bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Ihor Radchenko]

Steps to reproduce:

1. emacs -Q
2. M-x clone-indirect-buffer <RET>
3. M-: (setq-local after-change-functions (append after-change-functions
   '((lambda (&rest _) (message "Buffer 1"))))) <RET>
4. C-x o
5. M-: (setq-local after-change-functions (append after-change-functions
   '((lambda (&rest _) (message "Buffer 2"))))) <RET>
6. Type something. "Buffer 2" message is displayed. "Buffer 1" message
   is _not_ displayed.
7. C-x o
8. Type something. "Buffer 1" message is displayed. "Buffer 2" message
   is _not_ displayed.

Expected behaviour:

Since changes in direct buffer would automatically change text in the
indirect buffer, I expect the changes to trigger all the
after-change-functions in all the indirect buffers and the base buffer,
regardless of which buffer was active when changes were made.

The current behaviour can potentially break major modes using
after-change-functions if base buffer and indirect buffer do not have
the same major mode.

For my use-case, an after-change-function I want to implement depends on
buffer-local variable (which is set to different values in the base and
indirect buffers) and I expect it to run in both buffers. Current Emacs
behaviour leaves me with no options to handle changes made not in
current buffer, even though they do change the text in other (indirect
or base) buffer.

On the other hand, running after-change-functions in every indirect/base
buffer may lead to multiple invocations of the same function.

Maybe, Emacs can examine something like 'run-indirect symbol for each
element in after-change-functions and run the functions containing the
symbol in all the connected buffers upon change.

Best,
Ihor

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, cairo version 1.16.0)
 of 2021-02-20 built on localhost
Repository revision: 39792cf62987ecc1a772f6a2027d6b32c70e8312
Repository branch: feature/native-comp
Windowing system distributor 'The X.Org Foundation', version 11.0.12010000
System Description: Gentoo/Linux

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bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> 1. emacs -Q
> 2. M-x clone-indirect-buffer <RET>
> 3. M-: (setq-local after-change-functions (append after-change-functions
>    '((lambda (&rest _) (message "Buffer 1"))))) <RET>
> 4. C-x o
> 5. M-: (setq-local after-change-functions (append after-change-functions
>    '((lambda (&rest _) (message "Buffer 2"))))) <RET>
> 6. Type something. "Buffer 2" message is displayed. "Buffer 1" message
>    is _not_ displayed.
> 7. C-x o
> 8. Type something. "Buffer 1" message is displayed. "Buffer 2" message
>    is _not_ displayed.

That's on purpose, yes.

> The current behaviour can potentially break major modes using
> after-change-functions if base buffer and indirect buffer do not have
> the same major mode.

It's currently the responsibility of the code that sets up the indirect
buffer(s) to setup a `before/after-change-functions` in the base buffer
that runs (some of) the `before/after-change-functions` in the indirect
buffer(s) where they are needed.


        Stefan

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Eli Zaretskii]

> Cc: 46982@debbugs.gnu.org
> Date: Thu, 16 Jun 2022 22:36:29 -0400
> From:  Stefan Monnier via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> It's currently the responsibility of the code that sets up the indirect
> buffer(s) to setup a `before/after-change-functions` in the base buffer
> that runs (some of) the `before/after-change-functions` in the indirect
> buffer(s) where they are needed.

Do you think we should document this caveat in the ELisp manual?

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Eli Zaretskii [2022-06-17 08:42:33] wrote:
>> It's currently the responsibility of the code that sets up the indirect
>> buffer(s) to setup a `before/after-change-functions` in the base buffer
>> that runs (some of) the `before/after-change-functions` in the indirect
>> buffer(s) where they are needed.
>
> Do you think we should document this caveat in the ELisp manual?

It might be a good thing to mention somewhere around
`clone-buffer`, yes.  I'll see what I can come up with.


        Stefan

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: yantar92@gmail.com,  46982@debbugs.gnu.org
> Date: Fri, 17 Jun 2022 09:29:54 -0400
> 
> Eli Zaretskii [2022-06-17 08:42:33] wrote:
> >> It's currently the responsibility of the code that sets up the indirect
> >> buffer(s) to setup a `before/after-change-functions` in the base buffer
> >> that runs (some of) the `before/after-change-functions` in the indirect
> >> buffer(s) where they are needed.
> >
> > Do you think we should document this caveat in the ELisp manual?
> 
> It might be a good thing to mention somewhere around
> `clone-buffer`, yes.  I'll see what I can come up with.

Thanks.

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> It might be a good thing to mention somewhere around
> `clone-buffer`, yes.  I'll see what I can come up with.

Hmm... we don't document `clone-buffer` anywhere that I can see.
Any suggestion where I could put that kind of info?


        Stefan

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Ihor Radchenko]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> It might be a good thing to mention somewhere around
>> `clone-buffer`, yes.  I'll see what I can come up with.
>
> Hmm... we don't document `clone-buffer` anywhere that I can see.
> Any suggestion where I could put that kind of info?

`clone-indirect-buffer' I think. For example, in 19.6 Indirect Buffers
section of the manual.

Best,
Ihor

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>,  46982@debbugs.gnu.org
> Date: Wed, 22 Jun 2022 07:29:05 +0800
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> >> It might be a good thing to mention somewhere around
> >> `clone-buffer`, yes.  I'll see what I can come up with.
> >
> > Hmm... we don't document `clone-buffer` anywhere that I can see.
> > Any suggestion where I could put that kind of info?
> 
> `clone-indirect-buffer' I think. For example, in 19.6 Indirect Buffers
> section of the manual.

Yes, there, please.

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> >> It might be a good thing to mention somewhere around
>> >> `clone-buffer`, yes.  I'll see what I can come up with.
>> > Hmm... we don't document `clone-buffer` anywhere that I can see.
>> > Any suggestion where I could put that kind of info?
>> `clone-indirect-buffer' I think. For example, in 19.6 Indirect Buffers
>> section of the manual.
> Yes, there, please.

How does the patch below sound to you?


        Stefan


diff --git a/doc/emacs/buffers.texi b/doc/emacs/buffers.texi
index 94e9d2760ec..c07f3990ee8 100644
--- a/doc/emacs/buffers.texi
+++ b/doc/emacs/buffers.texi
@@ -616,10 +616,11 @@ Indirect Buffers
 
   The text of the indirect buffer is always identical to the text of its
 base buffer; changes made by editing either one are visible immediately
-in the other.  But in all other respects, the indirect buffer and its
+in the other.  ``Text'' here includes both the characters and their text
+properties.  But in all other respects, the indirect buffer and its
 base buffer are completely separate.  They can have different names,
 different values of point, different narrowing, different markers,
-different major modes, and different local variables.
+different overlays, different major modes, and different local variables.
 
   An indirect buffer cannot visit a file, but its base buffer can.  If
 you try to save the indirect buffer, that actually works by saving the
@@ -649,6 +650,14 @@ Indirect Buffers
 When this hook runs, the newly created indirect buffer is the current
 buffer.
 
+Note: When a modification is made to the text of a buffer, the
+modification hooks are only run in the base buffer, because most of
+the functions on those hooks are not prepared to work correctly in
+indirect buffers.  So if you need a modification hook function in an
+indirect buffer, you need to manually add that function to the hook
+@emph{in the base buffer} and then make the function operate in the
+desired indirect buffer.
+
 @node Buffer Convenience
 @section Convenience Features and Customization of Buffer Handling
 

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Ihor Radchenko <yantar92@gmail.com>,  46982@debbugs.gnu.org
> Date: Wed, 29 Jun 2022 11:19:37 -0400
> 
> >> >> It might be a good thing to mention somewhere around
> >> >> `clone-buffer`, yes.  I'll see what I can come up with.
> >> > Hmm... we don't document `clone-buffer` anywhere that I can see.
> >> > Any suggestion where I could put that kind of info?
> >> `clone-indirect-buffer' I think. For example, in 19.6 Indirect Buffers
> >> section of the manual.
> > Yes, there, please.
> 
> How does the patch below sound to you?

LGTM, thanks.

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> How does the patch below sound to you?
> LGTM, thanks.

IIUC 28.2 is super-near so I assume I should only push this to
`master`, right?  Or should I wait for 28.2 and then push to `emacs-28`?


        Stefan

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: yantar92@gmail.com,  46982@debbugs.gnu.org
> Date: Wed, 29 Jun 2022 13:16:15 -0400
> 
> >> How does the patch below sound to you?
> > LGTM, thanks.
> 
> IIUC 28.2 is super-near so I assume I should only push this to
> `master`, right?  Or should I wait for 28.2 and then push to `emacs-28`?

You can install on the emacs-28 branch now.

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> You can install on the emacs-28 branch now.

Done, thanks,


        Stefan

bug#46982: 28.0.50; after-change-functions in an indirect buffer are not called if the change is done while base buffer is active (and vice versa)

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> Hmm... we don't document `clone-buffer` anywhere that I can see.
>> Any suggestion where I could put that kind of info?
> `clone-indirect-buffer' I think.

Duh!  I need more sleep, sorry,


        Stefan