startup: Avoid VimL global. Introduce TriState enum.

- `syntax_on` is documented. Rather than introduce a new undocumented
  VimL global `g:syntax_off`, use a module-local flag.
- Rename "maybe" functions to follow style guidelines (use standard
  module prefix)

runtime/syntax/nosyntax.vim

@@ -24,9 +24,6 @@ augroup END
 
 if exists("syntax_on")
   unlet syntax_on
-else
-  " only used when starting, to disable the default syntax enable
-  let syntax_off = 1
 endif
 if exists("syntax_manual")
   unlet syntax_manual

src/nvim/ex_docmd.c

@@ -9222,15 +9222,9 @@ char_u *get_behave_arg(expand_T *xp, int idx)
   return NULL;
 }
 
-typedef enum {
-    ft_UNSET,
-    ft_DISABLED,
-    ft_ENABLED
-} ft_flag_state;
-
-static ft_flag_state filetype_detect = ft_UNSET;
-static ft_flag_state filetype_plugin = ft_UNSET;
-static ft_flag_state filetype_indent = ft_UNSET;
+static TriState filetype_detect = kNone;
+static TriState filetype_plugin = kNone;
+static TriState filetype_indent = kNone;
 
 /*
  * ":filetype [plugin] [indent] {on,off,detect}"
@@ -9244,15 +9238,15 @@ static ft_flag_state filetype_indent = ft_UNSET;
 static void ex_filetype(exarg_T *eap)
 {
   char_u      *arg = eap->arg;
-  int plugin = FALSE;
-  int indent = FALSE;
+  bool plugin = false;
+  bool indent = false;
 
   if (*eap->arg == NUL) {
     /* Print current status. */
     smsg("filetype detection:%s  plugin:%s  indent:%s",
-         filetype_detect == ft_ENABLED ? "ON" : "OFF",
-         filetype_plugin == ft_ENABLED ? (filetype_detect == ft_ENABLED ? "ON" : "(on)") : "OFF", //  NOLINT
-         filetype_indent == ft_ENABLED ? (filetype_detect == ft_ENABLED ? "ON" : "(on)") : "OFF");  //  NOLINT
+         filetype_detect == kTrue ? "ON" : "OFF",
+         filetype_plugin == kTrue ? (filetype_detect == kTrue ? "ON" : "(on)") : "OFF",   // NOLINT(whitespace/line_length)
+         filetype_indent == kTrue ? (filetype_detect == kTrue ? "ON" : "(on)") : "OFF");  // NOLINT(whitespace/line_length)
     return;
   }
 
@@ -9273,14 +9267,14 @@ static void ex_filetype(exarg_T *eap)
   if (STRCMP(arg, "on") == 0 || STRCMP(arg, "detect") == 0) {
     if (*arg == 'o' || !filetype_detect) {
       source_runtime((char_u *)FILETYPE_FILE, true);
-      filetype_detect = ft_ENABLED;
+      filetype_detect = kTrue;
       if (plugin) {
         source_runtime((char_u *)FTPLUGIN_FILE, true);
-        filetype_plugin = ft_ENABLED;
+        filetype_plugin = kTrue;
       }
       if (indent) {
         source_runtime((char_u *)INDENT_FILE, true);
-        filetype_indent = ft_ENABLED;
+        filetype_indent = kTrue;
       }
     }
     if (*arg == 'd') {
@@ -9291,15 +9285,15 @@ static void ex_filetype(exarg_T *eap)
     if (plugin || indent) {
       if (plugin) {
         source_runtime((char_u *)FTPLUGOF_FILE, true);
-        filetype_plugin = ft_DISABLED;
+        filetype_plugin = kFalse;
       }
       if (indent) {
         source_runtime((char_u *)INDOFF_FILE, true);
-        filetype_indent = ft_DISABLED;
+        filetype_indent = kFalse;
       }
     } else {
       source_runtime((char_u *)FTOFF_FILE, true);
-      filetype_detect = ft_DISABLED;
+      filetype_detect = kFalse;
     }
   } else
     EMSG2(_(e_invarg2), arg);
@@ -9307,17 +9301,17 @@ static void ex_filetype(exarg_T *eap)
 
 /// Do ":filetype plugin indent on" if user did not already do some
 /// permutation thereof.
-void maybe_enable_filetype(void)
+void filetype_maybe_enable(void)
 {
-  if (filetype_detect == ft_UNSET
-      && filetype_plugin == ft_UNSET
-      && filetype_indent == ft_UNSET) {
+  if (filetype_detect == kNone
+      && filetype_plugin == kNone
+      && filetype_indent == kNone) {
     source_runtime((char_u *)FILETYPE_FILE, true);
-    filetype_detect = ft_ENABLED;
+    filetype_detect = kTrue;
     source_runtime((char_u *)FTPLUGIN_FILE, true);
-    filetype_plugin = ft_ENABLED;
+    filetype_plugin = kTrue;
     source_runtime((char_u *)INDENT_FILE, true);
-    filetype_indent = ft_ENABLED;
+    filetype_indent = kTrue;
   }
 }
 

src/nvim/globals.h

@@ -100,6 +100,12 @@
 # define VIMRC_FILE     ".nvimrc"
 #endif
 
+typedef enum {
+  kNone  = -1,
+  kFalse = 0,
+  kTrue  = 1,
+} TriState;
+
 /* Values for "starting" */
 #define NO_SCREEN       2       /* no screen updating yet */
 #define NO_BUFFERS      1       /* not all buffers loaded yet */

src/nvim/main.c

@@ -334,11 +334,10 @@ int main(int argc, char **argv)
 
   // If using the runtime (-u is not NONE), enable syntax & filetype plugins.
   if (params.use_vimrc != NULL && strcmp(params.use_vimrc, "NONE") != 0) {
-    // Do ":filetype plugin indent on".
-    maybe_enable_filetype();
-    // Enable syntax (sources syntax/syntax.vim, which calls `:filetype on`).
-    do_cmdline_cmd("if !exists('syntax_off') | syntax on |"
-                   "else | unlet syntax_off | endif");
+    // Does ":filetype plugin indent on".
+    filetype_maybe_enable();
+    // Sources syntax/syntax.vim, which calls `:filetype on`.
+    syn_maybe_on();
   }
 
   /*

src/nvim/syntax.c

@@ -41,6 +41,8 @@
 #include "nvim/os/os.h"
 #include "nvim/os/time.h"
 
+static bool did_syntax_onoff = false;
+
 // Structure that stores information about a highlight group.
 // The ID of a highlight group is also called group ID.  It is the index in
 // the highlight_ga array PLUS ONE.
@@ -3288,19 +3290,24 @@ static void syn_cmd_off(exarg_T *eap, int syncing)
 static void syn_cmd_onoff(exarg_T *eap, char *name)
   FUNC_ATTR_NONNULL_ALL
 {
+  did_syntax_onoff = true;
   eap->nextcmd = check_nextcmd(eap->arg);
   if (!eap->skip) {
-    syn_cmd(name);
+    char buf[100];
+    strncpy(buf, "so ", 3);
+    vim_snprintf(buf + 3, sizeof(buf) - 3, SYNTAX_FNAME, name);
+    do_cmdline_cmd(buf);
   }
 }
 
-void syn_cmd(char *name)
-  FUNC_ATTR_NONNULL_ALL
+void syn_maybe_on(void)
 {
-  char buf[100];
-  strncpy(buf, "so ", 3);
-  vim_snprintf(buf + 3, sizeof(buf) - 3, SYNTAX_FNAME, name);
-  do_cmdline_cmd(buf);
+  if (!did_syntax_onoff) {
+    exarg_T ea;
+    ea.arg = (char_u *)"";
+    ea.skip = false;
+    syn_cmd_onoff(&ea, "syntax");
+  }
 }
 
 /*