SwiftData SchemaMigrationPlan and VersionedSchema not Sendable?

Question

Created Jun ’24

Replies 2

Boosts 4

Participants 4

I've just tried to update a project that uses SwiftData to Swift 6 using Xcode 16 beta 1, and it's not working due to missing Sendable conformance on a couple of types (MigrationStage and Schema.Version):

struct LocationsMigrationPlan: SchemaMigrationPlan {
    static let schemas: [VersionedSchema.Type] = [LocationsVersionedSchema.self]
    static let stages: [MigrationStage] = []
}

struct LocationsVersionedSchema: VersionedSchema {
    static let models: [any PersistentModel.Type] = [
        Location.self
    ]

    static let versionIdentifier = Schema.Version(1, 0, 0)
}

This code results in the following errors:

error: static property 'stages' is not concurrency-safe because non-'Sendable' type '[MigrationStage]' may have shared mutable state
    static let stages: [MigrationStage] = []
               ^
error: static property 'versionIdentifier' is not concurrency-safe because non-'Sendable' type 'Schema.Version' may have shared mutable state
    static let versionIdentifier = Schema.Version(1, 0, 0)
               ^

Am I missing something, or is this a bug in the current seed? I've filed this as FB13862584.

Answered by DTS Engineer in 790713022

Thanks for filing the feedback report. As of today, SwiftData does't run through Swift 6 check yet. I personally don't see any reason that MigrationStage and Schema.Version can't be sendable. You can probably consider using the following extensions to eliminate the warnings or errors related to Sensibility of the two types:

extension MigrationStage: @unchecked @retroactive Sendable { }
extension Schema.Version: @unchecked @retroactive Sendable { }

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

Boost

Answer 1

DTS Engineer OP

Apple

Jun ’24

Accepted Answer

Thanks for filing the feedback report. As of today, SwiftData does't run through Swift 6 check yet. I personally don't see any reason that MigrationStage and Schema.Version can't be sendable. You can probably consider using the following extensions to eliminate the warnings or errors related to Sensibility of the two types:

extension MigrationStage: @unchecked @retroactive Sendable { }
extension Schema.Version: @unchecked @retroactive Sendable { }

Best,
——
Ziqiao Chen
 Worldwide Developer Relations.

7

Answer 2

GeeBee2 OP

4d

I ran into the same issue yesterday.

@DTS Engineer Ziqiao, your proposed solution solves the compiler errors, many thanks, but I see that this fix has not made it into iOS 18 or 18.1.

Is it safe to use this workaround and should we expect the SwiftData API to incorporate this anytime soon ? If not, what are the risks/concerns ?

Thanks, Guy

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