Call ApplyStyling unconditionally in MeasureCore

[Fachep]

What does the pull request do?

This PR moves ApplyStyling earlier in Layoutable.MeasureCore.

What is the current behavior?

Layoutable.MeasureCore currently applies styling after checking visibility, even though styling may affect the control's visibility.

Due to this, if a style in Window.Styles sets the IsVisible property of a control inside WindowDrawnDecorationsContent to false, the control is hidden but still reports its full size during the first measurement pass.

What is the updated/expected behavior with this PR?

Layoutable.MeasureCore now applies styling before performing visibility checks and measurement.

Controls hidden via styles now correctly produce an empty desired size in the same scenario. A unit test has been added to verify this behavior.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Fixed issues

Fixes #21570

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR fixes a layout/measurement issue where styling (e.g., setting IsVisible=false via styles) was not applied early enough to influence measurement, particularly for drawn window decorations.

Changes:

• Added a unit test covering measurement of WindowDrawnDecorationsContent when styling hides a control.
• Adjusted Layoutable.MeasureCore to apply styling before checking IsVisible, ensuring style-driven visibility changes are respected during measure.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
tests/Avalonia.Controls.UnitTests/WindowTests.cs	Adds regression test ensuring styled visibility affects measurement of drawn decoration overlay content.
src/Avalonia.Base/Layout/Layoutable.cs	Applies styling earlier in measure so style changes (like visibility) take effect before measurement logic runs.

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0066351-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cla-avalonia]

• All contributors have signed the CLA.

[Fachep]

@cla-avalonia agree

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0066393-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0066581-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[Fachep]

I have no idea about the failed integration test. It was the Windows test last time, after rebase to master it becomes the Mac test this time...

[avaloniaui-bot]

You can test this PR using the following package version. 12.1.999-cibuild0067229-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[Fachep]

@MrJul Can you review this pls?

[MrJul]

You found a core framework bug here. It manifests more easily on WindowDrawnDecorations since that class doesn't have as many ApplyStyling() calls as standard controls, but the issue is real. See the test I added to your branch, which fails before this PR, with standard controls, no decorations involved: 4cb4192

I've modified the PR to just apply styles unconditionally in MeasureCore: 99% of the time they're already applied, so the call returns early and is basically free. It's also cheaper than checking IsVisible twice in a row, as you did (getting the value of a dependency property incurs a minimal cost, but it compounds in Measure/Arrange due to the sheer number of calls).

[avaloniaui-bot]

You can test this PR using the following package version. 12.2.999-cibuild0068509-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]