build: allow IWYU to fix includes for all .c files

Allow Include What You Use to remove unnecessary includes and only
include what is necessary. This helps with reducing compilation times
and makes it easier to visualise which dependencies are actually
required.

Work on https://github.com/neovim/neovim/issues/549, but doesn't close
it since this only works fully for .c files and not headers.

src/nvim/msgpack_rpc/channel.c

@@ -1,36 +1,42 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+#include <assert.h>
 #include <inttypes.h>
-#include <msgpack.h>
+#include <msgpack/object.h>
+#include <msgpack/pack.h>
+#include <msgpack/sbuffer.h>
+#include <msgpack/unpack.h>
 #include <stdbool.h>
-#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <uv.h>
 
 #include "klib/kvec.h"
+#include "nvim/api/private/defs.h"
+#include "nvim/api/private/dispatch.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/api/ui.h"
-#include "nvim/api/vim.h"
-#include "nvim/ascii.h"
 #include "nvim/channel.h"
-#include "nvim/eval.h"
-#include "nvim/event/libuv_process.h"
+#include "nvim/event/defs.h"
 #include "nvim/event/loop.h"
 #include "nvim/event/rstream.h"
-#include "nvim/event/socket.h"
+#include "nvim/event/stream.h"
 #include "nvim/event/wstream.h"
+#include "nvim/globals.h"
 #include "nvim/log.h"
 #include "nvim/main.h"
 #include "nvim/map.h"
 #include "nvim/memory.h"
-#include "nvim/message.h"
 #include "nvim/msgpack_rpc/channel.h"
+#include "nvim/msgpack_rpc/channel_defs.h"
 #include "nvim/msgpack_rpc/helpers.h"
 #include "nvim/msgpack_rpc/unpacker.h"
 #include "nvim/os/input.h"
-#include "nvim/os_unix.h"
+#include "nvim/rbuffer.h"
+#include "nvim/types.h"
 #include "nvim/ui.h"
-#include "nvim/vim.h"
+#include "nvim/ui_client.h"
 
 #if MIN_LOG_LEVEL > LOGLVL_DBG
 # define log_client_msg(...)

src/nvim/msgpack_rpc/channel.h

@@ -6,8 +6,10 @@
 
 #include "nvim/api/private/defs.h"
 #include "nvim/channel.h"
+#include "nvim/event/multiqueue.h"
 #include "nvim/event/process.h"
 #include "nvim/event/socket.h"
+#include "nvim/macros.h"
 #include "nvim/vim.h"
 
 #define METHOD_MAXLEN 512

src/nvim/msgpack_rpc/helpers.c

@@ -1,21 +1,25 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
-#include <inttypes.h>
-#include <msgpack.h>
+#include <msgpack/object.h>
+#include <msgpack/sbuffer.h>
+#include <msgpack/unpack.h>
+#include <msgpack/zone.h>
 #include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
 
 #include "klib/kvec.h"
-#include "nvim/api/private/dispatch.h"
+#include "msgpack/pack.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/assert.h"
-#include "nvim/log.h"
+#include "nvim/event/wstream.h"
 #include "nvim/memory.h"
 #include "nvim/msgpack_rpc/helpers.h"
-#include "nvim/vim.h"
+#include "nvim/types.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "keysets.generated.h"
+# include "keysets.generated.h"  // IWYU pragma: export
 # include "msgpack_rpc/helpers.c.generated.h"
 #endif
 

src/nvim/msgpack_rpc/server.c

@@ -1,25 +1,22 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
-#include <assert.h>
 #include <inttypes.h>
-#include <stdlib.h>
+#include <stdbool.h>
+#include <stdio.h>
 #include <string.h>
+#include <uv.h>
 
-#include "nvim/ascii.h"
+#include "nvim/channel.h"
 #include "nvim/eval.h"
 #include "nvim/event/socket.h"
-#include "nvim/fileio.h"
 #include "nvim/garray.h"
 #include "nvim/log.h"
 #include "nvim/main.h"
 #include "nvim/memory.h"
-#include "nvim/msgpack_rpc/channel.h"
 #include "nvim/msgpack_rpc/server.h"
 #include "nvim/os/os.h"
-#include "nvim/path.h"
-#include "nvim/strings.h"
-#include "nvim/vim.h"
+#include "nvim/os/stdpaths_defs.h"
 
 #define MAX_CONNECTIONS 32
 #define ENV_LISTEN "NVIM_LISTEN_ADDRESS"  // deprecated

src/nvim/msgpack_rpc/unpacker.c

@@ -1,9 +1,17 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include "klib/kvec.h"
+#include "mpack/conv.h"
 #include "nvim/api/private/helpers.h"
-#include "nvim/log.h"
+#include "nvim/ascii.h"
+#include "nvim/macros.h"
 #include "nvim/memory.h"
+#include "nvim/msgpack_rpc/channel_defs.h"
 #include "nvim/msgpack_rpc/helpers.h"
 #include "nvim/msgpack_rpc/unpacker.h"
 #include "nvim/ui_client.h"

src/nvim/msgpack_rpc/unpacker.h

@@ -7,10 +7,14 @@
 
 #include "mpack/mpack_core.h"
 #include "mpack/object.h"
+#include "nvim/api/private/defs.h"
 #include "nvim/api/private/dispatch.h"
 #include "nvim/api/private/helpers.h"
+#include "nvim/grid_defs.h"
 #include "nvim/memory.h"
 #include "nvim/msgpack_rpc/channel_defs.h"
+#include "nvim/types.h"
+#include "nvim/ui_client.h"
 
 struct Unpacker {
   mpack_parser_t parser;