OwnPtr: Add a way to turn an OwnPtr into a NonnullOwnPtr

Okay, so, OwnPtr<T>::release_nonnull() returns a NonnullOwnPtr<T>.
It assumes that the OwnPtr is non-null to begin with.

Note that this removes the value from the OwnPtr, as there can only be
a single owner.

AK/OwnPtr.h

@@ -120,6 +120,12 @@ public:
         return leaked_ptr;
     }
 
+    NonnullOwnPtr<T> release_nonnull()
+    {
+        ASSERT(m_ptr);
+        return NonnullOwnPtr<T>(NonnullOwnPtr<T>::Adopt, *leak_ptr());
+    }
+
     T* ptr() { return m_ptr; }
     const T* ptr() const { return m_ptr; }
 

AK/Tests/TestVector.cpp

@@ -1,6 +1,7 @@
 #include <AK/TestSuite.h>
 
 #include <AK/AKString.h>
+#include <AK/NonnullOwnPtrVector.h>
 #include <AK/OwnPtr.h>
 #include <AK/Vector.h>
 
@@ -252,4 +253,20 @@ TEST_CASE(vector_remove)
     EXPECT_EQ(ints[0], 4);
 }
 
+TEST_CASE(nonnullownptrvector)
+{
+    struct Object {
+        String string;
+    };
+    NonnullOwnPtrVector<Object> objects;
+
+    objects.append(make<Object>());
+    EXPECT_EQ(objects.size(), 1);
+
+    OwnPtr<Object> o = make<Object>();
+    objects.append(o.release_nonnull());
+    EXPECT(o == nullptr);
+    EXPECT_EQ(objects.size(), 2);
+}
+
 TEST_MAIN(Vector)