feat(highlight): add DiagnosticOk (and associated) highlight groups (#21286)

The existing groups, Error, Hint, Info, Warn cover many use cases, but
neglect the occasion where a diagnostic message should communicate a
non-informative (not a Hint or Info) event. DiagnosticOk covers this
with a generic green colorscheme.

runtime/doc/diagnostic.txt

@@ -206,6 +206,11 @@ DiagnosticInfo
 
                                                         *hl-DiagnosticHint*
 DiagnosticHint
+    Used as the base highlight group.
+    Other Diagnostic highlights link to this by default (except Underline)
+
+                                                        *hl-DiagnosticOk*
+DiagnosticOk
     Used as the base highlight group.
     Other Diagnostic highlights link to this by default (except Underline)
 
@@ -225,6 +230,10 @@ DiagnosticVirtualTextInfo
 DiagnosticVirtualTextHint
     Used for "Hint" diagnostic virtual text.
 
+                                                *hl-DiagnosticVirtualTextOk*
+DiagnosticVirtualTextOk
+    Used for "Ok" diagnostic virtual text.
+
                                                 *hl-DiagnosticUnderlineError*
 DiagnosticUnderlineError
     Used to underline "Error" diagnostics.
@@ -241,6 +250,10 @@ DiagnosticUnderlineInfo
 DiagnosticUnderlineHint
     Used to underline "Hint" diagnostics.
 
+                                                *hl-DiagnosticUnderlineOk*
+DiagnosticUnderlineOk
+    Used to underline "Ok" diagnostics.
+
                                                 *hl-DiagnosticFloatingError*
 DiagnosticFloatingError
     Used to color "Error" diagnostic messages in diagnostics float.
@@ -258,6 +271,10 @@ DiagnosticFloatingInfo
 DiagnosticFloatingHint
     Used to color "Hint" diagnostic messages in diagnostics float.
 
+                                                *hl-DiagnosticFloatingOk*
+DiagnosticFloatingOk
+    Used to color "Ok" diagnostic messages in diagnostics float.
+
                                                 *hl-DiagnosticSignError*
 DiagnosticSignError
     Used for "Error" signs in sign column.
@@ -274,6 +291,10 @@ DiagnosticSignInfo
 DiagnosticSignHint
     Used for "Hint" signs in sign column.
 
+                                                *hl-DiagnosticSignOk*
+DiagnosticSignOk
+    Used for "Ok" signs in sign column.
+
 ==============================================================================
 SIGNS                                                   *diagnostic-signs*
 

src/nvim/highlight_group.c

@@ -192,22 +192,27 @@ static const char *highlight_init_both[] = {
   "default DiagnosticWarn ctermfg=3 guifg=Orange",
   "default DiagnosticInfo ctermfg=4 guifg=LightBlue",
   "default DiagnosticHint ctermfg=7 guifg=LightGrey",
+  "default DiagnosticOk ctermfg=10 guifg=LightGreen",
   "default DiagnosticUnderlineError cterm=underline gui=underline guisp=Red",
   "default DiagnosticUnderlineWarn cterm=underline gui=underline guisp=Orange",
   "default DiagnosticUnderlineInfo cterm=underline gui=underline guisp=LightBlue",
   "default DiagnosticUnderlineHint cterm=underline gui=underline guisp=LightGrey",
+  "default DiagnosticUnderlineOk cterm=underline gui=underline guisp=LightGreen",
   "default link DiagnosticVirtualTextError DiagnosticError",
   "default link DiagnosticVirtualTextWarn DiagnosticWarn",
   "default link DiagnosticVirtualTextInfo DiagnosticInfo",
   "default link DiagnosticVirtualTextHint DiagnosticHint",
+  "default link DiagnosticVirtualTextOk DiagnosticOk",
   "default link DiagnosticFloatingError DiagnosticError",
   "default link DiagnosticFloatingWarn DiagnosticWarn",
   "default link DiagnosticFloatingInfo DiagnosticInfo",
   "default link DiagnosticFloatingHint DiagnosticHint",
+  "default link DiagnosticFloatingOk DiagnosticOk",
   "default link DiagnosticSignError DiagnosticError",
   "default link DiagnosticSignWarn DiagnosticWarn",
   "default link DiagnosticSignInfo DiagnosticInfo",
   "default link DiagnosticSignHint DiagnosticHint",
+  "default link DiagnosticSignOk DiagnosticOk",
 
   // Text
   "default link @text.literal Comment",

test/functional/lua/diagnostic_spec.lua

@@ -90,20 +90,25 @@ describe('vim.diagnostic', function()
       'DiagnosticFloatingError',
       'DiagnosticFloatingHint',
       'DiagnosticFloatingInfo',
+      'DiagnosticFloatingOk',
       'DiagnosticFloatingWarn',
       'DiagnosticHint',
       'DiagnosticInfo',
+      'DiagnosticOk',
       'DiagnosticSignError',
       'DiagnosticSignHint',
       'DiagnosticSignInfo',
+      'DiagnosticSignOk',
       'DiagnosticSignWarn',
       'DiagnosticUnderlineError',
       'DiagnosticUnderlineHint',
       'DiagnosticUnderlineInfo',
+      'DiagnosticUnderlineOk',
       'DiagnosticUnderlineWarn',
       'DiagnosticVirtualTextError',
       'DiagnosticVirtualTextHint',
       'DiagnosticVirtualTextInfo',
+      'DiagnosticVirtualTextOk',
       'DiagnosticVirtualTextWarn',
       'DiagnosticWarn',
     }, exec_lua([[return vim.fn.getcompletion('Diagnostic', 'highlight')]]))