Define and use the ARRAY_SIZE macro

A similar macro is defined in the Linux kernel [1].

To refactor the code I used a slightly modified Coccinelle script I found in
[2].

```diff
// Use the macro ARRAY_SIZE when possible
//
// Confidence: High
// Copyright: (C) Gilles Muller, Julia Lawall, EMN, DIKU.  GPLv2.
// URL: http://www.emn.fr/x-info/coccinelle/rules/array.html
// Options: -I ... -all_includes can give more complete results

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(*E))
+ ARRAY_SIZE(E)

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(E[...]))
+ ARRAY_SIZE(E)

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(T))
+ ARRAY_SIZE(E)

@n@
identifier AS,E;
@@

- #define AS(E) ARRAY_SIZE(E)

@@
expression E;
identifier n.AS;
@@

- AS(E)
+ ARRAY_SIZE(E)
```

`spatch --in-place --sp-file array_size.cocci -I src/ -I build/include/ -I build/src/nvim/auto/ src/nvim/*.c`

[1] http://lxr.free-electrons.com/source/include/linux/kernel.h#L54
[2] http://www.emn.fr/z-info/coccinelle/rules/#macros

src/nvim/eval.c

@@ -6652,7 +6652,7 @@ char_u *get_function_name(expand_T *xp, int idx)
     if (name != NULL)
       return name;
   }
-  if (++intidx < (int)(sizeof(functions) / sizeof(struct fst))) {
+  if (++intidx < (int)ARRAY_SIZE(functions)) {
     STRCPY(IObuff, functions[intidx].f_name);
     STRCAT(IObuff, "(");
     if (functions[intidx].f_max_argc == 0)
@@ -6695,7 +6695,7 @@ find_internal_func (
 )
 {
   int first = 0;
-  int last = (int)(sizeof(functions) / sizeof(struct fst)) - 1;
+  int last = (int)ARRAY_SIZE(functions) - 1;
 
   /*
    * Find the function name in the table. Binary search.

src/nvim/ex_cmds.c

@@ -4954,7 +4954,7 @@ int find_help_tags(char_u *arg, int *num_matches, char_u ***matches, int keep_la
    * Recognize a few exceptions to the rule.	Some strings that contain '*'
    * with "star".  Otherwise '*' is recognized as a wildcard.
    */
-  for (i = (int)(sizeof(mtable) / sizeof(char *)); --i >= 0; )
+  for (i = (int)ARRAY_SIZE(mtable); --i >= 0; )
     if (STRCMP(arg, mtable[i]) == 0) {
       STRCPY(d, rtable[i]);
       break;

src/nvim/ex_docmd.c

@@ -2281,7 +2281,7 @@ int modifier_len(char_u *cmd)
 
   if (VIM_ISDIGIT(*cmd))
     p = skipwhite(skipdigits(cmd));
-  for (i = 0; i < (int)(sizeof(cmdmods) / sizeof(struct cmdmod)); ++i) {
+  for (i = 0; i < (int)ARRAY_SIZE(cmdmods); ++i) {
     for (j = 0; p[j] != NUL; ++j)
       if (p[j] != cmdmods[i].name[j])
         break;
@@ -2306,7 +2306,7 @@ int cmd_exists(char_u *name)
   char_u      *p;
 
   /* Check command modifiers. */
-  for (i = 0; i < (int)(sizeof(cmdmods) / sizeof(struct cmdmod)); ++i) {
+  for (i = 0; i < (int)ARRAY_SIZE(cmdmods); ++i) {
     for (j = 0; name[j] != NUL; ++j)
       if (name[j] != cmdmods[i].name[j])
         break;
@@ -4974,7 +4974,7 @@ char_u *get_user_cmd_flags(expand_T *xp, int idx)
   {"bang", "bar", "buffer", "complete", "count",
    "nargs", "range", "register"};
 
-  if (idx >= (int)(sizeof(user_cmd_flags) / sizeof(user_cmd_flags[0])))
+  if (idx >= (int)ARRAY_SIZE(user_cmd_flags))
     return NULL;
   return (char_u *)user_cmd_flags[idx];
 }
@@ -4986,7 +4986,7 @@ char_u *get_user_cmd_nargs(expand_T *xp, int idx)
 {
   static char *user_cmd_nargs[] = {"0", "1", "*", "?", "+"};
 
-  if (idx >= (int)(sizeof(user_cmd_nargs) / sizeof(user_cmd_nargs[0])))
+  if (idx >= (int)ARRAY_SIZE(user_cmd_nargs))
     return NULL;
   return (char_u *)user_cmd_nargs[idx];
 }

src/nvim/ex_getln.c

@@ -3715,7 +3715,7 @@ ExpandFromContext (
      * right function to do the expansion.
      */
     ret = FAIL;
-    for (i = 0; i < (int)(sizeof(tab) / sizeof(struct expgen)); ++i)
+    for (i = 0; i < (int)ARRAY_SIZE(tab); ++i)
       if (xp->xp_context == tab[i].context) {
         if (tab[i].ic) {
           regmatch.rm_ic = TRUE;
@@ -4155,7 +4155,7 @@ static char_u *get_history_arg(expand_T *xp, int idx)
   static char_u compl[2] = { NUL, NUL };
   char *short_names = ":=@>?/";
   int short_names_count = (int)STRLEN(short_names);
-  int history_name_count = sizeof(history_names) / sizeof(char *) - 1;
+  int history_name_count = ARRAY_SIZE(history_names) - 1;
 
   if (idx < short_names_count) {
     compl[0] = (char_u)short_names[idx];

src/nvim/indent_c.c

@@ -303,7 +303,7 @@ static int cin_isinit(void)
   for (;; ) {
     int i, l;
 
-    for (i = 0; i < (int)(sizeof(skip) / sizeof(char *)); ++i) {
+    for (i = 0; i < (int)ARRAY_SIZE(skip); ++i) {
       l = (int)strlen(skip[i]);
       if (cin_starts_with(s, skip[i])) {
         s = cin_skipcomment(s + l);

src/nvim/keymap.c

@@ -284,8 +284,7 @@ static struct key_name_entry {
   {0,                 NULL}
 };
 
-#define KEY_NAMES_TABLE_LEN (sizeof(key_names_table) / \
-                             sizeof(struct key_name_entry))
+#define KEY_NAMES_TABLE_LEN ARRAY_SIZE(key_names_table)
 
 static struct mousetable {
   int pseudo_code;              /* Code for pseudo mouse event */

src/nvim/macros.h

@@ -152,4 +152,12 @@
 
 # define RESET_BINDING(wp)  (wp)->w_p_scb = FALSE; (wp)->w_p_crb = FALSE
 
+/// Calculate the length of a C array.
+///
+/// This should be called with a real array. Calling this with a pointer is an
+/// error. A mechanism to detect many (though not all) of those errors at compile
+/// time is implemented. It works by the second division producing a division by
+/// zero in those cases (-Wdiv-by-zero in GCC).
+#define ARRAY_SIZE(arr) ((sizeof(arr)/sizeof((arr)[0])) / ((size_t)(!(sizeof(arr) % sizeof((arr)[0])))))
+
 #endif  // NVIM_MACROS_H

src/nvim/mbyte.c

@@ -2138,7 +2138,7 @@ int utf_class(int c)
     {0x2f800, 0x2fa1f, 0x4e00},         /* CJK Ideographs */
   };
   int bot = 0;
-  int top = sizeof(classes) / sizeof(struct clinterval) - 1;
+  int top = ARRAY_SIZE(classes) - 1;
   int mid;
 
   /* First quick check for Latin1 characters, use 'iskeyword'. */

src/nvim/option.c

@@ -1883,7 +1883,7 @@ void set_init_1(void)
     int mustfree;
 
     ga_init(&ga, 1, 100);
-    for (n = 0; n < (long)(sizeof(names) / sizeof(char *)); ++n) {
+    for (n = 0; n < (long)ARRAY_SIZE(names); ++n) {
       mustfree = FALSE;
 # ifdef UNIX
       if (*names[n] == NUL)
@@ -4723,10 +4723,10 @@ static char_u *set_chars_option(char_u **varp)
 
   if (varp == &p_lcs) {
     tab = lcstab;
-    entries = sizeof(lcstab) / sizeof(struct charstab);
+    entries = ARRAY_SIZE(lcstab);
   } else {
     tab = filltab;
-    entries = sizeof(filltab) / sizeof(struct charstab);
+    entries = ARRAY_SIZE(filltab);
   }
 
   /* first round: check for valid value, second round: assign values */
@@ -7250,7 +7250,7 @@ int ExpandSettings(expand_T *xp, regmatch_T *regmatch, int *num_file, char_u ***
   for (loop = 0; loop <= 1; ++loop) {
     regmatch->rm_ic = ic;
     if (xp->xp_context != EXPAND_BOOL_SETTINGS) {
-      for (match = 0; match < (int)(sizeof(names) / sizeof(char *));
+      for (match = 0; match < (int)ARRAY_SIZE(names);
            ++match)
         if (vim_regexec(regmatch, (char_u *)names[match], (colnr_T)0)) {
           if (loop == 0)

src/nvim/regexp.c

@@ -602,7 +602,7 @@ static int get_char_class(char_u **pp)
   int i;
 
   if ((*pp)[1] == ':') {
-    for (i = 0; i < (int)(sizeof(class_names) / sizeof(*class_names)); ++i)
+    for (i = 0; i < (int)ARRAY_SIZE(class_names); ++i)
       if (STRNCMP(*pp + 2, class_names[i], STRLEN(class_names[i])) == 0) {
         *pp += STRLEN(class_names[i]) + 2;
         return i;

src/nvim/syntax.c

@@ -3943,7 +3943,7 @@ get_syn_options (
     if (strchr(first_letters, *arg) == NULL)
       break;
 
-    for (fidx = sizeof(flagtab) / sizeof(struct flag); --fidx >= 0; ) {
+    for (fidx = ARRAY_SIZE(flagtab); --fidx >= 0; ) {
       p = flagtab[fidx].name;
       int i;
       for (i = 0, len = 0; p[i] != NUL; i += 2, ++len)
@@ -6295,7 +6295,7 @@ do_highlight (
         attr = 0;
         off = 0;
         while (arg[off] != NUL) {
-          for (i = sizeof(hl_attr_table) / sizeof(int); --i >= 0; ) {
+          for (i = ARRAY_SIZE(hl_attr_table); --i >= 0; ) {
             len = (int)STRLEN(hl_name_table[i]);
             if (STRNICMP(arg + off, hl_name_table[i], len) == 0) {
               attr |= hl_attr_table[i];
@@ -6416,7 +6416,7 @@ do_highlight (
 
             /* reduce calls to STRICMP a bit, it can be slow */
             off = TOUPPER_ASC(*arg);
-            for (i = (sizeof(color_names) / sizeof(char *)); --i >= 0; )
+            for (i = ARRAY_SIZE(color_names); --i >= 0; )
               if (off == color_names[i][0]
                   && STRICMP(arg + 1, color_names[i] + 1) == 0)
                 break;

src/nvim/version.c

@@ -986,7 +986,7 @@ void intro_message(int colon)
   };
 
   // blanklines = screen height - # message lines
-  blanklines = (int)Rows - ((sizeof(lines) / sizeof(char *)) - 1);
+  blanklines = (int)Rows - (ARRAY_SIZE(lines) - 1);
 
   // Don't overwrite a statusline.  Depends on 'cmdheight'.
   if (p_ls > 1) {
@@ -1006,7 +1006,7 @@ void intro_message(int colon)
   row = blanklines / 2;
 
   if (((row >= 2) && (Columns >= 50)) || colon) {
-    for (i = 0; i < (int)(sizeof(lines) / sizeof(char *)); ++i) {
+    for (i = 0; i < (int)ARRAY_SIZE(lines); ++i) {
       p = lines[i];
 
       if (sponsor != 0) {