[RGen] Add an analyzer error for views that miss initWithFrame.

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

@@ -540,11 +540,24 @@
         <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>
 
+    <!-- RBI0040 -->
+
+    <data name="RBI0041Description" xml:space="preserve">
+        <value>Protocol inline constructor is hidden.</value>
+    </data>
+    <data name="RBI0041MessageFormat" xml:space="preserve">
+        <value>The class '{0}' contains a constructor with the selector '{1}' that hides a inline constructor from protocol '{2}'</value>
+        <comment>{0} is the name of the class, {1} is the selector, {2} is the name of the protocol</comment>
+    </data>
+    <data name="RBI0041Title" xml:space="preserve">
+        <value>Protocol constructor overlap:</value>
+    </data>
+
 </root>

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

@@ -603,7 +603,7 @@ public static class RgenDiagnostics {
 	);
 
 	/// <summary>
-	/// Disgnostic descriptor for when a method marked as async has does not provide a return type or return type name.
+	/// Diagnostic descriptor for when a method marked as async has does not provide a return type or return type name.
 	/// </summary>
 	internal static readonly DiagnosticDescriptor RBI0040 = new (
 		"RBI0040",
@@ -616,4 +616,19 @@ public static class RgenDiagnostics {
 		description: new LocalizableResourceString (nameof (Resources.RBI0040Description), Resources.ResourceManager,
 			typeof (Resources))
 	);
+
+	/// <summary>
+	/// Diagnostic 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.Warning,
+		isEnabledByDefault: true,
+		description: new LocalizableResourceString (nameof (Resources.RBI0041Description), Resources.ResourceManager,
+			typeof (Resources))
+	);
 }

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

@@ -318,6 +318,42 @@ bool ValidAsyncMethods (Binding binding, RootContext context,
 		return diagnostics.Length == 0;
 	}
 
+	bool ValidProtocolInlineConstructors (Binding binding, RootContext context,
+		out ImmutableArray<Diagnostic> diagnostics, Location? location = null)
+	{
+		diagnostics = [];
+		// ensure that if there are any constructors that are going to be inlined from the protocols that they
+		// do not conflict with the constructors that are already defined in the class. This is a warning, and we only
+		// are about those constructors that have the same selectors. The user can disable the warning if he really has
+		var builder = ImmutableArray.CreateBuilder<Diagnostic> ();
+		// get all the selectors from the constructors defined in the class as well as the protocol ones and find
+		// the duplicates
+		var constructorSelectorsSet = binding.Constructors.ToDictionary (x => x.Selector!, x => x);
+		var duplicates = binding.ProtocolConstructors
+			.Where (x => x.Selector is not null && constructorSelectorsSet.ContainsKey (x.Selector))
+			.Select (x => (Selector: x.Selector!, Constructor: x))
+			.ToArray ();
+		if (duplicates.Length > 0) {
+			// we have duplicates, create a warning for each of them
+			foreach (var (selector, protocolConstructor) in duplicates) {
+				// use the class constructor location
+				var constructorLocation = constructorSelectorsSet.TryGetValue (selector, out var constructor)
+					? constructor.Location : location;
+				var protocolName = protocolConstructor.IsProtocolConstructor ? protocolConstructor.ProtocolType : "unknown";
+				builder.Add (Diagnostic.Create (
+					descriptor: RBI0041, // The class '{0}' contains a constructor with the selector '{1}' that hides a inline constructor from a protocol
+					location: constructorLocation,
+					messageArgs: [
+						binding.Name,
+						selector,
+						protocolName
+					]));
+			}
+		}
+		diagnostics = builder.ToImmutable ();
+		return diagnostics.Length == 0;
+	}
+
 	/// <summary>
 	/// Initializes a new instance of the <see cref="ClassValidator"/> class.
 	/// </summary>
@@ -332,6 +368,9 @@ 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], ValidProtocolInlineConstructors);
+
 		// 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);