ENH - include a check with a heuristic to investigate whether the use…

…r accidentally forgot the cfg, and put a data argument upfront as input variable

utilities/private/ft_preamble_init.m

@@ -46,6 +46,20 @@
   error(msg);
 end % if nargin
 
+% check if there are fieldnames in the cfg that suggest as if the user
+% erroneously inputted a data argument
+checkdatafields = isfield(cfg, {'label' 'dimord' 'time' 'trialinfo' 'avg'});
+if any(checkdatafields)
+  stack = dbstack('-completenames');
+  stack = stack(3);
+  help(stack.name);
+  % throw the error as if it happened in the original function
+  msg.message     = 'It seems as if the first input argument is a FieldTrip data structure, while a cfg is expected';
+  msg.identifier  = '';
+  msg.stack       = stack;
+  error(msg);
+end
+
 % convert automatically from cell-array to structure
 if iscell(cfg)
   cfg = ft_keyval2cfg(cfg);