Space appended to completion when :annotation-function returns string

[non-Jedi]

Expected behavior

The first argument that :exit-function receives should be the un-annotated string that is being completed-to.

Actual behavior (from emacs-helm.sh if possible, see note at the bottom)

At least part of the the value returned from :annotation-function is appended to the completion name when its passed to :exit-function. The annotation also appears to be included in the final in-buffer completion.

The docstring for completion-extra-properties says:

The function must accept one argument, a completion string,
and return either nil or a string which is to be displayed
next to the completion (but which is not part of the
completion).

Steps to reproduce (recipe)

(defun my-capf ()
  (list (line-beginning-position) (point) '("foo" "foobar")
        :annotation-function (lambda (_) " ")
        :exit-function (lambda (string _status)
                         (message ":exit-function string: %s, length: %d"
                                  string (length string)))))

(setq completion-at-point-functions (list 'my-capf))

The message when completing "foo" should be :exit-function string: foo, length: 3; instead it is :exit-function string: foo , length: 4. "foo" should be inserted into the buffer by itself; instead a space is inserted after "foo".

Backtraces if any (M-x toggle-debug-on-error)

Describe versions of Helm, Emacs, operating system, etc.

Helm master, Emacs 26.3, Linux

Are you using emacs-helm.sh to reproduce this bug? (yes/no):

Yes

Are you using Spacemacs? (yes/no):

No

[non-Jedi]

Actually the space gets appended to the completion result if :annotation-function returns any string. The value returned by :annotation-function seems to be irrelevant for this bug:

(defun my-capf ()
  (list (line-beginning-position) (point) '("foo" "foobar")
	:annotation-function (lambda (_) "")
        :exit-function (lambda (string _status)
                         (message ":exit-function string: %s, length: %d" string (length string)))))

(setq completion-at-point-functions (list 'my-capf))

The above shows the same output of :exit-function string: foo, length: 4.

[thierryvolpiatto]

Adam B <notifications@github.com> writes:

Actually the space gets appended to the completion result if :annotation-function returns any string. The value returned by :annotation-function seems to be irrelevant for this bug: (defun my-capf () (list (line-beginning-position) (point) '("foo" "foobar") :annotation-function (lambda (_) "") :exit-function (lambda (string _status) (message ":exit-function string: %s, length: %d" string (length string))))) (setq completion-at-point-functions (list 'my-capf)) The above shows the same output of :exit-function string: foo , length: 4.

The space at end is added to display annotation in a display property added to this space (not by helm, but by minibuffer.el). I fixed this but at insertion only, that's mean the recipe above will still return :length 4, this to preserve properties that may be needed by the :exit-function, up to you to modify this in your :exit-function if needed. Let me know if this is correct for you. Thanks.

…

-- Thierry