`any P` check doesn't work for standard library protocols

ensan-hcl · April 8, 2023, 7:44am

I recently enabled --enable-upcoming-feature ExistentialAny in my project. It produced a lot of compiled error, but after adding any they are resolved as expected.
After a while, I noticed there are still overlooked bare protocol.

For example, this is one of the cases.

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

It should be init(from decoder: any Decoder), but it does not produce compile error.

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

Is it a bug, or intended behavior?

Environment

Xcode Version 14.3 (14E222b)
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

ensan-hcl · April 9, 2023, 8:49am

I've opened an issue.

github.com/apple/swift

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

opened 08:47AM - 09 Apr 23 UTC

ensan-hcl

bug triage needed

**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; ```swift protocol P {} extension Int: P {} ``` 3. put following: ```swift 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; ```swift 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