Hi! I'm running into an annoying crash related to variadic generics with the error message "Cannot mangle free-standing archetype"
I've posted an issue here: Cannot mangle free-standing archetype · Issue #83021 · swiftlang/swift · GitHub
I've reduced the problematic code to:
public protocol Schema<Value>: Sendable, SchemaCodable {
associatedtype Value
}
public protocol SchemaCodable {
associatedtype Schema: VariadicTest.Schema where Schema.Value == Self
static func schema() -> Schema
}
public struct BottomSchema<Value: SchemaCodable>: Schema {
public typealias Schema = BottomSchema<Self>
static public func schema() -> Schema {
Schema()
}
}
extension String: SchemaCodable {
public static func schema() -> BottomSchema<String> {
BottomSchema<String>()
}
}
public protocol StructSchema: Schema {
associatedtype Properties
associatedtype PropertyName: CodingKey
static var properties: Properties { get }
}
extension StructSchema {
fileprivate static func metaSchema<each PropertyValue: SchemaCodable>()
-> StructMetaSchema<Self, repeat each PropertyValue>
where
(repeat StructSchemaPropertyDefinition<Self.Value, PropertyName, each PropertyValue>)
== Properties
{
StructMetaSchema<Self, repeat each PropertyValue>()
}
}
public struct StructSchemaPropertyDefinition<
Root,
Name: CodingKey,
Value: SchemaCodable
>: Sendable {
let name: Name
let keyPath: KeyPath<Root, Value> & Sendable
let valueSchema: Value.Schema
}
public struct ExampleStruct {
let x, y: String
}
public struct ExampleStructSchema: StructSchema {
public typealias Value = ExampleStruct
public enum PropertyName: CodingKey {
case x, y
}
public static let properties = (
StructSchemaPropertyDefinition<ExampleStruct, PropertyName, String>(
name: .x,
keyPath: \ExampleStruct.x,
valueSchema: BottomSchema<String>()
),
StructSchemaPropertyDefinition<ExampleStruct, PropertyName, String>(
name: .y,
keyPath: \ExampleStruct.y,
valueSchema: BottomSchema<String>()
)
)
/// Removing this function causes the compiler to no longer crash.
public static func schema() -> StructMetaSchema<Self, String, String> {
metaSchema()
}
}
extension StructSchema {
fileprivate subscript<T: SchemaCodable>(
_ keyPath: KeyPath<Value, T>
) -> T.Schema {
T.schema()
}
}
public struct StructMetaSchema<
Base: StructSchema,
each BasePropertyValue: SchemaCodable
>: StructSchema
where
Base.Properties == (
repeat StructSchemaPropertyDefinition<
Base.Value,
Base.PropertyName,
each BasePropertyValue
>
)
{
public typealias Value = Base
public typealias PropertyName = Base.PropertyName
public typealias Properties = (
repeat StructSchemaPropertyDefinition<
Base, PropertyName, (each BasePropertyValue).Schema
>
)
public static var properties: Properties {
(repeat StructSchemaPropertyDefinition(
name: (each Value.properties).name,
keyPath: \Base.[(each Base.properties).keyPath],
valueSchema: type(of: (each Value.properties).valueSchema).schema()
))
}
public static func schema() -> StructMetaSchema<Self, repeat (each BasePropertyValue).Schema> {
StructMetaSchema<Self, repeat (each BasePropertyValue).Schema>()
}
}
Anyone else run into this crash, and/or have any suggestions for a workaround? (Claude thinks @Slava_Pestov might have the most context 
)