Windows Form warnings (#45189)

* Windows Form warnings

* date

Author: Cam Soper

docs/core/compatibility/10.0.md

@@ -56,6 +56,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 
 | Title                                                                                                             | Type of change      | Introduced version |
 |-------------------------------------------------------------------------------------------------------------------|---------------------|--------------------|
+| [API obsoletions](windows-forms/10.0/obsolete-apis.md)                                                    | Source incompatible | Preview 1          |
 | [Renamed parameter in HtmlElement.InsertAdjacentElement](windows-forms/10.0/insertadjacentelement-orientation.md) | Source incompatible | Preview 1          |
 | [TreeView checkbox image truncation](windows-forms/10.0/treeview-text-location.md)                                | Behavioral change   | Preview 1          |
 | [StatusStrip uses System RenderMode by default](windows-forms/10.0/statusstrip-renderer.md)                       | Behavioral change   | Preview 1          |

docs/core/compatibility/toc.yml

@@ -44,6 +44,8 @@ items:
                 href: sdk/10.0/custom-build-event-warning.md
           - name: Windows Forms
             items:
+              - name: API obsoletions
+                href: windows-forms/10.0/obsolete-apis.md
               - name: Renamed parameter in HtmlElement.InsertAdjacentElement
                 href: windows-forms/10.0/insertadjacentelement-orientation.md
               - name: TreeView checkbox image truncation
@@ -2124,6 +2126,8 @@ items:
         items:
           - name: .NET 10
             items:
+              - name: API obsoletions
+                href: windows-forms/10.0/obsolete-apis.md
               - name: Renamed parameter in HtmlElement.InsertAdjacentElement
                 href: windows-forms/10.0/insertadjacentelement-orientation.md
               - name: TreeView checkbox image truncation

docs/core/compatibility/windows-forms/10.0/obsolete-apis.md

@@ -0,0 +1,62 @@
+---
+title: "Breaking change: .NET 10 obsoletions in Windows Forms"
+titleSuffix: ""
+description: Learn about the .NET 10 breaking change where some Windows Forms APIs have been marked as obsolete.
+ms.date: 03/10/2025
+---
+# Windows Forms obsoletions (.NET 10)
+
+Some Windows Forms APIs have been marked as obsolete, starting in .NET 10.
+
+## Previous behavior
+
+In previous .NET versions, these APIs can be used without any build warning.
+
+## New behavior
+
+In .NET 10 and later versions, use of these APIs produces a compile-time warning with a custom diagnostic ID. The use of custom diagnostic IDs allows you to suppress the warnings individually instead of blanket-suppressing all obsoletion warnings.
+
+The following table lists the custom diagnostic IDs and their corresponding warning messages.
+
+| Diagnostic ID | Description | Severity | Version introduced |
+| - | - |
+| [WFDEV004](/dotnet/desktop/winforms/wfdev-diagnostics/wfdev004) | <xref:System.Windows.Forms.Form.OnClosing(System.ComponentModel.CancelEventArgs)?displayProperty=nameWithType>, <xref:System.Windows.Forms.Form.OnClosed(System.EventArgs)?displayProperty=nameWithType> and the corresponding events are obsolete. Use <xref:System.Windows.Forms.Form.OnFormClosing(System.Windows.Forms.FormClosingEventArgs)?displayProperty=nameWithType>, <xref:System.Windows.Forms.Form.OnFormClosed(System.Windows.Forms.FormClosedEventArgs)?displayProperty=nameWithType>, <xref:System.Windows.Forms.Form.FormClosing?displayProperty=nameWithType> and <xref:System.Windows.Forms.Form.FormClosed?displayProperty=nameWithType> instead. | Warning | Preview 1 |
+| [WFDEV005](/dotnet/desktop/winforms/wfdev-diagnostics/wfdev005) | <xref:System.Windows.Clipboard.GetData(System.String)?displayProperty=nameWithType> method is obsolete. Use <xref:System.Windows.Forms.Clipboard.TryGetData*?displayProperty=nameWithType> methods instead. | Warning | Preview 1 |
+| [WFDEV006](/dotnet/desktop/winforms/wfdev-diagnostics/wfdev006) | <xref:System.Windows.Forms.ContextMenu>, <xref:System.Windows.Forms.DataGrid>, <xref:System.Windows.Forms.MainMenu>, <xref:System.Windows.Forms.Menu>, <xref:System.Windows.Forms.StatusBar>, <xref:System.Windows.Forms.ToolBar> are obsolete. They're provided for binary compatibility with .NET Framework. | Warning | Preview 1 |
+
+## Version introduced
+
+.NET 10
+
+## Type of breaking change
+
+These obsoletion warnings can affect [source compatibility](../../categories.md#source-compatibility).
+
+## Recommended action
+
+- Follow the specific guidance provided for the each diagnostic ID using the URL link provided on the warning.
+- If necessary, you can suppress the warning using the custom `WFDEVxxx` diagnostic ID value.
+
+## Affected APIs
+
+### WFDEV004
+
+- <xref:System.Windows.Forms.Form.OnClosing(System.ComponentModel.CancelEventArgs)>
+- <xref:System.Windows.Forms.Form.OnClosed(System.EventArgs)?displayProperty=fullName>
+
+### WFDEV005
+
+- <xref:System.Windows.Clipboard.GetData(System.String)?displayProperty=fullName>
+
+### WFDEV006
+
+- <xref:System.Windows.Forms.ContextMenu?displayProperty=fullName>
+- <xref:System.Windows.Forms.DataGrid?displayProperty=fullName>
+- <xref:System.Windows.Forms.MainMenu?displayProperty=fullName>
+- <xref:System.Windows.Forms.Menu?displayProperty=fullName>
+- <xref:System.Windows.Forms.StatusBar?displayProperty=fullName>
+- <xref:System.Windows.Forms.ToolBar?displayProperty=fullName>
+
+## See also
+
+- [Obsolete Windows Forms features in .NET 10+](/dotnet/desktop/winforms/wfdev-diagnostics/obsoletions-overview)