Define a fallback implementation of the __promoted_t alias for
hypothetical C++17 compilers which don't define __cpp_fold_expressions.
Without this, <cmath> can't be compiled by such compilers, because the
3-arg form of std::hypot uses the alias.
libstdc++-v3/ChangeLog:
PR libstdc++/121097
* include/ext/type_traits.h (__promoted_t): Define fallback
implementation for the 3-arg case that std::hypot uses.
---
I tested this by bodging the header so that this definition is used
unconditionally, and it seemed to work.
libstdc++-v3/include/ext/type_traits.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/libstdc++-v3/include/ext/type_traits.h
b/libstdc++-v3/include/ext/type_traits.h
index 061555231468..ca5bc4e0d23e 100644
--- a/libstdc++-v3/include/ext/type_traits.h
+++ b/libstdc++-v3/include/ext/type_traits.h
@@ -269,6 +269,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
typedef __typeof__(_Tp2() + _Up2() + _Vp2() + _Wp2()) __type;
};
+
+#ifdef __glibcxx_hypot // C++ >= 17 && HOSTED
+ // __promoted_t is needed by the 3-arg std::hypot so define this in case
+ // any C++17 compiler doesn't define __cpp_fold_expressions (PR 121097).
+ template<typename _Tp1, typename _Tp2, typename _Tp3>
+ using __promoted_t = typename __promote_3<_Tp1, _Tp2, _Tp3>::__type;
+#endif
+
#endif
_GLIBCXX_END_NAMESPACE_VERSION
--
2.50.1
