Using ArraySlice<Substring> in a Set causes a flaky crash

[abdulowork]

Describe the bug
Using ArraySlice<Substring> in a Set or as a Dictionary key crashes sometimes with Fatal error: Duplicate elements of type 'ArraySlice<Substring>'. The crash is not stable but wrapping it in a loop makes it easy to reproduce.

In the provided reproduction example changing any of the following fixes the crash:

1. Mapping ArraySlice<Substring> to ArraySlice<String>
2. Removing 🫠 emoji
3. Changing import A.C to import D.C

To Reproduce

1. Create the following main.swift file:

   import Foundation
   
   var tryCrashSwiftHashingAttempt = 0
   
   while true {
       tryCrashSwiftHashingAttempt += 1
       
       let example = """
           🫠
           import A.B
           import A.C
           """
       
       let lines = example.components(
           separatedBy: CharacterSet(charactersIn: "\u{000A}\u{000D}")
       )
       
       func splitImports(contents: String) -> [ArraySlice<Substring>] {
           let importIdentifier = contents.split(separator: " ").last!
           let importedParts = importIdentifier.split(separator: ".")
           
           return stride(from: 0, to: importedParts.count, by: 1).map {
               importedParts[0..<importedParts.count - $0]
           }
       }
       
       var mySet = Set<ArraySlice<Substring>>()
       
       let lastLine           = lines[lines.index(lines.endIndex, offsetBy: -1)]
       let lastBeforeLastLine = lines[lines.index(lines.endIndex, offsetBy: -2)]
       
       [lastLine, lastBeforeLastLine].forEach { line in
           splitImports(contents: line).forEach { slice in
               mySet.insert(slice)
           }
       }
       
       print(tryCrashSwiftHashingAttempt)
   }

2. Compile with swiftc main.swift or swiftc -O main.swift.
3. Run ./main
4. Within a couple of seconds the process should crash with:

   Fatal error: Duplicate elements of type 'ArraySlice<Substring>' were found in a Set.
   This usually means either that the type violates Hashable's requirements, or
   that members of such a set were mutated after insertion.
   

Expected behavior
The process doesn't crash

Screenshots

Environment (please complete the following information):

• OS: macOS 12.5
• Xcode Version:
  • 13.4
  • 14 beta 1

[YOCKOW]

🤔 I suspect that this is related to #59388.