How to customize Helm buffers' mode-line

Question

I'm trying to customize Helm buffers' mode-line.

I have set mode-line-format with powerline package:

(setq-default
 mode-line-format
 '("%e"
   (:eval
    (let* ((active (powerline-selected-window-active))

           ;; Conditionnal faces (in function of `active')
           ...

           ;; Left elements
           (lhs ...)

           ;; Right elements
           (rhs ...))

      ;; Build the result
      (concat
       (powerline-render lhs)
       (powerline-fill mode-line-3-face (powerline-width rhs))
       (powerline-render rhs))))))

From what I understand from helm-mode-line-string's documentation:

Help string displayed in mode-line in helm'. It can be a string or a list of two args, in this case, first arg is a string that will be used as name for candidates number, second arg any string to display in mode line. If nil, use defaultmode-line-format'.

I should be able to have my customized mode-line everywhere (in every buffers) with:

(setq-default helm-mode-line-string nil)

Isn't this line from helm.el supposed to do exactly what I want?

(setq mode-line-format (default-value 'mode-line-format))

---

Edit

Works as intended with: helm-colors, helm-projectile-ag, helm-projectile-grep.

But not with: helm-M-x, helm-projectile-find-file, helm-projectile-switch-project.

Answer 1

Spaceline helped me customize the mode-line for Helm buffers (uses helm-alive-p).