build: -Wmissing-prototypes

ref #343

Though I don't see a strong benefit, it isn't too much of a burden, and
maybe avoids confusion in some cases.

CMakeLists.txt

@@ -259,7 +259,8 @@ if(MSVC)
   add_definitions(-DWIN32)
 else()
   add_definitions(-Wall -Wextra -pedantic -Wno-unused-parameter
-    -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion)
+    -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion
+    -Wmissing-prototypes)
 
   check_c_compiler_flag(-Wimplicit-fallthrough HAS_WIMPLICIT_FALLTHROUGH_FLAG)
   if(HAS_WIMPLICIT_FALLTHROUGH_FLAG)

src/nvim/aucmd.c

@@ -6,6 +6,7 @@
 #include "nvim/vim.h"
 #include "nvim/main.h"
 #include "nvim/ui.h"
+#include "nvim/aucmd.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "aucmd.c.generated.h"

src/nvim/eval.c

@@ -5958,6 +5958,10 @@ static int get_env_tv(char_u **arg, typval_T *rettv, int evaluate)
 #pragma function (floor)
 #endif
 
+// silence -Wmissing-prototypes for funcs.generated.h
+const VimLFuncDef *find_internal_func_gperf(register const char *str,
+                                            register size_t len);
+
 # include "funcs.generated.h"
 #endif
 

src/nvim/eval/decode.c

@@ -7,6 +7,7 @@
 
 #include "nvim/eval/typval.h"
 #include "nvim/eval.h"
+#include "nvim/eval/decode.h"
 #include "nvim/eval/encode.h"
 #include "nvim/ascii.h"
 #include "nvim/macros.h"

src/nvim/generators/gen_api_dispatch.lua

@@ -448,6 +448,7 @@ for _, fn in ipairs(functions) do
 end
 
 output:write(string.format([[
+void nlua_add_api_functions(lua_State *lstate);  // silence -Wmissing-prototypes
 void nlua_add_api_functions(lua_State *lstate)
   FUNC_ATTR_NONNULL_ALL
 {

src/nvim/main.c

@@ -222,6 +222,7 @@ void early_init(void)
 }
 
 #ifdef MAKE_LIB
+int nvim_main(int argc, char **argv);  // silence -Wmissing-prototypes
 int nvim_main(int argc, char **argv)
 #elif defined(WIN32)
 int wmain(int argc, wchar_t **argv_w)  // multibyte args on Windows. #7060

src/nvim/os/dl.c

@@ -7,6 +7,7 @@
 #include <stdint.h>
 #include <uv.h>
 
+#include "nvim/os/dl.h"
 #include "nvim/os/os.h"
 #include "nvim/memory.h"
 #include "nvim/message.h"

src/nvim/os/lang.c

@@ -11,6 +11,7 @@
 #ifdef HAVE_LOCALE_H
 # include <locale.h>
 #endif
+#include "nvim/os/lang.h"
 #include "nvim/os/os.h"
 
 void lang_init(void)

test/functional/fixtures/tty-test.c

@@ -20,6 +20,7 @@
 uv_tty_t tty;
 uv_tty_t tty_out;
 
+bool owns_tty(void);  // silence -Wmissing-prototypes
 bool owns_tty(void)
 {
 #ifdef _WIN32