duplicates:

• SR-2549 [CRTP] Non-generic class inheriting from a generic class with Self as generic parameter locks execution

Issue Description:

Even in one source file (i.e. not across compilation boundaries,) inheriting from a generic and using the derived class as a generic parameter results in a runtime crash. See included test case. This looks like a contrived example but comes up in frameworks code where the generic needs to know the type of the final class for type safety.

import XCTest

// swiftlint:disable private_over_fileprivate

fileprivate class G<T> {
    func foo(test: T) {
        print("\(test)")
    }
}

fileprivate class C: G<C> {

}

class TestSwiftSR6469: XCTestCase {
    func testSelfReferentialGeneric() {
        // this test breaks with locking loop at runtime
        _ = C()
    }
}