Fix DarkMode (a) StatusStrip background renderer A11Y Regression.

[KlausLoeffelmann]

Fixes #12909.
Fixes #12663.
Fixes #12041.
Fixes #12040.
Fixes #12027.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.57018%. Comparing base (330a7c6) to head (85d701e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13360         +/-   ##
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- Coverage   62.58082%   62.57018%   -0.01065%     
===================================================
  Files           1560        1560                 
  Lines         159763      159763                 
  Branches       14915       14915                 
===================================================
- Hits           99981       99964         -17     
- Misses         59007       59024         +17     
  Partials         775         775                 

Flag	Coverage Δ
Debug	62.57018% <ø> (-0.01065%)	⬇️
integration	11.32273% <ø> (-0.00525%)	⬇️
production	40.74266% <ø> (-0.01766%)	⬇️
test	95.69342% <ø> (ø)
unit	38.12901% <ø> (-0.01038%)	⬇️

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[Copilot]

Pull Request Overview

This PR addresses several A11Y regressions related to DarkMode rendering by removing experimental diagnostic attributes and refining related rendering logic. Key changes include the removal of experimental DarkMode attributes in form APIs, the introduction and integration of a dedicated dark mode renderer in ToolStripSystemRenderer, and various rendering improvements in ToolStripRenderer and StatusStrip.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
FormCornerPreference.cs	Removed experimental diagnostic attribute for DarkMode support.
Form.cs	Removed experimental attribute on DarkMode–related properties and events.
ToolStripSystemRenderer.cs	Introduced a dedicated dark mode renderer and updated RendererOverride logic.
ToolStripRenderer.cs	Updated rendering paths and optimized array initializations for DarkMode disabled images.
ToolStrip.cs	Modified background painting to use renderer overrides when available.
StatusStrip.cs	Updated comment spelling for clarity.
PublicAPI.Unshipped.txt	Updated API documentation entries for FormCornerPreference and related events.

Comments suppressed due to low confidence (6)

src/System.Windows.Forms/System/Windows/Forms/FormCornerPreference.cs:11

• Verify that the removal of the experimental DarkMode diagnostic attribute is intended and that any related tooling or documentation has been updated accordingly.

-[Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]

src/System.Windows.Forms/System/Windows/Forms/Form.cs:2185

• Ensure that removing the experimental attribute from the Form properties aligns with production readiness for DarkMode, and update any related diagnostic handling as needed.

-    [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/StatusStrip.cs:121

• Correct the spelling of 'accomodate' to 'accommodate' in the comment for clarity.

// we do some custom stuff with padding to accomodate size grip.

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripSystemRenderer.cs:18

• Confirm that prioritizing high contrast mode over dark mode in the RendererOverride is intended and that the newly introduced dark mode renderer meets accessibility guidelines.

+    private ToolStripRenderer? _toolStripDarkModeRenderer;

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripRenderer.cs:855

• Review the logic change for rendering item check images to ensure that returning early when the image rectangle is empty or the image is null does not inadvertently skip intended rendering in edge cases.

+        if (imageRect == Rectangle.Empty || image is null)

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs:3651

• [nitpick] Ensure that using the renderer override to draw the ToolStrip background and returning early does not conflict with any custom rendering requirements that downstream consumers might have.

+            if (Renderer.RendererOverride is ToolStripRenderer renderer)