Fix highlight position with unicode characters for vim and neovim

Introduce g:lsp_cxx_hl_use_byteidx

autoload/lsp_cxx_hl.vim

@@ -163,6 +163,24 @@ function! s:common_notify_checks(server, buffer, data) abort
     return l:bufnr
 endfunction
 
+" Convert range of bytes starting from s_line character s_char
+" to line e_line character e_char in buffer a:buf into a range of columns.
+" These are equal when each displayed character takes exactly one column,
+" but there's also UTF-8.
+function! lsp_cxx_hl#bytes_to_columns(buf, s_line, s_char, e_line, e_char)
+    if get(g:, 'lsp_cxx_hl_use_byteidx', 0)
+        try
+            return [byteidx(getbufline(a:buf, a:s_line)[0], a:s_char),
+                  \ byteidx(getbufline(a:buf, a:e_line)[0], a:e_char)]
+        " If the user fastly edits the file, this can be slower then the
+        " edits, and `getbufline` can return zero lines or these columns
+        " may just not exists anymore.
+        catch /^Vim\%((\a\+)\)\=:E684/
+        endtry
+    endif
+    return [ a:s_char, a:e_char ]
+endfunction
+
 " Section: Misc Helpers
 function! s:uri2bufnr(uri) abort
     " Absolute paths on windows has 3 leading /

autoload/lsp_cxx_hl/textprop/symbols.vim

@@ -152,6 +152,9 @@ function! s:hl_symbols(bufnr, timer) abort
 
         for l:prop in l:props
             call extend(l:prop[2], l:prop_extra)
+            let [ l:prop[1], l:prop[2]['end_col'] ] = lsp_cxx_hl#bytes_to_columns(
+                        \ a:bufnr, l:prop[0], l:prop[1],
+                        \ get(l:prop[2], 'end_lnum', l:prop[0]), l:prop[2]['end_col'])
 
             try
                 call prop_add(l:prop[0], l:prop[1], l:prop[2])

autoload/lsp_cxx_hl/textprop_nvim.vim

@@ -1,10 +1,11 @@
 " Textprops neovim
-" 
+"
 " It should be noted that neovim uses zero based indexing like LSP
 " this is unlike regular vim APIs which are 1 based.
 
 function! lsp_cxx_hl#textprop_nvim#buf_add_hl_lsrange(buf, ns_id, hl_group,
             \ range) abort
+    call lsp_cxx_hl#log('range = ', a:range)
     return s:buf_add_hl(a:buf, a:ns_id, a:hl_group,
                 \ a:range['start']['line'],
                 \ a:range['start']['character'],
@@ -18,13 +19,16 @@ function! s:buf_add_hl(buf, ns_id, hl_group,
 
     " single line symbol
     if a:s_line == a:e_line
-        if a:e_char - a:s_char > 0
-            call nvim_buf_add_highlight(a:buf, a:ns_id, a:hl_group,
-                        \ a:s_line, a:s_char, a:e_char)
-            return
-        else
-            return
+        let [ s_char, e_char ] = lsp_cxx_hl#bytes_to_columns(a:buf,
+                    \ a:s_line + 1, a:s_char, a:s_line + 1, a:e_char)
+        if s_char < e_char
+            try
+                call nvim_buf_add_highlight(a:buf, a:ns_id, a:hl_group,
+                            \ a:s_line, s_char, e_char)
+            catch /Column value outside range/
+            endtry
         endif
+        return
     endif
 
     call lsp_cxx_hl#log('Error (textprop_nvim): symbol (', a:hl_group,