Fix XamlC to respect ObsoleteAttribute message and isError parameter by StephaneDelcroix · Pull Request #32946 · dotnet/maui

StephaneDelcroix · 2025-12-01T20:11:31Z

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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

Fixes #23961

This PR fixes XamlC to properly handle the ObsoleteAttribute by:

Extracting and displaying the custom message from [Obsolete("message")] instead of a generic deprecation message
Respecting the isError parameter - when [Obsolete("message", error: true)] is used, XamlC now emits an error (XC0619) instead of a warning (XC0618)
Adding obsolete type detection for classes marked with [Obsolete] when used in XAML

Changes

ErrorMessages.resx: Updated ObsoleteProperty message format to include the custom message: "{0}" is deprecated: {1}
BuildException.cs: Added XC0619 (ObsoletePropertyError) for error cases when isError=true
SetPropertiesVisitor.cs:
- Added TryGetObsoleteAttribute() helper to extract message and isError from the attribute
- Added LogObsoleteWarningOrError() helper that logs the appropriate warning or error based on the attribute
- Updated property/field obsolete checking to use these helpers
CreateObjectVisitor.cs: Added obsolete type detection when XAML elements are created

Before

XamlC warning XC0618: Property, Property setter or BindableProperty "MyProperty" is deprecated.

After

XamlC warning XC0618: "MyProperty" is deprecated: Use NewProperty instead.
XamlC error XC0619: "MyProperty" is obsolete: This property will be removed in the next version.

Testing

Added Maui23961.xaml / .cs - tests for warnings with error: false
Added Maui23961Error.rt.xaml / .cs - tests for errors with error: true
All 1780+ existing Xaml.UnitTests pass
Samples build successfully

Copilot

Pull request overview

This PR enhances XamlC to properly handle the ObsoleteAttribute by extracting and displaying custom messages and respecting the isError parameter to differentiate between warnings (XC0618) and errors (XC0619).

Adds helper methods TryGetObsoleteAttribute() and LogObsoleteWarningOrError() to extract obsolete attribute information and log appropriate diagnostics
Updates error message resources to include custom messages from ObsoleteAttribute
Extends obsolete checking to types in addition to properties, fields, and bindable properties

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Controls/tests/Xaml.UnitTests/Issues/Maui23961Error.xaml.cs	Test code for obsolete attributes with `error: true` parameter
src/Controls/tests/Xaml.UnitTests/Issues/Maui23961Error.rt.xaml	XAML test file for obsolete error cases
src/Controls/tests/Xaml.UnitTests/Issues/Maui23961.xaml.cs	Test code for obsolete attributes with `error: false` parameter (warnings)
src/Controls/tests/Xaml.UnitTests/Issues/Maui23961.xaml	XAML test file for obsolete warning cases
src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj	Adds XC0619 to WarningsNotAsErrors to allow compilation of test files with obsolete errors
src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs	Implements obsolete attribute extraction logic and refactors obsolete checking to use new helper methods
src/Controls/src/Build.Tasks/ErrorMessages.resx	Updates error messages for obsolete warnings and errors to include custom messages
src/Controls/src/Build.Tasks/CreateObjectVisitor.cs	Adds obsolete type checking when XAML elements are created
src/Controls/src/Build.Tasks/BuildException.cs	Adds XC0619 error code for obsolete errors

Copilot · 2025-12-01T20:21:32Z

src/Controls/tests/Xaml.UnitTests/Issues/Maui23961Error.xaml.cs

+			else
+			{
+				// Runtime doesn't check for obsolete at compile time
+				var page = new Maui23961Error(inflator);


The constructor call new Maui23961Error(inflator) will fail because the class only has a parameterless constructor public Maui23961Error() => InitializeComponent(); (line 14). This parameterized constructor pattern with XamlInflator is not defined for this class.

Looking at other test files, the XamlInflator parameter constructor is typically auto-generated for regular XAML files (not .rt.xaml). However, this is a .rt.xaml file (runtime-only), which means the auto-generated XamlInflator constructor won't exist.

The test logic on lines 46-56 appears to have incorrect branching. For the XamlInflator.SourceGen case, it correctly recognizes that .rt.xaml files aren't processed, but the else block (line 51-56) attempts to use a non-existent constructor.

Consider revising the test to either:

Use the parameterless constructor: var page = new Maui23961Error();

Skip the runtime test path entirely for .rt.xaml files since they're meant for runtime-only processing

Suggested change

var page = new Maui23961Error(inflator);

var page = new Maui23961Error();

Copilot · 2025-12-01T20:21:32Z

src/Controls/src/Build.Tasks/ErrorMessages.resx

  </data>
  <data name="ObsoleteProperty" xml:space="preserve">
-    <value>Property, Property setter or BindableProperty "{0}" is deprecated.</value>
+    <value>"{0}" is deprecated: {1}</value>


The error message uses "is obsolete" while the warning message uses "is deprecated". For consistency with C# compiler behavior, both should use the same terminology. The C# compiler uses "is obsolete" for both warnings (CS0618) and errors (CS0619).

Consider changing the warning message from "{0}" is deprecated: {1} to "{0}" is obsolete: {1} to match standard C# compiler terminology and maintain consistency with the error message.

Suggested change

<value>"{0}" is deprecated: {1}</value>

<value>"{0}" is obsolete: {1}</value>

Copilot · 2025-12-01T20:21:33Z

src/Controls/src/Build.Tasks/SetPropertiesVisitor.cs

 			}

-			if (   dataTypeNode is ElementNode enode
+			if (dataTypeNode is ElementNode enode


[nitpick] This whitespace change (removing spaces after if) is unrelated to the PR's purpose of fixing ObsoleteAttribute handling. The PR should focus only on changes directly related to the obsolete attribute functionality to keep the changes minimal and reviewable.

Consider reverting this whitespace change.

Suggested change

if (dataTypeNode is ElementNode enode

if ( dataTypeNode is ElementNode enode

github-actions · 2026-02-27T10:48:23Z

🚀 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 -- 32946

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 32946"

StephaneDelcroix · 2026-03-04T07:47:37Z

/azp run maui-pr-devicetests, maui-pr-uitests

azure-pipelines · 2026-03-04T07:47:52Z

Azure Pipelines successfully started running 2 pipeline(s).

simonrozsival · 2026-03-10T12:29:10Z

src/Controls/tests/Xaml.UnitTests/Issues/Maui23961Error.xaml.cs

It appears copilot messed up indentation in this file.

simonrozsival · 2026-03-10T12:29:25Z

src/Controls/tests/Xaml.UnitTests/Issues/Maui23961.xaml.cs

It appears copilot messed up indentation in this file.

MauiBot · 2026-03-23T00:25:50Z

⚠️ Merge Conflict Detected — This PR has merge conflicts with its target branch. Please rebase onto the target branch and resolve the conflicts.

Fixes #23961 - Extract and display the custom message from ObsoleteAttribute - Respect the isError parameter: when true, emit XC0619 error instead of XC0618 warning - Add obsolete type detection for classes used in XAML - Add XC0619 (ObsoletePropertyError) for error cases - Update message format to include the attribute's message text - Add unit tests for both warning and error scenarios

Samples use obsolete types like ListView, ViewCell, etc. which now trigger XC0618 warnings. Add these codes to WarningsNotAsErrors to prevent build failures when TreatWarningsAsErrors is enabled.

The TestResultPage.xaml uses Frame which is obsolete.

The ManualTests use obsolete types like TextCell in CollectionView tests.

The test now receives AggregateException when treatWarningsAsErrors is true because both the obsolete Compatibility.StackLayout type and the binding without DataType produce errors. Updated test to use Assert.Catch and verify the expected XC0022 error is present.

- LogObsoleteWarningOrError: call LogError directly when isError=true, bypassing LogWarningOrError which ignores error semantics - Maui23961Error test: assert MockCompiler.Compile throws for [Obsolete(error: true)] - Maui23989 test: document AggregateException from multiple warnings-as-errors - HostApp csproj: preserve $(WarningsNotAsErrors) to not clobber XC0618 suppression Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Xaml.UnitTests migrated from NUnit to xUnit on net11.0. Convert Maui23961.xaml.cs and Maui23961Error.xaml.cs to use xUnit patterns: [TestFixture] → [Collection], [Test]+[Values] → [Theory]+[XamlInflatorData], [SetUp]/[TearDown] → constructor/IDisposable, Assert.That → Assert.NotNull. Also revert Maui23989.xaml.cs to net11.0 version (had NUnit remnants). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add missing Maui23961ObsoleteClass2 type referenced in Maui23961.xaml - Fix Maui23961Error test to use parameterless ctor (rt.xaml has no XamlInflator ctor) - Add comments to WarningsNotAsErrors entries clarifying XC0619 behavior Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Maui23961Error.xaml.cs: Use Assert.ThrowsAny<Exception> instead of Assert.Throws<Exception> — multiple [Obsolete(error:true)] members produce an AggregateException, not a bare Exception. ThrowsAny handles both BuildException (single error) and AggregateException (multiple). - CreateObjectVisitor.cs: Guard LogObsoleteWarningOrError behind 'typedef != null' check to prevent NullReferenceException when a type reference cannot be resolved (ResolveCached returns null in that case). - Add XC0619 explanatory comment to 5 remaining project files (TestCases.HostApp, Essentials/samples, ProfiledAot, DeviceTests.Runners, ManualTests) for consistency with the other 2 files already commented. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Guard propertySetter.CustomAttributes against NRE when SetMethod is null in Set(): CanSet() already gates this path, but the guard makes Set() safe to call defensively if that invariant ever changes. - Document that XC0619 intentionally bypasses <NoWarn>, matching C# CS0619 behavior: obsolete-as-error cannot be suppressed, users must remove usage. - Document dual obsolete check: property declaration and setter are each checked separately, so both carrying [Obsolete] emits two diagnostics (matching C# compiler behavior). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The PR's new ObsoleteAttribute handling in XamlC now correctly emits XC0618 when XAML uses deprecated types. Maui23989.xaml was using Compatibility.StackLayout which carries [Obsolete], causing XC0618 to be emitted alongside XC0022. With treatWarningsAsErrors:true, both errors wrapped in AggregateException instead of the expected single BuildException, failing the test. Replace <cmp:StackLayout> with the standard <StackLayout> so XamlC only sees the expected XC0022 warning in the test scenario. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Change XC0618 message from 'deprecated' to 'obsolete' to match C# CS0618 - Add MockCompiler.Compile overload that exposes logged warnings - Assert ObsoleteWarningIncludesMessage verifies custom message text is present - Assert ObsoleteErrorProducesCompilationError verifies XC0619 code in exception Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

… number - Add StringComparison.Ordinal to string.Contains and Assert.Contains calls to satisfy CA1307 analyzer rule - Update Maui23989 expected error line from 12 to 11 after removing the cmp:StackLayout namespace prefix line from the XAML Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

StephaneDelcroix · 2026-03-30T16:19:25Z

/azp run

azure-pipelines · 2026-03-30T16:19:49Z

Azure Pipelines successfully started running 3 pipeline(s).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings December 1, 2025 20:11

Copilot started reviewing on behalf of StephaneDelcroix December 1, 2025 20:12 View session

StephaneDelcroix added the area-xaml XAML, CSS, Triggers, Behaviors label Dec 1, 2025

StephaneDelcroix added this to the .NET 10.0 SR3 milestone Dec 1, 2025

Copilot finished reviewing on behalf of StephaneDelcroix December 1, 2025 20:14

Copilot AI reviewed Dec 1, 2025

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PureWeen added this to MAUI SDK Ongoing Dec 30, 2025

github-project-automation bot moved this to Todo in MAUI SDK Ongoing Dec 30, 2025

PureWeen modified the milestones: .NET 10.0 SR3, .NET 10.0 SR4 Jan 21, 2026

StephaneDelcroix force-pushed the fix/23961-obsolete-attribute-handling branch from be916b2 to 600c3dc Compare February 11, 2026 20:33

StephaneDelcroix modified the milestones: .NET 10.0 SR4, .NET 11.0-preview2 Feb 11, 2026

StephaneDelcroix changed the base branch from main to net11.0 February 11, 2026 20:33

kubaflo mentioned this pull request Feb 20, 2026

[PR Review Queue] February 20, 2026 #34164

Closed

StephaneDelcroix force-pushed the fix/23961-obsolete-attribute-handling branch 2 times, most recently from d232169 to 087a2cc Compare February 24, 2026 19:17

StephaneDelcroix force-pushed the fix/23961-obsolete-attribute-handling branch 4 times, most recently from e44fb8a to 65f091e Compare March 3, 2026 16:50

StephaneDelcroix force-pushed the fix/23961-obsolete-attribute-handling branch from fe4328a to 2578ec0 Compare March 6, 2026 12:49

simonrozsival reviewed Mar 10, 2026

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src/Controls/tests/Xaml.UnitTests/Issues/Maui23961.xaml.cs

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It appears copilot messed up indentation in this file.

PureWeen modified the milestones: .NET 11.0-preview2, .NET 11.0-preview3 Mar 12, 2026

StephaneDelcroix and others added 13 commits March 30, 2026 13:35

Add XC0618/XC0619 to WarningsNotAsErrors in samples

9910711

Samples use obsolete types like ListView, ViewCell, etc. which now trigger XC0618 warnings. Add these codes to WarningsNotAsErrors to prevent build failures when TreatWarningsAsErrors is enabled.

Add XC0618/XC0619 to WarningsNotAsErrors in DeviceTests.Runners

cc974f9

The TestResultPage.xaml uses Frame which is obsolete.

Add XC0618/XC0619 to WarningsNotAsErrors in ManualTests

9e504c9

The ManualTests use obsolete types like TextCell in CollectionView tests.

StephaneDelcroix force-pushed the fix/23961-obsolete-attribute-handling branch from a57ab80 to a17d19a Compare March 30, 2026 12:13

This was referenced Mar 30, 2026

[MacCatalyst] Issue16918Test screenshot baseline flaky on all net11.0 builds #34622

Open

[MacCatalyst] Issue16918Test screenshot baseline flaky on all net11.0 builds #34624

Open

Fix indentation in Maui23961 test files

647e690

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival approved these changes Mar 31, 2026

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github-project-automation bot moved this from Todo to Approved in MAUI SDK Ongoing Mar 31, 2026

StephaneDelcroix merged commit fc266e3 into net11.0 Mar 31, 2026
31 of 36 checks passed

StephaneDelcroix deleted the fix/23961-obsolete-attribute-handling branch March 31, 2026 20:00

github-project-automation bot moved this from Approved to Done in MAUI SDK Ongoing Mar 31, 2026

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Fix XamlC to respect ObsoleteAttribute message and isError parameter#32946

Fix XamlC to respect ObsoleteAttribute message and isError parameter#32946
StephaneDelcroix merged 14 commits intonet11.0from
fix/23961-obsolete-attribute-handling

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	var page = new Maui23961Error(inflator);
	var page = new Maui23961Error();

	<value>"{0}" is deprecated: {1}</value>
	<value>"{0}" is obsolete: {1}</value>

	if (dataTypeNode is ElementNode enode
	if ( dataTypeNode is ElementNode enode

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StephaneDelcroix commented Dec 1, 2025

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