Add breaking change for Thread.Abort (RC1)

docs/core/compatibility/3.1-5.0.md

@@ -150,6 +150,7 @@ If you're migrating from version 3.1 of .NET Core, ASP.NET Core, or EF Core to v
 
 ## Core .NET libraries
 
+- [Thread.Abort is obsolete](#threadabort-is-obsolete)
 - [Obsolete properties on ConsoleLoggerOptions](#obsolete-properties-on-consoleloggeroptions)
 - [Hardware intrinsic IsSupported checks may differ for nested types](#hardware-intrinsic-issupported-checks-may-differ-for-nested-types)
 - [Parameter names changed in reference assemblies](#parameter-names-changed-in-reference-assemblies)
@@ -168,6 +169,10 @@ If you're migrating from version 3.1 of .NET Core, ASP.NET Core, or EF Core to v
 - [CounterSet.CreateCounterSetInstance now throws InvalidOperationException if instance already exist](#countersetcreatecountersetinstance-now-throws-invalidoperationexception-if-instance-already-exists)
 - [Microsoft.DotNet.PlatformAbstractions package removed](#microsoftdotnetplatformabstractions-package-removed)
 
+[!INCLUDE [thread-abort-obsolete](../../../includes/core-changes/corefx/5.0/thread-abort-obsolete.md)]
+
+***
+
 [!INCLUDE [obsolete-consoleloggeroptions-properties](../../../includes/core-changes/corefx/5.0/obsolete-consoleloggeroptions-properties.md)]
 
 ***

docs/core/compatibility/corefx.md

@@ -11,6 +11,7 @@ The following breaking changes are documented on this page:
 
 | Breaking change | Version introduced |
 | - | :-: |
+| [Thread.Abort is obsolete](#threadabort-is-obsolete) | 5.0 |
 | [Obsolete properties on ConsoleLoggerOptions](#obsolete-properties-on-consoleloggeroptions) | 5.0 |
 | [Hardware intrinsic IsSupported checks may differ for nested types](#hardware-intrinsic-issupported-checks-may-differ-for-nested-types) | 5.0 |
 | [Parameter names changed in reference assemblies](#parameter-names-changed-in-reference-assemblies) | 5.0 |
@@ -47,6 +48,10 @@ The following breaking changes are documented on this page:
 
 ## .NET 5.0
 
+[!INCLUDE [thread-abort-obsolete](../../../includes/core-changes/corefx/5.0/thread-abort-obsolete.md)]
+
+***
+
 [!INCLUDE [obsolete-consoleloggeroptions-properties](../../../includes/core-changes/corefx/5.0/obsolete-consoleloggeroptions-properties.md)]
 
 ***

includes/core-changes/corefx/5.0/thread-abort-obsolete.md

@@ -0,0 +1,76 @@
+### Thread.Abort is obsolete
+
+The <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> APIs are obsolete. Projects that target .NET 5.0 or a later version will encounter compile-time warnings if these methods are called. If you suppress the warnings, a <xref:System.PlatformNotSupportedException> will be thrown at run time.
+
+#### Change description
+
+Previously, calls to <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> did not produce compile-time warnings, however, the method did throw a <xref:System.PlatformNotSupportedException> at run time.
+
+Starting in .NET 5.0, <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> is marked obsolete as warning. Calling this method produces compiler warning `SYSLIB0006`. The implementation of the method is unchanged, and it continues to throw a <xref:System.PlatformNotSupportedException>.
+
+#### Reason for change
+
+Given that <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> always throws a <xref:System.PlatformNotSupportedException> on all .NET implementations except .NET Framework, <xref:System.ObsoleteAttribute> was added to the method to draw attention to places where it's called.
+
+#### Version introduced
+
+5.0 RC 1
+
+#### Recommended action
+
+- Use a <xref:System.Threading.CancellationToken> to abort processing of a unit of work instead of calling <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType>. The following example illustrates the use of <xref:System.Threading.CancellationToken>.
+
+  ```csharp
+  void ProcessPendingWorkItemsNew(CancellationToken cancellationToken)
+  {
+      if (QueryIsMoreWorkPending())
+      {
+          // If the CancellationToken is marked as "needs to cancel",
+          // this will throw the appropriate exception.
+          cancellationToken.ThrowIfCancellationRequested();
+
+          WorkItem work = DequeueWorkItem();
+          ProcessWorkItem(work);
+      }
+  }
+  ```
+
+  For more information, see [Cancellation in managed threads](../../../../docs/standard/threading/cancellation-in-managed-threads.md).
+
+- To suppress the compile-time warning, suppress warning code `SYSLIB0006`. The warning code is specific to <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> and suppressing it doesn't suppress other obsoletion warnings in your code. However, we recommend that you remove calls to <xref:System.Threading.Thread.Abort%2A?displayProperty=nameWithType> instead of suppressing the warning.
+
+  ```csharp
+  void MyMethod()
+  {
+  #pragma warning disable SYSLIB0006
+      Thread.CurrentThread.Abort();
+  #pragma warning restore SYSLIB0006
+  }
+  ```
+
+  You can also suppress the warning in the project file.
+
+  ```xml
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+    <!-- Disable "Thread.Abort is obsolete" warnings for entire project. -->
+    <NoWarn>$(NoWarn);SYSLIB0006</NoWarn>
+  </PropertyGroup>
+  ```
+
+#### Category
+
+- Core .NET libraries
+
+#### Affected APIs
+
+- <xref:System.Threading.Thread.Abort%2A?displayProperty=fullName>
+
+<!--
+
+#### Affected APIs
+
+- `Overload:System.Threading.Thread.Abort`
+
+-->