pcomplete-arg-quote-list

pcomplete-arg-quote-list is a variable defined in `pcomplete.el'.
Its value is

nil

• This variable is an alias for `comint-file-name-quote-list'.
• This variable is obsolete since 24.3;
  use `comint-file-name-quote-list' instead.

Documentation:
List of characters to quote with `\' when in a file name.

This is a good thing to set in mode hooks.