'termguicolors' #4690

TODO: Only works at startup (i.e., in the user's init.vim/vimrc/--cmd),
      but it should probably work at any time.

---

patch 7.4.1799
Problem:    'guicolors' is a confusing option name.
Solution:   Use 'termguicolors' instead. (Hirohito Higashi)
61be73bb0f

patch 7.4.1806
Problem:    'termguicolors' option missing from the options window.
Solution:   Add the entry.
8e3d1b6326

patch 7.4.1808
Problem:    Using wrong feature name to check for 'termguicolors'.
Solution:   Use the right feature name. (Ken Takata)
8a24b794b8

patch 7.4.1809
Problem:    Using wrong short option name for 'termguicolors'.
Solution:   Use the option name.
868cfc19bb

src/nvim/eval.c

@@ -10684,6 +10684,7 @@ static void f_has(typval_T *argvars, typval_T *rettv)
     "tablineat",
     "tag_binary",
     "tag_old_static",
+    "termguicolors",
     "termresponse",
     "textobjects",
     "title",

src/nvim/option_defs.h

@@ -619,6 +619,7 @@ EXTERN long p_titlelen;         ///< 'titlelen'
 EXTERN char_u *p_titleold;      ///< 'titleold'
 EXTERN char_u *p_titlestring;   ///< 'titlestring'
 EXTERN char_u *p_tsr;           ///< 'thesaurus'
+EXTERN bool p_tgc;              ///< 'termguicolors'
 EXTERN int p_ttimeout;          ///< 'ttimeout'
 EXTERN long p_ttm;              ///< 'ttimeoutlen'
 EXTERN char_u *p_udir;          ///< 'undodir'

src/nvim/options.lua

@@ -2382,6 +2382,14 @@ return {
       redraw={'everything'},
       defaults={if_true={vi=""}}
     },
+    {
+      full_name='termguicolors', abbreviation='tgc',
+      type='bool', scope={'global'},
+      vi_def=false,
+      redraw={'everything'},
+      varname='p_tgc',
+      defaults={if_true={vi=false}}
+    },
     {
       full_name='terse',
       type='bool', scope={'global'},

src/nvim/tui/tui.c

@@ -81,7 +81,7 @@ UI *tui_start(void)
 {
   UI *ui = xcalloc(1, sizeof(UI));
   ui->stop = tui_stop;
-  ui->rgb = os_getenv("NVIM_TUI_ENABLE_TRUE_COLOR") != NULL;
+  ui->rgb = p_tgc;
   ui->resize = tui_resize;
   ui->clear = tui_clear;
   ui->eol_clear = tui_eol_clear;

src/nvim/version.c

@@ -69,6 +69,10 @@ static char *features[] = {
 
 // clang-format off
 static int included_patches[] = {
+  1809,
+  1808,
+  1806,
+  1799,
   1757,
   1755,
   1753,