Swift 6 source-breaking change cause `Container.resolve(_:arguments:)` to change behavior from Swift 5 #571

alexandre-pod · 2024-07-28T14:57:48Z

Hi, by trying using Swinject on a project I am working on migrating to Swift 6, I encountered an issue caused by the a new behavior introduced by SE-0352 when using Swift 6.

Here the issue, that I tried in form of a test in ContainerTests_Arguments test suite :

This test pass when using Swift 5, but when using the new Swift 6 language mode (done with SWIFT_VERSION = 6 in build settings) the test no longer pass, and we got a nil from the resolve call.

func testContainerArgumentsWorksWithExistentials() throws {
    container.register(Person.self) { (r, animal: Animal) in PetOwner(pet: animal) }

    let animal: Animal = Cat(name: "cat")
    let person = container.resolve(Person.self, argument: animal)

    let petOwner = try XCTUnwrap(person as? PetOwner) // error: XCTUnwrap failed: expected non-nil value of type "PetOwner"
    let cat = try XCTUnwrap(petOwner.pet as? Cat)
    XCTAssertEqual(cat.name, "cat")
}

And here is what is printed in the console:

Swinject: Resolution failed. Expected registration:
    { Service: Person, Factory: (Resolver, Cat) -> Person }
Available registrations:
    { Service: Person, Factory: (Resolver, Animal) -> Person, ObjectScope: graph }

After some investigation, this behavior change from Swift is documented in the section ""Losing" constraints when type-erasing resulting values" of SE-0352.
The solution is also provided by the proposal: opting out from this new implicit existential opening with as any P / as! any P. So in my example replacing the line resolving the person with this line makes the test pass in Swift 6:

let person = container.resolve(Person.self, argument: animal as Animal)

I didn't find another way to fix this issue, but at least I was able to understand what was happening. I am not sure what's the next step for this issue, maybe at least more documentation warning about this issue ?

You can find the project with some changes on top of main to make it compile with Swift 6 here: https://github.com/alexandre-pod/Swinject/tree/swift-6-support

(This was tried on Xcode 16.0 beta 3)

The text was updated successfully, but these errors were encountered:

niorko · 2025-02-21T09:45:25Z

Any updates please @maxim-chipeev?

…h Swift 6 Swift 6 implicitly open existentials, causing issue with Swinject without those explicit types. See Swinject/Swinject#571 for more details

alexandre-pod mentioned this issue Feb 28, 2025

ccios improvements faberNovel/ccios#25

Merged

alexandre-pod mentioned this issue Apr 3, 2025

Release/v5.1.0 faberNovel/ccios#27

Merged

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Uh oh!

Swift 6 source-breaking change cause `Container.resolve(_:arguments:)` to change behavior from Swift 5 #571

Swift 6 source-breaking change cause `Container.resolve(_:arguments:)` to change behavior from Swift 5 #571

Uh oh!

Swift 6 source-breaking change cause Container.resolve(_:arguments:) to change behavior from Swift 5 #571

Swift 6 source-breaking change cause Container.resolve(_:arguments:) to change behavior from Swift 5 #571

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Uh oh!

Swift 6 source-breaking change cause `Container.resolve(_:arguments:)` to change behavior from Swift 5 #571

Swift 6 source-breaking change cause `Container.resolve(_:arguments:)` to change behavior from Swift 5 #571