[XSG] Fix Setter.Value property element lookup for MauiGlobalUri namespace

[StephaneDelcroix]

Note

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Description

Fixes #34039

When <Setter.Value> is used as a property element, GetValueNode() in SetterValueProvider.cs looked up the Value property only by two specific namespace URIs ("" and MauiUri). When the property element resolved to MauiGlobalUri instead, the lookup returned null. Since PR #33681 changed the null-return behavior to a skip sentinel, this caused the Setter to be removed from Variables entirely, preventing the .Add() call from being generated.

Root Cause

GetValueNode() checked only two namespace URIs:

node.Properties.TryGetValue(new XmlName("", "Value"), out valueNode)
node.Properties.TryGetValue(new XmlName(XamlParser.MauiUri, "Value"), out valueNode)

Property elements like <Setter.Value> inherit their namespace URI from the XML reader, which varies depending on the xmlns declaration used. When the XAML used MauiGlobalUri, neither existing check matched, so GetValueNode() returned null, triggering the skip sentinel introduced in #33681, which suppressed the Setters.Add() call.

Fix

Added MauiGlobalUri as a third namespace to check in the GetValueNode() lookup chain:

!node.Properties.TryGetValue(new XmlName("", "Value"), out valueNode) &&
!node.Properties.TryGetValue(new XmlName(XamlParser.MauiUri, "Value"), out valueNode) &&
!node.Properties.TryGetValue(new XmlName(XamlParser.MauiGlobalUri, "Value"), out valueNode) &&

Testing

• Added XAML unit test (Maui34039) verifying Setter with property element value in a Trigger
• Added SourceGen unit test (SetterValueInTrigger) verifying correct codegen
• Tests fail without fix, pass with fix

[Copilot]

Pull request overview

This PR fixes a .NET MAUI XAML Source Generator (XSG) regression where Setter instances using the <Setter.Value> property element could be dropped (and therefore not added to Trigger.Setters) when implicit/alternative xmlns declarations caused the Value property element’s namespace URI to differ from the previously hard-coded lookups.

Changes:

• Update SetterValueProvider.GetValueNode() to locate the Value property element by LocalName == "Value" regardless of namespace URI.
• Add a SourceGen unit test reproducing the issue with implicit xmlns and verifying the generated code contains the Setters.Add(...) call.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Controls/src/SourceGen/SetterValueProvider.cs	Makes <Setter.Value> lookup namespace-agnostic so XSG doesn’t drop setters when property-element namespaces vary.
src/Controls/tests/SourceGen.UnitTests/InitializeComponent/SetterValueInTrigger.cs	Adds a regression test covering <Setter.Value> inside a Trigger under implicit xmlns conditions.