Open Radar

 
Summary:
Xcode 9 beta 1 is unable to build a workspace, where the app module's Swift code contains a subclass of an open class from a dependency module. The linker error only occurs if the said base open class is:

1. a nested type (e.g. is defined inside an empty struct), AND
2. contains a `private(set) public var` property

Xcode 8.x is able to build a workspace with such as setup fine and doesn't produce linker errors.

Steps to Reproduce:
1. Create an Xcode workspace with two Swift modules: an app and a framework dependency.
2. In the framework module, create a *nested* open class with a `private(set) public var` property.
3. In the app module, import the framework and create a subclass of the said base class and attempt to use it.
4. Build the workspace.

See attached sample project.

Expected Results:
The workspace builds and the app runs.

Observed Results:
The workspace fails to build with a linker error.

Version:
Xcode 9 beta 1 (9M136h), iOS 11 beta 1 SDK, running on macOS Sierra 10.12.5 (16F73).

Notes:
Workarounds that can be implemented to get such a workspace to build in Xcode 9 are:

* Un-nesting the base class (turning into a top level open class in the framework module), OR
* Changing the base class's `private(set)` property access level to `public`, OR
* Not subclassing the base class in the app module and simply using the base class directly all "resolve" the linker error.