Add Equatable and GuestPointee conformances

To support Swift Concurrency tested in WebAssembly System Interface environment, `Clock` and `Subscription` types should conform to `GuestPointee` types, which provides size and alignment for correct ABI implementation.

This fixes current build issues, where these types didn't have correct size and alignment specified.

Author: MaxDesiatov

Sources/WASI/WASI.swift

@@ -428,8 +428,8 @@ enum WASIAbi {
         case END = 2
     }
 
-    struct Clock: GuestPointee {
-        struct Flags: OptionSet, GuestPrimitivePointee {
+    struct Clock: Equatable, GuestPointee {
+        struct Flags: OptionSet, GuestPointee {
             let rawValue: UInt16
 
             static let isAbsoluteTime = Self(rawValue: 1)
@@ -462,15 +462,15 @@ enum WASIAbi {
         }
     }
 
-    enum EventType: UInt8 {
+    enum EventType: UInt8, GuestPointee {
         case clock
         case fdRead
         case fdWrite
     }
 
     typealias UserData = UInt64
 
-    struct Subscription: Equatable {
+    struct Subscription: Equatable, GuestPointee {
         enum Union: Equatable, GuestPointee {
             case clock(Clock)
             case fdRead(Fd)
@@ -514,6 +514,22 @@ enum WASIAbi {
                 }
             }
         }
+
+        let userData: UserData
+        let union: Union
+        static var sizeInGuest: UInt32 = 48
+        static var alignInGuest: UInt32 = max(UserData.alignInGuest, Union.alignInGuest)
+
+        static func readFromGuest(_ pointer: UnsafeGuestRawPointer) -> Self {
+            var pointer = pointer
+            return .init(userData: .readFromGuest(&pointer), union: .readFromGuest(&pointer))
+        }
+
+        static func writeToGuest(at pointer: UnsafeGuestRawPointer, value: Self) {
+            var pointer = pointer
+            UserData.writeToGuest(at: &pointer, value: value.userData)
+            Union.writeToGuest(at: &pointer, value: value.union)
+        }
     }
 
     struct Event: Equatable, GuestPointee {
@@ -563,7 +579,7 @@ enum WASIAbi {
         }
     }
 
-    enum ClockId: UInt32 {
+    enum ClockId: UInt32, GuestPointee {
         /// The clock measuring real time. Time value zero corresponds with
         /// 1970-01-01T00:00:00Z.
         case REALTIME = 0

Sources/WasmTypes/GuestMemory.swift

@@ -38,7 +38,15 @@ extension GuestPrimitivePointee {
 }
 
 /// Auto implementation of ``GuestPointee`` for ``RawRepresentable`` types
-extension GuestPrimitivePointee where Self: RawRepresentable, Self.RawValue: GuestPointee {
+extension GuestPointee where Self: RawRepresentable, Self.RawValue: GuestPointee {
+    public static var sizeInGuest: UInt32 {
+        RawValue.sizeInGuest
+    }
+
+    public static var alignInGuest: UInt32 {
+        RawValue.alignInGuest
+    }
+
     /// Reads a value of RawValue type and constructs a value of Self type
     public static func readFromGuest(_ pointer: UnsafeGuestRawPointer) -> Self {
         Self(rawValue: .readFromGuest(pointer))!