[RGen] Add the code generation for the data attributes. (#22053)

This change adds two more properties to the data models when they are
compile. One to check if the data attr is present, and a second one with
the attribute details.

The boolean property is decorated acordingly to help with the
nullability analisys.

An example of the generated code can be found here:
https://gist.github.com/mandel-macaque/04185ea481ca30ef9ff2ecf6dbf51ea0

---------

Co-authored-by: GitHub Actions Autoformatter <[email protected]>

src/rgen/Microsoft.Macios.Transformer.Generator/Microsoft.Macios.Transformer.Generator/XamarinBindingAPIGenerator.cs

@@ -73,6 +73,14 @@ static string [] GetFlagsForTarget (Dictionary<string, (string AttributeFullName
 			.Select (kv => kv.Key)
 			.ToArray ();
 
+	static (string AttributeFullName, string AttributeName, BindingAttributeData Data) [] GetAttributesForTarget (
+		Dictionary<string, (string AttributeFullName, string AttributeName, BindingAttributeData Data)> dataAttribute,
+		AttributeTargets targets)
+		=> dataAttribute.Where (kv => kv.Value.Data.Target.HasFlag (targets))
+			.Select (kv => kv.Value)
+			.ToArray ();
+
+
 	static void WriteFlagProperty (TabbedStringBuilder sb, string flagName)
 	{
 		// write the backing field
@@ -83,13 +91,34 @@ static void WriteFlagProperty (TabbedStringBuilder sb, string flagName)
 		}
 	}
 
-	static void WriteDataModelExtension (TabbedStringBuilder sb, string dataModel, string [] flags)
+	static void WriteAttributeProperty (TabbedStringBuilder sb,
+		(string AttributeFullName, string AttributeName, BindingAttributeData Data) attrData)
+	{
+		// add a property that will state if we have the attr, this will help with nullability
+		sb.AppendLine ($"readonly bool _has{attrData.AttributeName} = false;");
+		sb.AppendLine ($"[MemberNotNullWhen (true, nameof ({attrData.AttributeName}))]");
+		using (var flagPropertyBlock = sb.CreateBlock ($"public bool Has{attrData.AttributeName}", block: true)) {
+			flagPropertyBlock.AppendLine ($"get => _has{attrData.AttributeName};");
+			flagPropertyBlock.AppendLine ($"private init => _has{attrData.AttributeName} = value;");
+		}
+		sb.AppendLine ();
+		sb.AppendLine ($"readonly {attrData.Data.DataModelType}? _{attrData.AttributeName} = null;");
+		// decorate to help with nullability
+		using (var attributePropertyBlock = sb.CreateBlock ($"public {attrData.Data.DataModelType}? {attrData.AttributeName}", block: true)) {
+			attributePropertyBlock.AppendLine ($"get => _{attrData.AttributeName};");
+			attributePropertyBlock.AppendLine ($"private init => _{attrData.AttributeName} = value;");
+		}
+	}
+
+	static void WriteDataModelExtension (TabbedStringBuilder sb, string dataModel, string [] flags,
+		(string AttributeFullName, string AttributeName, BindingAttributeData Data) [] attributes)
 	{
 		sb.Clear ();
 		sb.AppendLine ("// <auto-generated/>");
 		sb.AppendLine ("#nullable enable");
 		sb.AppendLine ("");
 		sb.AppendLine ("using System;");
+		sb.AppendLine ("using System.Diagnostics.CodeAnalysis;");
 		sb.AppendLine ("using Microsoft.CodeAnalysis;");
 		sb.AppendLine ("using Microsoft.Macios.Transformer.Extensions;");
 		sb.AppendLine ();
@@ -103,6 +132,11 @@ static void WriteDataModelExtension (TabbedStringBuilder sb, string dataModel, s
 				WriteFlagProperty (modelBlock, flag);
 			}
 
+			foreach (var attrData in attributes) {
+				modelBlock.AppendLine ();
+				WriteAttributeProperty (modelBlock, attrData);
+			}
+
 			// property to store the dictionary
 			modelBlock.AppendLine ();
 			modelBlock.AppendLine ("readonly Dictionary<string, List<AttributeData>>? _attributesDictionary = null;");
@@ -114,7 +148,15 @@ static void WriteDataModelExtension (TabbedStringBuilder sb, string dataModel, s
 					initBlock.AppendLine ("_attributesDictionary = value;");
 					using (var ifBlock = initBlock.CreateBlock ("if (_attributesDictionary is not null)", block: true)) {
 						foreach (var flag in flags) {
-							ifBlock.AppendLine ($"_{flag} = _attributesDictionary.{flag} ();");
+							ifBlock.AppendLine ($"{flag} = _attributesDictionary.{flag} ();");
+						}
+
+						foreach (var attributeData in attributes) {
+							// check if the attribute is present, if it is, set the value
+							ifBlock.AppendLine ($"Has{attributeData.AttributeName} = _attributesDictionary.Has{attributeData.AttributeName} ();");
+							using (var attrIfBlock = ifBlock.CreateBlock ($"if (Has{attributeData.AttributeName})", block: true)) {
+								attrIfBlock.AppendLine ($"{attributeData.AttributeName} = _attributesDictionary.Get{attributeData.AttributeName} ();");
+							}
 						}
 					}
 				}
@@ -123,11 +165,14 @@ static void WriteDataModelExtension (TabbedStringBuilder sb, string dataModel, s
 	}
 
 	static void GenerateModelExtension (TabbedStringBuilder sb, string dataModel,
-		Dictionary<string, (string AttributeFullName, AttributeTargets Targets)> flags, AttributeTargets targets,
+		Dictionary<string, (string AttributeFullName, AttributeTargets Targets)> flags,
+		Dictionary<string, (string AttributeFullName, string AttributeName, BindingAttributeData Data)> attributes,
+		AttributeTargets targets,
 		SourceProductionContext context)
 	{
 		var methodFlags = GetFlagsForTarget (flags, targets);
-		WriteDataModelExtension (sb, dataModel, methodFlags);
+		var methodAttributes = GetAttributesForTarget (attributes, targets);
+		WriteDataModelExtension (sb, dataModel, methodFlags, methodAttributes);
 		context.AddSource ($"{dataModel}.Transformer.g.cs",
 			SourceText.From (sb.ToString (), Encoding.UTF8));
 	}
@@ -204,7 +249,7 @@ void GenerateCode (SourceProductionContext context, Compilation compilation,
 #pragma warning restore format 
 
 		foreach (var (model, target) in models) {
-			GenerateModelExtension (sb, model, flags, target, context);
+			GenerateModelExtension (sb, model, flags, dataAttributes, target, context);
 		}
 	}