RID-specific app breaking change

docs/core/compatibility/8.0.md

@@ -55,6 +55,7 @@ If you're migrating an app to .NET 8, the breaking changes listed here might aff
 | [CLI console output uses UTF-8](sdk/8.0/console-encoding.md)                    | Behavioral change/Source and binary incompatible | Preview 1  |
 | ['dotnet pack' uses Release configuration](sdk/8.0/dotnet-pack-config.md)       | Behavioral change/Source incompatible            | Preview 1  |
 | ['dotnet publish' uses Release configuration](sdk/8.0/dotnet-publish-config.md) | Behavioral change/Source incompatible            | Preview 1  |
+| [Runtime-specific apps no longer self-contained](sdk/8.0/runtimespecific-app-default.md) | Source/binary incompatible              | Preview 2  |
 
 ## Windows Forms
 

docs/core/compatibility/sdk/8.0/runtimespecific-app-default.md

@@ -0,0 +1,61 @@
+---
+title: "Breaking change: Runtime-specific apps no longer self-contained"
+description: Learn about a breaking change in the .NET 8 SDK where apps that specify a runtime identifier are no longer self-contained by default.
+ms.date: 03/09/2023
+---
+# Runtime-specific apps no longer self-contained
+
+Runtime-specific apps, or .NET apps with a `RuntimeIdentifier`, are no longer [self-contained](../../../deploying/index.md#publish-self-contained) by default. Instead, they are [framework-dependent](../../../deploying/index.md#publish-framework-dependent) by default.
+
+This is a breaking change in the following situations:
+
+- If you deployed, distributed, or published your app and didn't explicitly add the `SelfContained` property, but also didn't require that the .NET runtime be installed on the machine for it to work. In this case, you may have relied on the previous behavior to produce a non-framework-dependent app by default.
+
+- If you rely on the IL Link tool. In this case, you'll have to take the steps described under [Recommended action](#recommended-action) to use IL Link again.
+
+  > [!NOTE]
+  > Some publish properties, like `PublishTrimmed`, `PublishSingleFile`, and `PublishAot`, currently require `SelfContained` to work. If you use these properties, you'll need to add the `SelfContained` property.
+
+- For Blazor WebAssembly apps, because they relied on the previous behavior. However, the Blazor WASM team may side-step this breaking change in their SDK by adding `SelfContained` automatically for all apps, so Blazor customers shouldn't be affected.
+
+## Previous behavior
+
+Previously, if a runtime identifier (RID) was specified (via [RuntimeIdentifier](../../../project-sdk/msbuild-props.md#runtimeidentifier)), the app was published as self-contained, even if `SelfContained` wasn't explicitly specified.
+
+## New behavior
+
+Starting in .NET 8, for apps that target .NET 8 or a later version, `RuntimeIdentifier` no longer implies `SelfContained` by default. Instead, apps that specify a runtime identifier will be dependent on the .NET runtime by default (framework-dependent). Apps that target .NET 7 or earlier versions aren't affected.
+
+## Version introduced
+
+.NET 8 Preview 2
+
+## Type of breaking change
+
+This change can affect [source compatibility](../../categories.md#source-compatibility) and [binary compatibility](../../categories.md#binary-compatibility).
+
+## Reason for change
+
+- The new .NET SDK behavior aligns with Visual Studio behavior.
+- Framework-dependent apps are now smaller by default, since there aren't copies of .NET stored in each app.
+- Ideally, command-line options are orthogonal. In this case, the tooling supports both RID-specific self-contained deployment (SCD) and RID-specific framework-dependent deployment (FDD). So it didn't make sense that no RID defaulted to FDD and RID defaulted to SCD. This behavior was often confusing for users.
+
+.NET 6 alerted users to this breaking change with the following warning:
+
+**warning NETSDK1179: One of '--self-contained' or '--no-self-contained' options are required when '--runtime' is used.**
+
+Now that customers have had time to add `SelfContained` explicitly, we felt we could introduce the break.
+
+## Recommended action
+
+If you're using .NET 7 or an earlier version and relied on the previous behavior where `SelfContained` was inferred, you'll see this warning:
+
+**For projects with TargetFrameworks >= 8.0, RuntimeIdentifier no longer automatically gives a SelfContained app. To continue creating a .NET framework independent app after upgrading to 8.0, consider setting SelfContained explicitly.**
+
+Follow the guidance of the warning if you want to continue to produce self-contained apps. If you want to move to the new default, set `SelfContained` to `false` in the project file (`<SelfContained>false</SelfContained>`) or as a command-line argument, for example, `dotnet publish --no-self-contained`.
+
+If you're using .NET 8, you don't need to do anything unless you want to keep the previous behavior. In that case, set `SelfContained` to `true`.
+
+## See also
+
+- [.NET application publishing overview](../../../deploying/index.md)

docs/core/compatibility/toc.yml

@@ -50,6 +50,8 @@ items:
         href: sdk/8.0/dotnet-pack-config.md
       - name: "'dotnet publish' uses Release configuration"
         href: sdk/8.0/dotnet-publish-config.md
+      - name: Runtime-specific apps no longer self-contained
+        href: sdk/8.0/runtimespecific-app-default.md
     - name: Windows Forms
       items:
       - name: Anchor layout changes
@@ -1282,6 +1284,8 @@ items:
         href: sdk/8.0/dotnet-pack-config.md
       - name: "'dotnet publish' uses Release configuration"
         href: sdk/8.0/dotnet-publish-config.md
+      - name: Runtime-specific apps no longer self-contained
+        href: sdk/8.0/runtimespecific-app-default.md
     - name: .NET 7
       items:
       - name: Automatic RuntimeIdentifier for certain projects