One of the COMPLETE_* constants defined in the gdb module.
A procedure of three arguments: (lambda (self text word) ...).
Its result is one of:
- A list of strings.
- A <gdb:iterator> object that returns the set of possible completions,
- ending with #f.
+ A list of strings.
+ A <gdb:iterator> object that returns the set of possible completions,
+ ending with #f.
TODO(dje): Once PR 16699 is fixed, add support for returning
a COMPLETE_* constant.
If not specified, then completion is not supported for this command.