Fix bugprone-crtp-constructor-accessibility clang-tidy errors

CRTP base classes used in a two-level hierarchy (base -> intermediate
-> final) need protected constructors so the intermediate template can
call them. Add NOLINTNEXTLINE suppression since the tidy check doesn't
account for multi-level CRTP. Intermediate "finals" templates use
private constructors with friend Derived as the check recommends.

Author: mvandeberg

include/boost/corosio/native/detail/reactor/reactor_acceptor.hpp

@@ -60,6 +60,7 @@ class reactor_acceptor
     friend Derived;
 
 protected:
+    // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
     explicit reactor_acceptor(Service& svc) noexcept : svc_(svc) {}
 
 protected:

include/boost/corosio/native/detail/reactor/reactor_acceptor_service.hpp

@@ -48,6 +48,7 @@ class reactor_acceptor_service : public ServiceBase
     using state_type = reactor_service_state<Scheduler, Impl>;
 
 protected:
+    // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
     explicit reactor_acceptor_service(capy::execution_context& ctx)
         : ctx_(ctx)
         , state_(

include/boost/corosio/native/detail/reactor/reactor_datagram_socket.hpp

@@ -84,6 +84,7 @@ class reactor_datagram_socket
     friend Derived;
 
 protected:
+    // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
     explicit reactor_datagram_socket(Service& svc) noexcept : base_type(svc) {}
 
 protected:

include/boost/corosio/native/detail/reactor/reactor_service_finals.hpp

@@ -169,15 +169,16 @@ class reactor_tcp_service_impl
     using base_service = reactor_socket_service<
         Derived, tcp_service,
         typename Traits::scheduler_type, SocketFinal>;
+    friend Derived;
     friend base_service;
 
+    explicit reactor_tcp_service_impl(capy::execution_context& ctx)
+        : base_service(ctx) {}
+
 public:
     static constexpr bool needs_write_notification =
         Traits::needs_write_notification;
 
-    explicit reactor_tcp_service_impl(capy::execution_context& ctx)
-        : base_service(ctx) {}
-
     std::error_code open_socket(
         tcp_socket::implementation& impl,
         int family, int type, int protocol) override
@@ -219,15 +220,16 @@ class reactor_local_stream_service_impl
     using base_service = reactor_socket_service<
         Derived, local_stream_service,
         typename Traits::scheduler_type, SocketFinal>;
+    friend Derived;
     friend base_service;
 
+    explicit reactor_local_stream_service_impl(capy::execution_context& ctx)
+        : base_service(ctx) {}
+
 public:
     static constexpr bool needs_write_notification =
         Traits::needs_write_notification;
 
-    explicit reactor_local_stream_service_impl(capy::execution_context& ctx)
-        : base_service(ctx) {}
-
     std::error_code open_socket(
         local_stream_socket::implementation& impl,
         int family, int type, int protocol) override
@@ -260,15 +262,16 @@ class reactor_udp_service_impl
     using base_service = reactor_socket_service<
         Derived, udp_service,
         typename Traits::scheduler_type, SocketFinal>;
+    friend Derived;
     friend base_service;
 
+    explicit reactor_udp_service_impl(capy::execution_context& ctx)
+        : base_service(ctx) {}
+
 public:
     static constexpr bool needs_write_notification =
         Traits::needs_write_notification;
 
-    explicit reactor_udp_service_impl(capy::execution_context& ctx)
-        : base_service(ctx) {}
-
     std::error_code open_datagram_socket(
         udp_socket::implementation& impl,
         int family, int type, int protocol) override
@@ -300,15 +303,16 @@ class reactor_local_dgram_service_impl
     using base_service = reactor_socket_service<
         Derived, local_datagram_service,
         typename Traits::scheduler_type, SocketFinal>;
+    friend Derived;
     friend base_service;
 
+    explicit reactor_local_dgram_service_impl(capy::execution_context& ctx)
+        : base_service(ctx) {}
+
 public:
     static constexpr bool needs_write_notification =
         Traits::needs_write_notification;
 
-    explicit reactor_local_dgram_service_impl(capy::execution_context& ctx)
-        : base_service(ctx) {}
-
     std::error_code open_socket(
         local_datagram_socket::implementation& impl,
         int family, int type, int protocol) override
@@ -353,9 +357,9 @@ class reactor_acceptor_service_impl
         typename Traits::scheduler_type,
         AccFinal,
         StreamServiceFinal>;
+    friend Derived;
     friend base_service;
 
-public:
     explicit reactor_acceptor_service_impl(capy::execution_context& ctx)
         : base_service(ctx)
     {
@@ -364,6 +368,7 @@ class reactor_acceptor_service_impl
             this->ctx_.template find_service<StreamServiceFinal>();
     }
 
+public:
     std::error_code open_acceptor_socket(
         typename AccFinal::impl_base_type& impl,
         int family, int type, int protocol) override

include/boost/corosio/native/detail/reactor/reactor_socket_finals.hpp

@@ -65,19 +65,20 @@ class reactor_stream_socket_impl
           ImplBase,
           Endpoint>
 {
+    friend Derived;
     friend Service;
 
+    explicit reactor_stream_socket_impl(Service& svc) noexcept
+        : reactor_stream_socket_impl::reactor_stream_socket(svc)
+    {
+    }
+
 public:
     using impl_base_type = ImplBase;
 
     // Per-socket hook state (e.g., kqueue SO_LINGER tracking).
     [[no_unique_address]] typename Traits::stream_socket_hook hook_;
 
-    explicit reactor_stream_socket_impl(Service& svc) noexcept
-        : reactor_stream_socket_impl::reactor_stream_socket(svc)
-    {
-    }
-
     ~reactor_stream_socket_impl() override = default;
 
     std::error_code set_option(
@@ -124,16 +125,17 @@ class reactor_dgram_socket_impl
           ImplBase,
           Endpoint>
 {
+    friend Derived;
     friend Service;
 
-public:
-    using impl_base_type = ImplBase;
-
     explicit reactor_dgram_socket_impl(Service& svc) noexcept
         : reactor_dgram_socket_impl::reactor_datagram_socket(svc)
     {
     }
 
+public:
+    using impl_base_type = ImplBase;
+
     ~reactor_dgram_socket_impl() override = default;
 };
 
@@ -162,16 +164,17 @@ class reactor_acceptor_impl
           AccImplBase,
           Endpoint>
 {
+    friend Derived;
     friend Service;
 
-public:
-    using impl_base_type = AccImplBase;
-
     explicit reactor_acceptor_impl(Service& svc) noexcept
         : reactor_acceptor_impl::reactor_acceptor(svc)
     {
     }
 
+public:
+    using impl_base_type = AccImplBase;
+
     ~reactor_acceptor_impl() override = default;
 
     std::coroutine_handle<> accept(

include/boost/corosio/native/detail/reactor/reactor_socket_service.hpp

@@ -39,6 +39,7 @@ class reactor_socket_service : public ServiceBase
     using state_type = reactor_service_state<Scheduler, Impl>;
 
 protected:
+    // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
     explicit reactor_socket_service(capy::execution_context& ctx)
         : state_(
               std::make_unique<state_type>(

include/boost/corosio/native/detail/reactor/reactor_stream_socket.hpp

@@ -68,6 +68,7 @@ class reactor_stream_socket
     friend Derived;
 
 protected:
+    // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
     explicit reactor_stream_socket(Service& svc) noexcept : base_type(svc) {}
 
 protected: