bug#11520: 24.1.50; delete-selection-mode conflicts with electric-pair-mode

[Simon Law <sfllaw@sfllaw.ca>]

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Attached is a patch against trunk.

I have addressed your concerns below:

On Mon, Oct 8, 2012 at 6:25 PM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>> I proposed making delete-selection-pre-hook understand a function as
>> one of the legitimate types. If it were a function, it gets called and
>> its results would be interpreted as type, either: 'yank, 'kill,
>> 'supersede, t, or nil.
>
>> That way, electric-pair-mode can override the (put
>> 'self-insert-command 'delete-selection ...) with its own function that
>
> That's going in the right direction, but I have two problems with that:
> - I don't want electric-pair-mode to decide of the whole
>   self-insert-command behavior.  I.e. self-insert-command should have
>   a `delete-selection' property that is not specific to
>   electric-pair-mode, so that if someone implements some other
>   post-self-insert-hook that also interacts with
>   selection-selection-mode, they should be able to cooperate.
>   IOW, we need self-insert-command's delete-section property to be a new
>   function that runs a new hook on which electric-foo-mode can add their
>   respective function.

There is a new abnormal hook called delete-selection-self-insert-hooks
that delete-selection-mode attaches, by default, onto
self-insert-command and self-insert-iso.

Conceivably, the other functions may also need their own hooks, but I
couldn't think of a good use case right now. Therefore, YAGNI. It is
trivial to add this later.

> - this new hook should be good enough for delete-selection-mode,
>   obviously, but it should also be good enough for a replacement
>   of delete-selection-mode that works differently.
>   I guess the functions on that hook would mostly need to return
>   a boolean indicating whether they're going to make use of the region.

Instead of booleans, those functions return one of the types that
delete-selection understands.

-- 
Cheers,
Simon - http://ca.linkedin.com/in/sfllaw/

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diff --git a/lisp/delsel.el b/lisp/delsel.el
index a643567..09f58e0 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)
diff --git a/lisp/electric.el b/lisp/electric.el
index 3108a0e..e6fa1df 100644
--- a/lisp/electric.el
+++ b/lisp/electric.el
@@ -301,14 +301,17 @@ This can be convenient for people who find it easier to hit ) than C-f."
   :version "24.1"
   :type 'boolean)
 
+(defun electric-pair-syntax (command-event)
+  (and electric-pair-mode
+       (let ((x (assq command-event electric-pair-pairs)))
+	 (cond
+	  (x (if (eq (car x) (cdr x)) ?\" ?\())
+	  ((rassq command-event electric-pair-pairs) ?\))
+	  (t (char-syntax command-event))))))
+
 (defun electric-pair-post-self-insert-function ()
   (let* ((syntax (and (eq (char-before) last-command-event) ; Sanity check.
-                      electric-pair-mode
-                      (let ((x (assq last-command-event electric-pair-pairs)))
-                        (cond
-                         (x (if (eq (car x) (cdr x)) ?\" ?\())
-                         ((rassq last-command-event electric-pair-pairs) ?\))
-                         (t (char-syntax last-command-event))))))
+		      (electric-pair-syntax last-command-event)))
          ;; FIXME: when inserting the closer, we should maybe use
          ;; self-insert-command, although it may prove tricky running
          ;; post-self-insert-hook recursively, and we wouldn't want to trigger
@@ -355,6 +358,12 @@ This can be convenient for people who find it easier to hit ) than C-f."
                (eq (char-syntax (following-char)) ?w)))
       (save-excursion (insert closer))))))
 
+(defun electric-pair-delete-selection-self-insert-function ()
+  (let ((syntax (electric-pair-syntax last-command-event)))
+    (if (and (memq syntax '(?\( ?\" ?\$)) (use-region-p))
+	'keep
+      t)))
+
 ;;;###autoload
 (define-minor-mode electric-pair-mode
   "Toggle automatic parens pairing (Electric Pair mode).
@@ -370,10 +379,16 @@ See options `electric-pair-pairs' and `electric-pair-skip-self'."
   :global t
   :group 'electricity
   (if electric-pair-mode
-      (add-hook 'post-self-insert-hook
-                #'electric-pair-post-self-insert-function)
+      (progn
+	(require 'delsel)
+	(add-hook 'post-self-insert-hook
+		  #'electric-pair-post-self-insert-function)
+	(add-hook 'delete-selection-self-insert-hooks
+		  #'electric-pair-delete-selection-self-insert-function))
     (remove-hook 'post-self-insert-hook
-                 #'electric-pair-post-self-insert-function)))
+                 #'electric-pair-post-self-insert-function)
+    (remove-hook 'delete-selection-self-insert-hooks
+		  #'electric-pair-delete-selection-self-insert-function)))
 
 ;; Automatically add newlines after/before/around some chars.