From ff7d69dafda2f2cdc3a93f76ed8f77a113ac1a1c Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Tue, 28 Feb 2023 10:35:18 +0100
Subject: [PATCH] Refuse to relocate non-copy/move-constructible types

When a type was explicitly made non-copyable and non-movable, refuse
attempts to mark it as relocatable.

Trivial relocatability is an optimization for move+destroy, so we
shouldn't allow working around the class author's wish to have a
non-movable type by a user making it Q_RELOCATABLE_TYPE.

Therefore, add a static_assert() to Q_DECLARE_TYPEINFO that fires
when a non-copy/move-constructible type is made Q_RELOCATABLE_TYPE.

Also add a similar static assertion to QTypeInfoMerger: All members
of a class T may be Q_RELOCATABLE_TYPE. But that doesn't mean that
T itself is:

   class T {
      QString m_s;
      QByteArray m_b;
      Q_DISABLE_COPY(T)
   public:
      ~~~~
   };

so check that T is actually copyable (or movable) when QTypeInfoMerger
would have have yielded isRelocatable.

Since Q_DECLARE_TYPEINFO and QTypeInfoMerger are not the only ways in
which a user can mark a type as relocatable (manual QTypeInfo
specialization is another option, and required, for certain template
classes), also check in q_uninitialized_relocate_n().

[ChangeLog][QtCore][QTypeInfo/QTypeInfoMerger] No longer allows
marking as Q_RELOCATABLE_TYPE a type that is neither movable nor
copyable.

Change-Id: If6b3e5c1bfb6538bd280262eefbb08ba3c810e4c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/global/qtypeinfo.h           | 9 +++++++++
 src/corelib/tools/qcontainertools_impl.h | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/src/corelib/global/qtypeinfo.h b/src/corelib/global/qtypeinfo.h
index f89bf72635e..9b2119da1df 100644
--- a/src/corelib/global/qtypeinfo.h
+++ b/src/corelib/global/qtypeinfo.h
@@ -97,6 +97,11 @@ public:
     [[deprecated("Use std::is_pointer instead")]] static constexpr bool isPointer = false;
     [[deprecated("Use std::is_integral instead")]] static constexpr bool isIntegral = false;
     static constexpr bool isValueInitializationBitwiseZero = false;
+    static_assert(!isRelocatable ||
+                  std::is_copy_constructible_v<T> ||
+                  std::is_move_constructible_v<T>,
+                  "All Ts... are Q_RELOCATABLE_TYPE, but T is neither copy- nor move-constructible, "
+                  "so cannot be Q_RELOCATABLE_TYPE. Please mark T as Q_COMPLEX_TYPE manually.");
 };
 
 // QTypeInfo for std::pair:
@@ -158,6 +163,10 @@ public: \
         isIntegral [[deprecated("Use std::is_integral instead")]] = std::is_integral< TYPE >::value, \
         isValueInitializationBitwiseZero = QtPrivate::qIsValueInitializationBitwiseZero<TYPE>, \
     }; \
+    static_assert(!isRelocatable || \
+                  std::is_copy_constructible_v<TYPE > || \
+                  std::is_move_constructible_v<TYPE >, \
+                  #TYPE " is neither copy- nor move-constructible, so cannot be Q_RELOCATABLE_TYPE"); \
 }
 
 #define Q_DECLARE_TYPEINFO(TYPE, FLAGS) \
diff --git a/src/corelib/tools/qcontainertools_impl.h b/src/corelib/tools/qcontainertools_impl.h
index 40ed0a84e96..d66705ef4d4 100644
--- a/src/corelib/tools/qcontainertools_impl.h
+++ b/src/corelib/tools/qcontainertools_impl.h
@@ -72,6 +72,8 @@ template <typename T, typename N>
 void q_uninitialized_relocate_n(T* first, N n, T* out)
 {
     if constexpr (QTypeInfo<T>::isRelocatable) {
+        static_assert(std::is_copy_constructible_v<T> || std::is_move_constructible_v<T>,
+                      "Refusing to relocate this non-copy/non-move-constructible type.");
         if (n != N(0)) { // even if N == 0, out == nullptr or first == nullptr are UB for memcpy()
             std::memcpy(static_cast<void *>(out),
                         static_cast<const void *>(first),