refactor theme loading

autoload/utils.vim

@@ -193,3 +193,14 @@ function! utils#MultiEdit(patterns) abort
     endfor
   endfor
 endfunction
+
+function! utils#add_pack(name) abort
+  let l:success = v:true
+  try
+    execute printf("packadd! %s", a:name)
+  catch /^Vim\%((\a\+)\)\=:E919/
+    let l:success = v:false
+  endtry
+
+  return l:success
+endfunction

core/themes.vim

@@ -1,8 +1,6 @@
-let s:my_theme_dict = {}
-
-function! s:my_theme_dict.gruvbox8() dict abort
-  packadd! vim-gruvbox8
+let s:theme_func_dict = {}
 
+function! s:theme_func_dict.gruvbox8() dict abort
   " Italic options should be put before colorscheme setting,
   " see https://github.com/morhetz/gruvbox/wiki/Terminal-specific#1-italics-is-disabled
   let g:gruvbox_italics=1
@@ -12,83 +10,77 @@ function! s:my_theme_dict.gruvbox8() dict abort
   colorscheme gruvbox8_hard
 endfunction
 
-function! s:my_theme_dict.onedark() dict abort
-  packadd! onedark.nvim
-
+function! s:theme_func_dict.onedark() dict abort
   colorscheme onedark
 endfunction
 
-function! s:my_theme_dict.edge() dict abort
-  packadd! edge
-
+function! s:theme_func_dict.edge() dict abort
   let g:edge_enable_italic = 1
   let g:edge_better_performance = 1
   colorscheme edge
 endfunction
 
-function! s:my_theme_dict.sonokai() dict abort
-  packadd! sonokai
-
+function! s:theme_func_dict.sonokai() dict abort
   let g:sonokai_enable_italic = 1
   let g:sonokai_better_performance = 1
   colorscheme sonokai
 endfunction
 
-function! s:my_theme_dict.gruvbox_material() dict abort
-  packadd! gruvbox-material
-
+function! s:theme_func_dict.gruvbox_material() dict abort
   let g:gruvbox_material_enable_italic = 1
   let g:gruvbox_material_better_performance = 1
   colorscheme gruvbox-material
 endfunction
 
-function! s:my_theme_dict.nord() dict abort
-  packadd! nord.nvim
-
+function! s:theme_func_dict.nord() dict abort
   colorscheme nord
 endfunction
 
-function! s:my_theme_dict.doom_one() dict abort
-  packadd! doom-one.nvim
+function! s:theme_func_dict.doom_one() dict abort
   colorscheme doom-one
 endfunction
 
-function! s:my_theme_dict.everforest() dict abort
-  packadd! everforest
-
+function! s:theme_func_dict.everforest() dict abort
   let g:everforest_enable_italic = 1
   let g:everforest_better_performance = 1
   colorscheme everforest
 endfunction
 
-function! s:my_theme_dict.nightfox() dict abort
-  packadd! nightfox.nvim
-
+function! s:theme_func_dict.nightfox() dict abort
   colorscheme nordfox
 endfunction
 
-let s:candidate_theme = [
-      \ 'gruvbox8',
-      \ 'onedark',
-      \ 'edge',
-      \ 'sonokai',
-      \ 'gruvbox_material',
-      \ 'nord',
-      \ 'doom_one',
-      \ 'everforest',
-      \ 'nightfox'
-      \ ]
+" Theme to directory name mapping, because theme repo name is not necessarily
+" the same as the theme name itself.
+let s:theme2dir = {
+      \ 'gruvbox8' : 'vim-gruvbox8',
+      \ 'onedark': 'onedark.nvim',
+      \ 'edge' : 'edge',
+      \ 'sonokai': 'sonokai',
+      \ 'gruvbox_material': 'gruvbox-material',
+      \ 'nord': 'nord.nvim',
+      \ 'doom_one': 'doom-one.nvim',
+      \ 'everforest' :'everforest',
+      \ 'nightfox': 'nightfox.nvim'
+      \ }
 
-let s:theme = utils#RandElement(s:candidate_theme)
-let s:colorscheme_func = printf('s:my_theme_dict.%s()', s:theme)
+let s:theme = utils#RandElement(keys(s:theme2dir))
+let s:colorscheme_func = printf('s:theme_func_dict.%s()', s:theme)
 
-if has_key(s:my_theme_dict, s:theme)
-  execute 'call ' . s:colorscheme_func
-  if g:logging_level == 'debug'
-    let s:msg1 = "Currently loaded theme: " . s:theme
-    call v:lua.vim.notify(s:msg1, 'info', {'title': 'nvim-config'})
-  endif
-else
+if !has_key(s:theme_func_dict, s:theme)
   let s:msg = "Invalid colorscheme function: " . s:colorscheme_func
   call v:lua.vim.notify(s:msg, 'error', {'title': 'nvim-config'})
+  finish
+endif
+
+let s:res = utils#add_pack(s:theme2dir[s:theme])
+if !s:res
+  echomsg printf("Theme %s not installed. Run PackerSync to install.", s:theme)
+  finish
+endif
+
+execute 'call ' . s:colorscheme_func
+if g:logging_level == 'debug'
+  let s:msg1 = "Currently loaded theme: " . s:theme
+  call v:lua.vim.notify(s:msg1, 'info', {'title': 'nvim-config'})
 endif