Patch to fix Boost.Context 1.64 for gcc 4.9

context_fix_gcc49_callcc.patch

From e66b64c1ec0bcc496d3d9212d66959351a5af551 Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Thu, 20 Apr 2017 22:59:55 +0300
Subject: [PATCH] Fix compilation with gcc 4.9.

The compiler apparently has problems with template ordering, so:

- Remove callcc overloads that have no arguments for the function. These
  overloads are ambiguous with the overloads taking variadic args. The
  no-args case is covered by the variadic iverloads anyway.

- Enforce overload resolution with SFINAE. Disable instantiating templated
  overloads with arguments for which non-templated version of callcc is
  provided.

- Update friend declarations of callcc in continuation to match the callcc
  function signatures, including the template arguments. Otherwise, friend
  declarations declare additional overloads of callcc which ambiguate
  overload resolution. To do this, the callcc functions have to be
  forward-declared before the continuation class (default template arguments
  cannot be specified in friend declarations).
---
 boost/context/continuation.hpp | 95 +++++++++++++++++++---------------
 1 file changed, 52 insertions(+), 43 deletions(-)

Index: boost_1_64_0/boost/context/continuation.hpp
===================================================================
--- boost_1_64_0.orig/boost/context/continuation.hpp	2017-04-20 23:15:28.139768406 +0300
+++ boost_1_64_0/boost/context/continuation.hpp	2017-04-20 23:15:28.135768369 +0300
@@ -270,6 +270,31 @@ detail::transfer_t context_ontop_void( d
 #endif
 }
 
+class continuation;
+
+template<
+    typename StackAlloc,
+    typename Fn,
+    typename ... Arg,
+    typename = detail::disable_overload< preallocated, StackAlloc >
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+    , typename = detail::disable_overload< segmented_stack, StackAlloc >
+#endif
+>
+continuation
+callcc( std::allocator_arg_t, StackAlloc salloc, Fn && fn, Arg ... arg);
+
+template<
+    typename StackAlloc,
+    typename Fn,
+    typename ... Arg
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+    , typename = detail::disable_overload< segmented_stack, StackAlloc >
+#endif
+>
+continuation
+callcc( std::allocator_arg_t, preallocated palloc, StackAlloc salloc, Fn && fn, Arg ... arg);
+
 class continuation {
 private:
     template< typename Ctx, typename StackAlloc, typename Fn >
@@ -283,22 +308,29 @@ private:
     friend detail::transfer_t
     context_ontop_void( detail::transfer_t);
 
-    template< typename StackAlloc, typename Fn, typename ... Arg >
+    template<
+        typename StackAlloc,
+        typename Fn,
+        typename ... Arg,
+        typename
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+        , typename
+#endif
+     >
     friend continuation
     callcc( std::allocator_arg_t, StackAlloc, Fn &&, Arg ...);
 
-    template< typename StackAlloc, typename Fn, typename ... Arg >
+    template<
+        typename StackAlloc,
+        typename Fn,
+        typename ... Arg
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+        , typename
+#endif
+     >
     friend continuation
     callcc( std::allocator_arg_t, preallocated, StackAlloc, Fn &&, Arg ...);
 
-    template< typename StackAlloc, typename Fn >
-    friend continuation
-    callcc( std::allocator_arg_t, StackAlloc, Fn &&);
-
-    template< typename StackAlloc, typename Fn >
-    friend continuation
-    callcc( std::allocator_arg_t, preallocated, StackAlloc, Fn &&);
-
     detail::transfer_t  t_{ nullptr, nullptr };
 
     continuation( detail::fcontext_t fctx) noexcept :
@@ -447,11 +479,11 @@ public:
     }
 };
 
-// Arg
 template<
     typename Fn,
     typename ... Arg,
-    typename = detail::disable_overload< continuation, Fn >
+    typename = detail::disable_overload< continuation, Fn >,
+    typename = detail::disable_overload< std::allocator_arg_t, Fn >
 >
 continuation
 callcc( Fn && fn, Arg ... arg) {
@@ -463,7 +495,11 @@ callcc( Fn && fn, Arg ... arg) {
 template<
     typename StackAlloc,
     typename Fn,
-    typename ... Arg
+    typename ... Arg,
+    typename // = detail::disable_overload< preallocated, StackAlloc >
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+    , typename // = detail::disable_overload< segmented_stack, StackAlloc >
+#endif
 >
 continuation
 callcc( std::allocator_arg_t, StackAlloc salloc, Fn && fn, Arg ... arg) {
@@ -478,6 +514,9 @@ template<
     typename StackAlloc,
     typename Fn,
     typename ... Arg
+#if defined(BOOST_USE_SEGMENTED_STACKS)
+    , typename // = detail::disable_overload< segmented_stack, StackAlloc >
+#endif
 >
 continuation
 callcc( std::allocator_arg_t, preallocated palloc, StackAlloc salloc, Fn && fn, Arg ... arg) {
@@ -488,36 +527,6 @@ callcc( std::allocator_arg_t, preallocat
                    std::forward< Arg >( arg) ... );
 }
 
-// void
-template<
-    typename Fn,
-    typename = detail::disable_overload< continuation, Fn >
->
-continuation
-callcc( Fn && fn) {
-    return callcc(
-            std::allocator_arg, fixedsize_stack(),
-            std::forward< Fn >( fn) );
-}
-
-template< typename StackAlloc, typename Fn >
-continuation
-callcc( std::allocator_arg_t, StackAlloc salloc, Fn && fn) {
-    using Record = detail::record< continuation, StackAlloc, Fn >;
-    return continuation{
-                detail::context_create< Record >(
-                        salloc, std::forward< Fn >( fn) ) }.resume();
-}
-
-template< typename StackAlloc, typename Fn >
-continuation
-callcc( std::allocator_arg_t, preallocated palloc, StackAlloc salloc, Fn && fn) {
-    using Record = detail::record< continuation, StackAlloc, Fn >;
-    return continuation{
-                detail::context_create< Record >(
-                        palloc, salloc, std::forward< Fn >( fn) ) }.resume();
-}
-
 #if defined(BOOST_USE_SEGMENTED_STACKS)
 template<
     typename Fn,