fmtlib#2954: Provide std::conjunction and std::disjunction substitutes

include/fmt/core.h

@@ -292,6 +292,32 @@ template <typename T> using type_identity_t = typename type_identity<T>::type;
 template <typename T>
 using underlying_t = typename std::underlying_type<T>::type;
 
+template <typename...>
+struct disjunction;
+template <>
+struct disjunction<> : std::false_type {};
+template <typename P>
+struct disjunction<P> : P {};
+template <typename P1, typename P2>
+struct disjunction<P1, P2> : std::conditional<P1::value, P1, P2>::type {};
+template <typename P1, typename P2, typename P3, typename... Pn>
+struct disjunction<P1, P2, P3, Pn...> 
+  : std::conditional<P1::value, P1, disjunction<P2, P3, Pn...>>::type {
+};
+
+template <typename...>
+struct conjunction;
+template <>
+struct conjunction<> : std::true_type {};
+template <typename P>
+struct conjunction<P> : P {};
+template <typename P1, typename P2>
+struct conjunction<P1, P2> : std::conditional<P1::value, P2, P1>::type {};
+template <typename P1, typename P2, typename P3, typename... Pn>
+struct conjunction<P1, P2, P3, Pn...>
+  : std::conditional<P1::value, conjunction<P2, P3, Pn...>, P1>::type {
+};
+
 struct monostate {
   constexpr monostate() {}
 };