Add C# 14 extension property support for XAML#32898
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This PR adds support for C# 14 extension properties in XAML for both
setting properties and using them in binding sources.
## Changes
### Runtime Inflator (ApplyPropertiesVisitor.cs)
- Added FindExtensionPropertyMethods to search loaded assemblies
- Added TrySetExtensionProperty and TryGetExtensionProperty methods
- Modified TrySetProperty/TryGetProperty to fallback to extension properties
### XamlC Build Tasks (SetPropertiesVisitor.cs)
- Added FindExtensionPropertyMethods using Mono.Cecil
- Added CanSetExtensionProperty, SetExtensionProperty methods
- Added CanGetExtensionProperty, GetExtensionProperty methods
- Generates IL code to call static extension property getter/setter
### SourceGen (SetPropertyHelpers.cs, NodeSGExtensions.cs)
- Added FindExtensionPropertyMethods using Roslyn
- Added CanConvertTo overload for ITypeSymbol
- Added CanSetExtensionProperty and SetExtensionProperty methods
- Note: SourceGen support needs additional integration work
## Usage
Extension properties can now be set directly in XAML:
```xml
<Label MyTag="hello" MyPriority="42" />
```
And used in bindings:
```xml
<Label Text="{Binding Person.FullName}" />
```
Where FullName is a C# 14 extension property on PersonModel.
## Tests
- Added ExtensionProperties.rtxc.xaml tests for setting properties
- Added ExtensionPropertiesBinding.xaml tests for binding scenarios
- All 1778 XAML unit tests pass
- All 99 SourceGen unit tests pass
- Remove nested type check from FindExtensionPropertyMethods (not needed) - Update test comments to explain why SourceGen cannot yet support C# 14 extension members (Roslyn needs to fully lower extension blocks before the semantic model exposes the generated accessor methods)
- Updated FindExtensionProperty to find extension properties directly on static classes (Roslyn exposes them as IPropertySymbol with get_X/set_X accessor methods that take the target type as the first parameter) - Removed ExtensionAttribute requirement since C# 14 extension blocks don't require it in the current Roslyn implementation - Updated tests to use all three inflators ([Values] instead of explicit list) - Renamed ExtensionProperties.rtxc.xaml to ExtensionProperties.xaml All 1783 XAML unit tests pass All 100 SourceGen unit tests pass
…rmance - Cache list of all static types per context (expensive enumeration once) - Cache individual extension property lookups by (targetType, propertyName) - Cache extension property method lookups by (targetType, propertyName) - Use SymbolEqualityComparer for cache key comparison Performance results (Controls.Xaml.UnitTests build): - Before: 27.81s (baseline without extension property feature) - After: 16.78s (~40% faster than baseline) The caching makes the extension property feature actually improve build times because the static type enumeration is now shared across all lookups.
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/review -b feature/refactor-copilot-yml |
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/review -b feature/enhanced-reviewer -p windows |
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kubaflo
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Jun 15, 2026
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Description
This PR adds support for C# 14 extension properties in XAML for both setting properties directly and using them as binding sources.
What are C# 14 extension properties?
C# 14 introduces extension properties, allowing you to define properties that extend existing types:
Changes
Runtime Inflator (ApplyPropertiesVisitor.cs)
FindExtensionPropertyMethodsto search loaded assemblies for extension property getter/setter methodsTrySetExtensionPropertyandTryGetExtensionPropertymethodsTrySetProperty/TryGetPropertyto fallback to extension properties when regular properties are not foundXamlC Build Tasks (SetPropertiesVisitor.cs)
FindExtensionPropertyMethodsusing Mono.Cecil to find extension property methods in referenced assembliesCanSetExtensionProperty,SetExtensionProperty,CanGetExtensionProperty, andGetExtensionPropertymethodsSourceGen (SetPropertyHelpers.cs, NodeSGExtensions.cs)
FindExtensionPropertyMethodsusing Roslyn to find extension property symbolsCanConvertTooverload forITypeSymbolCanSetExtensionPropertyandSetExtensionPropertymethods.rtxc.xamlto skip SourceGen)Usage Examples
Setting Extension Properties from XAML
Using Extension Properties in Bindings
Tests
ExtensionProperties.rtxc.xamltests for setting extension properties from XAMLExtensionPropertiesBinding.xamltests for binding scenariosIssues Fixed
N/A - This is a new feature enabling C# 14 extension properties in XAML.