[RGen] Add validations for Category methods.

src/rgen/Microsoft.Macios.Bindings.Analyzer/Resources.resx

@@ -540,11 +540,63 @@
         <value>No result type or result type name was provided for an async method.</value>
     </data>
     <data name="RBI0040MessageFormat" xml:space="preserve">
-            <value>The method '{0}' was marked as async and has multiple parameters but does not provide a return type name, a nameless tuple will be generated for the async method</value>
+        <value>The method '{0}' was marked as async and has multiple parameters but does not provide a return type name, a nameless tuple will be generated for the async method</value>
         <comment>{0} is the name of the async method.</comment>
     </data>
     <data name="RBI0040Title" xml:space="preserve">
         <value>Not specified return type</value>
     </data>
 
+    <!-- RBI0041 -->
+
+    <data name="RBI0041Description" xml:space="preserve">
+        <value>UIView subclasses must have a initWithFrame: constructor..</value>
+    </data>
+    <data name="RBI0041MessageFormat" xml:space="preserve">
+        <value>The class '{0}' inherits from UIView but does not expose a 'initWithFrame:' constructor</value>
+        <comment>{0} is the name of the class.</comment>
+    </data>
+    <data name="RBI0041Title" xml:space="preserve">
+        <value>Missing UIView initWithFrame:</value>
+    </data>
+
+    <!-- RBI0042 -->
+
+    <data name="RBI0042Description" xml:space="preserve">
+        <value>Category methods have to be partial.</value>
+    </data>
+    <data name="RBI0042MessageFormat" xml:space="preserve">
+        <value>The method '{0}' must me partial</value>
+        <comment>{0} is the name of the method.</comment>
+    </data>
+    <data name="RBI0042Title" xml:space="preserve">
+        <value>Not partial category method</value>
+    </data>
+
+    <!-- RBI0043 -->
+
+    <data name="RBI0043Description" xml:space="preserve">
+        <value>All category methods have to be extensions.</value>
+    </data>
+    <data name="RBI0043MessageFormat" xml:space="preserve">
+        <value>The method '{0}' in category '{1}' has to be an extension method for '{2}'</value>
+        <comment>{0} is the name of the class.</comment>
+    </data>
+    <data name="RBI0043Title" xml:space="preserve">
+        <value>All methods in an category have to be extensions</value>
+    </data>
+
+    <!-- RBI0044 -->
+
+    <data name="RBI0044Description" xml:space="preserve">
+        <value>Extension methods have to be of the same type as of the category.</value>
+    </data>
+    <data name="RBI0044MessageFormat" xml:space="preserve">
+        <value>Extension method '{0}' in category '{1}' must have the first parameter type match the category's extended type '{2}' found '{3}'</value>
+        <comment>{0} is the name of the method, {1} the name of the categoyr, {2} is the category type and {3} is the type found</comment>
+    </data>
+    <data name="RBI0044Title" xml:space="preserve">
+        <value>Wrong 'this' parameter in category method</value>
+    </data>
+
 </root>

src/rgen/Microsoft.Macios.Bindings.Analyzer/RgenDiagnostics.cs

@@ -616,4 +616,64 @@ public static class RgenDiagnostics {
 		description: new LocalizableResourceString (nameof (Resources.RBI0040Description), Resources.ResourceManager,
 			typeof (Resources))
 	);
+
+	/// <summary>
+	/// Disgnostic descriptor for when a class inherits from UIView and is missing the initWithFrame: constructor.
+	/// </summary>
+	internal static readonly DiagnosticDescriptor RBI0041 = new (
+		"RBI0041",
+		new LocalizableResourceString (nameof (Resources.RBI0041Title), Resources.ResourceManager, typeof (Resources)),
+		new LocalizableResourceString (nameof (Resources.RBI0041MessageFormat), Resources.ResourceManager,
+			typeof (Resources)),
+		"Usage",
+		DiagnosticSeverity.Error,
+		isEnabledByDefault: true,
+		description: new LocalizableResourceString (nameof (Resources.RBI0041Description), Resources.ResourceManager,
+			typeof (Resources))
+	);
+
+	/// <summary>
+	/// Disgnostic descriptor for when a category method is not partial
+	/// </summary>
+	internal static readonly DiagnosticDescriptor RBI0042 = new (
+		"RBI0042",
+		new LocalizableResourceString (nameof (Resources.RBI0042Title), Resources.ResourceManager, typeof (Resources)),
+		new LocalizableResourceString (nameof (Resources.RBI0042MessageFormat), Resources.ResourceManager,
+			typeof (Resources)),
+		"Usage",
+		DiagnosticSeverity.Error,
+		isEnabledByDefault: true,
+		description: new LocalizableResourceString (nameof (Resources.RBI0042Description), Resources.ResourceManager,
+			typeof (Resources))
+	);
+
+	/// <summary>
+	/// Disgnostic descriptor for when a category method is not and extension
+	/// </summary>
+	internal static readonly DiagnosticDescriptor RBI0043 = new (
+		"RBI0043",
+		new LocalizableResourceString (nameof (Resources.RBI0043Title), Resources.ResourceManager, typeof (Resources)),
+		new LocalizableResourceString (nameof (Resources.RBI0043MessageFormat), Resources.ResourceManager,
+			typeof (Resources)),
+		"Usage",
+		DiagnosticSeverity.Error,
+		isEnabledByDefault: true,
+		description: new LocalizableResourceString (nameof (Resources.RBI0043Description), Resources.ResourceManager,
+			typeof (Resources))
+	);
+
+	/// <summary>
+	/// Disgnostic descriptor for when a category method is not and extension of the category's target type
+	/// </summary>
+	internal static readonly DiagnosticDescriptor RBI0044 = new (
+		"RBI0044",
+		new LocalizableResourceString (nameof (Resources.RBI0044Title), Resources.ResourceManager, typeof (Resources)),
+		new LocalizableResourceString (nameof (Resources.RBI0044MessageFormat), Resources.ResourceManager,
+			typeof (Resources)),
+		"Usage",
+		DiagnosticSeverity.Error,
+		isEnabledByDefault: true,
+		description: new LocalizableResourceString (nameof (Resources.RBI0044Description), Resources.ResourceManager,
+			typeof (Resources))
+	);
 }

src/rgen/Microsoft.Macios.Bindings.Analyzer/Validators/CategoryValidator.cs

@@ -1,7 +1,13 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
 using Microsoft.Macios.Generator;
+using Microsoft.Macios.Generator.Attributes;
+using Microsoft.Macios.Generator.Context;
+using Microsoft.Macios.Generator.DataModel;
+using ObjCBindings;
 using static Microsoft.Macios.Generator.RgenDiagnostics;
 
 namespace Microsoft.Macios.Bindings.Analyzer.Validators;
@@ -11,15 +17,69 @@ namespace Microsoft.Macios.Bindings.Analyzer.Validators;
 /// </summary>
 sealed class CategoryValidator : BindingValidator {
 
+	/// <summary>
+	/// Validates that all methods in a category binding are properly declared as partial extension methods
+	/// with the correct first parameter type matching the category's extended type.
+	/// </summary>
+	/// <param name="binding">The category binding to validate.</param>
+	/// <param name="context">The root context for validation.</param>
+	/// <param name="diagnostics">When this method returns, contains diagnostics for any invalid methods; otherwise, an empty array.</param>
+	/// <param name="location">The code location to be used for the diagnostics.</param>
+	/// <returns><c>true</c> if all methods are valid; otherwise, <c>false</c>.</returns>
+	bool ValidMethods (Binding binding, RootContext context,
+		out ImmutableArray<Diagnostic> diagnostics, Location? location = null)
+	{
+		// we need to make sure that all the methods of the category are:
+		// 1. partial
+		// 2. static
+		// 3. Have the correct first parameter type (the type that the category is extending)
+		var builder = ImmutableArray.CreateBuilder<Diagnostic> ();
+		foreach (var extensionMethod in binding.Methods) {
+			if (!ModifiersStrategies.IsPartial (extensionMethod.Modifiers, RBI0042,
+					out var partialDiagnostics, extensionMethod.Location, extensionMethod.Name)) {
+				builder.AddRange (partialDiagnostics);
+			}
+			// check that it is an extension method
+			var bindingData = (BindingTypeData<Category>) binding.BindingInfo;
+			if (extensionMethod.IsExtension) {
+				// ensure that the first parameter type matches the type that the category is extending
+				if (extensionMethod.Parameters [0].Type.FullyQualifiedName !=
+					bindingData.CategoryType.FullyQualifiedName) {
+					// we do not allow to mix types in the extension methods in a category
+					builder.Add (Diagnostic.Create (
+						RBI0044, // Extension methods in a category must have the first parameter type match the category's extended type.
+						extensionMethod.Location,
+						extensionMethod.Name,
+						binding.Name,
+						bindingData.CategoryType.FullyQualifiedName,
+						extensionMethod.Parameters [0].Type.FullyQualifiedName));
+				}
+			} else {
+				// method should be an extension
+				builder.Add (Diagnostic.Create (
+					RBI0043, // Extension methods in a category must be declared as extension methods.
+					extensionMethod.Location,
+					extensionMethod.Name,
+					binding.Name,
+					bindingData.CategoryType.FullyQualifiedName
+					));
+			}
+		}
+
+		diagnostics = builder.ToImmutable ();
+		return diagnostics.Length == 0;
+	}
+
 	/// <summary>
 	/// Initializes a new instance of the <see cref="CategoryValidator"/> class.
 	/// </summary>
 	public CategoryValidator ()
 	{
-
 		// all bindings must be partial
 		AddGlobalStrategy (RBI0001, IsPartial);
 		// categories must be static
 		AddGlobalStrategy (RBI0004, IsStatic);
+		// validate all methods in the category binding
+		AddGlobalStrategy ([RBI0042, RBI0043, RBI0044], ValidMethods);
 	}
 }

src/rgen/Microsoft.Macios.Bindings.Analyzer/Validators/ClassValidator.cs

@@ -316,6 +316,39 @@ bool ValidAsyncMethods (Binding binding, RootContext context,
 		return diagnostics.Length == 0;
 	}
 
+	/// <summary>
+	/// Validates that required constructors are present for specific base classes.
+	/// Currently checks that UIView bindings include the initWithFrame: constructor.
+	/// </summary>
+	/// <param name="binding">The binding to validate.</param>
+	/// <param name="context">The root context for validation.</param>
+	/// <param name="diagnostics">When this method returns, contains diagnostics for any missing required constructors; otherwise, an empty array.</param>
+	/// <param name="location">The code location to be used for the diagnostics.</param>
+	/// <returns><c>true</c> if all required constructors are present; otherwise, <c>false</c>.</returns>
+	bool ValidConstructors (Binding binding, RootContext context,
+		out ImmutableArray<Diagnostic> diagnostics, Location? location = null)
+	{
+		diagnostics = [];
+		// in this case we want to make sure that some base constructors are present. At the moment we only care about 
+		// the initWithFrame: constructor from the UIView base class.
+		if (!binding.TypeInfo.IsView)
+			return true;
+		// get all the constructors and ensure that the initWithFrame: constructor is present
+		var hasInitWithFrame = binding.Constructors.Any (ctor => ctor.ExportMethodData.Selector == "initWithFrame:");
+		if (!hasInitWithFrame) {
+			// error, all UIView bindings must provide the initWithFrame: constructor to be valid
+			diagnostics = [
+				Diagnostic.Create (
+				descriptor: RBI0041,
+				location: location,
+				messageArgs: [
+					binding.Name,
+				])
+			];
+		}
+		return diagnostics.Length == 0;
+	}
+
 	/// <summary>
 	/// Initializes a new instance of the <see cref="ClassValidator"/> class.
 	/// </summary>
@@ -330,6 +363,9 @@ public ClassValidator ()
 		// validate that the selectors are not duplicated, this includes properties and methods
 		AddGlobalStrategy ([RBI0034], SelectorsAreUnique);
 
+		// validate that we have the required constructors for certain base classes like UIView
+		AddGlobalStrategy ([RBI0041], ValidConstructors);
+
 		// validate async methods. This is a global strategy because it needs to look at all the methods in the binding
 		// are validated together so that async methods do not have the same names
 		AddGlobalStrategy ([RBI0035, RBI0036, RBI0037, RBI0038, RBI0039, RBI0040], ValidAsyncMethods);