Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> Or perhaps completion-emacs22-try-completion is violating the spec of
>>> completion-try-completion, and should be returning nil in this case?
>
> The "emacs22" style disregards the text after point to compute the
> completions, so "foo" would be a valid return value as well, but indeed
> t seems wrong because that should apply to the complete input.

I think "foo" (or more specifically '("foo" . 3)) might be a bit
unexpected, because then if you pressed TAB with the input foo|bar, the
bar would be deleted.  And emacs22 completion usually doesn't delete the
text after point, it just ignores it.

So '("foobar" . 3) seems better.  Open to counterarguments of course.

A patch which implements this is below.