incorrect warning "Instance method of non-Sendable type 'Self.Type' cannot be marked as '@Sendable'"

[lukaskollmer]

Description

marking a static function in a protocol as @Sendable causes the compiler to emit a warning "Instance method of non-Sendable type 'Self.Type' cannot be marked as '@sendable'", which doesn't seem to be correct since a) the method in question is a static method rather than an instance method, and b) it's irrelevant if the type is Sendable (bc it's a static method...)

Reproduction

protocol P {
    @Sendable static func f()
    // ^ Instance method of non-Sendable type 'Self.Type' cannot be marked as '@Sendable'
}

Expected behavior

this should work without warnings

Environment

swift-driver version: 1.127.14.1 Apple Swift version 6.2.1 (swiftlang-6.2.1.4.8 clang-1700.4.4.1)
Target: arm64-apple-macosx15.0

Additional information

i'm able to reproduce this when compiling an SPM package using swift build and when compiling via Xcode, but it seems that using either swiftc or swift to compile just a single file containing just this protocol definition compiles without emitting the warning

[jamieQ]

i think this may be an expected consequence of the 'isolated conformances' feature (see the proposal and search for 'sendable metatype'). if you write it like this:

protocol P: SendableMetatype {
    @Sendable static func f()
}

you should no longer get that error.

[lukaskollmer]

@jamieQ interesting; thanks pointing this out!

even then, tbh, i still feel like the warning could be clearer to explain what's going on...

[jamieQ]

i agree that the diagnostic seems like it could be more helpful/explanatory. edit: maybe that's what this issue should be used to track?