bun:test: stop leaking JSC scope objects through mock host functions

src/jsc/bindings/JSMockFunction.cpp

@@ -838,7 +838,7 @@ JSC_DEFINE_HOST_FUNCTION(jsMockFunctionCall, (JSGlobalObject * lexicalGlobalObje
     }
 
     JSC::ArgList args = JSC::ArgList(callframe);
-    JSValue thisValue = callframe->thisValue();
+    JSValue thisValue = callframe->thisValue().toThis(globalObject, JSC::ECMAMode::strict());
     JSC::JSArray* argumentsArray = nullptr;
     {
         JSC::ObjectInitializationScope object(vm);
@@ -1271,7 +1271,7 @@ JSC_DEFINE_HOST_FUNCTION(jsMockFunctionGetter_mockGetLastCall, (JSC::JSGlobalObj
 {
     auto& vm = JSC::getVM(globalObject);
     auto throwScope = DECLARE_THROW_SCOPE(vm);
-    JSValue thisObject = callframe->thisValue();
+    JSValue thisObject = callframe->thisValue().toThis(globalObject, JSC::ECMAMode::strict());
     if (!thisObject.isObject()) [[unlikely]] {
         return JSValue::encode(jsUndefined());
     }
@@ -1444,17 +1444,18 @@ BUN_DEFINE_HOST_FUNCTION(JSMock__jsNow, (JSC::JSGlobalObject * globalObject, JSC
 BUN_DEFINE_HOST_FUNCTION(JSMock__jsSetSystemTime, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callframe))
 {
     JSValue argument0 = callframe->argument(0);
+    JSValue thisValue = callframe->thisValue().toThis(globalObject, ECMAMode::strict());
 
     // JSGlobalObject::overridenDateNow's "no override" sentinel is NaN (see
     // JSGlobalObject::jsDateNow()), so every real timestamp, including 0 and
     // pre-epoch negatives, overrides; an omitted arg, NaN, or invalid Date resets.
     if (auto* dateInstance = dynamicDowncast<DateInstance>(argument0)) {
         globalObject->overridenDateNow = dateInstance->internalNumber();
-        return JSValue::encode(callframe->thisValue());
+        return JSValue::encode(thisValue);
     }
     globalObject->overridenDateNow = argument0.isNumber() ? argument0.asNumber() : PNaN;
 
-    return JSValue::encode(callframe->thisValue());
+    return JSValue::encode(thisValue);
 }
 
 BUN_DEFINE_HOST_FUNCTION(JSMock__jsRestoreAllMocks, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callframe))

test/js/bun/test/mock-fn.test.js

@@ -794,6 +794,31 @@ describe("mock()", () => {
 
     expect(bar()()).toBe(true);
   });
+
+  test("this is undefined for a bare call through a closure-captured binding", () => {
+    const fn = jest.fn().mockReturnThis();
+    const captured = 1;
+    // Referencing `fn` from an inner function forces it into the enclosing
+    // lexical environment, so `fn()` below resolves it through that scope.
+    function keepCaptured() {
+      return [fn, captured];
+    }
+    expect(fn()).toBeUndefined();
+    expect(fn.mock.contexts).toEqual([undefined]);
+  });
+
+  test("this seen by the implementation is undefined for a closure-captured bare call", () => {
+    let receivedThis = "not called";
+    const fn = jest.fn(function () {
+      receivedThis = this;
+    });
+    function keepCaptured() {
+      return fn;
+    }
+    fn();
+    expect(receivedThis).toBeUndefined();
+    expect(fn.mock.contexts).toEqual([undefined]);
+  });
 });
 
 describe("spyOn", () => {

test/js/bun/test/test-timers.test.ts

@@ -29,6 +29,16 @@ test("we can go back in time", () => {
   expect(now.toISOString()).toBe(orig.toISOString());
 });
 
+test("setSystemTime returns undefined for a bare call through a closure-captured binding", () => {
+  const { setSystemTime } = jest;
+  // Referencing `setSystemTime` from an inner function forces it into the
+  // enclosing lexical environment, so the bare call resolves through that scope.
+  function keepCaptured() {
+    return setSystemTime;
+  }
+  expect(setSystemTime()).toBeUndefined();
+});
+
 test("setSystemTime accepts pre-epoch and epoch times and resets with no argument", () => {
   const realBefore = Date.now();
   jest.useFakeTimers();