* lisp/delsel.el (delete-selection-helper): New function, extracted from

delete-selection-pre-hook.
(delete-selection-pre-hook): Use it.
(delete-selection-self-insert-function): New function.
(delete-selection-self-insert-hooks): New hook.
(self-insert-command, self-insert-iso): Use it.
* lisp/electric.el (electric-pair-syntax): New function, extracted from
electric-pair-post-self-insert-function.
(electric-pair-post-self-insert-function): Use it.
(electric-pair-delete-selection-self-insert-function): New function.
(electric-pair-mode): Require delsel and setup
delete-selection-self-insert-hooks.

Fixes: debbugs:11520

1 files changed, 93 insertions, 50 deletions

diff --git a/lisp/delsel.el b/lisp/delsel.el
index a6435672201..09f58e086a2 100644
--- a/lisp/delsel.el
+++ b/lisp/delsel.el
@@ -47,6 +47,9 @@
 ;;  non-nil
 ;;      The normal case: delete the active region prior to executing
 ;;      the command which will insert replacement text.
+;;  hooks
+;;      For commands which need to dynamically determine this behaviour.
+;;      Each hook should return one of the above values or nil.
 
 ;;; Code:
 
@@ -71,66 +74,106 @@ any selection."
     (transient-mark-mode t)))
 
 (defun delete-active-region (&optional killp)
+  "Delete the active region.
+If KILLP in not-nil, the active region is killed instead of deleted."
   (if killp
       (kill-region (point) (mark))
     (delete-region (point) (mark)))
   t)
 
+(defun delete-selection-helper (type)
+  "Deletes selection according to TYPE:
+ 'yank
+     For commands which do a yank; ensures the region about to be
+     deleted isn't yanked.
+ 'supersede
+     Delete the active region and ignore the current command,
+     i.e. the command will just delete the region.
+ 'kill
+     `kill-region' is used on the selection, rather than
+     `delete-region'.  (Text selected with the mouse will typically
+     be yankable anyhow.)
+ non-nil
+     The normal case: delete the active region prior to executing
+     the command which will insert replacement text.
+ hooks
+     For commands which need to dynamically determine this behaviour.
+     Each hook should return one of the above values or nil."
+  (condition-case data
+      (cond ((eq type 'kill)
+	     (delete-active-region t))
+	    ((eq type 'yank)
+	     ;; Before a yank command, make sure we don't yank the
+	     ;; head of the kill-ring that really comes from the
+	     ;; currently active region we are going to delete.
+	     ;; That would make yank a no-op.
+	     (when (and (string= (buffer-substring-no-properties
+				  (point) (mark))
+				 (car kill-ring))
+			(fboundp 'mouse-region-match)
+			(mouse-region-match))
+	       (current-kill 1))
+	     (delete-active-region))
+	    ((eq type 'supersede)
+	     (let ((empty-region (= (point) (mark))))
+	       (delete-active-region)
+	       (unless empty-region
+		 (setq this-command 'ignore))))
+	    ((and (symbolp type) (not (booleanp type)))
+	     (delete-selection-helper
+	      (run-hook-with-args-until-success type)))
+	    (type
+	     (delete-active-region)
+	     (if (and overwrite-mode
+		      (eq this-command 'self-insert-command))
+		 (let ((overwrite-mode nil))
+		   (self-insert-command
+		    (prefix-numeric-value current-prefix-arg))
+		   (setq this-command 'ignore)))))
+    ;; If ask-user-about-supersession-threat signals an error,
+    ;; stop safe_run_hooks from clearing out pre-command-hook.
+    (file-supersession (message "%s" (cadr data)) (ding))
+    (text-read-only
+     ;; This signal may come either from `delete-active-region' or
+     ;; `self-insert-command' (when `overwrite-mode' is non-nil).
+     ;; To avoid clearing out `pre-command-hook' we handle this case
+     ;; by issuing a simple message.  Note, however, that we do not
+     ;; handle all related problems: When read-only text ends before
+     ;; the end of the region, the latter is not deleted but any
+     ;; subsequent insertion will succeed.  We could avoid this case
+     ;; by doing a (setq this-command 'ignore) here.  This would,
+     ;; however, still not handle the case where read-only text ends
+     ;; precisely where the region starts: In that case the deletion
+     ;; would succeed but the subsequent insertion would fail with a
+     ;; text-read-only error.  To handle that case we would have to
+     ;; investigate text properties at both ends of the region and
+     ;; skip the deletion when inserting text is forbidden there.
+     (message "Text is read-only") (ding))))
+
 (defun delete-selection-pre-hook ()
+  "Normal hook run before commands that delete selections are executed.
+Commands which will delete the selection need a 'delete-selection
+property on their symbols; commands which insert text but don't
+have this property won't delete the selection.
+
+See `delete-selection-helper'.
+"
   (when (and delete-selection-mode transient-mark-mode mark-active
 	     (not buffer-read-only))
     (let ((type (and (symbolp this-command)
 		     (get this-command 'delete-selection))))
-      (condition-case data
-	  (cond ((eq type 'kill)
-		 (delete-active-region t))
-		((eq type 'yank)
-		 ;; Before a yank command, make sure we don't yank the
-		 ;; head of the kill-ring that really comes from the
-		 ;; currently active region we are going to delete.
-		 ;; That would make yank a no-op.
-		 (when (and (string= (buffer-substring-no-properties
-                                      (point) (mark))
-				     (car kill-ring))
-			    (fboundp 'mouse-region-match)
-			    (mouse-region-match))
-		   (current-kill 1))
-		 (delete-active-region))
-		((eq type 'supersede)
-		 (let ((empty-region (= (point) (mark))))
-		   (delete-active-region)
-		   (unless empty-region
-		     (setq this-command 'ignore))))
-		(type
-		 (delete-active-region)
-		 (if (and overwrite-mode
-                          (eq this-command 'self-insert-command))
-		   (let ((overwrite-mode nil))
-		     (self-insert-command
-                      (prefix-numeric-value current-prefix-arg))
-		     (setq this-command 'ignore)))))
-	 ;; If ask-user-about-supersession-threat signals an error,
-	 ;; stop safe_run_hooks from clearing out pre-command-hook.
-	(file-supersession (message "%s" (cadr data)) (ding))
-	(text-read-only
-	 ;; This signal may come either from `delete-active-region' or
-	 ;; `self-insert-command' (when `overwrite-mode' is non-nil).
-	 ;; To avoid clearing out `pre-command-hook' we handle this case
-	 ;; by issuing a simple message.  Note, however, that we do not
-	 ;; handle all related problems: When read-only text ends before
-	 ;; the end of the region, the latter is not deleted but any
-	 ;; subsequent insertion will succeed.  We could avoid this case
-	 ;; by doing a (setq this-command 'ignore) here.  This would,
-	 ;; however, still not handle the case where read-only text ends
-	 ;; precisely where the region starts: In that case the deletion
-	 ;; would succeed but the subsequent insertion would fail with a
-	 ;; text-read-only error.  To handle that case we would have to
-	 ;; investigate text properties at both ends of the region and
-	 ;; skip the deletion when inserting text is forbidden there.
-	 (message "Text is read-only") (ding))))))
-
-(put 'self-insert-command 'delete-selection t)
-(put 'self-insert-iso 'delete-selection t)
+      (delete-selection-helper type))))
+
+(defun delete-selection-self-insert-function ()
+  t)
+
+(defvar delete-selection-self-insert-hooks
+  '(delete-selection-self-insert-function)
+  "Abnormal hook run before commands that insert characters.
+This hook should return a TYPE that `delete-selection-helper' understands.")
+
+(put 'self-insert-command 'delete-selection 'delete-selection-self-insert-hooks)
+(put 'self-insert-iso 'delete-selection 'delete-selection-self-insert-hooks)
 
 (put 'yank 'delete-selection 'yank)
 (put 'clipboard-yank 'delete-selection 'yank)