Bad diagnostic when inheriting from class in extension

[AnthonyLatsis]

The following errors are misleading and could use a rewording as clear language rules, depending on the kinds of extended and inherited types.

protocol P {}
struct S {}
class C1 {}
class C2 {}

extension C2: S {} // error: inheritance from non-protocol type 'S'
extension C2: C1 {} // error: inheritance from non-protocol type 'C1'
extension C2: C1 & P {} // error: inheritance from class-constrained protocol composition type 'C1 & P'

Environment

• Swift version 5.9-dev (LLVM 6a04c4848990c70, Swift c1d5118)

NB: How to improve on these is left as an exercise to whoever takes the issue.

[StevenWong12]

Hey all, I'd like to give a try on solving this issue.😀

[Nallu-Swami]

Hello, can I work on this issue if no progress has been made yet for this issue?

[AnthonyLatsis]

@StevenWong12 Are you working on this?

[StevenWong12]

@Aringopalan Please feel free to take it😊

[Nallu-Swami]

Thanks a lot @AnthonyLatsis sir

[Nallu-Swami]

im really sorry i did that by mistake could you pls assign it back to me 😅

[Nallu-Swami]

The following errors are misleading and could use a rewording as clear language rules, depending on the kinds of extended and inherited types.

protocol P {}
struct S {}
class C1 {}
class C2 {}

extension C2: S {} // error: inheritance from non-protocol type 'S'
extension C2: C1 {} // error: inheritance from non-protocol type 'C1'
extension C2: C1 & P {} // error: inheritance from class-constrained protocol composition type 'C1 & P'

Environment

• Swift version 5.9-dev (LLVM 6a04c4848990c70, Swift f2bac1a22939a4d)

NB: How to improve on these is left as an exercise to whoever takes the issue.

Reviewing the code and after several tries i believe this to be one optimal rewording

protocol P {}
protocol S {}
class C1 {}
class C2class {}

extension C2class: S {}
class C2: C1 {} 
extension C2class:P {}

[Nallu-Swami]

If there is any further issue with the code ill work on it and reword it for better compilation

[StevenWong12]

I think the original vision of this issue is to rewrite the diagnostic message in the type check stage e.g.
error: class can only inherit from protocol in extension declaration

[Nallu-Swami]

I think the original vision of this issue is to rewrite the diagnostic message in the type check stage e.g.

error: class can only inherit from protocol in extension declaration

Ohhh 🫠, I did a total 360 here but I guess I can still work on it, rephrase all of them to be more readable.

[dk-talks]

Hey @Aringopalan , Are you still working on the issue?

[Nallu-Swami]

@dk-talks feel free to take it , im not working it.

[dk-talks]

Hey @AnthonyLatsis I have resolved this issues. Please have a look at my Pull Request. #65531