anchor.diff:  
         # Throw an error if trying to evaluate an non-valid derivation
         validityCondition =
  -			 let v = checkValidity attrs;
  +             let v = checkValidity attrs;
                in if !v.valid
                  then throwEvalHelp (removeAttrs v ["valid"])
                  else true;
  
positive.code:     , crossConfig ? null
      , meta ? {}
      , passthru ? {}
      , pos ? null # position used in error messages and for meta.position
      , separateDebugInfo ? false
      , outputs ? [ "out" ]
      , __impureHostDeps ? []
  
negative.code: 
        throwEvalHelp = { reason , errormsg ? "" }:
          throw (''
            Package ‘${attrs.name or "«name-missing»"}’ in ${pos_str} ${errormsg}, refusing to evaluate.
  
            '' + ((builtins.getAttr reason remediation) attrs));
  
  