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I want to make a few customizations to cmake-model.el. The big-picture view of this lisp file is as follows:

...

;; This function I want to modify
(defun cmake-indent ()
  ...
  )

...

;; Mode definition.
;;
;;;###autoload
(define-derived-mode cmake-mode cmake--parent-mode "CMake"
  "Major mode for editing CMake source files."
  ...
  )

What I want to do is to create a minor mode ros-mode which would override the cmake-indent() function with my own, but keep everything else the same compared to the original cmake-mode.el. The mode line should show ROS when the minor mode is active.

I have no experience with creating minor modes, but I feel like this should be easy for someone with experience. Thank you for helping!

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  • The key ingredient is this line: (set (make-local-variable 'indent-line-function) 'cmake-indent) All you need to do is change it to something like (set (make-local-variable 'indent-line-function) 'my-cmake-indent) where your new function is called my-cmake-indent. You don't really need a minor-mode, but you can Google that if you want -- you only need that one (1) line of code and change the mode-line lighter to " ROS" and you are done. You can also Google things like: setq "indent-line-function" emacs to see other examples.
    – lawlist
    Nov 8, 2016 at 11:18
  • That sounds like what I need. Would you mind writing it more fully as an answer, preferably adding a check to make sure that cmake-mode is available?
    – space_voyager
    Nov 8, 2016 at 11:24
  • I have a major project today and was just waiting for the coffee to brew while reading the latest threads. I'll need to let another forum participant take over from here . . . :) Your example uses a major-mode (which is not what you want) -- you may wish to instead Google for: "define-minor-mode" emacs And, of course, you want to restore the original value of indent-line-function when the minor-mode is turned off.
    – lawlist
    Nov 8, 2016 at 11:25
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    Wouldn't it be better to automatically detect that you are working with ROS-specific files and invoke a major ros-mode in the first place (with all the desired personal configurations) instead of cmake-mode? Or even if you have to invoke it manually, wouldn't a major mode still fit the bill? (i.e. would you ever want to toggle a minor ros-mode on and off again for any given file? It sounds like you would just want it on for such files?)
    – phils
    Nov 8, 2016 at 12:59
  • 1
    I recommend working with @phils, as that participant is highly knowledegable. (define-minor-mode ros-mode "A minor-mode for working with ROS (Robot Operating System)-specific files." :init-value nil :lighter " ROS" :keymap nil :global nil :group 'cmake (cond (ros-mode (setq-local indent-line-function 'my-cmake-indent) (when (called-interactively-p 'any) (message "Turned ON 'ros-mode'."))) (t (if (eq major-mode 'cmake-mode) (setq-local indent-line-function 'cmake-indent) (kill-local-variable 'indent-line-function)) (when (called-interactively-p 'any) (message "Turned OFF 'ros-mode'.")))))
    – lawlist
    Nov 8, 2016 at 13:33

1 Answer 1

Reset to default
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I ended up going for a derived major mode as suggested by phils. I wrote in ~/.emacs.d/lisp/ros-cmake-mode.el:

(require 'cmake-mode)

(defun ros-cmake-indent ()
   ;; my code here...
  )

;;;###autoload
(define-derived-mode ros-cmake-mode cmake-mode "CMake[ROS]"
  "Major mode for editing ROS CMakeLists.txt files."

  ;; Setup indentation function.
  (set (make-local-variable 'indent-line-function) 'ros-cmake-indent))

(provide 'ros-cmake-mode)

Then in ~/.emacs.d/lisp/init.el (using use-package):

(use-package cmake-mode
  ;; major-mode for editing CMake sources
  :load-path "lisp/"
  :config
  (add-to-list 'auto-mode-alist '("\\.cmake\\'" . cmake-mode))
  (autoload 'cmake-mode "lisp/cmake-mode.el" t))

(use-package ros-cmake-mode
  ;; major-mode for editing CMakeLists.txt files with ROS-style indentation
  :load-path "lisp/"
  :config
  (add-to-list 'auto-mode-alist '("CMakeLists\\.txt\\'" . ros-cmake-mode))
  (autoload 'ros-cmake-mode "lisp/ros-cmake-mode.el" t))

When I open a CMakeLists.txt file, the major mode CMake[ROS] is used by default. In case I want to switch to CMake major mode (as provided by cmake-mode.el), I can type M-x cmake-mode RET.

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