auto-complete Key binding doesn't work in one emacs mode

Question

I have changed the keybindings for yasnippet and autocomplete so that I can use tab for indentation anywhere in a line without accidentally autocompleting or inserting a snippet.

I have this in my init.el

(package-initialize)

(require 'auto-complete-config)
(ac-config-default)
(define-key ac-mode-map (kbd "TAB") nil)
(define-key ac-completing-map (kbd "TAB") nil)
(define-key ac-completing-map [tab] nil)

(ac-set-trigger-key "`") ;; sets the auto-complete key   

(require 'yasnippet)
(yas/initialize)
(yas/load-directory
  (dot-emacs "elpa/yasnippet/snippets"))

;; Remove Yasnippet's default tab key binding            
(define-key yas-minor-mode-map (kbd "<tab>") nil)
(define-key yas-minor-mode-map (kbd "TAB") nil)
;; Set Yasnippet's key binding to shift+tab              
(define-key yas-minor-mode-map (kbd "§") 'yas-expand)

This works for most emacs modes, however when I use one particular mode (vhdl-mode) the yasnippet key bind § works as expected but ` does not work for auto-complete and it resets to the default tab key for autocomplete.

This means when I go through my code using tab to indent or un-indent parts of it random words are auto-completed.

Answer 1

vhdl-mode binds tab to vhdl-electric-tab, which calls hippie-expand in most cases. That would explain unexpected/unwanted completions. You'll need to overwrite this in the vhdl-mode map.

(require 'vhdl-mode)
(define-key vhdl-mode-map "\t" nil)

Answer 2

I haven't looked at the source-code, but vhdl-mode is probably resetting the keybindings for auto-complete by itself. Does it work if you manually redefine them again after vhdl-mode loads?

(defun my-redefine-auto-complete-keys ()
  (define-key ac-mode-map (kbd "TAB") nil)
  (define-key ac-completing-map (kbd "TAB") nil)
  (define-key ac-completing-map [tab] nil)
  (ac-set-trigger-key "`"))

(add-hook 'vhdl-mode-hook 'my-redefine-auto-complete-keys)