libcc1: use variadic templates for callbacks

This patch completes the transition of libcc1 from the use of separate
template functions for different arities to the use of variadic
functions.  This is how I had wanted it to work from the very
beginning, and is possible now with C++11.

I had thought that variadic callbacks required C++17, but it turns out
that the approach taken here is basically equivalent to std::apply --
just a bit wordier.

libcc1

	* rpc.hh (argument_wrapper) <get>: Replace cast operator.
	(argument_wrapper<T *>) <get>: Likewise.
	(unmarshall): Add std::tuple overloads.
	(callback): Remove.
	(class invoker): New.
	* libcp1plugin.cc (plugin_init): Update.
	* libcp1.cc (libcp1::add_callbacks): Update.
	* libcc1plugin.cc (plugin_init): Update.
	* libcc1.cc (libcc1::add_callbacks): Update.
	* connection.cc (cc1_plugin::connection::do_wait): Update.

libcc1/connection.cc

@@ -129,7 +129,7 @@ cc1_plugin::connection::do_wait (bool want_result)
 		  return FAIL;
 
 		callback_ftype *callback
-		  = m_callbacks.find_callback (method_name);
+		  = m_callbacks.find_callback (method_name.get ());
 		// The call to CALLBACK is where we may end up in a
 		// reentrant call.
 		if (callback == NULL || !callback (this))

libcc1/libcc1.cc

@@ -143,15 +143,13 @@ void
 libcc1::add_callbacks ()
 {
   cc1_plugin::callback_ftype *fun
-    = cc1_plugin::callback<int,
+    = cc1_plugin::invoker<int,
 			  enum gcc_c_oracle_request,
-			   const char *,
+			  const char *>::invoke<c_call_binding_oracle>;
-			   c_call_binding_oracle>;
   connection->add_callback ("binding_oracle", fun);
 
-  fun = cc1_plugin::callback<gcc_address,
+  fun = cc1_plugin::invoker<gcc_address,
-			     const char *,
+			    const char *>::invoke<c_call_symbol_address>;
-			     c_call_symbol_address>;
   connection->add_callback ("address_oracle", fun);
 }
 

libcc1/libcc1plugin.cc

@@ -762,46 +762,46 @@ plugin_init (struct plugin_name_args *plugin_info,
 #define GCC_METHOD0(R, N)			\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD1(R, N, A)				\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD2(R, N, A, B)				\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A, B>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD3(R, N, A, B, C)			\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, C, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A, B, C>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD4(R, N, A, B, C, D)		\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, A, B, C, D,	\
+      = cc1_plugin::invoker<R, A, B, C,		\
-			     plugin_ ## N>;	\
+			    D>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD5(R, N, A, B, C, D, E)	\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, A, B, C, D, E,	\
+      = cc1_plugin::invoker<R, A, B, C, D,	\
-			     plugin_ ## N>;	\
+			    E>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD7(R, N, A, B, C, D, E, F, G)		\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, C, D, E, F, G,	\
+      = cc1_plugin::invoker<R, A, B, C, D,		\
-			     plugin_ ## N>;		\
+			    E, F, G>::invoke<plugin_ ## N>;		\
     current_context->add_callback (# N, fun);		\
   }
 

libcc1/libcp1.cc

@@ -166,23 +166,18 @@ void
 libcp1::add_callbacks ()
 {
   cc1_plugin::callback_ftype *fun
-    = cc1_plugin::callback<int,
+    = cc1_plugin::invoker<int, enum gcc_cp_oracle_request,
-			   enum gcc_cp_oracle_request,
+			  const char *>::invoke<cp_call_binding_oracle>;
-			   const char *,
-			   cp_call_binding_oracle>;
   connection->add_callback ("binding_oracle", fun);
 
-  fun = cc1_plugin::callback<gcc_address,
+  fun = cc1_plugin::invoker<gcc_address,
-			     const char *,
+			    const char *>::invoke<cp_call_symbol_address>;
-			     cp_call_symbol_address>;
   connection->add_callback ("address_oracle", fun);
 
-  fun = cc1_plugin::callback<int,
+  fun = cc1_plugin::invoker<int>::invoke<cp_call_enter_scope>;
-			     cp_call_enter_scope>;
   connection->add_callback ("enter_scope", fun);
 
-  fun = cc1_plugin::callback<int,
+  fun = cc1_plugin::invoker<int>::invoke<cp_call_leave_scope>;
-			     cp_call_leave_scope>;
   connection->add_callback ("leave_scope", fun);
 }
 

libcc1/libcp1plugin.cc

@@ -3509,46 +3509,46 @@ plugin_init (struct plugin_name_args *plugin_info,
 #define GCC_METHOD0(R, N)			\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD1(R, N, A)				\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD2(R, N, A, B)				\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A, B>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD3(R, N, A, B, C)			\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, C, plugin_ ## N>;	\
+      = cc1_plugin::invoker<R, A, B, C>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);		\
   }
 #define GCC_METHOD4(R, N, A, B, C, D)		\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, A, B, C, D,	\
+      = cc1_plugin::invoker<R, A, B, C,		\
-			     plugin_ ## N>;	\
+			    D>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD5(R, N, A, B, C, D, E)	\
   {						\
     cc1_plugin::callback_ftype *fun		\
-      = cc1_plugin::callback<R, A, B, C, D, E,	\
+      = cc1_plugin::invoker<R, A, B, C,		\
-			     plugin_ ## N>;	\
+			    D, E>::invoke<plugin_ ## N>;	\
     current_context->add_callback (# N, fun);	\
   }
 #define GCC_METHOD7(R, N, A, B, C, D, E, F, G)		\
   {							\
     cc1_plugin::callback_ftype *fun			\
-      = cc1_plugin::callback<R, A, B, C, D, E, F, G,	\
+      = cc1_plugin::invoker<R, A, B, C,			\
-			     plugin_ ## N>;		\
+			    D, E, F, G>::invoke<plugin_ ## N>;		\
     current_context->add_callback (# N, fun);		\
   }
 

libcc1/rpc.hh

@@ -43,7 +43,7 @@ namespace cc1_plugin
     argument_wrapper (const argument_wrapper &) = delete;
     argument_wrapper &operator= (const argument_wrapper &) = delete;
 
-    operator T () const { return m_object; }
+    T get () const { return m_object; }
 
     status unmarshall (connection *conn)
     {
@@ -68,7 +68,7 @@ namespace cc1_plugin
 
     typedef typename std::remove_const<T>::type type;
 
-    operator const type * () const
+    const type *get () const
     {
       return m_object.get ();
     }
@@ -88,17 +88,14 @@ namespace cc1_plugin
   };
 
   // There are two kinds of template functions here: "call" and
-  // "callback".  "call" is implemented with variadic templates, but
+  // "invoker".
-  // "callback" is repeated multiple times to handle different numbers
-  // of arguments.  (This could be improved with C++17 and
-  // std::apply.)
 
   // The "call" template is used for making a remote procedure call.
   // It starts a query ('Q') packet, marshalls its arguments, waits
   // for a result, and finally reads and returns the result via an
   // "out" parameter.
 
-  // The "callback" template is used when receiving a remote procedure
+  // The "invoker" template is used when receiving a remote procedure
   // call.  This template function is suitable for use with the
   // "callbacks" and "connection" classes.  It decodes incoming
   // arguments, passes them to the wrapped function, and finally
@@ -123,175 +120,71 @@ namespace cc1_plugin
     return OK;
   }
 
-  template<typename R, R (*func) (connection *)>
+  // The base case -- just return OK.
-  status
+  template<int I, typename... T>
-  callback (connection *conn)
+  typename std::enable_if<I == sizeof... (T), status>::type
+  unmarshall (connection *, std::tuple<T...> &)
   {
-    R result;
+    return OK;
-
-    if (!unmarshall_check (conn, 0))
-      return FAIL;
-    result = func (conn);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
   }
 
-  template<typename R, typename A, R (*func) (connection *, A)>
+  // Unmarshall this argument, then unmarshall all subsequent args.
-  status
+  template<int I, typename... T>
-  callback (connection *conn)
+  typename std::enable_if<I < sizeof... (T), status>::type
+  unmarshall (connection *conn, std::tuple<T...> &value)
   {
-    argument_wrapper<A> arg;
+    if (!std::get<I> (value).unmarshall (conn))
-    R result;
-
-    if (!unmarshall_check (conn, 1))
       return FAIL;
-    if (!arg.unmarshall (conn))
+    return unmarshall<I + 1, T...> (conn, value);
-      return FAIL;
-    result = func (conn, arg);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
   }
 
-  template<typename R, typename A1, typename A2, R (*func) (connection *,
+  // Wrap a static function that is suitable for use as a callback.
-							    A1, A2)>
+  // This is a template function inside a template class to work
-  status
+  // around limitations with multiple variadic packs.
-  callback (connection *conn)
+  template<typename R, typename... Arg>
+  class invoker
   {
-    argument_wrapper<A1> arg1;
+    // Base case -- we can call the function.
-    argument_wrapper<A2> arg2;
+    template<int I, R func (connection *, Arg...), typename... T>
-    R result;
+    static typename std::enable_if<I == sizeof... (Arg), R>::type
-
+    call (connection *conn, const std::tuple<argument_wrapper<Arg>...> &,
-    if (!unmarshall_check (conn, 2))
+	  T... args)
-      return FAIL;
+    {
-    if (!arg1.unmarshall (conn))
+      return func (conn, args...);
-      return FAIL;
-    if (!arg2.unmarshall (conn))
-      return FAIL;
-    result = func (conn, arg1, arg2);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
     }
 
-  template<typename R, typename A1, typename A2, typename A3,
+    // Unpack one argument and continue the recursion.
-	   R (*func) (connection *, A1, A2, A3)>
+    template<int I, R func (connection *, Arg...), typename... T>
-  status
+    static typename std::enable_if<I < sizeof... (Arg), R>::type
-  callback (connection *conn)
+    call (connection *conn, const std::tuple<argument_wrapper<Arg>...> &value,
+	  T... args)
     {
-    argument_wrapper<A1> arg1;
+      return call<I + 1, func> (conn, value, args...,
-    argument_wrapper<A2> arg2;
+				std::get<I> (value).get ());
-    argument_wrapper<A3> arg3;
-    R result;
-
-    if (!unmarshall_check (conn, 3))
-      return FAIL;
-    if (!arg1.unmarshall (conn))
-      return FAIL;
-    if (!arg2.unmarshall (conn))
-      return FAIL;
-    if (!arg3.unmarshall (conn))
-      return FAIL;
-    result = func (conn, arg1, arg2, arg3);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
     }
 
-  template<typename R, typename A1, typename A2, typename A3, typename A4,
+  public:
-	   R (*func) (connection *, A1, A2, A3, A4)>
+
-  status
+    // A callback function that reads arguments from the connection,
-  callback (connection *conn)
+    // calls the wrapped function, and then sends the result back on
+    // the connection.
+    template<R func (connection *, Arg...)>
+    static status
+    invoke (connection *conn)
     {
-    argument_wrapper<A1> arg1;
+      if (!unmarshall_check (conn, sizeof... (Arg)))
-    argument_wrapper<A2> arg2;
+	return FAIL;
-    argument_wrapper<A3> arg3;
+      std::tuple<argument_wrapper<Arg>...> wrapped;
-    argument_wrapper<A4> arg4;
+      if (!unmarshall<0> (conn, wrapped))
-    R result;
+	return FAIL;
 
-    if (!unmarshall_check (conn, 4))
+      R result = call<0, func> (conn, wrapped);
-      return FAIL;
-    if (!arg1.unmarshall (conn))
-      return FAIL;
-    if (!arg2.unmarshall (conn))
-      return FAIL;
-    if (!arg3.unmarshall (conn))
-      return FAIL;
-    if (!arg4.unmarshall (conn))
-      return FAIL;
-    result = func (conn, arg1, arg2, arg3, arg4);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
-  }
 
-  template<typename R, typename A1, typename A2, typename A3, typename A4,
-	   typename A5, R (*func) (connection *, A1, A2, A3, A4, A5)>
-  status
-  callback (connection *conn)
-  {
-    argument_wrapper<A1> arg1;
-    argument_wrapper<A2> arg2;
-    argument_wrapper<A3> arg3;
-    argument_wrapper<A4> arg4;
-    argument_wrapper<A5> arg5;
-    R result;
-
-    if (!unmarshall_check (conn, 5))
-      return FAIL;
-    if (!arg1.unmarshall (conn))
-      return FAIL;
-    if (!arg2.unmarshall (conn))
-      return FAIL;
-    if (!arg3.unmarshall (conn))
-      return FAIL;
-    if (!arg4.unmarshall (conn))
-      return FAIL;
-    if (!arg5.unmarshall (conn))
-      return FAIL;
-    result = func (conn, arg1, arg2, arg3, arg4, arg5);
-    if (!conn->send ('R'))
-      return FAIL;
-    return marshall (conn, result);
-  }
-
-  template<typename R, typename A1, typename A2, typename A3, typename A4,
-	   typename A5, typename A6, typename A7,
-	   R (*func) (connection *, A1, A2, A3, A4, A5, A6, A7)>
-  status
-  callback (connection *conn)
-  {
-    argument_wrapper<A1> arg1;
-    argument_wrapper<A2> arg2;
-    argument_wrapper<A3> arg3;
-    argument_wrapper<A4> arg4;
-    argument_wrapper<A5> arg5;
-    argument_wrapper<A6> arg6;
-    argument_wrapper<A7> arg7;
-    R result;
-
-    if (!unmarshall_check (conn, 7))
-      return FAIL;
-    if (!arg1.unmarshall (conn))
-      return FAIL;
-    if (!arg2.unmarshall (conn))
-      return FAIL;
-    if (!arg3.unmarshall (conn))
-      return FAIL;
-    if (!arg4.unmarshall (conn))
-      return FAIL;
-    if (!arg5.unmarshall (conn))
-      return FAIL;
-    if (!arg6.unmarshall (conn))
-      return FAIL;
-    if (!arg7.unmarshall (conn))
-      return FAIL;
-    result = func (conn, arg1, arg2, arg3, arg4, arg5, arg6, arg7);
       if (!conn->send ('R'))
 	return FAIL;
       return marshall (conn, result);
     }
   };
+};
 
 #endif // CC1_PLUGIN_RPC_HH