Fix Swift mock object deinit and add a test for them (#2717)

Author: bendk

Cargo.lock

@@ -67,6 +67,7 @@ members = [
   "fixtures/simple-iface",
   "fixtures/struct-default-values",
   "fixtures/swift-codable",
+  "fixtures/swift-mock-objects",
   "fixtures/swift-omit-labels",
   "fixtures/futures",
   "fixtures/swift-bridging-header-compile",

Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "uniffi-fixture-swift-mock-objects"
+version = "0.22.0"
+edition = "2021"
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_swift_mock_objects"
+
+[dependencies]
+uniffi = { workspace = true }
+
+[dev-dependencies]
+uniffi = { workspace = true, features = ["bindgen-tests"] }
+
+[features]
+ffi-trace = ["uniffi/ffi-trace"]

fixtures/swift-mock-objects/Cargo.toml

@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#[derive(uniffi::Object, Debug)]
+pub struct TestObject;
+
+#[uniffi::export]
+impl TestObject {
+    pub fn is_mock(&self) -> bool {
+        false
+    }
+}
+
+uniffi::setup_scaffolding!("swift_mock_objects");

fixtures/swift-mock-objects/src/lib.rs

@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import Foundation
+import swift_mock_objects
+
+// Swift version 6 gives a warning that we must restate `@unchecked Sendable`, however earlier
+// versions of Swift fail if we add that.  Let's leave it out and accept the warning for now.
+public class TestObjectMock: TestObject {
+
+    required public init(unsafeFromHandle handle: UInt64) {
+        fatalError("Not supported")
+    }
+
+    public init() {
+        super.init(noHandle: NoHandle.init())
+    }
+
+    // Override the "is_mock()" function
+
+    override public func isMock() -> Bool {
+        return true;
+    }
+}
+
+var mocked: TestObjectMock? = TestObjectMock()
+
+// Test that our mock object can override the functions of the real object
+assert(mocked!.isMock())
+
+// Test that we don't crash when deinitializing the mock object
+mocked = nil

fixtures/swift-mock-objects/tests/bindings/test_mock_objects.swift

@@ -0,0 +1 @@
+uniffi::build_foreign_language_testcases!("tests/bindings/test_mock_objects.swift",);

fixtures/swift-mock-objects/tests/test_generated_bindings.rs

@@ -56,6 +56,11 @@ open class {{ impl_class_name }}: {{ protocol_name }}, {{ config.conformance_lis
     {%- endmatch %}
 
     deinit {
+        if handle == 0 {
+            // Mock objects have handle=0 don't try to free them
+            return
+        }
+
         try! rustCall { {{ obj.ffi_object_free().name() }}(handle, $0) }
     }