Fixes #1974: Correct C-h behavior to ensure electric-pair deletes adjacent pairs

[jamescherti]

When using electric-pair-mode, the expected behavior when pressing C-h near a pair of adjacent delimiters (e.g., () [] {} "") is that both the opening and closing delimiters should be deleted together if they were inserted as a pair.

This pull request fixes #1974.

This pull request corrects C-h behavior to ensure electric-pair deletes adjacent pairs. It calls the same function as DEL (code 127) in electric-pair-mode-map:

electric-pair-mode-map is a variable defined in ‘elec-pair.el’.

Its value is
(keymap 
 (127 menu-item "" electric-pair-delete-pair :filter
  #f(compiled-function (cmd) #<bytecode 0x115035a9952592b3>)))

This pull request could be improved. Please don't hesitate to comment it if you have any suggestions.

[axelf4]

I agree that we should try to be compatible with the shenanigans of electric-pair-mode, even at the cost of a more fragile C-h binding. Some comments:

Will need to update the lookup-key check in the evil-want-C-h-delete setter:

              ((and (not value)
                    (eq (lookup-key evil-insert-state-map (kbd "C-h"))
                        'evil-delete-backward-char-and-join))

[jamescherti]

I agree that we should try to be compatible with the shenanigans of electric-pair-mode, even at the cost of a more fragile C-h binding. Some comments:

Will need to update the lookup-key check in the evil-want-C-h-delete setter:

              ((and (not value)
                    (eq (lookup-key evil-insert-state-map (kbd "C-h"))
                        'evil-delete-backward-char-and-join))

Yes, it is less conflusing to see that C-h behaves exactly like backspace (similar to #1980 for eldoc). It does not only fix electric-pair-mode, but also other packages that rely on backspace (e.g., paredit)

I have modified evil-vars.el to use the following instead:

(define-key evil-insert-state-map (kbd "C-h") (kbd "DEL"))

[jamescherti]

I enhanced the evil-insert-state-bindings mapping for C-h by improving the lambda function.

Have there been any updates on this pull request, @axelf4?