dotnet · rmarinho · Aug 20, 2025 · Aug 1, 2025
diff --git a/Directory.Build.props b/Directory.Build.props
@@ -2,6 +2,16 @@
   <Import Project="Sdk.props" Sdk="Microsoft.DotNet.Arcade.Sdk" />
   <Import Condition="'$(EnvironmentBuildPropsImported)' != 'True'" Project="$(MSBuildThisFileDirectory)eng\Environment.Build.props" />
 
+  <PropertyGroup>
+    <!-- 
+      Keep backward compatibility with XamlC, XamlCompilationAttribute, and xaml-comp processing instruction
+      When we're ready to turn this off, we can remove all code depending on this condition, and drop this property group
+      -->
+
+    <_MauiXamlSourceGenBackCompat>true</_MauiXamlSourceGenBackCompat>
+    <DefineConstants Condition=" '$(_MauiXamlSourceGenBackCompat)' == 'true' ">$(DefineConstants);_MAUIXAML_SOURCEGEN_BACKCOMPAT</DefineConstants>
+  </PropertyGroup>
+
   <PropertyGroup>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <!-- Detailed trimmer warnings, if present -->

diff --git a/src/Controls/samples/Controls.Sample.Embedding/Resources/Styles/Colors.xaml b/src/Controls/samples/Controls.Sample.Embedding/Resources/Styles/Colors.xaml
@@ -1,5 +1,4 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<?xaml-comp compile="true" ?>
 <ResourceDictionary 
     xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">

diff --git a/src/Controls/samples/Controls.Sample.Embedding/Resources/Styles/Styles.xaml b/src/Controls/samples/Controls.Sample.Embedding/Resources/Styles/Styles.xaml
@@ -1,5 +1,4 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<?xaml-comp compile="true" ?>
 <ResourceDictionary 
     xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">

diff --git a/src/Controls/src/Build.Tasks/XamlCTask.cs b/src/Controls/src/Build.Tasks/XamlCTask.cs
@@ -203,88 +203,50 @@ public override bool Execute(out IList<Exception> thrownExceptions)
 
 				using (var assemblyDefinition = AssemblyDefinition.ReadAssembly(IOPath.GetFullPath(Assembly), readerParameters))
 				{
-					CustomAttribute xamlProcessingAttr = null;
-					if (assemblyDefinition.HasCustomAttributes &&
-						(xamlProcessingAttr =
-							assemblyDefinition.CustomAttributes.FirstOrDefault(
-								ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlProcessingAttribute")) != null)
-					{
-						var inflator = (XamlInflator)xamlProcessingAttr.ConstructorArguments[0].Value;
-						var generateInflatorSwitch = xamlProcessingAttr.ConstructorArguments.Count > 1
-													&& (bool)xamlProcessingAttr.ConstructorArguments[1].Value;
-						assemblyInflatorOptions = (generateInflatorSwitch, inflator);
-						if (!generateInflatorSwitch)
-							skipassembly = (inflator & XamlInflator.XamlC) != XamlInflator.XamlC && inflator != XamlInflator.Default;
-
-					}
-
-#pragma warning disable CS0618 // Type or member is obsolete
+#if _MAUIXAML_SOURCEGEN_BACKCOMPAT
 					CustomAttribute xamlcAttr = null;
 					if (assemblyDefinition.HasCustomAttributes &&
 						(xamlcAttr =
 							assemblyDefinition.CustomAttributes.FirstOrDefault(
 								ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlCompilationAttribute")) != null)
 					{
-						if (xamlProcessingAttr == null)
-						{
-							var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
-							if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
-								skipassembly = true;
-							if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
-								skipassembly = false;
-						}
-						else
-							LoggingHelper.LogWarning($"{new string(' ', 2)}Assembly has both XamlCompilationAttribute and XamlProcessingAttribute. XamlCompilationAttribute will be ignored.");
+						var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
+						if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
+							skipassembly = true;
+						if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
+							skipassembly = false;
 					}
-#pragma warning restore CS0618 // Type or member is obsolete
 
-					xamlcAttr = xamlProcessingAttr = null;
+					xamlcAttr = null;
+#endif
 
 					foreach (var module in assemblyDefinition.Modules)
 					{
 						var skipmodule = skipassembly;
 						(bool, XamlInflator)? moduleInflatorOptions = assemblyInflatorOptions;
 
-						if (module.HasCustomAttributes &&
-							(xamlProcessingAttr =
-								module.CustomAttributes.FirstOrDefault(
-									ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlProcessingAttribute")) != null)
-						{
-							var inflator = (XamlInflator)xamlProcessingAttr.ConstructorArguments[0].Value;
-							var generateInflatorSwitch = xamlProcessingAttr.ConstructorArguments.Count > 1
-														&& (bool)xamlProcessingAttr.ConstructorArguments[1].Value;
-							moduleInflatorOptions = (generateInflatorSwitch, inflator);
-							if (!generateInflatorSwitch)
-								skipmodule = (inflator & XamlInflator.XamlC) != XamlInflator.XamlC && inflator != XamlInflator.Default;
-						}
-
-#pragma warning disable CS0618 // Type or member is obsolete
+#if _MAUIXAML_SOURCEGEN_BACKCOMPAT
 						if (module.HasCustomAttributes &&
 							(xamlcAttr =
 								module.CustomAttributes.FirstOrDefault(
 									ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlCompilationAttribute")) != null)
 						{
-							if (xamlProcessingAttr == null)
-							{
-
-								var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
-								if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
-									skipmodule = true;
-								if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
-									skipmodule = false;
-							}
-							else
-								LoggingHelper.LogWarning($"{new string(' ', 2)}Module {module.Name} has both XamlCompilationAttribute and XamlProcessingAttribute. XamlCompilationAttribute will be ignored.");
+							var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
+							if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
+								skipmodule = true;
+							if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
+								skipmodule = false;
 						}
-#pragma warning restore CS0618 // Type or member is obsolete
-
-						xamlcAttr = xamlProcessingAttr = null;
+						xamlcAttr = null;
+#endif
 
 						LoggingHelper.LogMessage(Low, $"{new string(' ', 2)}Module: {module.Name}");
 						var resourcesToPrune = new List<EmbeddedResource>();
 						foreach (var resource in module.Resources.OfType<EmbeddedResource>())
 						{
-							var initCompName = "InitializeComponent";
+							var generateInflatorSwitch = module.Assembly.Name.Name == "Microsoft.Maui.Controls.Xaml.UnitTests";
+							var initCompName = generateInflatorSwitch ? "InitializeComponentXamlC" : "InitializeComponent";
+
 							LoggingHelper.LogMessage(Low, $"{new string(' ', 4)}Resource: {resource.Name}");
 							string classname;
 							if (!resource.IsXaml(cache, module, out classname))
@@ -301,53 +263,27 @@ public override bool Execute(out IList<Exception> thrownExceptions)
 							var skiptype = skipmodule;
 							(bool, XamlInflator)? typeInflatorOptions = moduleInflatorOptions;
 
-							if (typeDef.HasCustomAttributes &&
-								(xamlProcessingAttr =
-									typeDef.CustomAttributes.FirstOrDefault(
-										ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlProcessingAttribute")) != null)
-							{
-								var inflator = (XamlInflator)xamlProcessingAttr.ConstructorArguments[0].Value;
-								var generateInflatorSwitch = xamlProcessingAttr.ConstructorArguments.Count > 1
-															&& (bool)xamlProcessingAttr.ConstructorArguments[1].Value;
-
-								typeInflatorOptions = (generateInflatorSwitch, inflator);
-								if (generateInflatorSwitch)
-								{
-									skiptype = (inflator & XamlInflator.XamlC) != XamlInflator.XamlC && inflator != XamlInflator.Default;
-									initCompName = "InitializeComponentXamlC";
-								}
-								else
-									skiptype = inflator != XamlInflator.XamlC;
-							}
-#pragma warning disable CS0618 // Type or member is obsolete
+#if _MAUIXAML_SOURCEGEN_BACKCOMPAT
 							if (typeDef.HasCustomAttributes &&
 								(xamlcAttr =
 									typeDef.CustomAttributes.FirstOrDefault(
 										ca => ca.AttributeType.FullName == "Microsoft.Maui.Controls.Xaml.XamlCompilationAttribute")) != null)
 							{
-								if (xamlProcessingAttr == null)
-								{
-									// XamlCompilationAttribute is obsolete, but we still need to support it
-									// for backwards compatibility
-									var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
-									if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
-										skiptype = true;
-									if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
-										skiptype = false;
-								}
-								else
-									LoggingHelper.LogWarning($"{new string(' ', 6)}Type {typeDef.Name} has both XamlCompilationAttribute and XamlProcessingAttribute. XamlCompilationAttribute will be ignored.");
+								var options = (XamlCompilationOptions)xamlcAttr.ConstructorArguments[0].Value;
+								if ((options & XamlCompilationOptions.Skip) == XamlCompilationOptions.Skip)
+									skiptype = true;
+								if ((options & XamlCompilationOptions.Compile) == XamlCompilationOptions.Compile)
+									skiptype = false;
 							}
-#pragma warning restore CS0618 // Type or member is obsolete
-
-							xamlcAttr = xamlProcessingAttr = null;
+							xamlcAttr = null;
+#endif
 
 							if (Type != null)
 								skiptype = !(Type == classname);
 
 							if (skiptype && !ForceCompile)
 							{
-								LoggingHelper.LogMessage(Low, $"{new string(' ', 6)}has XamlCompilation or XamlProceesing disabling XamlC... skipped.");
+								LoggingHelper.LogMessage(Low, $"{new string(' ', 6)}has XamlCompilation  disabling XamlC... skipped.");
 								continue;
 							}
 

diff --git a/...c/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.Common.targets b/...c/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.Common.targets
@@ -22,6 +22,14 @@
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="ManifestResourceName" />
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="TargetPath" />
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="RelativePath" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="Inflator" />
+    <CompilerVisibleProperty Include="MauiXamlNoWarn" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="NoWarn" />
+		<CompilerVisibleProperty Include="MauiXamlEnableDiagnostics" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="EnableDiagnostics" />
+    <CompilerVisibleProperty Include="MauiXamlLineInfo" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="LineInfo" />
+    <CompilerVisibleProperty Include="MauiXamlNullable" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="Nullable" />
 	</ItemGroup>
-
 </Project>
diff --git a/...rols/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.targets b/...rols/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.targets
@@ -6,6 +6,11 @@
 		<SynthesizeLinkMetadata>true</SynthesizeLinkMetadata>
 		<EnableDefaultXamlItems Condition="'$(EnableDefaultXamlItems)'==''">True</EnableDefaultXamlItems>
 		<EnableDefaultCssItems Condition="'$(EnableDefaultCssItems)'==''">True</EnableDefaultCssItems>
+    <!-- default MauiXaml inflators  -->
+    <_MauiXamlInflator Condition="' $(MauiXamlInflator)' != '' ">$(MauiXamlInflator)</_MauiXamlInflator>
+    <_MauiXamlInflator Condition=" '$(MauiXamlInflator)' == '' And '$(Configuration)' == 'Debug' ">Runtime</_MauiXamlInflator>
+    <_MauiXamlInflator Condition=" '$(MauiXamlInflator)' == '' And '$(Configuration)' != 'Debug' ">XamlC</_MauiXamlInflator>
+
 		<!-- The WINUI check for this only runs when there is an empty string so I just convert false to an empty string to fall in line with our other properties -->
 		<SkipMicrosoftUIXamlCheckTargetPlatformVersion Condition="'$(SkipMicrosoftUIXamlCheckTargetPlatformVersion)'==''">true</SkipMicrosoftUIXamlCheckTargetPlatformVersion>
 		<SkipMicrosoftUIXamlCheckTargetPlatformVersion Condition="'$(SkipMicrosoftUIXamlCheckTargetPlatformVersion)'=='false'"></SkipMicrosoftUIXamlCheckTargetPlatformVersion>
@@ -73,11 +78,34 @@
 			Condition="'$(_XFTargetsImported)' == 'true'"/>
 	</Target>
 
+  <Target Name="_MauiXamlComputeInflator">
+  	<ItemGroup>
+      <!-- Assign the default inflator to MauiXaml that don't have any -->
+      <!-- there's a roslyn bug that stops parsing value at the first semicolon. replace them all https://github.com/dotnet/roslyn/issues/43970 -->
+      <MauiXaml Inflator="$([MSBuild]::ValueOrDefault('%(MauiXaml.Inflator)','$(_MauiXamlInflator)').Replace(';', ','))"/>
+
+	    <_MauiXaml_SG Remove="@(_MauiXaml_SG)" />
+	    <_MauiXaml_RT Remove="@(_MauiXaml_RT)" />
+	    <_MauiXaml_XC Remove="@(_MauiXaml_XC)" />
+	    <_MauiXaml_SG Include="@(MauiXaml)" Condition="$([System.String]::new('%(MauiXaml.Inflator)').Contains('SourceGen', StringComparison.OrdinalIgnoreCase))" />
+	    <_MauiXaml_RT Include="@(MauiXaml)" Condition="$([System.String]::new('%(MauiXaml.Inflator)').Contains('Runtime', StringComparison.OrdinalIgnoreCase))" />
+	    <_MauiXaml_XC Include="@(MauiXaml)" Condition="$([System.String]::new('%(MauiXaml.Inflator)').Contains('XamlC', StringComparison.OrdinalIgnoreCase))" />
+      <_MauiXaml_AsEmbeddedResource Include="@(_MauiXaml_RT)" />
+      <_MauiXaml_AsEmbeddedResource Include="@(_MauiXaml_XC)" KeepDuplicates="false" />      
+	</ItemGroup>
+  </Target>
 
   <!-- Inject MauiXaml and MauiCss as AdditionalFiles for partial type generation-->
+  <PropertyGroup>
+    <_MauiInjectXamlCssAdditionalFilesDependsOn>
+      _MauiXamlComputeInflator;
+      $(CreateManifestResourceNamesDependsOn);
+    </_MauiInjectXamlCssAdditionalFilesDependsOn>
+  </PropertyGroup>
+
   <Target Name="_MauiInjectXamlCssAdditionalFiles"
           BeforeTargets="GenerateMSBuildEditorConfigFileShouldRun"
-          DependsOnTargets="$(CreateManifestResourceNamesDependsOn)">
+          DependsOnTargets="$(_MauiInjectXamlCssAdditionalFilesDependsOn)">
     <ItemGroup>
       <_MauiXamlWithResourceNames Remove="@(_MauiXamlWithResourceNames)" />
       <_MauiXamlWithTargetPath Remove="@(_MauiXamlWithTargetPath)" />
@@ -113,6 +141,7 @@
             TargetPath="%(_MauiXamlWithResourceNames.TargetPath)"
             RelativePath="$([MSBuild]::MakeRelative($(MSBuildProjectDirectory), %(_MauiXamlWithResourceNames.TargetPath)))"
             ItemSpec="%(_MauiXamlWithResourceNames.OriginalItemSpec)"
+            Inflator="%(_MauiXamlWithResourceNames.Inflator)"
             GenKind="Xaml"/>
       <AdditionalFiles Condition="%(_MauiCssWithResourceNames.TargetPath) != ''"
             Include="@(_MauiCssWithResourceNames)"
@@ -129,14 +158,19 @@
   </Target>
 
 
-  <!-- re-add MauiXaml and MauiCss as EmbeddedResources -->
+  <!-- re-add MauiXaml and MauiCss as EmbeddedResources for runtime inflation and XamlC -->
   <PropertyGroup>
     <PrepareResourcesDependsOn>
       _MauiAddXamlEmbeddedResources;
       $(PrepareResourcesDependsOn);
     </PrepareResourcesDependsOn>
+    <_MauiAddXamlEmbeddedResourcesDependsOn>
+      _MauiXamlComputeInflator
+    </_MauiAddXamlEmbeddedResourcesDependsOn>
   </PropertyGroup>
-  <Target Name="_MauiAddXamlEmbeddedResources">
+
+  <Target Name="_MauiAddXamlEmbeddedResources"
+          DependsOnTargets="$(_MauiAddXamlEmbeddedResourcesDependsOn)">
     <ItemGroup>
       <EmbeddedResource Include="@(MauiXaml)" />
       <EmbeddedResource Include="@(MauiCss)" />