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/api/private/converter.c

@@ -2,17 +2,24 @@
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
 #include <assert.h>
+#include <stdbool.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <stdlib.h>
 
+#include "klib/kvec.h"
 #include "nvim/api/private/converter.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/api/private/helpers.h"
 #include "nvim/assert.h"
 #include "nvim/eval/typval.h"
+#include "nvim/eval/typval_defs.h"
 #include "nvim/eval/userfunc.h"
-#include "nvim/lua/converter.h"
+#include "nvim/garray.h"
 #include "nvim/lua/executor.h"
+#include "nvim/memory.h"
+#include "nvim/types.h"
+#include "nvim/vim.h"
 
 /// Helper structure for vim_to_object
 typedef struct {

src/nvim/api/private/dispatch.c

@@ -1,38 +1,11 @@
 // 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 <stdbool.h>
+#include <stddef.h>
 
-#include "nvim/api/deprecated.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/api/private/dispatch.h"
 #include "nvim/api/private/helpers.h"
-#include "nvim/log.h"
-#include "nvim/map.h"
-#include "nvim/msgpack_rpc/helpers.h"
-#include "nvim/vim.h"
-
-// ===========================================================================
-// NEW API FILES MUST GO HERE.
-//
-//  When creating a new API file, you must include it here,
-//  so that the dispatcher can find the C functions that you are creating!
-// ===========================================================================
-#include "nvim/api/autocmd.h"
-#include "nvim/api/buffer.h"
-#include "nvim/api/command.h"
-#include "nvim/api/extmark.h"
-#include "nvim/api/options.h"
-#include "nvim/api/tabpage.h"
-#include "nvim/api/ui.h"
-#include "nvim/api/vim.h"
-#include "nvim/api/vimscript.h"
-#include "nvim/api/win_config.h"
-#include "nvim/api/window.h"
-#include "nvim/ui_client.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "api/private/dispatch_wrappers.generated.h"

src/nvim/api/private/dispatch.h

@@ -1,7 +1,12 @@
 #ifndef NVIM_API_PRIVATE_DISPATCH_H
 #define NVIM_API_PRIVATE_DISPATCH_H
 
+#include <stdbool.h>
+#include <stdint.h>
+
 #include "nvim/api/private/defs.h"
+#include "nvim/memory.h"
+#include "nvim/types.h"
 
 typedef Object (*ApiDispatchWrapper)(uint64_t channel_id, Array args, Arena *arena, Error *error);
 

src/nvim/api/private/helpers.c

@@ -3,8 +3,12 @@
 
 #include <assert.h>
 #include <inttypes.h>
+#include <limits.h>
+#include <msgpack/unpack.h>
+#include <stdarg.h>
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -12,28 +16,24 @@
 #include "nvim/api/private/converter.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/api/private/helpers.h"
-#include "nvim/api/vim.h"
 #include "nvim/ascii.h"
-#include "nvim/assert.h"
-#include "nvim/buffer.h"
-#include "nvim/charset.h"
-#include "nvim/eval.h"
+#include "nvim/buffer_defs.h"
 #include "nvim/eval/typval.h"
-#include "nvim/ex_cmds_defs.h"
+#include "nvim/eval/typval_defs.h"
 #include "nvim/ex_eval.h"
-#include "nvim/extmark.h"
+#include "nvim/garray.h"
 #include "nvim/highlight_group.h"
 #include "nvim/lua/executor.h"
 #include "nvim/map.h"
-#include "nvim/map_defs.h"
 #include "nvim/mark.h"
 #include "nvim/memline.h"
 #include "nvim/memory.h"
+#include "nvim/message.h"
 #include "nvim/msgpack_rpc/helpers.h"
+#include "nvim/pos.h"
 #include "nvim/ui.h"
 #include "nvim/version.h"
 #include "nvim/vim.h"
-#include "nvim/window.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "api/private/funcs_metadata.generated.h"

src/nvim/api/private/helpers.h

@@ -1,11 +1,17 @@
 #ifndef NVIM_API_PRIVATE_HELPERS_H
 #define NVIM_API_PRIVATE_HELPERS_H
 
+#include <stdbool.h>
+#include <stddef.h>
+
 #include "klib/kvec.h"
 #include "nvim/api/private/defs.h"
 #include "nvim/decoration.h"
 #include "nvim/ex_eval_defs.h"
 #include "nvim/getchar.h"
+#include "nvim/globals.h"
+#include "nvim/macros.h"
+#include "nvim/map.h"
 #include "nvim/memory.h"
 #include "nvim/vim.h"