Enabling upcoming feature ExistentialAny does not work for standard library protocols.

[ensan-hcl]

Description

Enabling upcoming feature ExistentialAny does not work for standard library protocols.

For example, it should produce a compile error, considering Decoder is a bare protocol. However, the compiler does not produce any error or warning, even though for other non-standard library protocols it produces errors and warnings correctly.

init(from decoder: Decoder) throws { /* ... */ }

Steps to reproduce

1. swift repl -enable-upcoming-feature ExistentialAny
2. put following;

protocol P {}
extension Int: P {}

3. put following:

let value: P = 42

It produces an error

expression failed to parse:
error: repl.swift:5:12: error: use of protocol 'P' as a type must be written 'any P'
let value: P = 42
           ^
           any P

4. put following;

let value: Codable = 42

It works!

Expected behavior
Codable should also produce a compile error, but it doesn't.

Environment

• Swift compiler version info

  swiftc -version
  swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
  Target: x86_64-apple-macosx13.0
  

• Xcode version info

  Xcode 14.3
  Build version 14E222b
  

• Deployment target: N/A

As I checked, it seems any P check is not working for standard library protocols without associated types including Codable, Decoder, Encoder, CustomStringConvertible, CustomDebugStringConvertible, ExpressibleBy*Literal, and so on.

Forum thread: https://forums.swift.org/t/any-p-check-doesnt-work-for-standard-library-protocols/64276

[ensan-hcl]

Thanks!