[net11.0] Compile x:Reference bindings against resolved element type by StephaneDelcroix · Pull Request #34513 · dotnet/maui

StephaneDelcroix · 2026-03-17T12:11:23Z

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Description

Follow-up to #34501 (which targets main with a minimal fix).

This PR enhances x:Reference binding compilation for net11.0 by resolving the referenced element's type and compiling the binding against it, instead of skipping compilation entirely.

What it does

When a binding uses Source={x:Reference Name}, the source generator now:

Walks namescopes to find the referenced element's type (e.g., ContentPage for x:Reference PageRoot, Label for x:Reference StatusLabel)
Compiles the binding against the resolved type when the path is fully resolvable (e.g., Path=Text on a Label)
Falls back silently to runtime binding when the path can't be resolved (e.g., Path=BindingContext.SelectItemCommand where BindingContext is object)

Key design decision: `out Diagnostic?` on `TryParsePath`

The MAUIG2045 ("property not found") diagnostic is now returned as an out parameter from TryParsePath/TryCompileBinding instead of being emitted directly. This lets the caller decide:

x:DataType bindings: emit MAUIG2045 as before (no behavior change)
x:Reference bindings: suppress MAUIG2045 and fall back to runtime (these were never compiled before, so a new warning would be a regression)

Tests added

BindingWithXReferenceSourceInDataTemplate_DoesNotReportFalsePositive — verifies no false MAUIG2045 for Path=BindingContext.X
BindingWithXReferenceToNonRootElement_ResolvesCorrectType — verifies Path=Text against a referenced Label compiles with no warnings
Maui34490.xaml — XAML unit test reproducing the original issue
Updated Gh3606 test — binding to Content via x:Reference now compiles

Fixes #34490

github-actions · 2026-03-17T12:11:32Z

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34513

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34513"

Copilot

Pull request overview

Enhances the XAML source generator on net11.0 to compile Binding expressions that use Source={x:Reference ...} by resolving the referenced element’s type (via namescopes) and using that type for binding-path compilation, while suppressing MAUIG2045 for x:Reference scenarios that can’t be resolved statically.

Changes:

Update binding compilation to resolve x:Reference source element types and compile against them (falling back to runtime binding without MAUIG2045 regressions).
Refactor compiled-binding diagnostics so MAUIG2045 can be returned to the caller (enabling conditional suppression/reporting).
Add/update unit tests covering x:Reference bindings in templates and type-resolution scenarios.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Controls/src/SourceGen/KnownMarkups.cs	Resolves `x:Reference` source types and conditionally suppresses/report MAUIG2045 based on binding origin.
src/Controls/src/SourceGen/CompiledBindingMarkup.cs	Changes compiled-binding path parsing to return (not directly emit) property-not-found diagnostics.
src/Controls/tests/SourceGen.UnitTests/BindingDiagnosticsTests.cs	Adds generator-level tests to ensure no false-positive MAUIG2045 and correct referenced-type resolution.
src/Controls/tests/Xaml.UnitTests/Issues/Maui34490.xaml	Adds XAML reproduction for the DataTemplate + `x:Reference` scenario.
src/Controls/tests/Xaml.UnitTests/Issues/Maui34490.xaml.cs	Adds XAML unit test asserting diagnostics behavior for the reproduced scenario.
src/Controls/tests/Xaml.UnitTests/Issues/Gh3606.xaml.cs	Updates an existing issue test intended to validate x:Reference source-type-based compilation.

src/Controls/tests/Xaml.UnitTests/Issues/Maui34490.xaml.cs

+				// BindingContext is 'object' on BindableObject, so SelectItemCommand warning on 'object' is expected,
+				// but a warning mentioning Maui34490ItemModel would mean it's still resolving against the wrong type.
+				Assert.DoesNotContain(result.Diagnostics, d => d.Id == "MAUIG2045" && d.GetMessage().Contains("Maui34490ItemModel", StringComparison.Ordinal));


simonrozsival · 2026-03-30T07:56:15Z

src/Controls/src/SourceGen/KnownMarkups.cs

+		// When Source={x:Reference Name} is set on a binding, resolves the referenced element's type
+		// by walking namescopes (same logic as ProvideValueForReferenceExtension).
+		// Returns null if Source is not an x:Reference or the name cannot be resolved.
+		static ITypeSymbol? TryResolveXReferenceSourceType(ElementNode bindingNode, SourceGenContext context)
+		{
+			if (!bindingNode.Properties.TryGetValue(new XmlName("", "Source"), out INode? sourceNode)
+				&& !bindingNode.Properties.TryGetValue(new XmlName(null, "Source"), out sourceNode))
+				return null;
+
+			if (sourceNode is not ElementNode refNode)
+				return null;
+
+			if (refNode.XmlType.Name is not "ReferenceExtension" and not "Reference")
+				return null;
+
+			// Extract the Name from the x:Reference markup
+			if (!refNode.Properties.TryGetValue(new XmlName("", "Name"), out INode? refNameNode)
+				&& !refNode.Properties.TryGetValue(new XmlName(null, "Name"), out refNameNode))
+			{
+				refNameNode = refNode.CollectionItems.Count > 0 ? refNode.CollectionItems[0] : null;
+			}
+
+			if (refNameNode is not ValueNode vn || vn.Value is not string name)
+				return null;
+
+			// Walk namescopes to find the referenced element's type
+			ElementNode? node = bindingNode;
+			var currentContext = context;
+			while (currentContext is not null && node is not null)
+			{
+				while (currentContext is not null && !currentContext.Scopes.ContainsKey(node))
+					currentContext = currentContext.ParentContext;
+				if (currentContext is null)
+					break;
+				var namescope = currentContext.Scopes[node];
+				if (namescope.namesInScope != null && namescope.namesInScope.ContainsKey(name))
+					return namescope.namesInScope[name].Type;
+				INode n = node;
+				while (n.Parent is ListNode ln)
+					n = ln.Parent;
+				node = n.Parent as ElementNode;
+			}
+
+			return null;
+		}


I agree with copilot here

simonrozsival · 2026-03-30T08:01:00Z

src/Controls/tests/Xaml.UnitTests/Issues/Gh3606.xaml.cs

+		internal void BindingsWithXReferenceSourceResolveAgainstReferencedType(XamlInflator inflator)
 		{
+			// Source={x:Reference page} points to ContentPage, which has a Content property.
+			// The binding path "Content" resolves against ContentPage, so the source generator
+			// compiles it instead of falling back to runtime Binding.
 			var view = new Gh3606(inflator);

 			var binding = view.Label.GetContext(Label.TextProperty).Bindings.GetValue();
-			Assert.IsType<Binding>(binding);
+			Assert.IsAssignableFrom<BindingBase>(binding);
 		}


I agree with copilot here, we should assert that the binding was compiled.

When a binding uses Source={x:Reference}, resolve the referenced element's type by walking namescopes and compile the binding against it. This enables compiled bindings for paths like Path=Text on a referenced Label. When the path can't be fully resolved (e.g. Path=BindingContext.X where BindingContext is 'object'), fall back silently to runtime binding without emitting MAUIG2045 — these bindings were never compiled before, so a new warning would be a regression. The MAUIG2045 diagnostic is moved from TryParsePath to the caller via an out parameter, letting the caller decide whether to emit it (only for x:DataType-sourced bindings, not x:Reference). Fixes #34490 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-03-30T07:54:30Z

src/Controls/src/SourceGen/KnownMarkups.cs

+			if (!bindingNode.Properties.TryGetValue(new XmlName("", "Source"), out INode? sourceNode)
+				&& !bindingNode.Properties.TryGetValue(new XmlName(null, "Source"), out sourceNode))


One day I'll make copilot an ext method TryGetPropertyNode("Source", out INode? sourceNode) 😆

simonrozsival

I think we could take this a step further and detect the type of BindingContext on the referenced node and correctly cast the BindingContext in the path. I can look into this in a follow up PR though.

Copilot AI review requested due to automatic review settings March 17, 2026 12:11

Copilot started reviewing on behalf of StephaneDelcroix March 17, 2026 12:12 View session

Copilot AI reviewed Mar 17, 2026

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github-actions bot mentioned this pull request Mar 18, 2026

[repo-status] 📊 Daily Repo Status - March 18, 2026 #34523

Closed

simonrozsival mentioned this pull request Mar 27, 2026

[Proposal] [XSG] Reduce compiled binding friction #34696

Open

StephaneDelcroix force-pushed the 34490-xref-compile-net11 branch from 893c4b9 to 6df5147 Compare March 30, 2026 07:36

simonrozsival reviewed Mar 30, 2026

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simonrozsival mentioned this pull request Mar 30, 2026

[XSG] Pre-compute x:DataType with PropagateDataTypeVisitor #34740

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simonrozsival approved these changes Apr 1, 2026

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StephaneDelcroix merged commit 150310c into net11.0 Apr 1, 2026
36 of 39 checks passed

StephaneDelcroix deleted the 34490-xref-compile-net11 branch April 1, 2026 08:16

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[net11.0] Compile x:Reference bindings against resolved element type#34513

[net11.0] Compile x:Reference bindings against resolved element type#34513
StephaneDelcroix merged 1 commit intonet11.0from
34490-xref-compile-net11

StephaneDelcroix commented Mar 17, 2026

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		if (!bindingNode.Properties.TryGetValue(new XmlName("", "Source"), out INode? sourceNode)
		&& !bindingNode.Properties.TryGetValue(new XmlName(null, "Source"), out sourceNode))

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StephaneDelcroix commented Mar 17, 2026

Description

What it does

Key design decision: out Diagnostic? on TryParsePath

Tests added

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Pull request overview

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Key design decision: `out Diagnostic?` on `TryParsePath`

github-actions bot commented Mar 17, 2026 •

edited

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