redundant sendable rule breaks code when a protocol has a sendable requirement

[andykent]

In our project we have 3 files:

struct MyModel: Equatable, Sendable { ... }

protocol MyProtocol: Sendable { ... }

extension MyModel: MyProtocol { ... }

using the redundantSendable the Sendable gets stripped from struct MyModel which results in a compilation error in the extension file:

Conformance to 'Sendable' must occur in the same source file as struct 'MyModel'; use '@unchecked Sendable' for retroactive conformance

We have had to disable this rule for now due to the compilation error..

[calda]

I see, this is not solvable in SwiftFormat other than disabling it in this case with // swiftformat:disable:next redundantSendable, or by restructuring the source code.

There's no way for SwiftFormat to know cross-file that the Sendable conformance on MyModel is not redundant.

@NachoSoto for thoughts, did this sort of thing come up in your codebase when adopting the rule?

[calda]

I wonder if this is actually a Swift compiler bug. Semantically, the extension in the other file is not adding a Sendable conformance, the type is already Sendable.

I will see if this can be fixed easily in the Swift compiler.

[NachoSoto]

Interesting. This didn't come up, but it's enough of an edge case that one would want to either explicitly ignore the rule in that line or do

extension MyModel: Sendable {}

Within the same file.