Deserialized error type 'Self'

Has anyone seen an error like this before?

<unknown>:0: error: deserialized error type 'Self' in module 'MyProject'

I don't see anything else out of the ordinary in the build log. The error appears twice: once for a file I'm working on, and then again for a file I haven't edited recently.

No errors show up while I'm editing the file in Xcode, and it still flags syntax errors and such, so why this comes up during a build but not during editing is mysterious.

I ended up finding a workaround. The situation is that I have a protocol similar to SwiftUI.View, where there is a property with a result builder on it:

public protocol DynamicTable {
    associatedtype SectionID: Hashable
    associatedtype RowID: Hashable

    @TableBuilder<SectionID, RowID> var model: TableModel<SectionID, RowID> { get }
}

If I remove the @TableBuilder part, the error goes away, and everything actually still works. Implementors of the protocol need to specify @TableBuilder on their model property either way.

This is with Xcode 13.0.