bug#71971: 31.0.50; Add user option server-window-alist

bug#71971: 31.0.50; Add user option server-window-alist

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

Severity: wishlist

A new user option `server-window-alist' shall be added to server.el. Every
entry shall be of type (REGEXP . SERVER-WINDOW). REGEXP is used to filter
for the buffer's file name, and if it matches, SERVER-WINDOW shall be
applied. SERVER-WINDOW itself has the same type as the `server-window'
user option.

If no regexp matches, the value of user option `server-window' shall be
used.

This new user option is the same as the existing
`with-editor-server-window-alist' from package with-editor.el. Mid-term,
the former shall replace the latter.


In GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.42, cairo version 1.18.0) of 2024-06-30 built on gandalf
Repository revision: c6a052f2fe53a26cdb0f3624a0b9af5201f3c487
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12401000
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bug#71971: 31.0.50; Add user option server-window-alist

[Eli Zaretskii]

> Cc: Jonas Bernoulli <jonas@bernoul.li>
> Date: Sat, 06 Jul 2024 13:06:57 +0200
> From:  Michael Albinus via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> A new user option `server-window-alist' shall be added to server.el. Every
> entry shall be of type (REGEXP . SERVER-WINDOW). REGEXP is used to filter
> for the buffer's file name, and if it matches, SERVER-WINDOW shall be
> applied. SERVER-WINDOW itself has the same type as the `server-window'
> user option.
> 
> If no regexp matches, the value of user option `server-window' shall be
> used.
> 
> This new user option is the same as the existing
> `with-editor-server-window-alist' from package with-editor.el. Mid-term,
> the former shall replace the latter.

Is it possible to describe the typical use cases which this option
targets?  Given that client frames/windows are not meant for specific
buffers (IOW, a client frame/window can be used for editing several
buffers), what kind of workflow will benefit from this option?

(And please don't say "the same cases as those where server-window is
useful", because I don't understand its usefulness, either.)

Thanks.

bug#71971: 31.0.50; Add user option server-window-alist

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

Eli Zaretskii <eliz@gnu.org> writes:

Hi Eli,

>> A new user option `server-window-alist' shall be added to server.el. Every
>> entry shall be of type (REGEXP . SERVER-WINDOW). REGEXP is used to filter
>> for the buffer's file name, and if it matches, SERVER-WINDOW shall be
>> applied. SERVER-WINDOW itself has the same type as the `server-window'
>> user option.
>>
>> If no regexp matches, the value of user option `server-window' shall be
>> used.
>>
>> This new user option is the same as the existing
>> `with-editor-server-window-alist' from package with-editor.el. Mid-term,
>> the former shall replace the latter.
>
> Is it possible to describe the typical use cases which this option
> targets?  Given that client frames/windows are not meant for specific
> buffers (IOW, a client frame/window can be used for editing several
> buffers), what kind of workflow will benefit from this option?
>
> (And please don't say "the same cases as those where server-window is
> useful", because I don't understand its usefulness, either.)

I would let this to Jonas. Perhaps a short description which would be
good for "(emacs) Invoking emacsclient".

> Thanks.

Best regards, Michael.

bug#71971: 31.0.50; Add user option server-window-alist

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

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: Jonas Bernoulli <jonas@bernoul.li>
>> Date: Sat, 06 Jul 2024 13:06:57 +0200
>> From:  Michael Albinus via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> A new user option `server-window-alist' shall be added to server.el. Every
>> entry shall be of type (REGEXP . SERVER-WINDOW). REGEXP is used to filter
>> for the buffer's file name, and if it matches, SERVER-WINDOW shall be
>> applied. SERVER-WINDOW itself has the same type as the `server-window'
>> user option.
>> 
>> If no regexp matches, the value of user option `server-window' shall be
>> used.
>> 
>> This new user option is the same as the existing
>> `with-editor-server-window-alist' from package with-editor.el. Mid-term,
>> the former shall replace the latter.
>
> Is it possible to describe the typical use cases which this option
> targets?  Given that client frames/windows are not meant for specific
> buffers (IOW, a client frame/window can be used for editing several
> buffers), what kind of workflow will benefit from this option?
>
> (And please don't say "the same cases as those where server-window is
> useful", because I don't understand its usefulness, either.)

It is possible for the same person to want the behavior to be different
in different situations.

I, for example, generally prefer switch-to-buffer-other-frame.  If I
invoke "emacsclient" multiple times, then I don't want the same
frame/window to be reused. I want a new frame for each invocation, so
that I can think of them as "dialogues" that can be handled individually
and not necessarily in order.  Using dedicated frames helps with that.

Other people might feel the same way and use the same value for
server-window -- after all it is one of the suggested values.

Usually I only edit one file via emacsclient at a time.  That file most
often has absolutely nothing to do with whatever else is happening in
the emacs instance it connects to.  Basically I want emacsclient to
behave as much like another emacs instance as possible.  If not for the
startup time, I would actually use a new instance to guarantee a clean
slate.  Using a new frame is both a good enough alternative to full
separation and the absolute minimal amount of separation I in such
cases.

However, when creating a commit from within Emacs using Magit, then the
situation is different.  Many users do not even realize that this
involves the use of $EDITOR=emacsclient.  And indeed it doesn't have to
be implemented that way.  Magit's commit command could instead create
a buffer to write the message itself and once the user indicates that
they are done, it would call "git commit -m (buffer-string)".

Especially if the latter is one's mental modal of what happens when
creating a commit, and one generally doesn't create many frames and
instead relies on buffer switching inside existing frame(s), then it
would be surprising if a new frame were created.  And even I who knows
what is going on and generally rely heavily on short-lived frames, would
not want a new frame to popup in this case.

I common sequence of tasks would be.
1. Edit file.
2. Bring up Magit status buffer.  The status buffer is displayed in the
   window previously displaying the file-visiting buffer.
3. Stage all or some of the changes.
4. Invoke the commit command.

At this point one would expect the commit command to behave the same as
the show-status command.  The current buffer is replaced with the new
"dialog like" buffer.  But if one configured server-window as I have
described above, to handle a completely different situation to one's
liking, then that is not what would happen.

So in summary, it is possible for the same person to want the behavior
to be different in different situations.  The fact that "committing from
Emacs using Magit" involves the use of emacsclient, just like "quickly
edit a file from the terminal" does, is an implementation detail, and
should not make it necessary for the user to decide which use-case
should be optimized to their liking, at the cost of undesirable behavior
in the other case.

bug#71971: 31.0.50; Add user option server-window-alist

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Cc: 71971@debbugs.gnu.org
> Date: Sat, 06 Jul 2024 16:16:21 +0200
> 
> So in summary, it is possible for the same person to want the behavior
> to be different in different situations.  The fact that "committing from
> Emacs using Magit" involves the use of emacsclient, just like "quickly
> edit a file from the terminal" does, is an implementation detail, and
> should not make it necessary for the user to decide which use-case
> should be optimized to their liking, at the cost of undesirable behavior
> in the other case.

That sounds to me like the value of $EDITOR should be "emacsclient -c"
whereas the value of $GIT_EDITOR should be just "emacsclient"?  IOW,
what you describe involves workflows some of which want a new client
frame and some want to reuse the same frame.

But the server-window variable and the proposed server-window-alist
are about having certain _buffers_ display in certain _windows_.  It
is not even possible to express the "give me a new frame" preference,
because the only frame you can mention in the value is an existing
frame, and I very much doubt that "normal" users will know how to
express even a specific frame there, with the sole exception of the
selected one.  So, AFAICT, to support the two varieties you described,
users will almost always need to write a function and put it into the
alist elements' SERVER-WINDOW slots, is that right?  And what will
they use for the REGEXP part? are they supposed to know by heart the
names of temporary files Git and other VCSes use for editing commit
messages?

My conclusion is that if we want to support the above workflows, we
need a more user-friendly feature, using which users will be able to
easily control the server's frame-creation behavior depending on some
predictably-deterministic attribute of the connection or the client.
One possibility would be to add a new protocol command telling
server.el how to create/reuse frames, and then tell users to set
$EDITOR and similar variables to invoke that command via the
emacsclient command-line arguments.  Other ideas are welcome.

bug#71971: 31.0.50; Add user option server-window-alist

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

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Jonas Bernoulli <jonas@bernoul.li>
>> Cc: 71971@debbugs.gnu.org
>> Date: Sat, 06 Jul 2024 16:16:21 +0200
>> 
>> So in summary, it is possible for the same person to want the behavior
>> to be different in different situations.  The fact that "committing from
>> Emacs using Magit" involves the use of emacsclient, just like "quickly
>> edit a file from the terminal" does, is an implementation detail, and
>> should not make it necessary for the user to decide which use-case
>> should be optimized to their liking, at the cost of undesirable behavior
>> in the other case.
>
> That sounds to me like the value of $EDITOR should be "emacsclient -c"
> whereas the value of $GIT_EDITOR should be just "emacsclient"?

Who would set those variables to those values? Where?

---

I am beginning to think that at least for Magit's needs the new
--create-frame is sufficient.  It could just call

  EDITOR="emacsclient -c" git commit

Unfortunately that's a fairly new argument, so with-editor will have
to keep providing an alternative.  But when it comes to the question
of whether server-window-alist should be added to future Emacs releases,
that isn't a concern.

I understand your hesitancy to add such a variable.  I am not sure it
is necessary anymore either.

> IOW,
> what you describe involves workflows some of which want a new client
> frame and some want to reuse the same frame.

Yes.

> But the server-window variable and the proposed server-window-alist
> are about having certain _buffers_ display in certain _windows_.  It
> is not even possible to express the "give me a new frame" preference,
> because the only frame you can mention in the value is an existing
> frame, and I very much doubt that "normal" users will know how to
> express even a specific frame there, with the sole exception of the
> selected one.  So, AFAICT, to support the two varieties you described,
> users will almost always need to write a function and put it into the
> alist elements' SERVER-WINDOW slots, is that right?

Oh, I see, there's no switch-to-buffer-new-frame, just
switch-to-buffer-other-frame.

So I think what happened is that "committing from Magit" needed a way
the override a universal user preference of "something other than the
default of server-window=nil" to go back to "server-window=nil".  And
then implemented it in a way that could potentially be useful for other
packages, without realizing that other pieces that would make that
actually useful (such as the new-frame function) weren't actually
available.

As I said before, had --create-frame been available, I would probably
have used that.

That being said, maybe adding switch-to-buffer-new-frame wouldn't be
such a bad idea.

> And what will
> they use for the REGEXP part? are they supposed to know by heart the
> names of temporary files Git and other VCSes use for editing commit
> messages?

Well no, Magit takes care of that, and so could VC.  Other packages
could also add their package-specific defaults to the alist.  Users
could edit these elements.  Users could also express their own
preferences for specific files that they want to handle differently,
and whose names they are well aware of.

I don't know whether anyone would want that.  I am not doing it.  As
I said, I might have over generalized it and added a feature nobody
actually uses.

> My conclusion is that if we want to support the above workflows, we
> need a more user-friendly feature, using which users will be able to
> easily control the server's frame-creation behavior depending on some
> predictably-deterministic attribute of the connection or the client.

Now that we have not only --tty and --reuse-frame but also
--create-frame, I personally don't need anything more.  But that of
course doesn't mean that I cannot imagine that others (including future
me) might not want more options.  It's worth considering what else
could be offered.

> One possibility would be to add a new protocol command telling
> server.el how to create/reuse frames, and then tell users to set
> $EDITOR and similar variables to invoke that command via the
> emacsclient command-line arguments.  Other ideas are welcome.

I'm not sure what you mean by "protocol".  More arguments?

You mention environment variables.  If I remember correctly, I did
experiment with that, but ran into the problem that while it was
possible to pass along additional environment variables when using
"emacsclient --tty", the same was not possible when using "emacsclient
--create-frame".

bug#71971: 31.0.50; Add user option server-window-alist

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Cc: michael.albinus@gmx.de, 71971@debbugs.gnu.org
> Date: Mon, 08 Jul 2024 19:41:16 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Jonas Bernoulli <jonas@bernoul.li>
> >> Cc: 71971@debbugs.gnu.org
> >> Date: Sat, 06 Jul 2024 16:16:21 +0200
> >> 
> >> So in summary, it is possible for the same person to want the behavior
> >> to be different in different situations.  The fact that "committing from
> >> Emacs using Magit" involves the use of emacsclient, just like "quickly
> >> edit a file from the terminal" does, is an implementation detail, and
> >> should not make it necessary for the user to decide which use-case
> >> should be optimized to their liking, at the cost of undesirable behavior
> >> in the other case.
> >
> > That sounds to me like the value of $EDITOR should be "emacsclient -c"
> > whereas the value of $GIT_EDITOR should be just "emacsclient"?
> 
> Who would set those variables to those values?

The user, of course.  But see below.

> Where?

In the system's or shell's init files, depending on the system and the
user's needs.

> I am beginning to think that at least for Magit's needs the new
> --create-frame is sufficient.  It could just call
> 
>   EDITOR="emacsclient -c" git commit
> 
> Unfortunately that's a fairly new argument

"New"? AFAICT, it exists since Emacs 23.1, i.e. for the last 15 years.

> so with-editor will have to keep providing an alternative.  But when
> it comes to the question of whether server-window-alist should be
> added to future Emacs releases, that isn't a concern.
> 
> I understand your hesitancy to add such a variable.  I am not sure it
> is necessary anymore either.

Agreed.

> That being said, maybe adding switch-to-buffer-new-frame wouldn't be
> such a bad idea.

I'm quite sure you can have that already by using a suitable
display-buffer-alist.  All you want is to force
switch-to-buffer-other-frame always create a new frame.

> > And what will
> > they use for the REGEXP part? are they supposed to know by heart the
> > names of temporary files Git and other VCSes use for editing commit
> > messages?
> 
> Well no, Magit takes care of that, and so could VC.

Takes care how? what do you use for REGEXP?

> > One possibility would be to add a new protocol command telling
> > server.el how to create/reuse frames, and then tell users to set
> > $EDITOR and similar variables to invoke that command via the
> > emacsclient command-line arguments.  Other ideas are welcome.
> 
> I'm not sure what you mean by "protocol".  More arguments?

No, the protocol between emacsclient and the server.  So that the
client could tell the server how to create/reuse frames in a more
flexible manner than what we have now.

> You mention environment variables.  If I remember correctly, I did
> experiment with that, but ran into the problem that while it was
> possible to pass along additional environment variables when using
> "emacsclient --tty", the same was not possible when using "emacsclient
> --create-frame".

I meant to use environment variables only if the preference to reuse
an existing frame when editing commit log messages for Git is a
globally fixed preference for the user.  In any other case,
environment variables are not a good means, because they have global
effect and are by default inherited by child processes.

bug#71971: 31.0.50; Add user option server-window-alist

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

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Jonas Bernoulli <jonas@bernoul.li>
>> Cc: michael.albinus@gmx.de, 71971@debbugs.gnu.org
>> Date: Mon, 08 Jul 2024 19:41:16 +0200
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Jonas Bernoulli <jonas@bernoul.li>
>> >> Cc: 71971@debbugs.gnu.org
>> >> Date: Sat, 06 Jul 2024 16:16:21 +0200
>> >> 
>> >> So in summary, it is possible for the same person to want the behavior
>> >> to be different in different situations.  The fact that "committing from
>> >> Emacs using Magit" involves the use of emacsclient, just like "quickly
>> >> edit a file from the terminal" does, is an implementation detail, and
>> >> should not make it necessary for the user to decide which use-case
>> >> should be optimized to their liking, at the cost of undesirable behavior
>> >> in the other case.
>> >
>> > That sounds to me like the value of $EDITOR should be "emacsclient -c"
>> > whereas the value of $GIT_EDITOR should be just "emacsclient"?
>> 
>> Who would set those variables to those values?
>
> The user, of course.  But see below.
>
>> Where?
>
> In the system's or shell's init files, depending on the system and the
> user's needs.

[[[ Re-reading the message I am responding to, I realize that you are
already aware of what I am about to say:

> I meant to use environment variables only if the preference to reuse
> an existing frame when editing commit log messages for Git is a
> globally fixed preference for the user.

I am leaving it in my response anyway, to make it a bit more explicit.
]]]

The fault line isn't between "creating a Git commit" and "everything
else that uses $EDITOR".

If I type "git commit" in a terminal, then I want a new frame to popup
instead of the frame being reused in which I am writing this email.

If I have staged changes to Emacs in the Magit status buffer for that
repository and then invoke Magit's command for creating a commit, then
I do want that frame to be used to write the commit message.

Only being able to define the behavior globally is exactly what is not
desirable and taking advantage of the fact that Git allows overriding
$EDITOR for Git by using $GIT_EDITOR instead, does not solve that
problem.

(with-editor.el also fails to solve that problem either, but that's not
what we are discussing here.)

>
>> I am beginning to think that at least for Magit's needs the new
>> --create-frame is sufficient.  It could just call
>> 
>>   EDITOR="emacsclient -c" git commit
>> 
>> Unfortunately that's a fairly new argument
>
> "New"? AFAICT, it exists since Emacs 23.1, i.e. for the last 15 years.

Ah sorry, it is "-r"/"--reuse-frame" that was added in Emacs 29.1.  The
evidence thickens that I should/could just have used "emacsclient -c".

I was only trying to reconstruct why I have made the decision to add
`with-editor-server-window-alist' back when I did that.  It's possible
that I didn't realize back then that I could have used "-c" instead.
Or it is possible, that I had some good (or otherwise) reason not to
do it despite knowing about that argument.

>> so with-editor will have to keep providing an alternative.  But when
>> it comes to the question of whether server-window-alist should be
>> added to future Emacs releases, that isn't a concern.
>> 
>> I understand your hesitancy to add such a variable.  I am not sure it
>> is necessary anymore either.
>
> Agreed.
>
>> That being said, maybe adding switch-to-buffer-new-frame wouldn't be
>> such a bad idea.
>
> I'm quite sure you can have that already by using a suitable
> display-buffer-alist.  All you want is to force
> switch-to-buffer-other-frame always create a new frame.

I made that suggestion in response to you writing:

> It is not even possible to express the "give me a new frame"
> preference, because the only frame you can mention in the value is an
> existing frame, and I very much doubt that "normal" users will know
> how to express even a specific frame there, with the sole exception of
> the selected one.

I tough you were saying "there is no way to trivially say 'give me a new
frame' (so users have to use a mechanism that is to complex for many of
them)" and responded by saying "we could make it trivial by making
switch-to-buffer-new-frame available".

>> > And what will
>> > they use for the REGEXP part? are they supposed to know by heart the
>> > names of temporary files Git and other VCSes use for editing commit
>> > messages?
>> 
>> Well no, Magit takes care of that, and so could VC.
>
> Takes care how? what do you use for REGEXP?

It adds an entry to with-editor-server-window-alist (which due to an
advice takes precedence over window-alist), using this regexp:

"/\\(\
\\(\\(COMMIT\\|NOTES\\|PULLREQ\\|MERGEREQ\\|TAG\\)_EDIT\\|MERGE_\\|\\)MSG\
\\|\\(BRANCH\\|EDIT\\)_DESCRIPTION\\)\\'"

>> > One possibility would be to add a new protocol command telling
>> > server.el how to create/reuse frames, and then tell users to set
>> > $EDITOR and similar variables to invoke that command via the
>> > emacsclient command-line arguments.  Other ideas are welcome.
>> 
>> I'm not sure what you mean by "protocol".  More arguments?
>
> No, the protocol between emacsclient and the server.  So that the
> client could tell the server how to create/reuse frames in a more
> flexible manner than what we have now.

I still don't understand what kind of suggestion you are looking for.

Without looking up commonly accepted definitions of the term "protocol",
I assume(d) that you either meant:

1. The mechanism by which two or more entities exchange information,
   and/or
2. The kind of values and/or concrete values/"commands", that can be
   exchanged over said channel.

You also said,

> Other ideas are welcome.

So for (1) I suggested "environment variables" and for (2)
"implement switch-to-buffer-new-frame".

I'm not saying those are necessarily good suggestions, but that is what
came to mind, and they seem at least applicable and should be mentioned
in the idea collection phase.

>> You mention environment variables.  If I remember correctly, I did
>> experiment with that, but ran into the problem that while it was
>> possible to pass along additional environment variables when using
>> "emacsclient --tty", the same was not possible when using "emacsclient
>> --create-frame".
>
> I meant to use environment variables only if the preference to reuse
> an existing frame when editing commit log messages for Git is a
> globally fixed preference for the user.  In any other case,
> environment variables are not a good means, because they have global
> effect and are by default inherited by child processes.

Environment variables do _not_ have global effect per se, i.e., unless
they are set in the global environment.  Magit essentially calls

  EDITOR="emacsclient [...]" git commit

That $EDITOR only affects this one "git" invocation and its children.

If the "protocol" could be extended to pass along other preferences,
that would be useful (and it was my impression that you requested input
on how that could be done).  Environment variables could be used, as
could new arguments

  SERVER_WINDOW=switch-to-buffer-new-frame EDITOR=emacsclient git commit

or

  EDITOR="emacsclient --server-window=switch-to-buffer-new-frame" git commit

Of course if the only choices we care about are "--create-frame" and
"--reuse-frame", well, these already exist.

[[[Side-note: And these are actually the only choices *I* have come
to care about.  So I am not particularly interested, in making other
choices available anymore.  This limited interest likely affect the
quality of my suggestions.]]]

But you said

> we
> need a more user-friendly feature, using which users will be able to
> easily control the server's frame-creation behavior depending on some
> predictably-deterministic attribute of the connection or the client.

I.e., "having the choice between -c/-r/-t is not enough".  In this
context my suggestion to support --server-window=SENSIBLE-FUNCTION
continues to make sense to me.

I guess it's this part that is too vague for me:

> ... depending on some predictably-deterministic attribute ...

because, to me, command-line arguments, environment variables and
server-window-alist all satisfy this requirement, i.e., they are
channels that could be used to "communicate" that "attribute".

bug#71971: 31.0.50; Add user option server-window-alist

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Cc: michael.albinus@gmx.de, 71971@debbugs.gnu.org
> Date: Tue, 09 Jul 2024 21:05:03 +0200
> 
> The fault line isn't between "creating a Git commit" and "everything
> else that uses $EDITOR".
> 
> If I type "git commit" in a terminal, then I want a new frame to popup
> instead of the frame being reused in which I am writing this email.
> 
> If I have staged changes to Emacs in the Magit status buffer for that
> repository and then invoke Magit's command for creating a commit, then
> I do want that frame to be used to write the commit message.
> 
> Only being able to define the behavior globally is exactly what is not
> desirable and taking advantage of the fact that Git allows overriding
> $EDITOR for Git by using $GIT_EDITOR instead, does not solve that
> problem.

One way of solving this is to set $EDITOR outside Emacs, and set
$GIT_EDITOR in process-environment inside Emacs.

> > I'm quite sure you can have that already by using a suitable
> > display-buffer-alist.  All you want is to force
> > switch-to-buffer-other-frame always create a new frame.
> 
> I made that suggestion in response to you writing:
> 
> > It is not even possible to express the "give me a new frame"
> > preference, because the only frame you can mention in the value is an
> > existing frame, and I very much doubt that "normal" users will know
> > how to express even a specific frame there, with the sole exception of
> > the selected one.
> 
> I tough you were saying "there is no way to trivially say 'give me a new
> frame' (so users have to use a mechanism that is to complex for many of
> them)" and responded by saying "we could make it trivial by making
> switch-to-buffer-new-frame available".

What I meant that it's impossible using the server-window like
options.

> >> > And what will
> >> > they use for the REGEXP part? are they supposed to know by heart the
> >> > names of temporary files Git and other VCSes use for editing commit
> >> > messages?
> >> 
> >> Well no, Magit takes care of that, and so could VC.
> >
> > Takes care how? what do you use for REGEXP?
> 
> It adds an entry to with-editor-server-window-alist (which due to an
> advice takes precedence over window-alist), using this regexp:
> 
> "/\\(\
> \\(\\(COMMIT\\|NOTES\\|PULLREQ\\|MERGEREQ\\|TAG\\)_EDIT\\|MERGE_\\|\\)MSG\
> \\|\\(BRANCH\\|EDIT\\)_DESCRIPTION\\)\\'"

That's exactly what I thought: to do something like that the user
needs to know the possible names of files created by Git (and other
VCSes) for editing log messages.  Many/most people don't know that,
and so will have trouble customizing such options.  IOW, the REGEXP
part makes this option work on a very low level, and thus less
friendly than it could be.

> >> > One possibility would be to add a new protocol command telling
> >> > server.el how to create/reuse frames, and then tell users to set
> >> > $EDITOR and similar variables to invoke that command via the
> >> > emacsclient command-line arguments.  Other ideas are welcome.
> >> 
> >> I'm not sure what you mean by "protocol".  More arguments?
> >
> > No, the protocol between emacsclient and the server.  So that the
> > client could tell the server how to create/reuse frames in a more
> > flexible manner than what we have now.
> 
> I still don't understand what kind of suggestion you are looking for.

How does server.el know whether to create a new client frame or reuse
the current one, and what kind of frame to create?  Answer:
emacsclient tells it, via the appropriate commands that are part of
the emacs server to emacsclient protocol.  The protocol is documented
in the doc string of server-process-filter.  In particular, the
command -current-frame tells the server not to create new frames; -tty
tells it to create a TTY frame; etc.

> > I meant to use environment variables only if the preference to reuse
> > an existing frame when editing commit log messages for Git is a
> > globally fixed preference for the user.  In any other case,
> > environment variables are not a good means, because they have global
> > effect and are by default inherited by child processes.
> 
> Environment variables do _not_ have global effect per se, i.e., unless
> they are set in the global environment.  Magit essentially calls
> 
>   EDITOR="emacsclient [...]" git commit
> 
> That $EDITOR only affects this one "git" invocation and its children.

That's unportable.  On some systems, environment variables will be
inherited by subprocesses of "git commit".

> If the "protocol" could be extended to pass along other preferences,
> that would be useful (and it was my impression that you requested input
> on how that could be done).  Environment variables could be used, as
> could new arguments
> 
>   SERVER_WINDOW=switch-to-buffer-new-frame EDITOR=emacsclient git commit
> 
> or
> 
>   EDITOR="emacsclient --server-window=switch-to-buffer-new-frame" git commit
> 
> Of course if the only choices we care about are "--create-frame" and
> "--reuse-frame", well, these already exist.
> 
> [[[Side-note: And these are actually the only choices *I* have come
> to care about.  So I am not particularly interested, in making other
> choices available anymore.  This limited interest likely affect the
> quality of my suggestions.]]]
> 
> But you said
> 
> > we
> > need a more user-friendly feature, using which users will be able to
> > easily control the server's frame-creation behavior depending on some
> > predictably-deterministic attribute of the connection or the client.
> 
> I.e., "having the choice between -c/-r/-t is not enough".  In this
> context my suggestion to support --server-window=SENSIBLE-FUNCTION
> continues to make sense to me.
> 
> I guess it's this part that is too vague for me:
> 
> > ... depending on some predictably-deterministic attribute ...
> 
> because, to me, command-line arguments, environment variables and
> server-window-alist all satisfy this requirement, i.e., they are
> channels that could be used to "communicate" that "attribute".

Not when commands (such as emacsclient) are invoked from Emacs by Lisp
programs.  In that case, it is the Lisp program that must decide which
command-line switches of emacsclient to use, and my bothr is how to
let users specify that in a way that is both powerful and flexible,
and user-friendly.  Using regexps that match files or buffers is not
user-friendly enough to my palate in this case.

bug#71971: 31.0.50; Add user option server-window-alist

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

Thanks for the clarifications, I understand better now and agree its
a worthwhile goal.  Unfortunately I have no idea how to do it, but I
look forward to see what you and others come up with.  I can't think
of anything myself, for now at least.

Cheers!

bug#71971: 31.0.50; Add user option server-window-alist

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

Jonas Bernoulli <jonas@bernoul.li> writes:

Hi,

> Thanks for the clarifications, I understand better now and agree its
> a worthwhile goal.  Unfortunately I have no idea how to do it, but I
> look forward to see what you and others come up with.  I can't think
> of anything myself, for now at least.

What I could imagine is, that emacsclient gets the option to send an
identification, a string, to the server. With this, on the server side,
a set of preferences (variables) could be set for a given
identification, which matches a regexp. Not only for server-window, but
any variable. This would look like

((REGEXP (VAR . VALUE) .. (VAR . VALUE))
 (REGEXP (VAR . VALUE) .. (VAR . VALUE))
 ...)

Any VAR, like server-window, would use its related VALUE, which has
precedence.

Packages, like magit, could prepare such preferences, and activate if
the corresponding emacsclient sends an identification which matches a
regexp. User could prepare their own preferences, and invoke emacsclient
with their private identification, like 'emacsclient --ident="my-identification"'.

On protocol level between emacsclient and server.el, we would need a new
command '-ident'. Or, if we must be backwards compatible, we could use
'eval' to set it, or we could use a special formatted '-comment'.

This doesn't say which variables we recommend to use for
preferences. Just a mean to communicate between emacsclient and
server.el.

> Cheers!

Best regards, Michael.

bug#71971: 31.0.50; Add user option server-window-alist

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

Michael Albinus <michael.albinus@gmx.de> writes:

Hi,

> What I could imagine is, that emacsclient gets the option to send an
> identification, a string, to the server. With this, on the server side,
> a set of preferences (variables) could be set for a given
> identification, which matches a regexp. Not only for server-window, but
> any variable. This would look like
>
> ((REGEXP (VAR . VALUE) .. (VAR . VALUE))
>  (REGEXP (VAR . VALUE) .. (VAR . VALUE))
>  ...)
>
> Any VAR, like server-window, would use its related VALUE, which has
> precedence.
>
> Packages, like magit, could prepare such preferences, and activate if
> the corresponding emacsclient sends an identification which matches a
> regexp. User could prepare their own preferences, and invoke emacsclient
> with their private identification, like 'emacsclient --ident="my-identification"'.
>
> On protocol level between emacsclient and server.el, we would need a new
> command '-ident'. Or, if we must be backwards compatible, we could use
> 'eval' to set it, or we could use a special formatted '-comment'.
>
> This doesn't say which variables we recommend to use for
> preferences. Just a mean to communicate between emacsclient and
> server.el.

Unfortunately, no reaction yet. I'm undecided whether we shall go this way.

Best regards, Michael.