Alter regex for \ref to provide completion for most cleveref commands.

autoload/vimtex/complete.vim

@@ -223,7 +223,7 @@ endfunction
 " {{{1 Labels
 
 let s:ref = {
-      \ 'pattern' : '\v\\v?%(auto|eq|page|[cC]|labelc)?ref\s*\{[^{}]*',
+      \ 'pattern' : '\v\\v?%(auto|eq|[cC]?%(page)?|labelc)?%(ref)%(\s*\{[^\{\}]*|%(range)\s*\{[^,\{\}]*%(\}\{)?)',
       \ 'enabled' : 1,
       \}
 

doc/vimtex.txt

@@ -1387,7 +1387,8 @@ documents with |neocomplete| and |vimtex|s omni completion function: >
   endif
   let g:neocomplete#sources#omni#input_patterns.tex =
         \ '\v\\%('
-        \ . '\a*%(ref|cite)\a*%(\s*\[[^]]*\])?\s*\{[^{}]*'
+        \ . '\a*%(cite)\a*%(\s*\[[^\{\}\]]*\]){0,2}\s*\{[^\{\}]*'
+        \ . '\a*%(ref)%(\s*\{[^\{\}]*|%(range)\s*\{[^,\{\}]*%(\}\{)?)'
         \ . '|includegraphics%(\s*\[[^]]*\])?\s*\{[^{}]*'
         \ . '|%(include|input)\s*\{[^{}]*'
         \ . ')'
@@ -1413,7 +1414,8 @@ To enable automatic completion with |youcompleteme|, use the following options:
     let g:ycm_semantic_triggers = {}
   endif
   let g:ycm_semantic_triggers.tex = [
-        \ 're!\\[A-Za-z]*(ref|cite)[A-Za-z]*([^]]*])?{([^}]*,?)*',
+        \ 're!\\[A-Za-z]*(cite)[A-Za-z]*(\[[^\{\}\]]*\]){0,2}\{[^\{\}]*',
+        \ 're!\\[A-Za-z]*(ref)(\{[^\{\}]*|(range)\{([^,\{\}]*(\}\{)?))',
         \ 're!\\includegraphics([^]]*])?{[^}]*',
         \ 're!\\(include|input){[^}]*'
         \ ]