completion-all-completions is a compiled Lisp function in `minibuffer.el'.

(completion-all-completions STRING TABLE PRED POINT &optional METADATA)

List the possible completions of STRING in completion table TABLE.
Only the elements of table that satisfy predicate PRED are considered.
POINT is the position of point within STRING.
The return value is a list of completions and may contain the base-size
in the last `cdr'.