Do not reset user fonts in DataGridView

[RussKie]

Fixes #3033

Proposed changes

• Do not override user-configured font styles in the DataGridView whenever ambient (e.g. form's) font changes.
  This scenario is likely to occur when users migrate their applications from .NET Framework to .NET Core/.NET and wish to retain the original default font.

Whilst the behaviour goes all the way back to .NET Framework, it becomes a significant migration issue for projects that want to keep the original default font (that was changed in #656).

Customer Impact

• User will be able to migrate existing applications while retaining original default font (for .NET Framework).

Regression?

• Not direct, however a side effect of Default Font change in Set Control.Defaultfont to SystemFonts.MessageBoxFont #656

Risk

• Small

Screenshots

Before

After

Test methodology

• manual (via WinformsControlsTest project)
• unit tests

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Merging #3875 into release/5.0-rc2 will decrease coverage by 31.02774%.
The diff coverage is 0.00000%.

@@                    Coverage Diff                     @@
##           release/5.0-rc2       #3875          +/-   ##
==========================================================
- Coverage         67.60904%   36.58130%   -31.02774%     
==========================================================
  Files                 1408         921         -487     
  Lines               507123      250967      -256156     
  Branches             41178       36862        -4316     
==========================================================
- Hits                342861       91807      -251054     
+ Misses              158290      153877        -4413     
+ Partials              5972        5283         -689     

Flag	Coverage Δ
#Debug	36.58130% <0.00000%> (-31.02774%)	⬇️
#production	36.58130% <0.00000%> (+0.10318%)	⬆️
#test	?

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

[merriemcgaw]

@dreddy-work @Tanya-Solyanik @KlausLoeffelmann - do you all like this fix? Seems like a reasonable approach, but another set of eyes on it would be great. I know @RussKie has a bit more to do to polish things up, but if we can get this in for RC2 that would rock.

[dreddy-work]

@RussKie , did you investigate other controls that has text input? Are we confirming that this is happening to only DataGridView* controls?

[RussKie]

@JeremyKuhne I didn't include EMF-based tests as I ran into few issues with those (e.g. it wouldn't size columns, and we don't appear to have Font validators available).
I will add those to the master branch.

[RussKie]

did you investigate other controls that has text input? Are we confirming that this is happening to only DataGridView* controls?

Yes, appears to be only DGV cellstyles-related issue.

[JeremyKuhne]

I didn't include EMF-based tests as I ran into few issues with those (e.g. it wouldn't size columns, and we don't appear to have Font validators available).

We do have a text out validator- it is how we validate the button text. What records were you getting that you couldn't validate?

[RussKie]

Tested by CTI.

[Tanya-Solyanik]

@merriemcgaw, @RussKie , @OliaG - is there a place to document the scenario that this change is breaking? Perhaps in the application migration guide?

[merriemcgaw]

@merriemcgaw Merrie McGaw FTE, @ru, @OliaG Olia Gavrysh FTE - is there a place to document the scenario that this change is breaking? Perhaps in the application migration guide?

@RussKie , do you have all the info you need to doc the breaking change?

[RussKie]

This will need to be doc'ed in https://docs.microsoft.com/en-us/dotnet/core/compatibility/winforms once we take it.

[RussKie]

I've revisited the fix, and we can do away with the new property. All the existing and interactive test results remained positive:

However I found another related bug or ("feature" if you like) that makes it very awkward user experience. If one of DefaultCellStyle properties is reset (e.g. dataGridView1.DefaultCellStyle.Font = null;) it becomes no longer possible to update it, and the whole style object must be re-assigned.
This is due to the logic here:

winforms/src/System.Windows.Forms/src/System/Windows/Forms/DataGridView.cs

Lines 2072 to 2115 in 1185aac

	else if (_defaultCellStyle.BackColor == Color.Empty ||
	_defaultCellStyle.ForeColor == Color.Empty ||
	_defaultCellStyle.SelectionBackColor == Color.Empty ||
	_defaultCellStyle.SelectionForeColor == Color.Empty ||
	_defaultCellStyle.Font is null ||
	_defaultCellStyle.Alignment == DataGridViewContentAlignment.NotSet ||
	_defaultCellStyle.WrapMode == DataGridViewTriState.NotSet)
	{
	DataGridViewCellStyle defaultCellStyleTmp = new DataGridViewCellStyle(_defaultCellStyle)
	{
	Scope = DataGridViewCellStyleScopes.None
	};
	if (_defaultCellStyle.BackColor == Color.Empty)
	{
	defaultCellStyleTmp.BackColor = s_defaultBackColor;
	}
	if (_defaultCellStyle.ForeColor == Color.Empty)
	{
	defaultCellStyleTmp.ForeColor = base.ForeColor;
	_dataGridViewState1[State1_AmbientForeColor] = true;
	}
	if (_defaultCellStyle.SelectionBackColor == Color.Empty)
	{
	defaultCellStyleTmp.SelectionBackColor = DefaultSelectionBackBrush.Color;
	}
	if (_defaultCellStyle.SelectionForeColor == Color.Empty)
	{
	defaultCellStyleTmp.SelectionForeColor = DefaultSelectionForeBrush.Color;
	}
	if (_defaultCellStyle.Font is null)
	{
	defaultCellStyleTmp.Font = base.Font;
	_dataGridViewState1[State1_AmbientFont] = true;
	}
	if (_defaultCellStyle.Alignment == DataGridViewContentAlignment.NotSet)
	{
	defaultCellStyleTmp.AlignmentInternal = DataGridViewContentAlignment.MiddleLeft;
	}
	if (_defaultCellStyle.WrapMode == DataGridViewTriState.NotSet)
	{
	defaultCellStyleTmp.WrapModeInternal = DataGridViewTriState.False;
	}
	defaultCellStyleTmp.AddScope(this, DataGridViewCellStyleScopes.DataGridView);
	return defaultCellStyleTmp;

This isn't something we're fixing in the context of this PR, or in .NET 5.0 timeframe.

[merriemcgaw]

This isn't something we're fixing in the context of this PR, or in .NET 5.0 timeframe.

@RussKie can you file a separate issue for this related potential problem?

[RussKie]

Docs: dotnet/docs#20803