[generator] Add C#8 nullability into generated code (dotnet#7570)

Goals
* Reflect Apple nullability annotations in our bindings using C#8
* No warnings when building bindings

Non-Goals
* Update (add or fix) `[NullAllowed]` to match Apple headers (next phase)
* Make the generator or internal code fully nullable aware (`nowarn` is used)

Notes
* Apple's own annotations are not 100% accurate :(
* Where known issue exists we have _fixed_ our attributes to match reality :)
* We also do additional null-checks internally that might seems not required (better safe than sorry).

Author: spouliot

msbuild/tests/MyBindingsReferences/LibraryA/LibraryA.csproj

@@ -11,6 +11,7 @@
     <AssemblyName>LibraryA</AssemblyName>
     <TargetFrameworkIdentifier>Xamarin.iOS</TargetFrameworkIdentifier>
     <TargetFrameworkVersion>v1.0</TargetFrameworkVersion>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

msbuild/tests/MyBindingsReferences/LibraryB/LibraryB.csproj

@@ -11,6 +11,7 @@
     <AssemblyName>LibraryB</AssemblyName>
     <TargetFrameworkIdentifier>Xamarin.iOS</TargetFrameworkIdentifier>
     <TargetFrameworkVersion>v1.0</TargetFrameworkVersion>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

msbuild/tests/MySatelliteAssembliesBug/iOSBinding/iOSBinding.csproj

@@ -9,6 +9,7 @@
     <RootNamespace>iOSBinding</RootNamespace>
     <AssemblyName>iOSBinding</AssemblyName>
     <IPhoneResourcePrefix>Resources</IPhoneResourcePrefix>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

msbuild/tests/MyiOSAppWithBinding/MyiOSAppWithBinding.csproj

@@ -9,6 +9,7 @@
     <RootNamespace>MyiOSAppWithBinding</RootNamespace>
     <IPhoneResourcePrefix>Resources</IPhoneResourcePrefix>
     <AssemblyName>MyiOSAppWithBinding</AssemblyName>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhoneSimulator' ">
     <DebugSymbols>true</DebugSymbols>

msbuild/tests/MyiOSFrameworkBinding/MyiOSFrameworkBinding.csproj

@@ -10,6 +10,7 @@
     <RootNamespace>MyiOSFrameworkBinding</RootNamespace>
     <IPhoneResourcePrefix>Resources</IPhoneResourcePrefix>
     <AssemblyName>MyiOSFrameworkBinding</AssemblyName>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
     <DebugSymbols>true</DebugSymbols>

src/Foundation/DictionaryContainer.cs

@@ -40,6 +40,8 @@
 #endif // !WATCH
 #endif
 
+#nullable enable
+
 namespace Foundation {
 
 	public abstract class DictionaryContainer
@@ -50,16 +52,14 @@ protected DictionaryContainer ()
 			Dictionary = new NSMutableDictionary ();
 		}
 
-		protected DictionaryContainer (NSDictionary dictionary)
+		protected DictionaryContainer (NSDictionary? dictionary)
 		{
-			if (dictionary == null)
-				throw new ArgumentNullException ("dictionary");
-			Dictionary = dictionary;
+			Dictionary = dictionary ?? new NSMutableDictionary ();
 		}
 
 		public NSDictionary Dictionary { get; private set; }
 
-		protected T[] GetArray<T> (NSString key) where T : NSObject
+		protected T[]? GetArray<T> (NSString key) where T : NSObject
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -71,7 +71,7 @@ protected T[] GetArray<T> (NSString key) where T : NSObject
 			return NSArray.ArrayFromHandle<T> (value);
 		}
 
-		protected T[] GetArray<T> (NSString key, Func<IntPtr, T> creator)
+		protected T[]? GetArray<T> (NSString key, Func<IntPtr, T> creator)
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -199,15 +199,15 @@ protected T[] GetArray<T> (NSString key, Func<IntPtr, T> creator)
 			return CFBoolean.GetValue (value);
 		}
 
-		protected T GetNativeValue<T> (NSString key) where T : class, INativeObject
+		protected T? GetNativeValue<T> (NSString key) where T : class, INativeObject
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
 
 			return Runtime.GetINativeObject<T> (Dictionary.LowlevelObjectForKey (key.Handle), false);
 		}
 
-		protected NSDictionary GetNSDictionary (NSString key)
+		protected NSDictionary? GetNSDictionary (NSString key)
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -218,7 +218,7 @@ protected NSDictionary GetNSDictionary (NSString key)
 		}
 
 #if XAMCORE_2_0
-		protected NSDictionary <TKey, TValue> GetNSDictionary <TKey, TValue> (NSString key)
+		protected NSDictionary <TKey, TValue>? GetNSDictionary <TKey, TValue> (NSString key)
 			where TKey : class, INativeObject
 			where TValue : class, INativeObject
 		{
@@ -231,22 +231,20 @@ protected NSDictionary GetNSDictionary (NSString key)
 		}
 #endif
 
-		protected T GetStrongDictionary<T> (NSString key) where T : DictionaryContainer
+		protected T? GetStrongDictionary<T> (NSString key) where T : DictionaryContainer
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
 
 			var dict = GetNSDictionary (key);
 			if (dict == null)
 				return null;
-			T value = (T)Activator.CreateInstance (typeof(T),
+			return (T?) Activator.CreateInstance (typeof(T),
 				new object[] { dict }
 			);
-
-			return value;
 		}
 
-		protected NSString GetNSStringValue (NSString key)
+		protected NSString? GetNSStringValue (NSString key)
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -256,7 +254,7 @@ protected NSString GetNSStringValue (NSString key)
 			return value as NSString;
 		}
 
-		protected string GetStringValue (NSString key)
+		protected string? GetStringValue (NSString key)
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -268,7 +266,7 @@ protected string GetStringValue (NSString key)
 			return CFString.FetchString (value.Handle);
 		}
 
-		protected string GetStringValue (string key)
+		protected string? GetStringValue (string key)
 		{
 			if (key == null)
 				throw new ArgumentNullException ("key");
@@ -330,36 +328,36 @@ bool NullCheckAndRemoveKey (NSString key, bool removeEntry)
 			return !removeEntry;
 		}
 
-		protected void SetArrayValue (NSString key, NSNumber[] values)
+		protected void SetArrayValue (NSString key, NSNumber[]? values)
 		{
 			if (NullCheckAndRemoveKey (key, values == null))
 				Dictionary [key] = NSArray.FromNSObjects (values);
 		}
 
-		protected void SetArrayValue<T> (NSString key, T[] values)
+		protected void SetArrayValue<T> (NSString key, T[]? values)
 		{
 			if (NullCheckAndRemoveKey (key, values == null))
 				Dictionary [key] = NSArray.FromNSObjects (values.Select (x => NSObject.FromObject (x)).ToArray ());
 		}
 
-		protected void SetArrayValue (NSString key, string[] values)
+		protected void SetArrayValue (NSString key, string[]? values)
 		{
 			if (NullCheckAndRemoveKey (key, values == null))
-				Dictionary [key] = NSArray.FromStrings (values);
+				Dictionary [key!] = NSArray.FromStrings (values);
 		}
 
-		protected void SetArrayValue (NSString key, INativeObject[] values)
+		protected void SetArrayValue (NSString key, INativeObject[]? values)
 		{
 			if (NullCheckAndRemoveKey (key, values == null))
-				CFMutableDictionary.SetValue (Dictionary.Handle, key.Handle, CFArray.FromNativeObjects (values).Handle);
+				CFMutableDictionary.SetValue (Dictionary.Handle, key!.Handle, CFArray.FromNativeObjects (values).Handle);
 		}
 
 		#region Sets CFBoolean value
 
 		protected void SetBooleanValue (NSString key, bool? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				CFMutableDictionary.SetValue (Dictionary.Handle, key.Handle, value.Value ? CFBoolean.TrueHandle : CFBoolean.FalseHandle);			
+				CFMutableDictionary.SetValue (Dictionary.Handle, key!.Handle, value!.Value ? CFBoolean.TrueHandle : CFBoolean.FalseHandle);			
 		}
 
 		#endregion
@@ -369,67 +367,67 @@ protected void SetBooleanValue (NSString key, bool? value)
 		protected void SetNumberValue (NSString key, int? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);				
+				Dictionary [key!] = new NSNumber (value!.Value);				
 		}
 
 		protected void SetNumberValue (NSString key, uint? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);				
+				Dictionary [key!] = new NSNumber (value!.Value);				
 		}
 
 #if XAMCORE_2_0
 		protected void SetNumberValue (NSString key, nint? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);	
+				Dictionary [key!] = new NSNumber (value!.Value);	
 		}
 
 		protected void SetNumberValue (NSString key, nuint? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);	
+				Dictionary [key!] = new NSNumber (value!.Value);	
 		}
 #endif
 
 		protected void SetNumberValue (NSString key, long? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);				
+				Dictionary [key!] = new NSNumber (value!.Value);				
 		}
 
 		protected void SetNumberValue (NSString key, float? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);				
+				Dictionary [key!] = new NSNumber (value!.Value);				
 		}
 
 		protected void SetNumberValue (NSString key, double? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = new NSNumber (value.Value);				
+				Dictionary [key!] = new NSNumber (value!.Value);				
 		}
 
 		#endregion
 
 		#region Sets NSString value
 
-		protected void SetStringValue (NSString key, string value)
+		protected void SetStringValue (NSString key, string? value)
 		{
-			SetStringValue (key, value == null ? (NSString) null : new NSString (value));
+			SetStringValue (key, value == null ? (NSString) null! : new NSString (value));
 		}
 
-		protected void SetStringValue (NSString key, NSString value)
+		protected void SetStringValue (NSString key, NSString? value)
 		{
 			if (NullCheckAndRemoveKey (key, value == null))
-				Dictionary [key] = value;
+				Dictionary [key!] = value;
 		}
 
 		#endregion
 
 		#region Sets Native value
 
-		protected void SetNativeValue (NSString key, INativeObject value, bool removeNullValue = true)
+		protected void SetNativeValue (NSString key, INativeObject? value, bool removeNullValue = true)
 		{
 			if (NullCheckAndRemoveKey (key, removeNullValue && value == null))
 				CFMutableDictionary.SetValue (Dictionary.Handle, key.Handle, value == null ? IntPtr.Zero : value.Handle);
@@ -451,26 +449,26 @@ protected void RemoveValue (NSString key)
 		protected void SetCGRectValue (NSString key, CGRect? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = value.Value.ToDictionary ();
+				Dictionary [key!] = value!.Value.ToDictionary ();
 		}
 
 		protected void SetCGSizeValue (NSString key, CGSize? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = value.Value.ToDictionary ();
+				Dictionary [key!] = value!.Value.ToDictionary ();
 		}
 
 		protected void SetCGPointValue (NSString key, CGPoint? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = value.Value.ToDictionary ();
+				Dictionary [key!] = value!.Value.ToDictionary ();
 		}
 #endif // XAMCORE_2_0
 #if !WATCH
 		protected void SetCMTimeValue (NSString key, CMTime? value)
 		{
 			if (NullCheckAndRemoveKey (key, !value.HasValue))
-				Dictionary [key] = value.Value.ToDictionary ();
+				Dictionary [key!] = value!.Value.ToDictionary ();
 		}
 #endif //!WATCH
 		#endregion
@@ -482,14 +480,14 @@ static class DictionaryContainerHelper {
 
 		// helper to avoid the (common pattern)
 		// 	var p = x == null ? IntPtr.Zero : h.Dictionary.Handle;
-		static public IntPtr GetHandle (this DictionaryContainer self)
+		static public IntPtr GetHandle (this DictionaryContainer? self)
 		{
 			return self == null ? IntPtr.Zero : self.Dictionary.Handle;
 		}
 
 		// helper to avoid the (common pattern)
 		// 	var p = x == null ? null : x.Dictionary;
-		static public NSDictionary GetDictionary (this DictionaryContainer self)
+		static public NSDictionary? GetDictionary (this DictionaryContainer? self)
 		{
 			return self == null ? null : self.Dictionary;
 		}

src/Foundation/ProtocolAttribute.cs

@@ -24,20 +24,22 @@
 
 using ObjCRuntime;
 
+#nullable enable
+
 namespace Foundation {
 
 	[AttributeUsage (AttributeTargets.Class | AttributeTargets.Interface)]
 	public sealed class ProtocolAttribute : Attribute {
 
 		public ProtocolAttribute () {}
 
-		public Type WrapperType { get; set; }
-		public string Name { get; set; }
+		public Type? WrapperType { get; set; }
+		public string? Name { get; set; }
 		public bool IsInformal { get; set; }
 		// In which SDK version this protocol switched from being informal (i.e. a category) to a formal protocol.
 		// System.Version is not a valid type for attributes, so we're using a string instead.
-		string informal_until;
-		public string FormalSince {
+		string? informal_until;
+		public string? FormalSince {
 			get {
 				return informal_until;
 			}
@@ -56,18 +58,18 @@ public ProtocolMemberAttribute () {}
 		public bool IsRequired { get; set; }
 		public bool IsProperty { get; set; }
 		public bool IsStatic { get; set; }
-		public string Name { get; set; }
-		public string Selector { get; set; }
-		public Type ReturnType { get; set; }
-		public Type ReturnTypeDelegateProxy { get; set; }
-		public Type[] ParameterType { get; set; }
-		public bool[] ParameterByRef { get; set; }
-		public Type[] ParameterBlockProxy { get; set; }
+		public string? Name { get; set; }
+		public string? Selector { get; set; }
+		public Type? ReturnType { get; set; }
+		public Type? ReturnTypeDelegateProxy { get; set; }
+		public Type[]? ParameterType { get; set; }
+		public bool[]? ParameterByRef { get; set; }
+		public Type?[]? ParameterBlockProxy { get; set; }
 		public bool IsVariadic { get; set; }
 
-		public Type PropertyType { get; set; }
-		public string GetterSelector { get; set; }
-		public string SetterSelector { get; set; }
+		public Type? PropertyType { get; set; }
+		public string? GetterSelector { get; set; }
+		public string? SetterSelector { get; set; }
 		public ArgumentSemantic ArgumentSemantic { get; set; }
 	}
 }