Improve vim script fold with custom foldexpr

after/ftplugin/vim.vim

@@ -1,3 +1,48 @@
-setlocal foldmethod=marker
 " Mapping for Vim help of the word under cursor.
 nnoremap K :help <C-r><C-w><CR>
+
+setlocal foldmethod=expr
+setlocal foldexpr=GetVimFold(v:lnum)
+
+" Regex for vim script blocks & markers {{{
+let s:vim_funciton_start = '^\s*fun\(c\(tion\)\=\)\=!\=\s\+.*#\=\w*(.*).*$'
+let s:vim_function_end = '^\s*endfun\(c\(tion\)\=\)\=\s*$'
+
+let s:vim_if_start = '^\s*if\s*.*$'
+let s:vim_if_end = '\s*en\(dif\)\=\s*$'
+
+let s:vim_while_start = '^\s*wh\(ile)\=\s*.*$'
+let s:vim_while_end = '\s*endw\(hile\)\=\s*$'
+
+let s:vim_for_start = '^\s*for\s*.*$'
+let s:vim_for_end = '\s*endfo\(r\)\=\s*$'
+
+let s:vim_try_start = '^\s*try\s*.*$'
+let s:vim_try_end = '\s*endt\(ry\)\=\s*$'
+
+let s:vim_augroup_start = '^\s*aug\(roup\)\=\s*.*\(END\)\@<!$'
+let s:vim_augroup_end = '^\s*aug\(roup\)\=\s*END\s*$'
+
+let s:vim_marker_start = '\s*".*{{{\s*$'
+let s:vim_marker_end = '\s*".*}}}\s*$'
+" }}}
+
+function! GetVimFold(lnum)
+  let l:line = getline(a:lnum)
+
+  if l:line =~ s:vim_function_end || l:line =~ s:vim_if_end ||
+   \ l:line =~ s:vim_while_end || l:line =~ s:vim_for_end ||
+   \ l:line =~ s:vim_try_end || l:line =~ s:vim_augroup_end ||
+   \ l:line =~ s:vim_marker_end
+    return "s1"
+  endif
+
+  if l:line =~ s:vim_funciton_start || l:line =~ s:vim_if_start ||
+   \ l:line =~ s:vim_while_start || l:line =~ s:vim_for_start ||
+   \ l:line =~ s:vim_try_start || l:line =~ s:vim_augroup_start ||
+   \ l:line =~ s:vim_marker_start
+    return 'a1'
+  endif
+
+  return '='
+endfunction