From 5c3394e21fcad7c18d1307fb7d4053e61315cf5d Mon Sep 17 00:00:00 2001
From: Stephane Delcroix <stephane@delcroix.org>
Date: Wed, 13 Dec 2023 13:48:16 +0100
Subject: [PATCH] warn on datatype explicitly null

---
 .../src/Core/Compatibility.ControlGallery.Core.csproj      | 7 +++----
 src/Controls/samples/Directory.Build.props                 | 3 ++-
 src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs       | 3 +++
 .../tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj    | 4 ++--
 src/Essentials/samples/Directory.Build.props               | 3 ++-
 .../TestUtils.DeviceTests.Runners.csproj                   | 2 +-
 6 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/Compatibility/ControlGallery/src/Core/Compatibility.ControlGallery.Core.csproj b/src/Compatibility/ControlGallery/src/Core/Compatibility.ControlGallery.Core.csproj
index 4fe496c4db99..edd776ae4569 100644
--- a/src/Compatibility/ControlGallery/src/Core/Compatibility.ControlGallery.Core.csproj
+++ b/src/Compatibility/ControlGallery/src/Core/Compatibility.ControlGallery.Core.csproj
@@ -3,6 +3,9 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <AssemblyName>Microsoft.Maui.Controls.Compatibility.ControlGallery</AssemblyName>
     <RootNamespace>Microsoft.Maui.Controls.Compatibility.ControlGallery</RootNamespace>
+    <WarningLevel>4</WarningLevel>
+    <NoWarn>0114;0108;0109;4014;0649;0169;0472;0414;0168;0219;0429;0618;0612</NoWarn>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC10101;XC10102</WarningsNotAsErrors>
   </PropertyGroup>
   <PropertyGroup>
     <XFDisableTargetsValidation>True</XFDisableTargetsValidation>
@@ -10,14 +13,10 @@
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DefineConstants>TRACE;DEBUG;PERF;APP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <NoWarn>0114;0108;0109;4014;0649;0169;0472;0414;0168;0219;0429;0618;0612</NoWarn>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DefineConstants>TRACE;APP</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <NoWarn>0114;0108;0109;4014;0649;0169;0472;0414;0168;0219;0429;0618;0612</NoWarn>
   </PropertyGroup>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('uap10.0'))">
     <DefineConstants>$(DefineConstants);WINDOWS</DefineConstants>
diff --git a/src/Controls/samples/Directory.Build.props b/src/Controls/samples/Directory.Build.props
index 70564c58672c..241a359433ad 100644
--- a/src/Controls/samples/Directory.Build.props
+++ b/src/Controls/samples/Directory.Build.props
@@ -2,6 +2,7 @@
   <PropertyGroup>
     <SampleProject>true</SampleProject>
     <UseMaui Condition=" '$(UseWorkload)' == 'true' ">true</UseMaui>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC10101;XC10102</WarningsNotAsErrors>
   </PropertyGroup>
   <Import Project="../../../Directory.Build.props" />
-</Project>
\ No newline at end of file
+</Project>
diff --git a/src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs b/src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs
index 0db5f2c6a11a..f70f7e42f694 100644
--- a/src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs
+++ b/src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs
@@ -397,7 +397,10 @@ static IEnumerable<Instruction> CompileBindingPath(ElementNode node, ILContext c
 			if (dataTypeNode is ElementNode enode
 				&& enode.XmlType.NamespaceUri == XamlParser.X2009Uri
 				&& enode.XmlType.Name == nameof(Microsoft.Maui.Controls.Xaml.NullExtension))
+			{
+				context.LoggingHelper.LogWarningOrError(10102, context.XamlFilePath, node.LineNumber, node.LinePosition, 0, 0, $"Binding could be compiled if x:DataType is not explicitly null", null);
 				yield break;
+			}
 
 			string dataType = null;
 
diff --git a/src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj b/src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj
index c28d6b2ff0ff..d958099c7f7c 100644
--- a/src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj
+++ b/src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj
@@ -5,8 +5,8 @@
     <RootNamespace>Microsoft.Maui.Controls.Xaml.UnitTests</RootNamespace>
     <AssemblyName>Microsoft.Maui.Controls.Xaml.UnitTests</AssemblyName>
     <WarningLevel>4</WarningLevel>
-    <NoWarn>0672;0219;0414;CS0436;CS0618</NoWarn>
-    <WarningsNotAsErrors>XC0618;XC10101</WarningsNotAsErrors>
+    <NoWarn>$(NoWarn);0672;0219;0414;CS0436;CS0618</NoWarn>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC0618;XC10101;XC10102</WarningsNotAsErrors>
     <IsPackable>false</IsPackable>
     <DisableMSBuildAssemblyCopyCheck>true</DisableMSBuildAssemblyCopyCheck>
   </PropertyGroup>
diff --git a/src/Essentials/samples/Directory.Build.props b/src/Essentials/samples/Directory.Build.props
index 70564c58672c..241a359433ad 100644
--- a/src/Essentials/samples/Directory.Build.props
+++ b/src/Essentials/samples/Directory.Build.props
@@ -2,6 +2,7 @@
   <PropertyGroup>
     <SampleProject>true</SampleProject>
     <UseMaui Condition=" '$(UseWorkload)' == 'true' ">true</UseMaui>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC10101;XC10102</WarningsNotAsErrors>
   </PropertyGroup>
   <Import Project="../../../Directory.Build.props" />
-</Project>
\ No newline at end of file
+</Project>
diff --git a/src/TestUtils/src/DeviceTests.Runners/TestUtils.DeviceTests.Runners.csproj b/src/TestUtils/src/DeviceTests.Runners/TestUtils.DeviceTests.Runners.csproj
index 546b378eff74..ffdcea8bc68c 100644
--- a/src/TestUtils/src/DeviceTests.Runners/TestUtils.DeviceTests.Runners.csproj
+++ b/src/TestUtils/src/DeviceTests.Runners/TestUtils.DeviceTests.Runners.csproj
@@ -7,7 +7,7 @@
     <AssemblyName>Microsoft.Maui.TestUtils.DeviceTests.Runners</AssemblyName>
     <!--<Nullable>enable</Nullable>-->
     <NoWarn>$(NoWarn);CA1416</NoWarn>
-    <WarningsNotAsErrors>XC10101</WarningsNotAsErrors>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC10101;XC10102</WarningsNotAsErrors>
   </PropertyGroup>
 
   <ItemGroup>