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Optimize DataTemplateExtension as KnownMarkup in source generator#32761

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StephaneDelcroix merged 1 commit intomainfrom
datatemplate-knownmarkup
Nov 20, 2025
Merged

Optimize DataTemplateExtension as KnownMarkup in source generator#32761
StephaneDelcroix merged 1 commit intomainfrom
datatemplate-knownmarkup

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@StephaneDelcroix StephaneDelcroix commented Nov 20, 2025

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It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Description

This PR implements DataTemplateExtension as a KnownMarkup in the XAML source generator, reducing generated code size by ~95% and improving performance through direct constructor calls instead of reflection-based ProvideValue.

Changes Made

Source Generator Implementation

KnownMarkups.cs:

  • Added ProvideValueForDataTemplateExtension method
  • Resolves TypeName to Type at compile time
  • Generates direct new DataTemplate(typeof(...)) constructor calls

NodeSGExtensions.cs:

  • Registered DataTemplateExtension in GetKnownEarlyMarkupExtensions
  • Classified as "early" since it only needs string TypeName input

Unit Tests

DataTemplateMarkupExtension.cs:

  • DataTemplateMarkupExtensionWithType: Tests with custom ViewCell class
  • DataTemplateMarkupExtensionInListView: Tests with built-in Label control
  • Both validate the simplified generated code

Code Generation Comparison

Before (ProvideValue pattern - ~40 lines)

var dataTemplateExtension = new global::Microsoft.Maui.Controls.Xaml.DataTemplateExtension();
dataTemplateExtension.TypeName = "local:CustomCell";
var xamlServiceProvider = new global::Microsoft.Maui.Controls.Xaml.Internals.XamlServiceProvider(__root);
var iProvideValueTarget = new global::Microsoft.Maui.Controls.Xaml.Internals.SimpleValueTargetProvider(
    new object?[] {collectionView, __root},
    global::Microsoft.Maui.Controls.ItemsView.ItemTemplateProperty,
    new [] { iNameScope },
    __root);
xamlServiceProvider.Add(typeof(global::Microsoft.Maui.Controls.Xaml.IReferenceProvider), iProvideValueTarget);
xamlServiceProvider.Add(typeof(global::Microsoft.Maui.Controls.Xaml.IProvideValueTarget), iProvideValueTarget);
var xmlNamespaceResolver = new global::Microsoft.Maui.Controls.Xaml.Internals.XmlNamespaceResolver();
xmlNamespaceResolver.Add("__f__", "http://schemas.microsoft.com/dotnet/2021/maui");
xmlNamespaceResolver.Add("__g__", "http://schemas.microsoft.com/dotnet/maui/global");
xmlNamespaceResolver.Add("", "http://schemas.microsoft.com/dotnet/2021/maui");
xmlNamespaceResolver.Add("x", "http://schemas.microsoft.com/winfx/2009/xaml");
xmlNamespaceResolver.Add("local", "clr-namespace:Test");
xamlServiceProvider.Add(typeof(global::Microsoft.Maui.Controls.Xaml.IXamlTypeResolver), new global::Microsoft.Maui.Controls.Xaml.Internals.XamlTypeResolver(xmlNamespaceResolver, typeof(global::Test.TestPage).Assembly));
xamlServiceProvider.Add(typeof(global::Microsoft.Maui.Controls.Xaml.IXmlLineInfoProvider), new global::Microsoft.Maui.Controls.Xaml.Internals.XmlLineInfoProvider(new global::Microsoft.Maui.Controls.Xaml.XmlLineInfo(7, 18)));
var dataTemplate = (global::Microsoft.Maui.Controls.DataTemplate)((global::Microsoft.Maui.Controls.Xaml.IMarkupExtension<global::Microsoft.Maui.Controls.DataTemplate>)dataTemplateExtension).ProvideValue(xamlServiceProvider);
collectionView.SetValue(global::Microsoft.Maui.Controls.ItemsView.ItemTemplateProperty, dataTemplate);

After (KnownMarkup - ~2 lines)

var dataTemplateExtension = new global::Microsoft.Maui.Controls.DataTemplate(typeof(global::Test.CustomCell));
collectionView.SetValue(global::Microsoft.Maui.Controls.ItemsView.ItemTemplateProperty, dataTemplateExtension);

Benefits

  1. Simpler Generated Code: ~95% reduction in code size per DataTemplate usage
  2. Better Performance: Direct constructor calls instead of reflection-based ProvideValue
  3. Compile-Time Type Resolution: Type errors caught during compilation
  4. Better Code Quality: Easier to read and debug generated code
  5. Consistency: Follows the same pattern as TypeExtension, StaticExtension, etc.

Testing

✅ All 75 SourceGen unit tests pass
✅ 2 new DataTemplate-specific tests added and passing
✅ No regressions in existing functionality

Issues Fixed

Fixes #32760

@StephaneDelcroix
Implement DataTemplateExtension as KnownMarkup for simpler code gener…
1140a99 
…ation

- Add ProvideValueForDataTemplateExtension to KnownMarkups.cs
- Register DataTemplateExtension in GetKnownEarlyMarkupExtensions
- Create comprehensive unit tests for DataTemplate markup extension
- Generate direct DataTemplate constructor calls instead of ProvideValue pattern
- Reduces generated code from ~40 lines to ~2 lines per usage
- All 75 SourceGen unit tests pass
Copilot AI review requested due to automatic review settings November 20, 2025 09:02
@StephaneDelcroix StephaneDelcroix added area-xaml XAML, CSS, Triggers, Behaviors xsg Xaml sourceGen labels Nov 20, 2025
@StephaneDelcroix StephaneDelcroix added this to the .NET 10.0 SR2 milestone Nov 20, 2025
Copilot AI reviewed Nov 20, 2025
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Pull Request Overview

This PR successfully optimizes DataTemplateExtension by implementing it as a KnownMarkup in the XAML source generator, achieving ~95% code reduction and eliminating reflection overhead. The implementation follows the established pattern used by TypeExtension and other early markup extensions.

Key Changes

  • Added ProvideValueForDataTemplateExtension method that resolves type names at compile-time and generates direct DataTemplate constructor calls
  • Registered DataTemplateExtension as an early markup extension alongside TypeExtension, StaticExtension, etc.
  • Added comprehensive unit tests validating the optimized code generation for both custom and built-in types

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File Description
src/Controls/tests/SourceGen.UnitTests/InitializeComponent/DataTemplateMarkupExtension.cs New test file with two tests covering DataTemplate usage with custom ViewCell types and built-in Label controls, validating simplified generated code
src/Controls/src/SourceGen/NodeSGExtensions.cs Registration of DataTemplateExtension in GetKnownEarlyMarkupExtensions dictionary to enable compile-time optimization
src/Controls/src/SourceGen/KnownMarkups.cs Core implementation that resolves TypeName to Type at compile-time and generates direct constructor calls, following TypeExtension pattern with proper error handling and fallback logic

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StephaneDelcroix commented Nov 20, 2025

/azp run MAUI-UITests-public

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@StephaneDelcroix StephaneDelcroix mentioned this pull request Nov 20, 2025
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@StephaneDelcroix StephaneDelcroix merged commit 4667153 into main Nov 20, 2025
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@StephaneDelcroix StephaneDelcroix deleted the datatemplate-knownmarkup branch November 20, 2025 20:19
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@simonrozsival simonrozsival simonrozsival approved these changes

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area-xaml XAML, CSS, Triggers, Behaviors xsg Xaml sourceGen

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.NET 10.0 SR2

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Optimize DataTemplateExtension as KnownMarkup in source generator

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