From 4f200def9c735c97a0a2a2571ad455d3af644aa9 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 5 Apr 2020 11:32:30 +0200
Subject: [PATCH] AK: Stop allowing implicit downcast with OwnPtr and
 NonnullOwnPtr

Same issue here as we had with RefPtr and NonnullRefPtr.

Since we can't make copies of an owning pointer, we don't get quite the
same static_ptr_cast<T> here. Instead I've only added a new templated
version of OwnPtr::release_nonnull() in this patch, to solve the only
issue that popped up.

I'm not sure what the best solution here is, but this works for now.
---
 AK/NonnullOwnPtr.h                  |  2 +-
 AK/OwnPtr.h                         | 11 +++++++++--
 Libraries/LibIPC/ServerConnection.h |  4 ++--
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/AK/NonnullOwnPtr.h b/AK/NonnullOwnPtr.h
index c34b09de2fd..ddf2c6e50d7 100644
--- a/AK/NonnullOwnPtr.h
+++ b/AK/NonnullOwnPtr.h
@@ -62,7 +62,7 @@ public:
     template<typename U>
     RETURN_TYPESTATE(unconsumed)
     NonnullOwnPtr(NonnullOwnPtr<U>&& other)
-        : m_ptr(static_cast<T*>(other.leak_ptr()))
+        : m_ptr(other.leak_ptr())
     {
         ASSERT(m_ptr);
     }
diff --git a/AK/OwnPtr.h b/AK/OwnPtr.h
index b975abd8739..ed351be0600 100644
--- a/AK/OwnPtr.h
+++ b/AK/OwnPtr.h
@@ -45,12 +45,12 @@ public:
 
     template<typename U>
     OwnPtr(NonnullOwnPtr<U>&& other)
-        : m_ptr(static_cast<T*>(other.leak_ptr()))
+        : m_ptr(other.leak_ptr())
     {
     }
     template<typename U>
     OwnPtr(OwnPtr<U>&& other)
-        : m_ptr(static_cast<T*>(other.leak_ptr()))
+        : m_ptr(other.leak_ptr())
     {
     }
     OwnPtr(std::nullptr_t) {};
@@ -148,6 +148,13 @@ public:
         return NonnullOwnPtr<T>(NonnullOwnPtr<T>::Adopt, *leak_ptr());
     }
 
+    template<typename U>
+    NonnullOwnPtr<U> release_nonnull()
+    {
+        ASSERT(m_ptr);
+        return NonnullOwnPtr<U>(NonnullOwnPtr<U>::Adopt, static_cast<U&>(*leak_ptr()));
+    }
+
     T* ptr() { return m_ptr; }
     const T* ptr() const { return m_ptr; }
 
diff --git a/Libraries/LibIPC/ServerConnection.h b/Libraries/LibIPC/ServerConnection.h
index bd8dfad71bd..949a0787442 100644
--- a/Libraries/LibIPC/ServerConnection.h
+++ b/Libraries/LibIPC/ServerConnection.h
@@ -93,7 +93,7 @@ public:
             if (m_unprocessed_messages[i]->message_id() == MessageType::static_message_id()) {
                 auto message = move(m_unprocessed_messages[i]);
                 m_unprocessed_messages.remove(i);
-                return message;
+                return message.template release_nonnull<MessageType>();
             }
         }
         for (;;) {
@@ -112,7 +112,7 @@ public:
                 if (m_unprocessed_messages[i]->message_id() == MessageType::static_message_id()) {
                     auto message = move(m_unprocessed_messages[i]);
                     m_unprocessed_messages.remove(i);
-                    return message;
+                    return message.template release_nonnull<MessageType>();
                 }
             }
         }