Add electric-indent actions to reindent (bug#79371)

* lisp/electric.el (electric-indent-actions)
(electric-indent-function): New user options.
(electric-indent-should-reindent-p, electric-indent--yank-advice)
(electric-indent-save-hook): New functions.
(electric-indent-post-self-insert-function): Use them.

1 files changed, 73 insertions, 5 deletions

diff --git a/lisp/electric.el b/lisp/electric.el
index 302fb8d08bc..7825bbe43ec 100644
--- a/lisp/electric.el
+++ b/lisp/electric.el
@@ -192,6 +192,29 @@ Returns nil when we can't find this char."
 
 ;;; Electric indentation.
 
+(defcustom electric-indent-actions nil
+  "List of actions to indent.
+
+The valid elements of this list can be:
+ - yank: Indent the yanked text only if point is not in a string or
+         comment and yanked region is longer than 1 line.
+ - save: Indent the whole buffer before saving it.
+
+The indentation will not happen when the major mode is unable to
+reindent code reliably, such as in buffers where indentation is
+significant."
+  :type '(repeat (choice (const :tag "After yanking" yank)
+                         (const :tag "Before saving" before-save)))
+  :set (lambda (var val)
+         (set-default var val)
+         (when electric-indent-mode
+           (electric-indent-mode -1)
+           (electric-indent-mode +1)))
+  :safe (lambda (v)
+          (and (proper-list-p v)
+               (null (seq-filter (lambda (e) (not (symbolp e)) ) v))))
+  :version "31.1")
+
 ;; Autoloading variables is generally undesirable, but major modes
 ;; should usually set this variable by adding elements to the default
 ;; value, which only works well if the variable is preloaded.
@@ -218,6 +241,50 @@ If `indent-line-function' is one of those, then `electric-indent-mode' will
 not try to reindent lines.  It is normally better to make the major
 mode set `electric-indent-inhibit', but this can be used as a workaround.")
 
+(defun electric-indent-can-reindent-p ()
+  "Return t if `electric-indent-mode' can performs reindentation."
+  (not (or (memq indent-line-function
+                 electric-indent-functions-without-reindent)
+           electric-indent-inhibit)))
+
+(defun electric-indent--yank-advice (fn &rest r)
+  (let ((p (point))
+        (end (line-beginning-position)))
+    (apply fn r)
+    (when (and electric-indent-mode
+               (memq 'yank electric-indent-actions)
+               (electric-indent-can-reindent-p)
+               ;; Ensure yanked text is longer than 1 line
+               (> (point) p)
+               (not (= end (line-beginning-position))))
+      (undo-boundary)
+      (save-excursion
+        (with-demoted-errors "Error reindenting: %S"
+          (indent-region p (point)))))))
+
+(defun electric-indent-save-hook ()
+  (when (and electric-indent-mode
+             ;; Ensure this hook is called interactively
+             (memq real-this-command '(save-buffer basic-save-buffer))
+             (memq 'before-save electric-indent-actions)
+             (not buffer-read-only)
+             (electric-indent-can-reindent-p))
+    (save-excursion
+      (with-demoted-errors "Error reindenting: %S"
+        (indent-region (point-min) (point-max))))))
+
+(defun electric-indent-toggle-indent-actions (enable)
+  "Enable the actions specified in `electric-indent-actions'."
+  (cond
+   ((memq 'yank electric-indent-actions)
+    (if enable
+        (advice-add #'yank :around #'electric-indent--yank-advice)
+      (advice-remove #'yank #'electric-indent--yank-advice)))
+   ((memq 'before-save electric-indent-actions)
+    (if enable
+        (add-hook 'before-save-hook #'electric-indent-save-hook)
+      (remove-hook 'before-save-hook #'electric-indent-save-hook)))))
+
 (defun electric-indent-post-self-insert-function ()
   "Function that `electric-indent-mode' adds to `post-self-insert-hook'.
 This indents if the hook `electric-indent-functions' returns non-nil,
@@ -256,10 +323,7 @@ or comment."
           (when at-newline
             (let ((before (copy-marker (1- pos) t)))
               (save-excursion
-                (unless
-                    (or (memq indent-line-function
-                              electric-indent-functions-without-reindent)
-                        electric-indent-inhibit)
+                (when (electric-indent-can-reindent-p)
                   ;; Don't reindent the previous line if the
                   ;; indentation function is not a real one.
                   (goto-char before)
@@ -331,9 +395,13 @@ use `electric-indent-local-mode'."
                     (if electric-indent-mode (throw 'found t)))))
         (remove-hook 'post-self-insert-hook
                      #'electric-indent-post-self-insert-function))
+
     (add-hook 'post-self-insert-hook
               #'electric-indent-post-self-insert-function
-              60)))
+              60))
+
+  ;; Toggle the reindentation on actions
+  (electric-indent-toggle-indent-actions electric-indent-mode))
 
 ;;;###autoload
 (define-minor-mode electric-indent-local-mode