refactor(options): reduce `findoption()` usage

Problem: Many places in the code use `findoption()` to access an option using its name, even if the option index is available. This is very slow because it requires looping through the options array over and over.

Solution: Use option index instead of name wherever possible. Also introduce an `OptIndex` enum which contains the index for every option as enum constants, this eliminates the need to pass static option names as strings.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/nvim/help.c b/src/nvim/help.c
index dc4f6c44ff..28b95b2346 100644
--- a/src/nvim/help.c
+++ b/src/nvim/help.c
@@ -608,7 +608,7 @@ void cleanup_help_tags(int num_file, char **file)
 void prepare_help_buffer(void)
 {
   curbuf->b_help = true;
-  set_string_option_direct("buftype", -1, "help", OPT_FREE|OPT_LOCAL, 0);
+  set_string_option_direct(kOptBuftype, "help", OPT_FREE|OPT_LOCAL, 0);
 
   // Always set these options after jumping to a help tag, because the
   // user may have an autocommand that gets in the way.
@@ -617,13 +617,13 @@ void prepare_help_buffer(void)
   // Only set it when needed, buf_init_chartab() is some work.
   char *p = "!-~,^*,^|,^\",192-255";
   if (strcmp(curbuf->b_p_isk, p) != 0) {
-    set_string_option_direct("isk", -1, p, OPT_FREE|OPT_LOCAL, 0);
+    set_string_option_direct(kOptIskeyword, p, OPT_FREE|OPT_LOCAL, 0);
     check_buf_options(curbuf);
     (void)buf_init_chartab(curbuf, false);
   }
 
   // Don't use the global foldmethod.
-  set_string_option_direct("fdm", -1, "manual", OPT_FREE|OPT_LOCAL, 0);
+  set_string_option_direct(kOptFoldmethod, "manual", OPT_FREE|OPT_LOCAL, 0);
 
   curbuf->b_p_ts = 8;         // 'tabstop' is 8.
   curwin->w_p_list = false;   // No list mode.
@@ -649,7 +649,7 @@ void fix_help_buffer(void)
   // Set filetype to "help".
   if (strcmp(curbuf->b_p_ft, "help") != 0) {
     curbuf->b_ro_locked++;
-    set_option_value_give_err("ft", STATIC_CSTR_AS_OPTVAL("help"), OPT_LOCAL);
+    set_option_value_give_err(kOptFiletype, STATIC_CSTR_AS_OPTVAL("help"), OPT_LOCAL);
     curbuf->b_ro_locked--;
   }