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##
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## distribution or <https://octave.org/copyright/>.
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## -*- texinfo -*-
## @deftypefn {} {@var{names} =} __all_opts__ (@dots{})
## Internal function.
##
## Query all options from all known optimization functions and return a
## list of possible values.
## @end deftypefn

function names = __all_opts__ (varargin)

  ## This variable is filled by the auto-generated PKG_ADD script at
  ## Octave startup.
  persistent saved_names = {};

  ## do not clear this function
  mlock ();

  ## guard against recursive calls.
  persistent recursive = false;

  if (recursive)
    names = {};
  elseif (nargin == 0)
    names = saved_names;
  else
    ## Query all options from all known functions.  These may call optimset,
    ## which will in turn call us, but we won't answer.
    recursive = true;
    names = saved_names;
    for i = 1:nargin
      try
        opts = optimset (varargin{i});
        fn = fieldnames (opts).';
        names = [names, fn];
      catch
        ## throw the error as a warning.
        warning (lasterr ());
      end_try_catch
    endfor
    names = unique (names);
    [lnames, idx] = unique (tolower (names));
    if (length (lnames) < length (names))
      ## This is bad.
      error ("__all_opts__: duplicate options with inconsistent case");
    else
      names = names(idx);
    endif
    saved_names = names;
    recursive = false;
  endif

endfunction


## No test needed for internal helper function.
%!assert (1)
