Marks the next_layer() functions as deprecated (#256)

CI builds now use BOOST_ALLOW_DEPRECATED to prevent warnings

Author: anarthal

include/boost/redis/connection.hpp

@@ -42,6 +42,7 @@
 #include <boost/asio/steady_timer.hpp>
 #include <boost/asio/write.hpp>
 #include <boost/assert.hpp>
+#include <boost/config.hpp>
 #include <boost/core/ignore_unused.hpp>
 
 #include <array>
@@ -745,9 +746,15 @@ class basic_connection {
    }
 
    /// Returns a reference to the next layer.
+   BOOST_DEPRECATED(
+      "Accessing the underlying stream is deprecated and will be removed in the next release. Use "
+      "the other member functions to interact with the connection.")
    auto& next_layer() noexcept { return *stream_; }
 
    /// Returns a const reference to the next layer.
+   BOOST_DEPRECATED(
+      "Accessing the underlying stream is deprecated and will be removed in the next release. Use "
+      "the other member functions to interact with the connection.")
    auto const& next_layer() const noexcept { return *stream_; }
 
    /// Sets the response object of `async_receive` operations.
@@ -915,9 +922,15 @@ class connection {
    bool will_reconnect() const noexcept { return impl_.will_reconnect(); }
 
    /// Calls `boost::redis::basic_connection::next_layer`.
+   BOOST_DEPRECATED(
+      "Accessing the underlying stream is deprecated and will be removed in the next release. Use "
+      "the other member functions to interact with the connection.")
    auto& next_layer() noexcept { return impl_.next_layer(); }
 
    /// Calls `boost::redis::basic_connection::next_layer`.
+   BOOST_DEPRECATED(
+      "Accessing the underlying stream is deprecated and will be removed in the next release. Use "
+      "the other member functions to interact with the connection.")
    auto const& next_layer() const noexcept { return impl_.next_layer(); }
 
    /// Calls `boost::redis::basic_connection::reset_stream`.

test/CMakeLists.txt

@@ -9,6 +9,7 @@ if (MSVC)
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   target_compile_options(boost_redis_project_options INTERFACE -Wall -Wextra -Werror)
 endif()
+target_compile_definitions(boost_redis_project_options INTERFACE BOOST_ALLOW_DEPRECATED=1) # we need to still test deprecated fns
 
 add_library(boost_redis_src STATIC boost_redis.cpp)
 target_compile_features(boost_redis_src PRIVATE cxx_std_17)

test/Jamfile

@@ -14,6 +14,7 @@ local requirements =
         <define>BOOST_ASIO_DISABLE_BOOST_BIND=1
         <define>BOOST_ASIO_DISABLE_BOOST_DATE_TIME=1
         <define>BOOST_ASIO_DISABLE_BOOST_REGEX=1
+        <define>BOOST_ALLOW_DEPRECATED=1 # we need to test deprecated fns
         <toolset>msvc:<cxxflags>"/bigobj"
         <target-os>windows:<define>_WIN32_WINNT=0x0601
         [ requires