Support getInterfaceID for IActivationFactory (#62)

Sources/WindowsMetadata/InterfaceID.swift

@@ -5,14 +5,27 @@ public func getInterfaceID(_ typeDefinition: TypeDefinition, genericArgs: [TypeN
     guard typeDefinition is InterfaceDefinition || typeDefinition is DelegateDefinition else {
         throw UnexpectedTypeError(typeDefinition.fullName, context: #function, reason: "Only interfaces and delegates have interface IDs")
     }
-    if let genericArgs = genericArgs, genericArgs.count > 0 {
+
+    /// Generic interfaces/delegates have a GUID computed based on the generic arguments.
+    if let genericArgs, genericArgs.count > 0 {
         let signature = try WinRTTypeSignature(typeDefinition.bindType(genericArgs: genericArgs))
         return signature.parameterizedID
     }
-    else {
-        guard let attribute = try typeDefinition.findAttribute(GuidAttribute.self) else { throw WinMDError.missingAttribute }
+    /// Non-generic interfaces/delegates defined in winmd files specify their GUID via Windows.Foundation.Metadata.GuidAttribute.
+    else if let attribute = try typeDefinition.findAttribute(WindowsMetadata.GuidAttribute.self) {
         return attribute.value
     }
+    /// We consider System.Runtime.InteropServices.WindowsRuntime.IActivationFactory to be a WinRT interface,
+    /// but since it's defined in mscorlib, it uses System.Runtime.InteropServices.GuidAttribute instead.
+    else if typeDefinition.namespace == "System.Runtime.InteropServices.WindowsRuntime",
+            typeDefinition.name == "IActivationFactory",
+            let attribute = try typeDefinition.findAttribute(DotNetMetadata.GuidAttribute.self) {
+        guard let guid = UUID(uuidString: attribute.value) else { throw InvalidMetadataError.attributeArguments }
+        return guid
+    }
+    else {
+        throw WinMDError.missingAttribute
+    }
 }
 
 public func getInterfaceID(_ type: BoundType) throws -> UUID {

Tests/WindowsMetadata/InterfaceIDTests.swift

@@ -0,0 +1,29 @@
+import DotNetMetadata
+import XCTest
+import WindowsMetadata
+
+final class InterfaceIDTests: XCTestCase {
+    internal static var context: WinMDLoadContext!
+    internal static var mscorlib: Assembly!
+
+    override func setUpWithError() throws {
+        if Self.mscorlib == nil {
+            Self.context = WinMDLoadContext()
+
+            // Expect mscorlib.winmd side-by-side with the test executable
+            let mscorlibURL = Bundle.main.bundleURL.appendingPathComponent("mscorlib.winmd", isDirectory: false)
+            Self.mscorlib = try Self.context.load(url: mscorlibURL)
+        }
+    }
+
+    /// Test that we can get the interface ID for `IActivationFactory`,
+    /// which lives in the core library rather than a Windows Metadata file,
+    /// so uses System's GuidAttribute, not Windows.Foundation's.
+    public func testCoreLibraryIActivationFactory() throws {
+        let typeDefinition = try XCTUnwrap(Self.mscorlib.resolveTypeDefinition(
+            namespace: "System.Runtime.InteropServices.WindowsRuntime", name: "IActivationFactory"))
+        XCTAssertEqual(
+            try getInterfaceID(typeDefinition),
+            UUID(uuidString: "00000035-0000-0000-c000-000000000046"))
+    }
+}

WindowsMetadataCoreLibrary/mscorlib.il

@@ -44,7 +44,10 @@
 // Attributes
 .class public System.AttributeUsageAttribute extends System.Attribute {}
 .class public System.FlagsAttribute extends System.Attribute {}
-.class public System.Runtime.InteropServices.GuidAttribute extends System.Attribute {}
+
+.class public System.Runtime.InteropServices.GuidAttribute extends System.Attribute {
+    .method public hidebysig specialname rtspecialname instance void .ctor(string guid) runtime managed internalcall {}
+}
 
 // IActivationFactory interface
 .class interface public abstract import windowsruntime System.Runtime.InteropServices.WindowsRuntime.IActivationFactory