test: Add GC lifecycle test for identity-cached wrappers (swiftwasm#731)

Author: krodak

Tests/BridgeJSIdentityTests/Generated/BridgeJS.swift

@@ -333,6 +333,25 @@ fileprivate func _bjs_ArrayIdentityElement_wrap_extern(_ pointer: UnsafeMutableR
     return _bjs_ArrayIdentityElement_wrap_extern(pointer)
 }
 
+#if arch(wasm32)
+@_extern(wasm, module: "BridgeJSIdentityTests", name: "bjs_gc")
+fileprivate func bjs_gc_extern() -> Void
+#else
+fileprivate func bjs_gc_extern() -> Void {
+    fatalError("Only available on WebAssembly")
+}
+#endif
+@inline(never) fileprivate func bjs_gc() -> Void {
+    return bjs_gc_extern()
+}
+
+func _$gc() throws(JSException) -> Void {
+    bjs_gc()
+    if let error = _swift_js_take_exception() {
+        throw error
+    }
+}
+
 #if arch(wasm32)
 @_extern(wasm, module: "BridgeJSIdentityTests", name: "bjs_IdentityModeTestImports_runJsIdentityModeTests_static")
 fileprivate func bjs_IdentityModeTestImports_runJsIdentityModeTests_static_extern() -> Void

Tests/BridgeJSIdentityTests/Generated/JavaScript/BridgeJS.json

@@ -406,7 +406,23 @@
     "children" : [
       {
         "functions" : [
+          {
+            "effects" : {
+              "isAsync" : false,
+              "isStatic" : false,
+              "isThrows" : true
+            },
+            "from" : "global",
+            "name" : "gc",
+            "parameters" : [
+
+            ],
+            "returnType" : {
+              "void" : {
 
+              }
+            }
+          }
         ],
         "types" : [
           {

Tests/BridgeJSIdentityTests/IdentityModeTests.swift

@@ -1,6 +1,8 @@
 import XCTest
 import JavaScriptKit
 
+@JSFunction(from: .global) func gc() throws(JSException) -> Void
+
 @JSClass struct IdentityModeTestImports {
     @JSFunction static func runJsIdentityModeTests() throws(JSException)
 }
@@ -9,6 +11,44 @@ final class IdentityModeTests: XCTestCase {
     func testRunJsIdentityModeTests() throws {
         try IdentityModeTestImports.runJsIdentityModeTests()
     }
+
+    /// Verifies that identity-cached wrappers are properly reclaimed by GC.
+    ///
+    /// Creates an identity-mode object, crosses it multiple times (filling the
+    /// identity cache), drops all references, triggers GC + event loop ticks,
+    /// and verifies the Swift object is deallocated. This proves that the
+    /// WeakRef-based identity cache does not prevent garbage collection.
+    func testIdentityCachedWrapperIsReclaimedByGC() async throws {
+        RetainLeakSubject.deinits = 0
+
+        // Create object and cross it multiple times to fill identity cache
+        _retainLeakSubject = RetainLeakSubject(tag: 99)
+        weak var weakSubject = _retainLeakSubject
+
+        // Cross to JS 5 times (populates identity cache with WeakRef)
+        for _ in 0..<5 {
+            _ = getRetainLeakSubject()
+        }
+
+        // Drop Swift-side strong reference
+        _retainLeakSubject = nil
+
+        // JS wrapper should still be alive via the identity cache's WeakRef,
+        // but WeakRef doesn't prevent GC. Trigger GC + event loop ticks to
+        // let FinalizationRegistry fire and call deinit.
+        for _ in 0..<100 {
+            try gc()
+            try await Task.sleep(for: .milliseconds(0))
+            if weakSubject == nil {
+                break
+            }
+        }
+
+        // The identity-cached wrapper should have been collected,
+        // FinalizationRegistry should have fired, deinit should have run.
+        XCTAssertNil(weakSubject, "Identity-cached object should be deallocated after GC")
+        XCTAssertEqual(RetainLeakSubject.deinits, 1, "Deinit should fire exactly once")
+    }
 }
 
 @JS class IdentityTestSubject {