymbol":
@@ -154,13 +159,13 @@ namespace Uno.Helpers
 						return asImmutable;
 				}
 
-				return IsImmutableByRequirements(t, treatArrayAsImmutable);
+				return IsImmutableByRequirements(t, treatArrayAsImmutable, knownAsImmutable);
 			}
 
 			return ImmutableInterlocked.GetOrAdd(ref _isImmutable, (type, treatArrayAsImmutable), GetIsImmutable);
 		}
 
-		private static bool IsImmutableByRequirements(ITypeSymbol type, bool treatArrayAsImmutable)
+		private static bool IsImmutableByRequirements(ITypeSymbol type, bool treatArrayAsImmutable, IReadOnlyList<ITypeSymbol> knownAsImmutable)
 		{
 			// Check if type is complying to immutable requirements
 			// 1) all instance fields are readonly
@@ -169,11 +174,11 @@ namespace Uno.Helpers
 
 			foreach (var member in type.GetMembers())
 			{
-				if (member is IFieldSymbol f && !(f.IsStatic || f.IsReadOnly || f.IsImplicitlyDeclared) && f.Type.IsImmutable(treatArrayAsImmutable))
+				if (member is IFieldSymbol f && !(f.IsStatic || f.IsReadOnly || f.IsImplicitlyDeclared) && f.Type.IsImmutable(treatArrayAsImmutable, knownAsImmutable))
 				{
 					return false; // there's a non-readonly non-static field
 				}
-				if (member is IPropertySymbol p && !(p.IsStatic || p.IsReadOnly || p.IsImplicitlyDeclared) && p.Type.IsImmutable(treatArrayAsImmutable))
+				if (member is IPropertySymbol p && !(p.IsStatic || p.IsReadOnly || p.IsImplicitlyDeclared) && p.Type.IsImmutable(treatArrayAsImmutable, knownAsImmutable))
 				{
 					return false; // there's a non-readonly non-static property
 				}
@@ -183,7 +188,7 @@ namespace Uno.Helpers
 			return type.BaseType == null
 				|| type.BaseType.SpecialType == SpecialType.System_Object
 				|| type.BaseType.SpecialType == SpecialType.System_ValueType
-				|| type.BaseType.IsImmutable(treatArrayAsImmutable);
+				|| type.BaseType.IsImmutable(treatArrayAsImmutable, knownAsImmutable);
 		}
 
 		public static ITypeSymbol GetDefinitionType(this ITypeSymbol type)

src/Uno.CodeGen/ImmutableGenerator.cs

@@ -17,6 +17,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Reflection;
 using System.Text.RegularExpressions;
@@ -46,6 +47,7 @@ namespace Uno
 		private INamedTypeSymbol _immutableBuilderAttributeSymbol;
 		private INamedTypeSymbol _immutableAttributeCopyIgnoreAttributeSymbol;
 		private INamedTypeSymbol _immutableGenerationOptionsAttributeSymbol;
+		private INamedTypeSymbol _immutableKnownAsImmutableAttributeSymbol;
 
 		private (bool generateOptionCode, bool treatArrayAsImmutable, bool generateEqualityByDefault, bool generateJsonNet) _generationOptions;
 		private bool _generateOptionCode = true;
@@ -53,6 +55,8 @@ namespace Uno
 
 		private Regex[] _copyIgnoreAttributeRegexes;
 
+		private IReadOnlyList<ITypeSymbol> _knownAsImmutableTypes;
+
 		/// <inheritdoc />
 		public override void Execute(SourceGeneratorContext context)
 		{
@@ -63,6 +67,7 @@ namespace Uno
 			_immutableBuilderAttributeSymbol = context.Compilation.GetTypeByMetadataName("Uno.ImmutableBuilderAttribute");
 			_immutableAttributeCopyIgnoreAttributeSymbol = context.Compilation.GetTypeByMetadataName("Uno.ImmutableAttributeCopyIgnoreAttribute");
 			_immutableGenerationOptionsAttributeSymbol = context.Compilation.GetTypeByMetadataName("Uno.ImmutableGenerationOptionsAttribute");
+			_immutableKnownAsImmutableAttributeSymbol = context.Compilation.GetTypeByMetadataName("Uno.KnownAsImmutableAttribute");
 
 			var generationData = EnumerateImmutableGeneratedEntities()
 				.OrderBy(x => x.symbol.Name)
@@ -70,6 +75,13 @@ namespace Uno
 
 			var immutableEntitiesToGenerate = generationData.Select(x => x.Item1).ToArray();
 
+			if (immutableEntitiesToGenerate.Length == 0)
+			{
+				return; // nothing to do
+			}
+
+			_knownAsImmutableTypes = EnumerateKnownAsImmutables();
+
 			_copyIgnoreAttributeRegexes =
 				ExtractCopyIgnoreAttributes(context.Compilation.Assembly)
 					.Concat(new[] {new Regex(@"^Uno\.Immutable"), new Regex(@"^Uno\.Equality")})
@@ -849,7 +861,7 @@ $@"public sealed class {symbolName}BuilderJsonConverterTo{symbolName}{genericArg
 					builder.AppendLineInvariant(
 						$"#error {nameof(ImmutableGenerator)}: {typeSource} type {type} IS A BUILDER! It cannot be used in an immutable entity.");
 				}
-				else if (!type.IsImmutable(_generationOptions.treatArrayAsImmutable))
+				else if (!type.IsImmutable(_generationOptions.treatArrayAsImmutable, _knownAsImmutableTypes))
 				{
 					if (type is IArrayTypeSymbol)
 					{
@@ -950,5 +962,22 @@ $@"public sealed class {symbolName}BuilderJsonConverterTo{symbolName}{genericArg
 				where moduleAttribute != null
 				//where (bool) moduleAttribute.ConstructorArguments[0].Value
 				select (type, moduleAttribute);
+
+		private IReadOnlyList<ITypeSymbol> EnumerateKnownAsImmutables()
+		{
+			var currentModuleAttributes = _context.Compilation.Assembly.GetAttributes();
+			var referencedAssembliesAttributes =
+				_context.Compilation.SourceModule.ReferencedAssemblySymbols.SelectMany(a => a.GetAttributes());
+
+			var knownTypeAttributes = currentModuleAttributes
+				.Concat(referencedAssembliesAttributes)
+				.Where(a => a.AttributeClass.Equals(_immutableKnownAsImmutableAttributeSymbol))
+				.Select(a => a.ConstructorArguments[0].Value)
+				.Cast<ITypeSymbol>()
+				.Distinct()
+				.ToImmutableArray();
+
+			return knownTypeAttributes;
+		}
 	}
 }

src/Uno.Immutables/ImmutableGenerationOptionsAttribute.cs

@@ -21,7 +21,7 @@ namespace Uno
 	/// <summary>
 	/// Global settings for [GenerateImmutable] generator.
 	/// </summary>
-	[System.AttributeUsage(AttributeTargets.Assembly, Inherited = false, AllowMultiple = false)]
+	[System.AttributeUsage(AttributeTargets.Assembly, AllowMultiple = false)]
 	public sealed class ImmutableGenerationOptionsAttribute : Attribute
 	{
 		/// <summary>

src/Uno.Immutables/KnownAsImmutableAttribute.cs

@@ -0,0 +1,41 @@
+// ******************************************************************
+// 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;
+
+namespace Uno
+{
+	/// <summary>
+	/// Define a type (usually external) as immutable
+	/// </summary>
+	[System.AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
+	public sealed class KnownAsImmutableAttribute : Attribute
+	{
+		/// <summary>
+		/// The type known to be immutable
+		/// </summary>
+		public Type Type { get; }
+
+		/// <summary>
+		/// .ctor
+		/// </summary>
+		/// <param name="type"></param>
+		public KnownAsImmutableAttribute(Type type)
+		{
+			Type = type;
+		}
+	}
+}