Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>  (defun completion-emacs22-try-completion (string table pred point)
>>    (let ((suffix (substring string point))
>>          (completion (try-completion (substring string 0 point) table pred)))
>> -    (if (not (stringp completion))
>> -        completion
>> +    (cond
>> +     ((eq completion t)
>> +      ;; The prefix is an exact and unique completion, but STRING
>> +      ;; might not be a completion.
>> +      (if (test-completion string table)
>> +          t
>> +        (cons string point)))
>
> I think we should test (equal "" suffix) instead.
> The cases where (equal "" suffix) is false but (test-completion string table)
> are sufficiently weird that returning t seems risky and I can't think of
> any reason why it's worthwhile to take this risk.

True.  I was thinking about the case where STRING is a completion, so it
would be nice to just return t.  But that would be caught by other
completion styles before emacs22 anyway.

Fixed.