Implement C(-S)-tab buffer switch in Helm layer

[dalanicolai]

Equivalent to PR #14287 for ivy-layer

[smile13241324]

Cool, thanks for adding this to helm too :)

[dalanicolai]

No problem. Personally I prefer to bind this functionality to C-j and C-k as in evil those bindings do not really add useful functionality (C-j in normal mode is somewhat equivalent to j in vim or o in evil, C-k is somewhat equivalent to dd in evil and enter digraph in vim). In Helm you can then set helm-follow-mode-persistent and toggle follow-mode.

For Ivy a solution to use C-j/k for buffer switching has been posted here.

   (defun trigger-ivy-switch-buffer ()
    (interactive)
    (minibuffer-with-setup-hook
        (lambda () (run-at-time nil nil #'ivy-toggle-calling))
      (ivy-switch-buffer)))

  (defun spacemacs/evilified-buffer-switch ()
    (interactive)
    (define-key evil-evilified-state-map (kbd "C-j") 'trigger-ivy-switch-buffer)
    (define-key evil-evilified-state-map (kbd "C-k") 'trigger-ivy-switch-buffer))

  (evil-global-set-key 'motion (kbd "C-j") 'trigger-ivy-switch-buffer)
  (evil-global-set-key 'motion (kbd "C-k") 'trigger-ivy-switch-buffer)
  (add-hook 'evil-evilified-state-entry-hook 'spacemacs/evilified-buffer-switch)

Maybe we could add these bindings to Spacemacs too, if you think that would be nice then let me know.

[lebensterben]

Bindings with TAB is more "expected" than j/k:

• In many desktop environments, across Linux, MacOS, and Windows, <MODIFIER> TAB is the default keybinding to switch between active windows.
• In Spacemacs, SPC TAB is the default keybinding to switch between the last two buffers.

A possible solution is to add a layer variable to helm and ivy:

• When it's non-nil, SPC TAB is used to switch to next buffer and SPC S TAB is used to switch to last buffer.
• When it's nil, it keeps the current default behaviour, that SPC TAB switches between last two buffers. And the new functionality in this commit is bound to C TAB and C S TAB.

The motivation for setting such variable to non-nil is that:

• C TAB, and especially C S TAB, are really not comfortable to press on PC keyboard.
• The original functionality of switching between last two buffers can be superseded by the new ones.

[dalanicolai]

@lebensterben Well it is not about expectation (although that is why I implemented the C-tab). It is about offering and suggesting to users the most convenient workflow. I think there is no need to not improve things because of conventions/expectations (although it is important to consider such improvements carefully).

Well, otherwise users can find the suggestion here anyway.

EDIT
Also you suggest an alternative because C TAB and C S TAB would not be comfortable... well so that is why I suggest the C-j/k alternative which is very comfortable. It fits well with the additionally required C-l (or RET) to select the buffer. Also I think users do/should not really have keybinding expectations other than vim's when they start using Spacemacs.