Silence MSVC warnings when using certain std algorithms

The MSVC STL warns when passing naked pointers as non-bounded
iterators to algorithms such as std::equal and std::copy, in
an attempt to inform users that the range specified by that
iterator has an implicit minimum size that the caller of the
algorithm must ensure is met:

  warning C4996: 'std::_Equal1': Function call with parameters that may be unsafe - \
  this call relies on the caller to check that the passed values are correct. To \
  disable this warning, use -D_SCL_SECURE_NO_WARNINGS. See documentation on how to \
  use Visual C++ 'Checked Iterators'

When building Qt, as well as when building user projects with
qmake (cf. 0a76b6bc7f98900ea884cd10ccca1a332e5bdba5), we
globally disable this warning (with -D_SCL_SECURE_NO_WARNINGS),
but since we started using STL algorithms in public headers (e.g.
in qvector.h), users get this warning in their own projects now,
unless they, too, define said macro. But such a requirement is
against the Qt policy to have headers that are warning-free as
much as possible.

The suggested way of fixing this warning is to wrap the naked
pointer in a stdext::unchecked_array_iterator before passing it
to the algorithm, cf. examples in

  https://msdn.microsoft.com/en-us/library/ttcz0bys%28v=vs.120%29.aspx

or, together with the capacity-made-explicit, in a
stdext::checked_array_iterator.

To avoid ifdefs for platforms that don't have these extensions
(which, incidentally, for the unchecked case, includes MSVC 2012),
wrap the calls in macros.

The end game here is to drop -D_SCL_SECURE_NO_WARNINGS, at least
for public headers, even though this commit also adds the wrapper
to implementation and private header files.

An alternative to the wrapper would have been the version of
std::equal that takes four iterators. However, that is a C++14
library feature, while this version of Qt still needs to compile
with a C++98 compiler, and, more importantly, there isn't, and
never will be, a corresponding 4-iterator version of std::copy.

Task-number: QTBUG-47948
Done-with: Stephen Kelly <steveire@gmail.com>
Change-Id: I1bbab257fb5f1c5042939c382a412b596112ff26
Reviewed-by: Stephen Kelly <ske@ableton.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/corelib/global/qcompilerdetection.h b/src/corelib/global/qcompilerdetection.h
index b11237dce5..25043dab75 100644
--- a/src/corelib/global/qcompilerdetection.h
+++ b/src/corelib/global/qcompilerdetection.h
@@ -94,6 +94,12 @@
 #  define Q_DECL_DEPRECATED_X(text) __declspec(deprecated(text))
 #  define Q_DECL_EXPORT __declspec(dllexport)
 #  define Q_DECL_IMPORT __declspec(dllimport)
+#  if _MSC_VER >= 1800
+#    define QT_MAKE_UNCHECKED_ARRAY_ITERATOR(x) stdext::make_unchecked_array_iterator(x)
+#  endif
+#  if _MSC_VER >= 1500
+#    define QT_MAKE_CHECKED_ARRAY_ITERATOR(x, N) stdext::make_checked_array_iterator(x, size_t(N))
+#  endif
 /* Intel C++ disguising as Visual C++: the `using' keyword avoids warnings */
 #  if defined(__INTEL_COMPILER)
 #    define Q_DECL_VARIABLE_DEPRECATED
@@ -1117,6 +1123,12 @@
 #ifndef Q_DECL_CONST_FUNCTION
 #  define Q_DECL_CONST_FUNCTION Q_DECL_PURE_FUNCTION
 #endif
+#ifndef QT_MAKE_UNCHECKED_ARRAY_ITERATOR
+#  define QT_MAKE_UNCHECKED_ARRAY_ITERATOR(x) (x)
+#endif
+#ifndef QT_MAKE_CHECKED_ARRAY_ITERATOR
+#  define QT_MAKE_CHECKED_ARRAY_ITERATOR(x, N) (x)
+#endif
 
 /*
  * Warning/diagnostic handling