cannot define property-wrapper-based property with omitted type, if the property wrapper isn't directly initialized

[lukaskollmer]

Description

The program below fails to compile, with the compiler complaining that the property-wrapper-backed property is missing an explicity type annotation.

Reproduction

@propertyWrapper
struct Query<T> {
    init(_ type: T.Type = T.self, limit: Int?) {}
    var wrappedValue: [T] { [] }
}


struct Item {}

struct S {
    @Query<Item> var items // error: type annotation missing in pattern
}

Expected behavior

IMO, this should compile, since there is no ambiguity w.r.t. the resulting wrappedValue type.

this would be different if the property were defined as @Query var items instead of @Query<Item> var items, since in that case the init call would be required to provide the type for T.

Environment

swift-driver version: 1.120.5 Apple Swift version 6.1 (swiftlang-6.1.0.110.21 clang-1700.0.13.3)
Target: arm64-apple-macosx15.0

Additional information

No response

[jamieQ]

if you provide a default value for the optional limit: Int? parameter or explicitly specify a value in the property wrapper attribute, it seems like it works (for this and the other issue). does that seem like a solution to these, or do you think it should still be able to compile without that? IIUC even if it did compile, using the value without specifying that init param would perhaps be an error since it wouldn't be fully initialized...

@propertyWrapper
struct Query<T> {
    init(_ type: T.Type = T.self, limit: Int? = nil) {} // add this
    var wrappedValue: [T] { [] }
}


struct Item {}

struct S {
    @Query<Item>(limit: 42) var items // or add this
}

[lukaskollmer]

@jamieQ my use case doesn't allow for default parameters (the actual property wrapper i have requires the caller to specify a much more fine-grained querying input than just the raw Swift type).

i'm not saying that it should be possible to use the property wrapper without initializing it; this responsibility would then fall to the containing struct's init (S in this case).

in the example above, if you define the property as @Query<Item> var items: [Item], swift will already correctly synthesize an init(items: Query<Item>).

IMO, this should also happen if the property is defined as @Query<Item> var items, ie with the explicit type omitted (since the compiler knows that the type will always be [Item], as evidenced by the fact that specifying any type other than [Item] will result in a compilation error as well, with the compiler complaining about non-matching types)