Re: Major mode and implementation of expected editing facilities

["Clément Pit-Claudel" <cpitclaudel@gmail.com>]

On 2019-05-28 22:33, Eli Zaretskii wrote:
> If you or someone else want to suggest improvements for that chapter
> of the manual, please do, and thanks in advance.

To get the ball rolling, I'll mention a few facilities that I like major modes to hook into.  Others can likely point out many omissions:

* Syntax tables: see Syntax Tables in the ELisp manual (this helps with font-locking and motion) and syntax-propertize-function

* Font-locking: see font-lock-defaults and font-lock-keywords, and often font-lock-extra-managed-props and font-lock-syntactic-face-function

* Completion: see completion-at-point-functions, or (in ELPA) company-mode

* Outline: See outline-level, outline-regexp, and outline-heading-end-regexp; or hs-special-modes-alist; or both; or (in ELPA) many other packages

* Jump to definition: See xref-backend-functions

* Project: See project-find-functions

* On-the-fly errors: See flymake-mode, or (in ELPA) flycheck-mode

* Filling: See fill-paragraph-function, adaptive-fill-regexp, adaptive-fill-first-line-regexp, and fill-paragraph-handle-comment

* Comments: See comment-start-skip, comment-use-syntax, and comment-multi-line

* Indentation: See indent-line-function, indent-tabs-mode, indent-region-function, and possibly electric-indent-inhibit and electric-indent-chars

* Prettification: See prettify-symbols-alist.

* Auto-insert: See auto-insert-alist

* Eldoc: See eldoc-documentation-function

* Current function: See which-func-functions and add-log-current-defun-function

* Toolbars and menus: See tool-bar-map, easy-menu-define, and imenu-create-index-function

* Compilation: compilation-error-regexp-alist

* Navigation: See forward-sexp-function, parse-sexp-lookup-properties, parse-sexp-ignore-comments, paragraph-start, beginning-of-defun-function, and end-of-defun-function

* Snippets: See skeleton.el, or (in ELPA) yasnippet.

* Key bindings: You don't usually need to define or override many of these, because most keys that are supposed to operate consistently across modes call standardized functions or hooks that your major mode can configure (instead of redefining the corresponding key).  This is the case for M-q or TAB, for example (and even, despite what the manual say, for C-M-a as well).  If you override or create keybindings, please please don't forget the 'delete-selection property, to ensure that the overridden key works well with delete-selection-mode.

Btw, a good place to find these things is existing mode functions; look for setq-local or (set (make-local-variable …) …) in define-derived-mode blocks.

Clément.