10.0.20 breaks implicit styles

[JPfahl]

Description

After switching to 10.0.20 most of my implicit styles are not being applied to my xaml. This worked fine in 10.0.11 and every previous release for years. I use implicit styling for almost all of my xaml. This is in a debug build on multiple platforms. I have tried turning SourceGen off and on, no effect. Seems to work at least sometimes for classes basedon native maui classes, but anything based on them does not get styled.

Steps to Reproduce

Just compile and run the app, it is unusable as most of the styling is missing.

Link to public reproduction project repository

No response

Version with bug

10.0.20

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

10.0.11

Affected platforms

Windows, Android

Affected platform versions

Android 35, windows 10.0.19041.0

Did you find any workaround?

No

Relevant log output

[PureWeen]

@StephaneDelcroix

[StephaneDelcroix]

Issue33203Repro.zip

Reproduction Attempt

I attempted to reproduce this issue but was unable to confirm the regression with my test scenario.

What I tested:

1. Native MAUI controls (Button, Label) with implicit styles
2. Derived controls (CustomButton : Button, CustomLabel : Label) with implicit styles for the derived types

Test Results:

• All existing XAML unit tests for implicit styles pass (15 tests)
• The ApplyToDerivedTypes functionality tests pass
• Style inheritance via BasedOn tests pass

Important Note:

By default, implicit styles only apply to the exact type specified in TargetType, NOT to derived types. For example:

• <Style TargetType="Button"> only applies to Button instances, NOT to CustomButton : Button
• To have styles apply to derived types, you must use ApplyToDerivedTypes="True" on the Style

Request:

Could you please provide a minimal reproduction project that demonstrates the issue? The description mentions "classes based on native maui classes" not getting styled - a concrete example would help us identify if this is:

1. A regression in style resolution
2. A change in expected behavior
3. A specific scenario not covered by existing tests

I'm attaching a reproduction attempt project (targeting 10.0.20) that you can use as a starting point. Please modify it to demonstrate the issue you're seeing.

[JPfahl]

I have attached a sample page that demonstrates the issue, the second border should be red. I have to define the style with a key because it will be used as the base for multiple descendants. This has worked perfectly for years until 10.0.20, I have been using Maui since the first beta was available. I have thousands of lines of styles in our Maui library. For example BorderBase has 16 unique descendants . I have also tested the attached sample in 10.011 and it works properly. I normally define the styles in a resource dictionary and reference that dictionary in the app.xaml, but I embedded them in the page for simplicity.

StyleIssueDemo.zip