From 390a35e5815d1cb4e40e87d332df711de379a852 Mon Sep 17 00:00:00 2001
From: Eric Niebler <eniebler@nvidia.com>
Date: Wed, 22 Jun 2022 22:56:28 -0700
Subject: [PATCH] work around strange gcc bug causing constraint recursion in
 ranges::any

---
 include/range/v3/detail/config.hpp |  8 ++---
 include/range/v3/utility/any.hpp   | 58 +++++++++++++++++-------------
 2 files changed, 36 insertions(+), 30 deletions(-)

diff --git a/include/range/v3/detail/config.hpp b/include/range/v3/detail/config.hpp
index f8015f436..d29dada10 100644
--- a/include/range/v3/detail/config.hpp
+++ b/include/range/v3/detail/config.hpp
@@ -351,9 +351,6 @@ namespace ranges
 #define RANGES_WORKAROUND_CLANG_43400 // template friend is redefinition of itself
 #endif
 #else                                 // __GNUC__
-#if __GNUC__ < 6
-#define RANGES_WORKAROUND_GCC_UNFILED0 /* Workaround old GCC name lookup bug */
-#endif
 #if __GNUC__ == 7 || __GNUC__ == 8
 #define RANGES_WORKAROUND_GCC_91525 /* Workaround strange GCC ICE */
 #endif
@@ -724,8 +721,9 @@ namespace ranges
 #endif
 #endif // RANGES_CONSTEXPR_IF
 
-#if !defined(RANGES_BROKEN_CPO_LOOKUP) && !defined(RANGES_DOXYGEN_INVOKED) && \
-    (defined(RANGES_WORKAROUND_GCC_UNFILED0) || defined(RANGES_WORKAROUND_MSVC_895622))
+#if !defined(RANGES_BROKEN_CPO_LOOKUP) && \
+    !defined(RANGES_DOXYGEN_INVOKED) && \
+    defined(RANGES_WORKAROUND_MSVC_895622)
 #define RANGES_BROKEN_CPO_LOOKUP 1
 #endif
 #ifndef RANGES_BROKEN_CPO_LOOKUP
diff --git a/include/range/v3/utility/any.hpp b/include/range/v3/utility/any.hpp
index 5feb2f8cd..7a3807499 100644
--- a/include/range/v3/utility/any.hpp
+++ b/include/range/v3/utility/any.hpp
@@ -61,25 +61,9 @@ namespace ranges
     template<typename T>
     T const * any_cast(any const *) noexcept;
 
-    struct any
+    namespace _any_
     {
-    private:
-        template<typename T>
-        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(any &);
-
-        template<typename T>
-        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(
-            any const &);
-
-        template<typename T>
-        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(
-            any &&);
-
-        template<typename T>
-        friend T * any_cast(any *) noexcept;
-
-        template<typename T>
-        friend T const * any_cast(any const *) noexcept;
+        struct _base {};
 
         struct interface
         {
@@ -117,15 +101,39 @@ namespace ranges
                 return typeid(T);
             }
         };
+    } // namespace _any_
+
+    struct any
+      #if RANGES_BROKEN_CPO_LOOKUP
+      : private _any_::_base
+      #endif
+    {
+    private:
+        template<typename T>
+        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(any &);
+
+        template<typename T>
+        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(
+            any const &);
+
+        template<typename T>
+        friend meta::if_c<std::is_reference<T>() || (bool)copyable<T>, T> any_cast(
+            any &&);
+
+        template<typename T>
+        friend T * any_cast(any *) noexcept;
+
+        template<typename T>
+        friend T const * any_cast(any const *) noexcept;
 
-        std::unique_ptr<interface> ptr_;
+        std::unique_ptr<_any_::interface> ptr_;
 
     public:
         any() noexcept = default;
         template(typename TRef, typename T = detail::decay_t<TRef>)(
             requires (!same_as<T, any>) AND copyable<T>) //
         any(TRef && t)
-          : ptr_(new impl<T>(static_cast<TRef &&>(t)))
+          : ptr_(new _any_::impl<T>(static_cast<TRef &&>(t)))
         {}
         any(any &&) noexcept = default;
         any(any const & that)
@@ -185,7 +193,7 @@ namespace ranges
     {
         if(x.type() != typeid(detail::decay_t<T>))
             throw bad_any_cast{};
-        return static_cast<any::impl<detail::decay_t<T>> *>(x.ptr_.get())->get();
+        return static_cast<_any_::impl<detail::decay_t<T>> *>(x.ptr_.get())->get();
     }
 
     /// \overload
@@ -194,7 +202,7 @@ namespace ranges
     {
         if(x.type() != typeid(detail::decay_t<T>))
             throw bad_any_cast{};
-        return static_cast<any::impl<detail::decay_t<T>> const *>(x.ptr_.get())->get();
+        return static_cast<_any_::impl<detail::decay_t<T>> const *>(x.ptr_.get())->get();
     }
 
     /// \overload
@@ -203,7 +211,7 @@ namespace ranges
     {
         if(x.type() != typeid(detail::decay_t<T>))
             throw bad_any_cast{};
-        return static_cast<any::impl<detail::decay_t<T>> *>(x.ptr_.get())->get();
+        return static_cast<_any_::impl<detail::decay_t<T>> *>(x.ptr_.get())->get();
     }
 
     /// \overload
@@ -211,7 +219,7 @@ namespace ranges
     T * any_cast(any * p) noexcept
     {
         if(p && p->ptr_)
-            if(any::impl<T> * q = dynamic_cast<any::impl<T> *>(p->ptr_.get()))
+            if(_any_::impl<T> * q = dynamic_cast<_any_::impl<T> *>(p->ptr_.get()))
                 return &q->get();
         return nullptr;
     }
@@ -221,7 +229,7 @@ namespace ranges
     T const * any_cast(any const * p) noexcept
     {
         if(p && p->ptr_)
-            if(any::impl<T> const * q = dynamic_cast<any::impl<T> const *>(p->ptr_.get()))
+            if(_any_::impl<T> const * q = dynamic_cast<_any_::impl<T> const *>(p->ptr_.get()))
                 return &q->get();
         return nullptr;
     }