Rework fix for PR19460 - Use explicit bool as an extension instead.

In the previous fix I used a PMF type as a semi-safe bool type in C++03.
However immediately after committing I realized clang offered explicit
conversion operators as an extension. This patch removes the old fix and
enables _LIBCPP_EXPLICIT using __has_extension instead.

This change also affects the following other classes, which have
'_LIBCPP_EXPLICIT operator bool()'.

* shared_ptr
* unique_ptr
* error_condition
* basic_ios
* function (already C++11 only)
* istream::sentry
* experimental::string_view.

In all of the above cases I believe it is safe to enable the extension, except
in the experimental::string_view case. There seem to be some Clang bugs
affecting the experimental::string_view conversion to std::basic_string. To
work around that I manually disabled _LIBCPP_EXPLICIT in that case.

llvm-svn: 290831

1 files changed, 0 insertions, 17 deletions

diff --git a/libcxx/include/ios b/libcxx/include/ios
index fb8f88dddab..ea83822ac16 100644
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -572,13 +572,6 @@ ios_base::exceptions(iostate __iostate)
     clear(__rdstate_);
 }
 
-#if defined(_LIBCPP_CXX03_LANG)
-struct _LIBCPP_TYPE_VIS_ONLY __cxx03_bool {
-  typedef void (__cxx03_bool::*__bool_type)();
-  void __true_value() {}
-};
-#endif
-
 template <class _CharT, class _Traits>
 class _LIBCPP_TYPE_VIS_ONLY basic_ios
     : public ios_base
@@ -592,18 +585,8 @@ public:
     typedef typename traits_type::pos_type pos_type;
     typedef typename traits_type::off_type off_type;
 
-  // __true_value will generate undefined references when linking unless
-  // we give it internal linkage.
-
-#if defined(_LIBCPP_CXX03_LANG)
-    _LIBCPP_ALWAYS_INLINE
-    operator __cxx03_bool::__bool_type() const {
-        return !fail() ? &__cxx03_bool::__true_value : nullptr;
-    }
-#else
     _LIBCPP_ALWAYS_INLINE
     _LIBCPP_EXPLICIT operator bool() const {return !fail();}
-#endif
 
     _LIBCPP_ALWAYS_INLINE bool operator!() const    {return  fail();}
     _LIBCPP_ALWAYS_INLINE iostate rdstate() const   {return ios_base::rdstate();}