Weird Swift 5.2 error - works in Swift 5.3

Weird.swift

// full definition omitted:
public struct ValidatorOf<Value, Error> {
    public let validate: (Value) -> Validated<Value, Error>
}

extension ValidatorOf {
    static func its<T>(_ transform: @escaping (Value) -> T, _ validator: ValidatorOf<T, Error>) -> Self {
        validator.pullback(transform)
    }
}

// @Validating is a property wrapper that can take an array or variadic list of validators (ValidatorOf)

// Works in Swift 5.2 and 5.3:

struct ValidatingContainer {
    @Validating(
        .its({ $0.first }, .isEqualTo(1))
    )
    var numbers: [Int] = []
}

// Works in Swift 5.3 but errors in Swift 5.2:

struct ValidatingContainer {
    @Validating(
        .its(\.first, .isEqualTo(1))
    )
    var numbers: [Int] = []
}

// Swift 5.2 errors:
// Struct declaration cannot close over value '$0' defined in outer scope
// Struct declaration cannot close over value '$kp$' defined in outer scope

// However, I can use the keypath form in a simple let in 5.2 without errors:

struct ValidatingContainer {
    let arrayValidator: ValidatorOf<[Int], String> = .its(\.first, .isEqualTo(1))
}