[Suggestion] Replace symbol hacks with AssociatedTypeRequirementsVisitor hacks

Package.swift

@@ -14,14 +14,12 @@ let package = Package(
     ],
     dependencies: [
         .package(name: "SnapshotTesting", url: "https://github.com/pointfreeco/swift-snapshot-testing.git", from: "1.8.1"),
+        .package(url: "https://github.com/nerdsupremacist/AssociatedTypeRequirementsKit.git", from: "0.2.0"),
     ],
     targets: [
-        .target(
-            name: "CSymbols",
-            dependencies: []),
         .target(
             name: "SwiftShortcuts",
-            dependencies: ["CSymbols"]),
+            dependencies: ["AssociatedTypeRequirementsKit"]),
         .testTarget(
             name: "SwiftShortcutsTests",
             dependencies: ["SwiftShortcuts", "SnapshotTesting"],

Sources/SwiftShortcuts/Internal/ActionDecomposable.swift

@@ -83,6 +83,6 @@ extension Optional: ActionDecomposable where Wrapped: Shortcut {
 extension TupleShortcut: ActionDecomposable {
     func decompose() -> [Action] {
         let mirror = Mirror(reflecting: value)
-        return mirror.children.flatMap { _, value in AnyShortcut(_fromValue: value)!.decompose() }
+        return mirror.children.flatMap { _, value in actionComponents(from: value)! }
     }
 }

Sources/SwiftShortcuts/Internal/FromAny.swift

@@ -1,142 +1,47 @@
-#if os(Linux)
-import CSymbols
-#else
-import Foundation
-#endif
+
+import AssociatedTypeRequirementsVisitor
+
+private let typeEraser = ShortcutTypeEraser()
+private let decomposer = ShortcutDecomposer()
 
 // MARK: - AnyShortcut from Any
 
 extension AnyShortcut {
     init?(_fromValue value: Any) {
-        // Synthesize a fake protocol conformance record to AnyShortcutConvertible
-        let conformance = ProtocolConformanceRecord(type: type(of: value), witnessTable: 0)
-        let type = unsafeBitCast(conformance, to: AnyShortcutConvertible.Type.self)
-
-        guard let action = type.anyShortcut(from: value) else {
-            return nil
-        }
+        guard let action = typeEraser(value) else { return nil }
 
         self = action
     }
 }
 
-// MARK: - AnyViewConvertible
-
-private let actionMetadata: ProtocolMetadata = {
-    let module = "SwiftShortcuts"
-    let name = "Shortcut"
-    let postfix = "_p"
-    let mangled = "\(module.count)\(module)\(name.count)\(name)\(postfix)"
-    return ProtocolMetadata(type: _typeByName(mangled)!)
-}()
-
-private protocol AnyShortcutConvertible {}
-
-extension AnyShortcutConvertible {
-    static func anyShortcut(from action: Any) -> AnyShortcut? {
-        guard let witnessTable = _conformsToProtocol(Self.self, actionMetadata.protocolDescriptorVector) else {
-            return nil
-        }
-
-        let conformanceRecord = ProtocolConformanceRecord(type: Self.self, witnessTable: Int(bitPattern: witnessTable))
-        return withUnsafePointer(to: action as! Self) { pointer in makeAnyShortcut(pointer, conformanceRecord) }
-    }
-}
+// MARK: - Actions from Any
 
-@_silgen_name("_swift_shortcuts_makeAnyShortcut")
-@available(*, unavailable)
-public func makeAnyShortcut<S: Shortcut>(from shortcut: S) -> AnyShortcut {
-    return AnyShortcut(shortcut)
+func actionComponents(from value: Any) -> [Action]? {
+    return decomposer(value)
 }
 
-private typealias ShortcutToAnyShortcutFunction = @convention(thin) (UnsafeRawPointer, ProtocolConformanceRecord) -> AnyShortcut
-
-#if os(Linux)
-private let makeAnyShortcut = unsafeBitCast(makeAnyShortcutSymbol(), to: ShortcutToAnyShortcutFunction.self)
-#else
-private let makeAnyShortcut: ShortcutToAnyShortcutFunction = {
-    let symbolName = "_swift_shortcuts_makeAnyShortcut"
-    let handle = dlopen(nil, RTLD_GLOBAL)
-    let pointer = dlsym(handle, symbolName)
-    return unsafeBitCast(pointer, to: ShortcutToAnyShortcutFunction.self)
-}()
-#endif
-
-// MARK: - [ActionComponent] from Any
-
-private protocol ActionsConvertible {}
-
-extension ActionsConvertible {
-    static func actions(from shortcut: Any) -> [Action]? {
-        guard let witnessTable = _conformsToProtocol(Self.self, actionMetadata.protocolDescriptorVector) else {
-            return nil
-        }
+// MARK: - ShortcutVisitor
 
-        let conformanceRecord = ProtocolConformanceRecord(type: Self.self, witnessTable: Int(bitPattern: witnessTable))
-        return withUnsafePointer(to: shortcut as! Self) { pointer in decomposeIntoActions(pointer, conformanceRecord) }
-    }
-}
+private protocol ShortcutVisitor: AssociatedTypeRequirementsVisitor {
+    associatedtype Visitor = ShortcutVisitor
+    associatedtype Input = Shortcut
+    associatedtype Output
 
-@_silgen_name("_swift_shortcuts_decomposeIntoActions")
-@available(*, unavailable)
-public func decomposeIntoActions<S: Shortcut>(shortcut: S) -> [Action] {
-    _decomposeIntoActions(shortcut: shortcut)
+    func callAsFunction<S : Shortcut>(_ shortcut: S) -> Output
 }
 
-private func _decomposeIntoActions<S: Shortcut>(shortcut: S) -> [Action] {
-    if S.Body.self == Never.self {
-        return shortcut.decompose()
-    }
+private struct ShortcutTypeEraser : ShortcutVisitor {
 
-    let body = shortcut.body
-    if let component = body as? Action {
-        return [component]
-    } else {
-        return _decomposeIntoActions(shortcut: body)
+    func callAsFunction<S : Shortcut>(_ shortcut: S) -> AnyShortcut {
+        return AnyShortcut(shortcut)
     }
-}
-
-private typealias ShortcutToActionsFunction = @convention(thin) (UnsafeRawPointer, ProtocolConformanceRecord) -> [Action]
-#if os(Linux)
-private let decomposeIntoActions = unsafeBitCast(decomposeIntoActionsSymbol(), to: ShortcutToActionsFunction.self)
-#else
-private let decomposeIntoActions: ShortcutToActionsFunction = {
-    let symbolName = "_swift_shortcuts_decomposeIntoActions"
-    let handle = dlopen(nil, RTLD_GLOBAL)
-    let pointer = dlsym(handle, symbolName)
-    return unsafeBitCast(pointer, to: ShortcutToActionsFunction.self)
-}()
-#endif
-
-func actionComponents(from value: Any) -> [Action]? {
-    // Synthesize a fake protocol conformance record to ActionStepsConvertible
-    let conformance = ProtocolConformanceRecord(type: type(of: value), witnessTable: 0)
-    let type = unsafeBitCast(conformance, to: ActionsConvertible.Type.self)
-    return type.actions(from: value)
-}
 
-// MARK: - Protocol Runtime Information
-
-private struct ProtocolConformanceRecord {
-    let type: Any.Type
-    let witnessTable: Int
 }
 
-private struct ProtocolDescriptor {}
-
-private struct ProtocolMetadata {
-    let kind: Int
-    let layoutFlags: UInt32
-    let numberOfProtocols: UInt32
-    let protocolDescriptorVector: UnsafeMutablePointer<ProtocolDescriptor>
+private struct ShortcutDecomposer : ShortcutVisitor {
 
-    init(type: Any.Type) {
-        self = unsafeBitCast(type, to: UnsafeMutablePointer<Self>.self).pointee
+    func callAsFunction<S : Shortcut>(_ shortcut: S) -> [Action] {
+        return shortcut.decompose()
     }
-}
 
-@_silgen_name("swift_conformsToProtocol")
-private func _conformsToProtocol(
-    _ type: Any.Type,
-    _ protocolDescriptor: UnsafeMutablePointer<ProtocolDescriptor>
-) -> UnsafeRawPointer?
+}