Special-case the forward declaration of STL types for libc++.

This is somewhat of a follow-up to 5210d47aa66214e3cb16f394d0510a91f770c1b1.
libc++ declares the STL types in an inline namespace within the "std" one if
clang is used.

If one includes a header such as <iterator> before a Qt one and builds with
QT_NO_STL, the following ends up happening:

  // <iterator>
  namespace std {
      inline namespace __1 {
          struct random_access_iterator ... ;
      }
  }

  // qiterator.h
  #ifdef QT_NO_STL
  namespace std {
     struct random_access_iterator;
  }
  #endif

qiterator.h's declaration shadows the original one, and the compiler
complains random_access_iterator lacks an actual declaration.

Solve this by checking for libc++ and forward-declaring the iterator types
we need within the same inline namespace.

Not backported from qtbase because QT_NO_STL does not exist in Qt 5.

Change-Id: I6742d540f6538a30aa060a4447c288cfb9cd781d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/corelib/tools/qiterator.h b/src/corelib/tools/qiterator.h
index c859d37178..54c331e0eb 100644
--- a/src/corelib/tools/qiterator.h
+++ b/src/corelib/tools/qiterator.h
@@ -47,10 +47,33 @@
 QT_BEGIN_HEADER
 
 #ifdef QT_NO_STL
+# include <ciso646> // No-op, indirectly include additional configuration headers.
+# if defined(_LIBCPP_VERSION)
+// libc++ may declare these structs in an inline namespace. Forward-declare
+// these iterators in the same namespace so that we do not shadow the original
+// declarations.
+
+// Tell clang not to warn about the use of inline namespaces when not building
+// in C++11 mode.
+#  if defined(Q_CC_CLANG)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wc++11-extensions"
+#  endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+    struct bidirectional_iterator_tag;
+    struct random_access_iterator_tag;
+_LIBCPP_END_NAMESPACE_STD
+
+#  if defined(Q_CC_CLANG)
+#   pragma GCC diagnostic pop
+#  endif
+# else
 namespace std {
     struct bidirectional_iterator_tag;
     struct random_access_iterator_tag;
 }
+# endif
 #endif
 
 QT_BEGIN_NAMESPACE