bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Yuen Ho Wong]

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How to reproduce:
1. Turn on `desktop-save-mode`
2. dired some directory
3. Press `(` to turn on `dired-hide-details-mode`
4. C-x C-c, when asked to save desktop, choose yes
5. Launch emacs again, desktop restored the dired buffer but not
`dired-hide-details-mode`

What went wrong:
`dired-hide-details-mode`'s definition does not declare a lighter or a
keymap, thus it is not added to `minor-mode-alist` by
`define-minor-mode`. So when `desktop` tries to get the buffer's info to
save to `.emacs.desktop` via `desktop-buffer-info`,
`dired-hide-details-mode` does not exist, and thus not saved to the
session file.

Fix:
Just declare an empty lighter. I've attached a patch for this.



[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: Add dired-hide-details-mode to minor-mode-alist --]
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From 49b10c2f4b17809d0b34354699e6a1a35d7be785 Mon Sep 17 00:00:00 2001
From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
Date: Wed, 3 Jan 2018 23:43:27 +0000
Subject: [PATCH] Add dired-hide-details-mode to minor-mode-alist

---
 lisp/dired.el | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lisp/dired.el b/lisp/dired.el
index b853d64c56..97f41400f8 100644
--- a/lisp/dired.el
+++ b/lisp/dired.el
@@ -2433,6 +2433,7 @@ permissions are hidden from view.
 See options: `dired-hide-details-hide-symlink-targets' and
 `dired-hide-details-hide-information-lines'."
   :group 'dired
+  :lighter: ""
   (unless (derived-mode-p 'dired-mode)
     (error "Not a Dired buffer"))
   (dired-hide-details-update-invisibility-spec)
-- 
2.15.1


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Jimmy Yuen Ho Wong

In GNU Emacs 25.3.3 (x86_64-apple-darwin13.4.0, Carbon Version 157 AppKit 1265.21)
 of 2017-09-28 built on Atago.local
Repository revision: 67b78428be670691c240a20bb7af9248b884d583
Windowing system distributor 'Apple Inc.', version 10.13.2
Configured using:
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Configured features:
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Recent messages:
Updating buffer list...done
Commands: m, u, t, RET, g, k, S, D, Q; q to quit; h for help
imenu-list: couldn’t create index because of error: (imenu-unavailable "This buffer cannot use ‘imenu-default-create-index-function’")
Loading /Users/wyuenho/.emacs.d/company-statistics-cache.el (source)...done
Warning: symbolic link to Git-controlled source file
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Wrote /Users/wyuenho/.emacs.d/.emacs.desktop.lock
Desktop: 1 frame, 2 buffers restored.
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For information about GNU Emacs and the GNU system, type C-h C-a.

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bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Yuen Ho Wong <wyuenho@gmail.com>
> Date: Thu, 04 Jan 2018 01:11:13 +0000
> 
> How to reproduce:
> 1. Turn on `desktop-save-mode`
> 2. dired some directory
> 3. Press `(` to turn on `dired-hide-details-mode`
> 4. C-x C-c, when asked to save desktop, choose yes
> 5. Launch emacs again, desktop restored the dired buffer but not
> `dired-hide-details-mode`
> 
> What went wrong:
> `dired-hide-details-mode`'s definition does not declare a lighter or a
> keymap, thus it is not added to `minor-mode-alist` by
> `define-minor-mode`. So when `desktop` tries to get the buffer's info to
> save to `.emacs.desktop` via `desktop-buffer-info`,
> `dired-hide-details-mode` does not exist, and thus not saved to the
> session file.
> 
> Fix:
> Just declare an empty lighter. I've attached a patch for this.

Can't you instead customize desktop-locals-to-save?

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Jimmy Yuen Ho Wong]

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I don't believe so. I've looked at a number of approaches.

1. `desktop-minor-mode-handlers` on desktop-read
    Not going to be consulted unless `dired-hide-details-mode` is saved as
a buffer minor mode.
2. `desktop-minor-mode-table` on desktop-save
    If `dired-hide-details-mode` is not in `minor-mode-alist`,
`desktop-minor-mode-table` will not even be consulted.
3. `desktop-locals-to-save`
    This does save the minor mode local variable to the desktop file, but
desktop won't be able to restore the minor mode because minor modes are
activated before buffer local variables are restored, not after.

So the only choices left to me are:
- :lighter ""
- (add-minor-mode 'dired-hide-details-mode "")

Either way adds an empty string as a lighter, and the second option makes
you ask why you are declaring *and* adding a minor mode, so I picked the
first option. It's more concise.

Jimmy Wong

On Thu, Jan 4, 2018 at 4:42 PM, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Yuen Ho Wong <wyuenho@gmail.com>
> > Date: Thu, 04 Jan 2018 01:11:13 +0000
> >
> > How to reproduce:
> > 1. Turn on `desktop-save-mode`
> > 2. dired some directory
> > 3. Press `(` to turn on `dired-hide-details-mode`
> > 4. C-x C-c, when asked to save desktop, choose yes
> > 5. Launch emacs again, desktop restored the dired buffer but not
> > `dired-hide-details-mode`
> >
> > What went wrong:
> > `dired-hide-details-mode`'s definition does not declare a lighter or a
> > keymap, thus it is not added to `minor-mode-alist` by
> > `define-minor-mode`. So when `desktop` tries to get the buffer's info to
> > save to `.emacs.desktop` via `desktop-buffer-info`,
> > `dired-hide-details-mode` does not exist, and thus not saved to the
> > session file.
> >
> > Fix:
> > Just declare an empty lighter. I've attached a patch for this.
>
> Can't you instead customize desktop-locals-to-save?
>

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bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> Date: Fri, 5 Jan 2018 13:08:35 +0000
> Cc: 29972@debbugs.gnu.org
> 
> I don't believe so. I've looked at a number of approaches.
> 
> 1. `desktop-minor-mode-handlers` on desktop-read
>     Not going to be consulted unless `dired-hide-details-mode` is saved as a buffer minor mode.
> 2. `desktop-minor-mode-table` on desktop-save
>     If `dired-hide-details-mode` is not in `minor-mode-alist`, `desktop-minor-mode-table` will not even be
> consulted.
> 3. `desktop-locals-to-save`
>     This does save the minor mode local variable to the desktop file, but desktop won't be able to restore the
> minor mode because minor modes are activated before buffer local variables are restored, not after.
> 
> So the only choices left to me are:
> - :lighter ""
> - (add-minor-mode 'dired-hide-details-mode "")
> 
> Either way adds an empty string as a lighter, and the second option makes you ask why you are declaring
> *and* adding a minor mode, so I picked the first option. It's more concise.

Then maybe we need a new, more thorough customization facility for
desktop.el, or a change in the facilities you tried to make them
handle this case as well.  It doesn't sound right to me to make tricky
changes in a minor mode just so it could be restored by desktop.el.

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Jimmy Yuen Ho Wong]

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Actually I would question why we have minor modes not added to
minor-mode-alist at all just because both lighter and keymap are missing.

What do you think about changing define-minor-mode?
On Fri, 5 Jan 2018 at 2:26 pm, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> > Date: Fri, 5 Jan 2018 13:08:35 +0000
> > Cc: 29972@debbugs.gnu.org
> >
> > I don't believe so. I've looked at a number of approaches.
> >
> > 1. `desktop-minor-mode-handlers` on desktop-read
> >     Not going to be consulted unless `dired-hide-details-mode` is saved
> as a buffer minor mode.
> > 2. `desktop-minor-mode-table` on desktop-save
> >     If `dired-hide-details-mode` is not in `minor-mode-alist`,
> `desktop-minor-mode-table` will not even be
> > consulted.
> > 3. `desktop-locals-to-save`
> >     This does save the minor mode local variable to the desktop file,
> but desktop won't be able to restore the
> > minor mode because minor modes are activated before buffer local
> variables are restored, not after.
> >
> > So the only choices left to me are:
> > - :lighter ""
> > - (add-minor-mode 'dired-hide-details-mode "")
> >
> > Either way adds an empty string as a lighter, and the second option
> makes you ask why you are declaring
> > *and* adding a minor mode, so I picked the first option. It's more
> concise.
>
> Then maybe we need a new, more thorough customization facility for
> desktop.el, or a change in the facilities you tried to make them
> handle this case as well.  It doesn't sound right to me to make tricky
> changes in a minor mode just so it could be restored by desktop.el.
>

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bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> Date: Fri, 05 Jan 2018 15:02:21 +0000
> Cc: 29972@debbugs.gnu.org
> 
> Actually I would question why we have minor modes not added to minor-mode-alist at all just because both
> lighter and keymap are missing.

Because minor-mode-alist is for displaying an indication of a minor
mode in the mode line?

> What do you think about changing define-minor-mode?

IMO, a better idea is to find out why desktop.el requires a minor mode
to be in minor-mode-alist before it saves it.  Is there really a
justification for that?

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Jimmy Yuen Ho Wong]

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> Because minor-mode-alist is for displaying an indication of a minor
mode in the mode line?

Right, but there doesn't appear to be any other more reliable way to know
what minor mode is active in a buffer. An alternative I can think of is see
if there's buffer local variable that also exists in `minor-mode-list`, but
that's still not reliable, hence we have these `desktop-minor-mode-*` vars.

The fundamental reason appears to be desktop.el needs an efficient and
reliable way to know what buffer local variables are minor modes, since
`minor-mode-list` is just a global list of loaded minor-modes,
`minor-mode-alist` is as close as you get.

If my patch make it in, it will not be the first minor mode in emacs that
defines an empty string lighter. `xref`, `linum`, `erc-track` and `rcirc`
all do this. There are even more examples in the wild. I have at least 8
other packages in my ~/.emacs.d/elpa that do the same thing.

I agree, however, that this is an abuse. There should be perhaps some
buffer local variable called `buffer-minor-modes`, but I think this should
be a separate issue and a new feature, so perhaps wait til after 26.1?


On Fri, Jan 5, 2018 at 3:16 PM, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> > Date: Fri, 05 Jan 2018 15:02:21 +0000
> > Cc: 29972@debbugs.gnu.org
> >
> > Actually I would question why we have minor modes not added to
> minor-mode-alist at all just because both
> > lighter and keymap are missing.
>
> Because minor-mode-alist is for displaying an indication of a minor
> mode in the mode line?
>
> > What do you think about changing define-minor-mode?
>
> IMO, a better idea is to find out why desktop.el requires a minor mode
> to be in minor-mode-alist before it saves it.  Is there really a
> justification for that?
>

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bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> Date: Fri, 5 Jan 2018 17:42:49 +0000
> Cc: 29972@debbugs.gnu.org
> 
> The fundamental reason appears to be desktop.el needs an efficient and reliable way to know what buffer
> local variables are minor modes, since `minor-mode-list` is just a global list of loaded minor-modes,
> `minor-mode-alist` is as close as you get.

So maybe desktop.el should have defcustom with the list of minor
modes, whose default value is computed from minor-mode-alist, but
which users could customize to add any additional minor modes?

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Noam Postavsky]

On Fri, Jan 5, 2018 at 1:20 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
>> Date: Fri, 5 Jan 2018 17:42:49 +0000
>> Cc: 29972@debbugs.gnu.org
>>
>> The fundamental reason appears to be desktop.el needs an efficient and reliable way to know what buffer
>> local variables are minor modes, since `minor-mode-list` is just a global list of loaded minor-modes,
>> `minor-mode-alist` is as close as you get.
>
> So maybe desktop.el should have defcustom with the list of minor
> modes, whose default value is computed from minor-mode-alist, but
> which users could customize to add any additional minor modes?

Would it help if define-minor-mode recorded what the
variable/expression is (e.g., by putting a property on the function
symbol)?
This could also be useful for define-globalized-minor-mode (see
Bug#29081 - for which the current suggestion is to do without that,
but if such a thing has two uses, it will likely be helpful in even
more situations).

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Drew Adams]

`describe-mode' uses `minor-mode-list' (`list', not
`alist') to determine which minor modes are active
in the current buffer.

It also uses `minor-mode-alist', because of what
this comment says:

;; Older packages do not register in minor-mode-list
;; but only in `minor-mode-alist'.

The code that determines which minor modes are
active in the current buffer could be factored
out into a separate funtion, and that could be
used, for example, by desktop.

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Fri, 5 Jan 2018 13:29:49 -0500
> Cc: Jimmy Yuen Ho Wong <wyuenho@gmail.com>, 29972@debbugs.gnu.org
> 
> Would it help if define-minor-mode recorded what the
> variable/expression is (e.g., by putting a property on the function
> symbol)?

Not sure what should desktop.el do with that.  Loop on all symbols in
obarray looking for those with that property?

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Noam Postavsky]

On Fri, Jan 5, 2018 at 2:41 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Noam Postavsky <npostavs@users.sourceforge.net>
>> Date: Fri, 5 Jan 2018 13:29:49 -0500
>> Cc: Jimmy Yuen Ho Wong <wyuenho@gmail.com>, 29972@debbugs.gnu.org
>>
>> Would it help if define-minor-mode recorded what the
>> variable/expression is (e.g., by putting a property on the function
>> symbol)?
>
> Not sure what should desktop.el do with that.  Loop on all symbols in
> obarray looking for those with that property?

I thought looping over symbols in minor-mode-list would make sense.

(I see describe-mode only takes minor modes which have function and
variable using the same symbol)

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Fri, 5 Jan 2018 14:54:01 -0500
> Cc: Jimmy Yuen Ho Wong <wyuenho@gmail.com>, 29972@debbugs.gnu.org
> 
> >> Would it help if define-minor-mode recorded what the
> >> variable/expression is (e.g., by putting a property on the function
> >> symbol)?
> >
> > Not sure what should desktop.el do with that.  Loop on all symbols in
> > obarray looking for those with that property?
> 
> I thought looping over symbols in minor-mode-list would make sense.

Yes, but your suggestion never mentioned minor-mode-list, so I
probably missed the point.

> (I see describe-mode only takes minor modes which have function and
> variable using the same symbol)

That happens automagically if one uses define-minor-mode, right?

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Noam Postavsky]

On Fri, Jan 5, 2018 at 2:56 PM, Eli Zaretskii <eliz@gnu.org> wrote:

>> (I see describe-mode only takes minor modes which have function and
>> variable using the same symbol)
>
> That happens automagically if one uses define-minor-mode, right?

Except if you use its :variable option.

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Jimmy Yuen Ho Wong]

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Does that mean this patch can't be merged until we've figured a way out by
changing `define-minor-mode` to introduce a new `buffer-minor-modes` buffer
local variable?

On Fri, Jan 5, 2018 at 7:59 PM, Noam Postavsky <
npostavs@users.sourceforge.net> wrote:

> On Fri, Jan 5, 2018 at 2:56 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>
> >> (I see describe-mode only takes minor modes which have function and
> >> variable using the same symbol)
> >
> > That happens automagically if one uses define-minor-mode, right?
>
> Except if you use its :variable option.
>

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bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Eli Zaretskii]

> From: Jimmy Yuen Ho Wong <wyuenho@gmail.com>
> Date: Mon, 8 Jan 2018 12:43:38 +0000
> 
> Does that mean this patch can't be merged until we've figured a way out by changing `define-minor-mode` to
> introduce a new `buffer-minor-modes` buffer local variable?

We need to figure out some way for desktop.el to record
dired-hide-details-mode, either automatically or given user
customizations.

It's possible that looking at minor-mode-list (not minor-mode-alist!)
is such a way.

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Drew Adams]

> We need to figure out some way for desktop.el to record
> dired-hide-details-mode, either automatically or given user
> customizations.
> 
> It's possible that looking at minor-mode-list (not minor-mode-alist!)
> is such a way.

Yes, that's no doubt possible.  Perhaps it's also possible
to make changes to variable `dired-hide-details-mode' change
the mode.  If so then you could just add that variable to
the default value of `desktop-locals-to-save'.  And since
that's a user option, users could then control whether that's
the behavior they want, i.e., whether desktop should restore
whether details were shown/hidden.

bug#29972: 25.3; dired-hide-details-mode does not persist in desktop session

[Lars Ingebrigtsen]

Yuen Ho Wong <wyuenho@gmail.com> writes:

> How to reproduce:
> 1. Turn on `desktop-save-mode`
> 2. dired some directory
> 3. Press `(` to turn on `dired-hide-details-mode`
> 4. C-x C-c, when asked to save desktop, choose yes
> 5. Launch emacs again, desktop restored the dired buffer but not
> `dired-hide-details-mode`
>
> What went wrong:
> `dired-hide-details-mode`'s definition does not declare a lighter or a
> keymap, thus it is not added to `minor-mode-alist` by
> `define-minor-mode`. So when `desktop` tries to get the buffer's info to
> save to `.emacs.desktop` via `desktop-buffer-info`,
> `dired-hide-details-mode` does not exist, and thus not saved to the
> session file.
>
> Fix:
> Just declare an empty lighter. I've attached a patch for this.

I've fixed this in a differently way in Emacs 29 -- I'm using the
local-minor-modes variable instead, which does not depend on lighters
and keymaps.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no