Subject: bug#25111: (Inaccurate documentation of inhibit-modification-hooks)

From: Alan Mackenzie <[email-masked]>
Date: Tue, 4 Jun 2019 09:32:41 +0000

Hello, Noam.

On Mon, Jun 03, 2019 at 15:26:38 -0400, [email-masked] wrote:
> Alan Mackenzie <[email-masked]> writes:

> > Hello, Eli.

> > To recap, the problem we were talking about was the modification-hooks
> > overlay property, whose value is a function which gets called before and
> > after modification of the text under an overlay.

> > When such a function gets called, inhibit-modification-hooks is left at
> > nil.  When the other four similar overlay/text-property "change
> > functions" get called, inhibit-modification-hooks gets bound to t.

> Minor correction: it's the modification-hooks text property which have
> inhibit-modification-hooks left at nil, when the overlay property
> modification-hooks get called inhibit-modification-hooks is bound to t,
> just like in the after/before-change-functions case.

Oh, bother.  ;-)

> > This is difficult to document coherently.

> And confusing, as evidenced by the fact that we both got confused about
> it in this very thread :)

> > My proposal of last week was to fix the code, also to bind
> > inhibit-modification-hooks to t for the modification-hooks overlay
> > property, even though this would be an incompatibility in Lisp.

How about this?

diff --git a/src/textprop.c b/src/textprop.c
index ae42c44185..607bd40676 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -2247,6 +2247,8 @@ verify_interval_modification (struct buffer *buf,
 
       if (!inhibit_modification_hooks)
 	{
+          int count = SPECPDL_INDEX ();
+          specbind (Qinhibit_modification_hooks, Qt);
 	  hooks = Fnreverse (hooks);
 	  while (! NILP (hooks))
 	    {
@@ -2254,6 +2256,7 @@ verify_interval_modification (struct buffer *buf,
 			      make_fixnum (end));
 	      hooks = Fcdr (hooks);
 	    }
+          unbind_to (count, Qnil);
 	}
     }
 }

-- 
Alan Mackenzie (Nuremberg, Germany).