Do not activate the form if MinimumSize changes

[LeafShi1]

Fixes #13698

Root Cause

In the original code, changing the MinimumSize of a form calls SetWindowPos with the flag SWP_NOZORDER. While this ensures that the Z-order of the forms is unchanged, it is not enough to prevent the affected forms from becoming active.

Proposed changes

• In UpdateMinimumSize of Form.cs add SET_WINDOW_POS_FLAGS.SWP_NOACTIVATE so that the form is not automatically activated when the MinimumSize property changes

Customer Impact

• Setting MinimumSize will not activate form

Regression?

• No

Risk

• Minimal

Screenshots

Before

BeforeChange.mp4

After

AfterChanges.mp4

Test methodology

• Manually
• Unit test

Test environment(s)

• .net 10.0.0-preview.7.25365.101

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR fixes an issue where changing a form's MinimumSize property would unintentionally activate the form, disrupting the display order of multiple forms. The fix adds the SWP_NOACTIVATE flag to prevent unwanted form activation during minimum size updates.

• Adds SWP_NOACTIVATE flag to SetWindowPos call in UpdateMinimumSize method
• Includes a unit test to verify the fix prevents display order changes

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/System.Windows.Forms/System/Windows/Forms/Form.cs	Adds SWP_NOACTIVATE flag to prevent form activation when updating minimum size
src/test/integration/UIIntegrationTests/FormTests.cs	Adds test to verify form display order remains unchanged when MinimumSize is set

Comments suppressed due to low confidence (2)

src/test/integration/UIIntegrationTests/FormTests.cs:169

• The test assertion logic is flawed. TopMost is a property that can be set independently and doesn't indicate display order, while Focused only tells us about input focus, not visual z-order. This test may produce false positives or negatives. Consider using Windows API calls to check actual z-order or a more reliable method to verify form layering.

        Assert.True(form2.TopMost || form2.Focused, "Form2 should be displayed in front of Form1");

src/test/integration/UIIntegrationTests/FormTests.cs:175

• Same assertion logic issue as line 169. The test uses the same flawed logic to verify the fix worked. A robust test should verify that the z-order or activation state hasn't changed, rather than relying on TopMost or Focused properties which don't accurately represent visual display order.

        Assert.True(form2.TopMost || form2.Focused, "Form2 should still be displayed in front after setting MinimumSize");

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.58047%. Comparing base (118a672) to head (72a84c0).
Report is 11 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (118a672) and HEAD (72a84c0). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (118a672)	HEAD (72a84c0)
Debug	3	2
test	1	0

Additional details and impacted files

@@                 Coverage Diff                  @@
##                main      #13715          +/-   ##
====================================================
- Coverage   76.82947%   51.58047%   -25.24901%     
====================================================
  Files           3257        2063        -1194     
  Lines         642592      287762      -354830     
  Branches       47565       42059        -5506     
====================================================
- Hits          493700      148429      -345271     
+ Misses        145232      136448        -8784     
+ Partials        3660        2885         -775     

Flag	Coverage Δ
Debug	51.58047% <100.00000%> (-25.24901%)	⬇️
integration	18.99905% <100.00000%> (+0.00886%)	⬆️
production	51.58047% <100.00000%> (+0.13880%)	⬆️
test	?
unit	48.95990% <100.00000%> (+0.13918%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Epica3055]

looks good

[ricardobossan]

All LGTM!

[filipnavara]

Thanks!