Add `BindablePropertyDefaultValueCreatorAnalyzer` to to avoid Static References from being passed into `CreateDefaultValueMethodName` when using `[BindableProperty]` and `[AttachedBindableProperty<T>]`. by TheCodeTraveler · Pull Request #3096 · CommunityToolkit/Maui

TheCodeTraveler · 2026-02-14T22:48:23Z

Description of Change

This PR continues the effort started in #3095 to avoid Static References from being passed into CreateDefaultValueMethodName when using [BindableProperty] and [AttachedBindableProperty<T>].

This PR adds the BindablePropertyDefaultValueCreatorAnalyzer to detect these scenarios and generate a Warning when one is found. This Analyzer is public and will also be leveraged by any developer using CommunityToolkit.Maui. It also adds a comprehensive unit test suite to verify the different scenarios where a static reference may be passed into CreateDefaultValueMethodName.

To ensure we on the Community Toolkit team do not introduce improper usage I have promoted this Warning to an Error in Directory.Build.props: <WarningsAsErrors>MCT003</WarnindsAsErrors>.

Lastly, this PR fixes the one discovered violation of this new Analyzer, found in NavigationBar.CreateColorDefaultValue.

PR Checklist

Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
Has tests (if omitted, state reason in description)
Has samples (if omitted, state reason in description)
Rebased on top of main at time of PR
Changes adhere to coding standard

Additional information

This PR also adds Benchmarks for the new Analyzer

Copilot

Pull request overview

This pull request adds a new Roslyn analyzer (BindablePropertyDefaultValueCreatorAnalyzer, diagnostic ID MCT003) to detect and prevent the use of static readonly fields or properties as return values in DefaultValueCreatorMethodName methods for both BindableProperty and AttachedBindableProperty attributes. This continues the bug fix from PR #3095, which addressed an issue where shared static instances caused state to be inadvertently shared across multiple BindableObject instances.

Changes:

Adds a new analyzer that detects static readonly references in DefaultValueCreator methods and emits a warning
Promotes the MCT003 warning to an error in Directory.Build.props to enforce compliance
Fixes one violation found in NavigationBar.CreateColorDefaultValue by replacing Colors.Transparent with Color.FromUint(0u)
Includes comprehensive unit tests covering various scenarios including conditional expressions, switch expressions, and edge cases

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs	New analyzer implementation that detects static readonly field/property returns in DefaultValueCreator methods with support for complex expressions
src/CommunityToolkit.Maui.Analyzers/Resources.resx	Added localized resource strings for the new analyzer diagnostic messages
src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs	Auto-generated resource accessor code with version update to 18.0.0.0
src/CommunityToolkit.Maui.Analyzers.UnitTests/BindablePropertyDefaultValueCreatorAnalyzerTests.cs	Comprehensive test suite with 22 tests covering positive and negative cases for BindableProperty
src/CommunityToolkit.Maui.Analyzers.UnitTests/AttachedBindablePropertyDefaultValueCreatorAnalyzerTests.cs	Comprehensive test suite with 19 tests covering positive and negative cases for AttachedBindableProperty
src/CommunityToolkit.Maui/PlatformConfiguration/AndroidSpecific/NavigationBar.shared.cs	Fixed violation by changing from Colors.Transparent to Color.FromUint(0u)
src/CommunityToolkit.Maui/CommunityToolkit.Maui.csproj	Added project reference to the Analyzers project
Directory.Build.props	Added MCT003 to WarningsAsErrors to promote the warning to an error

Files not reviewed (1)

src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

…ueCreatorAnalyzer.cs Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 1 comment.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

...ommunityToolkit.Maui.Analyzers.UnitTests/BindablePropertyDefaultValueCreatorAnalyzerTests.cs

Copilot

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Copilot reviewed 8 out of 9 changed files in this pull request and generated 1 comment.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs

Copilot

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Copilot reviewed 10 out of 11 changed files in this pull request and generated no new comments.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

bijington

The changes look good. Just one question around whether we should be covering the const option

...Toolkit.Maui.Analyzers.UnitTests/AttachedBindablePropertyDefaultValueCreatorAnalyzerTests.cs

…ultValue

TheCodeTraveler · 2026-02-21T19:18:34Z

The changes look good. Just one question around whether we should be covering the const option

Thanks Shaun! Nah, we're good. The bug occurs when a static reference is used that is writable. Since we can't write to a const, it won't produce the bug.

Copilot

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Copilot reviewed 10 out of 11 changed files in this pull request and generated no new comments.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

Copilot

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Copilot reviewed 10 out of 11 changed files in this pull request and generated 4 comments.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

Comments suppressed due to low confidence (1)

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs:332

The diagnostic message/resources say "static readonly field or property", but the analyzer logic flags any static field/property (regardless of readonly). Either update the analyzer to check readonly as well, or adjust the rule title/message/description (and related helper method names) to match the intended behavior (e.g., warn on any static shared instance).

}
}

Copilot · 2026-02-23T01:05:20Z

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

+	static MethodDeclarationSyntax? FindMethodInType(TypeDeclarationSyntax typeDeclaration, string methodName)
+	{
+		return typeDeclaration
+			.DescendantNodes()
+			.OfType<MethodDeclarationSyntax>()
+			.FirstOrDefault(method => method.Identifier.ValueText == methodName);
+	}


FindMethodInType uses DescendantNodes(), which can pick up methods inside nested types and miss methods declared in other partial declarations of the same type (in different files). Consider resolving the containing type symbol via the semantic model and using INamedTypeSymbol.GetMembers(methodName) (or restricting to direct members) to avoid false positives/negatives.

Copilot · 2026-02-23T01:05:20Z

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

+	static bool DoesReturnStaticReadOnlyFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)
+	{
+		var returnStatements = methodDeclaration
+			.DescendantNodes()
+			.OfType<ReturnStatementSyntax>();
+


DoesReturnStaticReadOnlyFieldOrProperty enumerates return statements via DescendantNodes(), which also walks into lambdas/local functions inside the method. A nested return inside a lambda can incorrectly trigger the diagnostic even if the default value creator itself returns a new instance. Consider limiting traversal to the method body excluding nested functions/lambdas.

...ommunityToolkit.Maui.Analyzers.UnitTests/BindablePropertyDefaultValueCreatorAnalyzerTests.cs

src/CommunityToolkit.Maui.Analyzers/Resources.resx

Copilot

Pull request overview

Copilot reviewed 10 out of 11 changed files in this pull request and generated 5 comments.

Files not reviewed (1)

src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

Directory.Build.props

src/CommunityToolkit.Maui.Analyzers/AnalyzerReleases.Shipped.md

src/CommunityToolkit.Maui/PlatformConfiguration/AndroidSpecific/NavigationBar.shared.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

TheCodeTraveler · 2026-02-23T01:18:15Z

Thanks @pictos + @bijington! Could we get one more review?

I've updated the Analyzer to support both Delegate and const. Great recommendations 🙌

Copilot

Pull request overview

Copilot reviewed 10 out of 11 changed files in this pull request and generated 2 comments.

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src/CommunityToolkit.Maui.Analyzers/Resources.Designer.cs: Language not supported

Copilot · 2026-02-23T01:20:50Z

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

+		return propertyDeclaration;
+	}
+
+	static bool DoesReturnStaticReadOnlyFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)


The method name "DoesReturnStaticReadOnlyFieldOrProperty" suggests it only checks for readonly static members, but the implementation at line 324 actually checks for ANY static field (non-const) or static property, regardless of whether it's readonly. Consider renaming to "DoesReturnStaticFieldOrProperty" to better reflect the actual behavior and avoid confusion.

Suggested change

static bool DoesReturnStaticReadOnlyFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)

static bool DoesReturnStaticFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)

Copilot · 2026-02-23T01:20:50Z

src/CommunityToolkit.Maui.Analyzers/BindablePropertyDefaultValueCreatorAnalyzer.cs

+		return false;
+	}
+
+	static bool DoesDelegateInitializerReturnStaticReadOnlyMember(SyntaxNode memberDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)


The method name "DoesDelegateInitializerReturnStaticReadOnlyMember" suggests it only checks for readonly static members, but the implementation delegates to "IsStaticFieldOrProperty" which checks for ANY static field (non-const) or static property. Consider renaming to "DoesDelegateInitializerReturnStaticMember" to better reflect the actual behavior.

…ultValue

TheCodeTraveler added 4 commits February 14, 2026 14:28

Add Analyzers

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Update BindablePropertyDefaultValueCreatorAnalyzerTests.cs

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Update NavigationBar.shared.cs

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Update BindablePropertyDefaultValueCreatorAnalyzerBenchmarks.cs

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Merge branch 'main' into Remove-All-Static-References-From-CreateDefa…

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…ultValue

	static bool DoesReturnStaticReadOnlyFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)
	static bool DoesReturnStaticFieldOrProperty(MethodDeclarationSyntax methodDeclaration, SemanticModel semanticModel, CancellationToken cancellationToken)

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TheCodeTraveler commented Feb 14, 2026 •

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