@args --debugger
  error:
         … while evaluating the error message passed to builtin.throw

         error: cannot coerce a list to a string: [ ]

We expect to be able to see locals like r in the debugger:

  nix-repl> r
  [ ]

  nix-repl> :env
  Env level 0
  static: r x

  Env level 1
  abort baseNameOf break builtins derivation derivationStrict dirOf false fetchGit fetchMercurial fetchTarball fetchTree fromTOML import isNull map null placeholder removeAttrs scopedImport throw toString true

  nix-repl> :quit
  error:
         … while evaluating the file '$TEST_DATA/regression_9918.nix':

         … while calling the 'throw' builtin
           at $TEST_DATA/regression_9918.nix:3:7:
              2|   r = [];
              3|   x = builtins.throw r;
               |       ^
              4| in

         … while evaluating the error message passed to builtin.throw

         error: cannot coerce a list to a string: [ ]