Allow company-mode in minibuffer.

company-minibuffer.el

(with-eval-after-load "company-autoloads"
  (global-company-mode 1)

  (setq company-tooltip-limit 20
        company-minimum-prefix-length 1
        company-echo-delay 0
        company-begin-commands '(self-insert-command
                                 c-electric-lt-gt c-electric-colon
                                 completion-separator-self-insert-command)
        company-idle-delay 0.2
        company-show-numbers t
        company-tooltip-align-annotations t)

  (defvar-local company-col-offset 0 "Horisontal tooltip offset.")
  (defvar-local company-row-offset 0 "Vertical tooltip offset.")

  (defun company--posn-col-row (posn)
    (let ((col (car (posn-col-row posn)))
          ;; `posn-col-row' doesn't work well with lines of different height.
          ;; `posn-actual-col-row' doesn't handle multiple-width characters.
          (row (cdr (posn-actual-col-row posn))))
      (when (and header-line-format (version< emacs-version "24.3.93.3"))
        ;; http://debbugs.gnu.org/18384
        (cl-decf row))
      (cons (+ col (window-hscroll) company-col-offset) (+ row company-row-offset))))

  (defun company-elisp-minibuffer (command &optional arg &rest ignored)
    "`company-mode' completion back-end for Emacs Lisp in the minibuffer."
    (interactive (list 'interactive))
    (case command
      ('prefix (and (minibufferp)
                    (case company-minibuffer-mode
                      ('execute-extended-command (company-grab-symbol))
                      (t (company-capf `prefix)))))
      ('candidates
       (case company-minibuffer-mode
         ('execute-extended-command (all-completions arg obarray 'commandp))
         (t nil)))))

  (defun minibuffer-company ()
    (unless company-mode
      (when (and global-company-mode (or (eq this-command #'execute-extended-command)
                                         (eq this-command #'eval-expression)))

        (setq-local company-minibuffer-mode this-command)

        (setq-local completion-at-point-functions
                    (list (if (fboundp 'elisp-completion-at-point)
                              #'elisp-completion-at-point
                            #'lisp-completion-at-point) t))

        (setq-local company-show-numbers nil)
        (setq-local company-backends '((company-elisp-minibuffer company-capf)))
        (setq-local company-tooltip-limit 8)
        (setq-local company-col-offset 1)
        (setq-local company-row-offset 1)
        (setq-local company-frontends '(company-pseudo-tooltip-unless-just-one-frontend
                                        company-preview-if-just-one-frontend))

        (company-mode 1)
        (when (eq this-command #'execute-extended-command)
          (company-complete)))))

  (add-hook 'minibuffer-setup-hook #'minibuffer-company)
  ;;(remove-hook 'minibuffer-setup-hook #'minibuffer-company)
  ;;(add-hook 'eval-expression-minibuffer-setup-hook #'minibuffer-company)
  ;; (with-eval-after-load "company-flx-autoloads"
  ;; (company-flx-mode))
  )

Thanks.