Add support for neovim 0.6.0 diagnostic API highlight groups (#282)

In Neovim `0.6.0` [1] the naming scheme for the highlight groups of the
diagnostic API changed [2]. The new groups have been added as default while
the previous groups are conditionally guarded when using Neovim `0.5.0`.

[1]: https://github.com/neovim/neovim/releases/tag/v0.6.0
[2]: neovim/neovim@a5bbb93#diff-51fab2b766d0a3b606462e95de492190df173b7296147912307cdad636cd492aR77


Co-authored-by: Arctic Ice Studio <[email protected]>
Co-authored-by: Sven Greb <[email protected]>

GH-282

Author: Jan Steinke

colors/nord.vim

@@ -216,6 +216,16 @@ if has('nvim')
   let g:terminal_color_15 = s:nord6_gui
 endif
 
+"+- Neovim Diagnostics API -+
+call s:hi("DiagnosticWarn", s:nord13_gui, "", s:nord13_term, "", "", "")
+call s:hi("DiagnosticError" , s:nord11_gui, "", s:nord11_term, "", "", "")
+call s:hi("DiagnosticInfo" , s:nord8_gui, "", s:nord8_term, "", "", "")
+call s:hi("DiagnosticHint" , s:nord10_gui, "", s:nord10_term, "", "", "")
+call s:hi("DiagnosticUnderlineWarn" , s:nord13_gui, "", s:nord13_term, "", "undercurl", "")
+call s:hi("DiagnosticUnderlineError" , s:nord11_gui, "", s:nord11_term, "", "undercurl", "")
+call s:hi("DiagnosticUnderlineInfo" , s:nord8_gui, "", s:nord8_term, "", "undercurl", "")
+call s:hi("DiagnosticUnderlineHint" , s:nord10_gui, "", s:nord10_term, "", "undercurl", "")
+
 "+--- Gutter ---+
 call s:hi("CursorColumn", "", s:nord1_gui, "NONE", s:nord1_term, "", "")
 if g:nord_cursor_line_number_background == 0
@@ -575,14 +585,16 @@ call s:hi("CocHintSign" , s:nord10_gui, "", s:nord10_term, "", "", "")
 " Neovim LSP
 " > neovim/nvim-lspconfig
 call s:hi("LspCodeLens", s:nord3_gui_bright, "", s:nord3_term, "", "", "")
-call s:hi("LspDiagnosticsDefaultWarning", s:nord13_gui, "", s:nord13_term, "", "", "")
-call s:hi("LspDiagnosticsDefaultError" , s:nord11_gui, "", s:nord11_term, "", "", "")
-call s:hi("LspDiagnosticsDefaultInformation" , s:nord8_gui, "", s:nord8_term, "", "", "")
-call s:hi("LspDiagnosticsDefaultHint" , s:nord10_gui, "", s:nord10_term, "", "", "")
-call s:hi("LspDiagnosticsUnderlineWarning" , s:nord13_gui, "", s:nord13_term, "", "undercurl", "")
-call s:hi("LspDiagnosticsUnderlineError" , s:nord11_gui, "", s:nord11_term, "", "undercurl", "")
-call s:hi("LspDiagnosticsUnderlineInformation" , s:nord8_gui, "", s:nord8_term, "", "undercurl", "")
-call s:hi("LspDiagnosticsUnderlineHint" , s:nord10_gui, "", s:nord10_term, "", "undercurl", "")
+if has("nvim-0.5")
+  call s:hi("LspDiagnosticsDefaultWarning", s:nord13_gui, "", s:nord13_term, "", "", "")
+  call s:hi("LspDiagnosticsDefaultError" , s:nord11_gui, "", s:nord11_term, "", "", "")
+  call s:hi("LspDiagnosticsDefaultInformation" , s:nord8_gui, "", s:nord8_term, "", "", "")
+  call s:hi("LspDiagnosticsDefaultHint" , s:nord10_gui, "", s:nord10_term, "", "", "")
+  call s:hi("LspDiagnosticsUnderlineWarning" , s:nord13_gui, "", s:nord13_term, "", "undercurl", "")
+  call s:hi("LspDiagnosticsUnderlineError" , s:nord11_gui, "", s:nord11_term, "", "undercurl", "")
+  call s:hi("LspDiagnosticsUnderlineInformation" , s:nord8_gui, "", s:nord8_term, "", "undercurl", "")
+  call s:hi("LspDiagnosticsUnderlineHint" , s:nord10_gui, "", s:nord10_term, "", "undercurl", "")
+endif
 
 " GitGutter
 " > airblade/vim-gitgutter