'fetchAll' is only available in iOS 17 or newer for tuple selections

[mertalev]

Description

The query builder doesn't allow selecting tuples unless I increase the iOS requirement to iOS 17, which seems rather arbitrary rather than an actual limitation. The minimum iOS version in my project is 14.

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Given that it can select all columns or one column, the API for selecting some columns should not have different version requirements.

Actual behavior

Any tuple output type results in the version requirement increasing to iOS 17, while other parts of the API do not require this version.

Reproducing project

Given the table:

@Table
struct Asset {
  let id: String
  let foo: Bool
  let bar: Bool
}

Compilation fails if I try to query it as such:

let foo = try await db.read { conn in
  return try Asset.select { ($0.foo, $0.bar) }.fetchAll(conn) // `'fetchAll' is only available in iOS 17 or newer`
}

Selecting one column works, as does selecting self:

let ids = try await db.read { conn in
  return try Asset.select(\.id).fetchAll(conn)
}

let assets = try await db.read { conn in
  return try Asset.select(\.self).fetchAll(conn)
}

Interestingly, selecting one column doesn't work either for returning:

let ids = try await db.read { conn in
  return try Asset.update { $0.foo = ""}.returning(\.id).fetchAll(conn) // `'fetchAll' is only available in iOS 17 or newer`
}

let assets = try await db.read { conn in
  return try Asset.update { $0.foo = ""}.returning(\.self).fetchAll(conn) // works
}

Structured Queries version information

0.25.2 (sqlite-data is 1.3.0)

Destination operating system

iOS 26.1

Xcode version information

Version 26.0.1 (17A400)

Swift Compiler version information

swift-driver version: 1.127.14.1 Apple Swift version 6.2 (swiftlang-6.2.0.19.9 clang-1700.3.19.1)
Target: arm64-apple-macosx26.0

[stephencelis]

@mertalev Tupling requires parameter packs, which is an iOS 17+-only feature. But we also don't think this is a big deal: you can introduce a struct and the @Selection macro to work around the issue for iOS <17.

So we don't consider this a bug and don't think there's a reasonable way to support tuple selections without parameter packs. I'm going to convert this to a discussion, for now, but if you have any ideas on how we can reasonably support such a feature, please continue the conversation there!

[mertalev]

Oh, that makes sense. I'm fine with using structs, but it doesn't seem like I can use a @Selection struct for returning, right? Could that gap in the API be filled?

[stephencelis]

@mertalev We'll have to look into whether or not that's possible. Ideally it is! Currently returning is quite strict in requiring all table columns or a tuple of table columns, but we could potentially weaken that constraint to support @Selection structs. It does mean introducing more failures at runtime, but probably unlikely ones. We'll discuss soon!

[mertalev]

FWIW, the returning limitation cropped up when I was trying to return just a single column as well. Since that works for normal selects, it seems like that bit could be made to work with returning without sacrificing any type safety.