[XamlC] check eventhandler signature (#3086)

- fixes #3082

Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs

@@ -856,12 +856,12 @@ namespace Xamarin.Forms.Build.Tasks
 
 			var value = ((ValueNode)valueNode).Value;
 
-			yield return Instruction.Create(OpCodes.Ldloc, parent);
+			yield return Create(Ldloc, parent);
 			if (context.Root is VariableDefinition)
-				yield return Instruction.Create(OpCodes.Ldloc, context.Root as VariableDefinition);
+				yield return Create(Ldloc, context.Root as VariableDefinition);
 			else if (context.Root is FieldDefinition) {
-				yield return Instruction.Create(OpCodes.Ldarg_0);
-				yield return Instruction.Create(OpCodes.Ldfld, context.Root as FieldDefinition);
+				yield return Create(Ldarg_0);
+				yield return Create(Ldfld, context.Root as FieldDefinition);
 			} else 
 				throw new InvalidProgramException();
 			var declaringType = context.Body.Method.DeclaringType;
@@ -870,19 +870,33 @@ namespace Xamarin.Forms.Build.Tasks
 			var handler = declaringType.AllMethods().FirstOrDefault(md => md.Name == value as string);
 			if (handler == null) 
 				throw new XamlParseException($"EventHandler \"{value}\" not found in type \"{context.Body.Method.DeclaringType.FullName}\"", iXmlLineInfo);
+
+			//check if the handler signature matches the Invoke signature;
+			var invoke = module.ImportReference(eventinfo.EventType.ResolveCached().GetMethods().First(md => md.Name == "Invoke"));
+			invoke = invoke.ResolveGenericParameters(eventinfo.EventType, module);
+			if (!handler.ReturnType.InheritsFromOrImplements(invoke.ReturnType))
+				throw new XamlParseException($"Signature (return type) of EventHandler \"{context.Body.Method.DeclaringType.FullName}.{value}\" doesn't match the event type", iXmlLineInfo);
+			if (invoke.Parameters.Count != handler.Parameters.Count)
+				throw new XamlParseException($"Signature (number of arguments) of EventHandler \"{context.Body.Method.DeclaringType.FullName}.{value}\" doesn't match the event type", iXmlLineInfo);
+			if (!invoke.ContainsGenericParameter)
+				for (var i = 0; i < invoke.Parameters.Count;i++)
+					if (!handler.Parameters[i].ParameterType.InheritsFromOrImplements(invoke.Parameters[i].ParameterType))
+						throw new XamlParseException($"Signature (parameter {i}) of EventHandler \"{context.Body.Method.DeclaringType.FullName}.{value}\" doesn't match the event type", iXmlLineInfo);
+
 			if (handler.IsVirtual) {
-				yield return Instruction.Create(OpCodes.Ldarg_0);
-				yield return Instruction.Create(OpCodes.Ldvirtftn, handler);
+				yield return Create(Ldarg_0);
+				yield return Create(Ldvirtftn, handler);
 			} else
-				yield return Instruction.Create(OpCodes.Ldftn, handler);
+				yield return Create(Ldftn, handler);
 
 			//FIXME: eventually get the right ctor instead fo the First() one, just in case another one could exists (not even sure it's possible).
 			var ctor = module.ImportReference(eventinfo.EventType.ResolveCached().GetConstructors().First());
 			ctor = ctor.ResolveGenericParameters(eventinfo.EventType, module);
-			yield return Instruction.Create(OpCodes.Newobj, module.ImportReference(ctor));
+			yield return Create(Newobj, module.ImportReference(ctor));
+			//Check if the handler has the same signature as the ctor (it should)
 			var adder = module.ImportReference(eventinfo.AddMethod);
 			adder = adder.ResolveGenericParameters(eventDeclaringTypeRef, module);
-			yield return Instruction.Create(OpCodes.Callvirt, module.ImportReference(adder));
+			yield return Create(Callvirt, module.ImportReference(adder));
 		}
 
 		static bool CanSetDynamicResource(FieldReference bpRef, INode valueNode, ILContext context)

Xamarin.Forms.Xaml.UnitTests/Issues/Gh3082.xaml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage 
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    x:Class="Xamarin.Forms.Xaml.UnitTests.Gh3082">
+    <Button Clicked="OnClicked" />
+</ContentPage>

Xamarin.Forms.Xaml.UnitTests/Issues/Gh3082.xaml.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Threading.Tasks;
+using System.Collections.Generic;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UnitTests;
+
+
+using Xamarin.Forms;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	[XamlCompilation(XamlCompilationOptions.Skip)]
+	public partial class Gh3082 : ContentPage
+	{
+		public Gh3082()
+		{
+			InitializeComponent();
+		}
+
+		public Gh3082(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		async Task OnClicked(object sender, EventArgs e)
+		{
+			await Task.Delay(1000);
+		}
+
+
+		[TestFixture]
+		class Tests
+		{
+			[SetUp]
+			public void Setup()
+			{
+				Device.PlatformServices = new MockPlatformServices();
+			}
+
+			[TearDown]
+			public void TearDown()
+			{
+				Device.PlatformServices = null;
+			}
+
+			[TestCase(false), TestCase(true)]
+			public void ThrowsOnWrongEventHandlerSignature(bool useCompiledXaml)
+			{
+				if (useCompiledXaml)
+					Assert.Throws<XamlParseException>(()=>MockCompiler.Compile(typeof(Gh3082)));
+				else
+					Assert.Throws<XamlParseException>(()=>new Gh3082(false));
+			}
+		}
+	}
+}

Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj

@@ -625,6 +625,9 @@
       <DependentUpon>Gh2574.xaml</DependentUpon>
     </Compile>
     <Compile Include="XFCorePostProcessorCodeInjected.cs" />
+    <Compile Include="Issues\Gh3082.xaml.cs">
+      <DependentUpon>Gh3082.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="..\.nuspec\Xamarin.Forms.Debug.targets" Condition="'$(BuildingInsideVisualStudio)' == 'true' AND Exists('..\.nuspec\Xamarin.Forms.Build.Tasks.dll')" />
@@ -1131,6 +1134,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="Issues\Gh3082.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />