[WTF] Strengthen Box when it's build bare

https://bugs.webkit.org/show_bug.cgi?id=296689

Reviewed by Chris Dumez.

When building an empty Box you can end up with an empty RefPtr. We should ensure it's valid before accessing it.

Test: Tools/TestWebKitAPI/Tests/WTF/BoxPtr.cpp

* Source/WTF/wtf/Box.h:
(WTF::Box::isValid const):
(WTF::Box::get const):
(WTF::Box::operator* const):
(WTF::Box::operator-> const):
(WTF::Box::operator bool const):
* Tools/TestWebKitAPI/Tests/WTF/BoxPtr.cpp:
(TestWebKitAPI::BoxPtrClassTest::method):
(TestWebKitAPI::boxPtrClassTestDeleter):
(TestWebKitAPI::TEST(WTF_BoxPtr, NoCrash)):

Canonical link: https://commits.webkit.org/300573@main

Author: calvaris

Source/WTF/wtf/Box.h

@@ -55,21 +55,28 @@ class Box {
         return result;
     }
 
-    T* get() const { return &m_data->value; }
+    bool isValid() const { return static_cast<bool>(m_data); }
 
-    T& operator*() const { return m_data->value; }
-    T* operator->() const { return &m_data->value; }
+    T* get() const
+    {
+        if (!isValid())
+            return nullptr;
+        return &m_data->value;
+    }
+
+    T& operator*() const { RELEASE_ASSERT(isValid()); return m_data->value; }
+    T* operator->() const { RELEASE_ASSERT(isValid()); return &m_data->value; }
+
+    explicit operator bool() const { return isValid(); }
 
-    explicit operator bool() const { return static_cast<bool>(m_data); }
-    
 private:
     struct Data : ThreadSafeRefCounted<Data> {
         template<typename... Arguments>
         Data(Arguments&&... arguments)
             : value(std::forward<Arguments>(arguments)...)
         {
         }
-        
+
         T value;
     };
 

Tools/TestWebKitAPI/Tests/WTF/BoxPtr.cpp

@@ -50,11 +50,23 @@ void boxPtrLoggerDeleter(BoxPtrLogger* logger)
     delete logger;
 }
 
+class BoxPtrClassTest {
+public:
+    void method() { ++value; }
+    int value { 1 };
+};
+
+void boxPtrClassTestDeleter(BoxPtrClassTest* theObject)
+{
+    delete theObject;
+}
+
 };
 
 namespace WTF {
 
 WTF_DEFINE_BOXPTR_DELETER(TestWebKitAPI::BoxPtrLogger, TestWebKitAPI::boxPtrLoggerDeleter);
+WTF_DEFINE_BOXPTR_DELETER(TestWebKitAPI::BoxPtrClassTest, TestWebKitAPI::boxPtrClassTestDeleter);
 
 }
 
@@ -123,6 +135,14 @@ TEST(WTF_BoxPtr, Basic)
     EXPECT_STREQ("create(a) delete(a) ", takeLogStr().c_str());
 }
 
+TEST(WTF_BoxPtr, NoCrash)
+{
+    BoxPtr<BoxPtrClassTest> ptr;
+    EXPECT_EQ(false, static_cast<bool>(ptr));
+    EXPECT_EQ(false, ptr.isValid());
+    EXPECT_EQ(nullptr, ptr.get());
+}
+
 TEST(WTF_BoxPtr, Assignment)
 {
     {