[SR-8763] Compiler hangs when passing inner enum as a generic base class parameter

[MaxDesiatov]

Previous ID	SR-8763
Radar	None
Original Reporter	@MaxDesiatov
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 9.4.1 Swift version 4.1.2 (swiftlang-902.0.54 clang-902.0.39.2) and Xcode 10.0 GM (Swift version 4.2 (swiftlang-1000.11.37.1 clang-1000.11.45.1) on mac 10.13.6

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: eddb8fbacb12de4d44e8f1efd4b3473b

is duplicated by:

• SR-9160 Nested enums, passed as generic to superclass, cannot conform to RawRepresentable (or inline conform to any other protocol)

Issue Description:

This code causes the compiler to hang in an infinite loop:

import Foundation

class Base<P> {
}

final class Derived: Base<Derived.Inner> {
  enum Inner: Hashable {
  }
}

Interestingly enough, removing `Hashable` makes a difference, this code compiles without a problem:

import Foundation

class Base<P> {
}

final class Derived: Base<Derived.Inner> {
  enum Inner {
  }
}

[belkadan]

Seems to be fixed on master.

[belkadan]

@rjmccall, I knew we had run-time issues with this at one point, but I didn't realize it made a compile-time difference too.

[rjmccall]

Sure, it's not too hard to write naive recursion in the compiler.

[belkadan]

Adding a test case in #23920