Cleanup COMIInspectableStruct and add HString.

Support/Sources/WindowsRuntime/HString.swift

@@ -0,0 +1,68 @@
+import WindowsRuntime_ABI
+import COM
+
+/// Wraps a Windows Runtime HSTRING.
+public struct HString: ~Copyable {
+    public static var empty: HString { HString(transferring: nil) }
+
+    public let abi: WindowsRuntime_ABI.SWRT_HString?
+
+    public init(transferring abi: WindowsRuntime_ABI.SWRT_HString?) {
+        self.abi = abi
+    }
+
+    public init(duplicating abi: WindowsRuntime_ABI.SWRT_HString?) throws {
+        var duplicated: WindowsRuntime_ABI.SWRT_HString?
+        try HResult.throwIfFailed(WindowsRuntime_ABI.SWRT_WindowsDuplicateString(abi, &duplicated))
+        self.init(transferring: duplicated)
+    }
+
+    deinit { Self.delete(abi) }
+
+    public static func create(_ value: String) throws -> HString {
+        if value.isEmpty { return .empty }
+
+        // Preallocate and fill a UTF-16 HSTRING_BUFFER
+        var buffer: WindowsRuntime_ABI.SWRT_HStringBuffer? = nil
+        var pointer: UnsafeMutablePointer<UInt16>? = nil
+        let codeUnitCount = value.utf16.count
+        try HResult.throwIfFailed(WindowsRuntime_ABI.SWRT_WindowsPreallocateStringBuffer(UInt32(codeUnitCount), &pointer, &buffer))
+        guard let pointer else { throw HResult.Error.pointer }
+        _ = UnsafeMutableBufferPointer(start: pointer, count: codeUnitCount).initialize(from: value.utf16)
+
+        var abi: WindowsRuntime_ABI.SWRT_HString?
+        do { try HResult.throwIfFailed(WindowsRuntime_ABI.SWRT_WindowsPromoteStringBuffer(buffer, &abi)) }
+        catch {
+            WindowsRuntime_ABI.SWRT_WindowsDeleteStringBuffer(buffer)
+            throw error
+        }
+
+        return .init(transferring: abi)
+    }
+
+    public static func toString(_ abi: WindowsRuntime_ABI.SWRT_HString?) -> String {
+        var length: UInt32 = 0
+        guard let ptr = WindowsRuntime_ABI.SWRT_WindowsGetStringRawBuffer(abi, &length) else { return "" }
+        let buffer: UnsafeBufferPointer<UTF16.CodeUnit> = .init(start: ptr, count: Int(length))
+        return String(decoding: buffer, as: UTF16.self)
+    }
+
+    public func toString() -> String { Self.toString(abi) }
+
+    public func duplicate() throws -> Self {
+        var duplicated: WindowsRuntime_ABI.SWRT_HString?
+        try HResult.throwIfFailed(WindowsRuntime_ABI.SWRT_WindowsDuplicateString(abi, &duplicated))
+        return .init(transferring: duplicated)
+    }
+
+    public static func delete(_ abi: WindowsRuntime_ABI.SWRT_HString?) {
+        let hr = WindowsRuntime_ABI.SWRT_WindowsDeleteString(abi)
+        assert(HResult.isSuccess(hr), "Failed to delete HSTRING")
+    }
+
+    public consuming func detach() -> WindowsRuntime_ABI.SWRT_HString? {
+        let abi = self.abi
+        discard self
+        return abi
+    }
+}

Support/Sources/WindowsRuntime/HStringProjection.swift

@@ -8,15 +8,15 @@ public enum HStringProjection: ABIProjection {
     public static var abiDefaultValue: ABIValue { nil }
 
     public static func toSwift(_ value: WindowsRuntime_ABI.SWRT_HString?) -> SwiftValue {
-        value.toString()
+        HString.toString(value)
     }
 
     public static func toABI(_ value: String) throws -> WindowsRuntime_ABI.SWRT_HString? {
-        try WindowsRuntime_ABI.SWRT_HString.create(value)
+        try HString.create(value).detach()
     }
 
     public static func release(_ value: inout WindowsRuntime_ABI.SWRT_HString?) {
-        WindowsRuntime_ABI.SWRT_HString.delete(value)
+        HString.delete(value)
         value = nil
     }
 }

Support/Sources/WindowsRuntime/IInspectable.swift

@@ -1,5 +1,6 @@
 import COM
 import WindowsRuntime_ABI
+import struct Foundation.UUID
 
 public protocol IInspectableProtocol: IUnknownProtocol {
     func getIids() throws -> [COMInterfaceID]
@@ -36,10 +37,39 @@ public enum IInspectableProjection: WinRTTwoWayProjection {
         GetTrustLevel: { WinRTExportedInterface.GetTrustLevel($0, $1) })
 }
 
+/// Identifies COM interface structs as deriving from IInspectable.
+/// Do not use for dynamic casting because conformances will be @retroactive.
+public protocol COMIInspectableStruct: COMIUnknownStruct {}
+
 #if swift(>=5.10)
 extension WindowsRuntime_ABI.SWRT_IInspectable: @retroactive COMIUnknownStruct {}
 #endif
 
 extension WindowsRuntime_ABI.SWRT_IInspectable: /* @retroactive */ COMIInspectableStruct {
     public static let iid = COMInterfaceID(0xAF86E2E0, 0xB12D, 0x4C6A, 0x9C5A, 0xD7AA65101E90)
+}
+
+extension COMInterop where Interface: /* @retroactive */ COMIInspectableStruct {
+    private var inspectable: UnsafeMutablePointer<WindowsRuntime_ABI.SWRT_IInspectable>{
+        this.withMemoryRebound(to: WindowsRuntime_ABI.SWRT_IInspectable.self, capacity: 1) { $0 }
+    }
+
+    public func getIids() throws -> [Foundation.UUID] {
+        var iids: COMArray<WindowsRuntime_ABI.SWRT_Guid> = .null
+        try WinRTError.throwIfFailed(inspectable.pointee.lpVtbl.pointee.GetIids(inspectable, &iids.count, &iids.pointer))
+        defer { iids.deallocate() }
+        return WinRTArrayProjection<GUIDProjection>.toSwift(consuming: &iids)
+    }
+
+    public func getRuntimeClassName() throws -> String {
+        var runtimeClassName: WindowsRuntime_ABI.SWRT_HString?
+        try WinRTError.throwIfFailed(inspectable.pointee.lpVtbl.pointee.GetRuntimeClassName(inspectable, &runtimeClassName))
+        return HStringProjection.toSwift(consuming: &runtimeClassName)
+    }
+
+    public func getTrustLevel() throws -> TrustLevel {
+        var trustLevel: WindowsRuntime_ABI.SWRT_TrustLevel = 0
+        try WinRTError.throwIfFailed(inspectable.pointee.lpVtbl.pointee.GetTrustLevel(inspectable, &trustLevel))
+        return TrustLevel.toSwift(trustLevel)
+    }
 }