When MATLAB mode is installed opening an m file gives a file mode specification error

Question

I have installed the matlab-mode-20160902.459 package from MELPA and whenever I open an m file (i.e., a file with the file extension .m which is the file extension of most MATLAB/GNU Octave scripts) I get an error message shown in the below screenshot:

Here is my present ~/.emacs file. As you can see on line 129 I have added the line:

(add-to-list 'auto-mode-alist '("\\.m$" . matlab-mode))

to hopefully autoload matlab-mode whenever I open an m file. I really have no idea how to fix this error as I haven't pressed C-x when I opened this file... If relevant I opened my m files using the Emacs directory browser shown in the screenshot.

Is it perhaps that this ~/.emacs line that sets .m files to be handled by matlab-mode conflicts with the default handling of .m files as Objective C files? Regardless of the cause a solution would be wonderful. I don't ever code in objective C (I am a loyal Linux user with no interest in iOS or macOS development), but I do code in GNU Octave / MATLAB, so setting m files as being associated with matlab-mode would be ideal.

EDIT:

I have tried using octave-mod instead by adding:

(setq auto-mode-alist
      (cons '("\\.m$" . octave-mode) auto-mode-alist))
(add-hook 'octave-mode-hook
          (lambda ()
            (abbrev-mode 1)
            (auto-fill-mode 1)
            (if (eq window-system 'x)
                (font-lock-mode 1))))

to my ~/.emacs file (in accordance with this guide). That gave the same error when opening an ~/.emacs file (and yes I did remove the matlab-mode line before I added these lines to make it a fair test of whether it works).

I have seen this question at StackOverflow but neither upvoted answer (which presently are this and this) worked for me: they both returned the same error whenever I opened an m file and neither caused syntax-highlighting of the m file to occur.

The backtrace generated by going to Options→Enter Debugger on Error was, when I opened the m file /home/fusion809/GitHub/mine/scripts/GNU_Octave/first.m:

Debugger entered--Lisp error: (file-error "Cannot open load file" "No such file or directory" "octave-mode")
  octave-mode()
  set-auto-mode-0(octave-mode nil)
  set-auto-mode()
  normal-mode(t)
  after-find-file(nil t)
  find-file-noselect-1(#<buffer first.m> "~/GitHub/mine/scripts/GNU_Octave/first.m" nil nil "~/GitHub/mine/scripts/GNU_Octave/first.m" (21370145 2052))
  find-file-noselect("/home/fusion809/GitHub/mine/scripts/GNU_Octave/first.m" nil nil nil)
  find-file-other-window("/home/fusion809/GitHub/mine/scripts/GNU_Octave/first.m")
  dired-mouse-find-file-other-window((mouse-2 (#<window 3 on GNU_Octave> 419 (546 . 123) 39532480 nil 419 (60 . 6) nil (6 . 15) (9 . 18))))
  funcall-interactively(dired-mouse-find-file-other-window (mouse-2 (#<window 3 on GNU_Octave> 419 (546 . 123) 39532480 nil 419 (60 . 6) nil (6 . 15) (9 . 18))))
  call-interactively(dired-mouse-find-file-other-window nil nil)
  command-execute(dired-mouse-find-file-other-window)

With MATLAB mode (instead of Octave mode as in the last backtrace) I get the backtrace http://paste2.org/wDE8VcbV (too long to paste here).

Answer 1

This part of your config is causing the problem. You should use something like cua-mode instead of binding keys like C-c and C-x, which conflict with commonly used prefixes in emacs. cua-mode should make some of key combinations you use work as expected, and give you a way to use proper keybindings that begin with C-c and C-x.

https://www.gnu.org/software/emacs/manual/html_node/emacs/CUA-Bindings.html