saving/restoring text and overlays

saving/restoring text and overlays

[Leo Butler]

If I have a buffer with, e.g. display properties set to images, how can
I save that to disk and re-open the saved data so that emacs displays the
same "stuff"? I am not looking to export the buffer using html or latex
or any other markup. I just want to be able to save the formatting
information so that another emacs instance can display exactly the same
document.

I can see how this might be cobbled together by a save-file hook that
stuffs (buffer-substring) of a narrowed buffer into an Eval: stanza at
the end of file. But I am hoping that there is a pre-existing mode that
does what I want.

TIA,
Leo

Re: saving/restoring text and overlays

[Michael Heerdegen]

Leo Butler <leo.butler@umanitoba.ca> writes:

> If I have a buffer with, e.g. display properties set to images, how can
> I save that to disk and re-open the saved data so that emacs displays the
> same "stuff"? I am not looking to export the buffer using html or latex
> or any other markup.

Without _any_ form of markup?  No, Emacs can't save buffers containing
images directly to a file.

We often had a discussion whether `enriched-mode' should be improved, or
something new could be created, to do what you want (among other things
like saving text properties).  But nobody has done it yet.

Michael.

Re: saving/restoring text and overlays

[Leo Butler]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> ********************************************************
> Caution: This message was sent from outside the University of Manitoba.
> ********************************************************
>
> Leo Butler <leo.butler@umanitoba.ca> writes:
>
>> If I have a buffer with, e.g. display properties set to images, how can
>> I save that to disk and re-open the saved data so that emacs displays the
>> same "stuff"? I am not looking to export the buffer using html or latex
>> or any other markup.
>
> Without _any_ form of markup?  No, Emacs can't save buffers containing
> images directly to a file.

Yes, what I mean is that I want something like enriched text mode or a
wysiwyg mode that let's me copy text with properties from other buffers
(or create it and insert it), including images, save the buffer to disk
and when I open it in another emacs I see the same thing and can
continue editing the document if need be. In other words, I am not
looking to export to another document format using e.g. html or latex.

My use case is copying snippets from *imaxima* (a front-end for Maxima
that uses latex to create its output) into another buffer that contains
text and so on.

>
> We often had a discussion whether `enriched-mode' should be improved, or
> something new could be created, to do what you want (among other things
> like saving text properties).  But nobody has done it yet.
>
> Michael.

Well, after poking around a bit, I found this in NEWS.25:
  
  * Changes in Emacs 25.3
  
  This is an emergency release to fix a security vulnerability in Emacs.
  
  ** Security vulnerability related to Enriched Text mode is removed.
  
  *** Enriched Text mode has its support for decoding 'x-display' disabled.
  This feature allows saving 'display' properties as part of text.
  Emacs 'display' properties support evaluation of arbitrary Lisp forms
  as part of instantiating the property, so decoding 'x-display' is
  vulnerable to executing arbitrary malicious Lisp code included in the
  text (e.g., sent as part of an email message).
  
So it appears that enriched text mode did do what I want, but the way
Emacs handles display properties is too permissive...

This leads me to ask why the feature was nuked rather than handling it
like file variables
(https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Variables.html).

Leo

Re: saving/restoring text and overlays

[Michael Heerdegen]

Leo Butler <leo.butler@umanitoba.ca> writes:

> So it appears that enriched text mode did do what I want, but the way
> Emacs handles display properties is too permissive...

Oh - indeed!  I tested quickly, and it even seems that simple stuff that
doesn't need to evaluate "arbitrary" Lisp still works out of the box.
Images at least work for me in emacs -Q, without changing any defaults.

> This leads me to ask why the feature was nuked rather than handling it
> like file variables
> (https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Variables.html).

Doesn't using `enriched-allow-eval-in-display-props' (the option
mentioned in the text you cited but later) as file-local var work?


Michael.

Re: saving/restoring text and overlays

[Michael Heerdegen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Images at least work for me in emacs -Q, without changing any defaults.

"Works" here means: worked with a locally saved file after ignoring lots
of warnings printed to *Messages*.  An image yanked from an *eww* buffer
didn't work, after opening the file Emacs only showed an empty box.

Michael.

Re: saving/restoring text and overlays

[Noam Postavsky]

On Sun, 29 Mar 2020 at 16:21, Leo Butler <leo.butler@umanitoba.ca> wrote:

> Well, after poking around a bit, I found this in NEWS.25:

>   *** Enriched Text mode has its support for decoding 'x-display' disabled.

> So it appears that enriched text mode did do what I want, but the way
> Emacs handles display properties is too permissive...
>
> This leads me to ask why the feature was nuked rather than handling it
> like file variables
> (https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Variables.html).

You might want to check NEWS for Emacs 26:

* Changes in Emacs 26.1

** Security vulnerability related to Enriched Text mode is removed.

*** Enriched Text mode does not evaluate Lisp in 'display' properties.
[...] decoded by Enriched Text mode is now disabled by default.  Customize
the new option 'enriched-allow-eval-in-display-props' to a non-nil
value to allow Lisp evaluation in decoded 'display' properties.

Re: saving/restoring text and overlays

[Eli Zaretskii]

> From: Leo Butler <leo.butler@umanitoba.ca>
> Date: Sun, 29 Mar 2020 15:21:39 -0500
> Cc: help-gnu-emacs@gnu.org
> 
> So it appears that enriched text mode did do what I want, but the way
> Emacs handles display properties is too permissive...
> 
> This leads me to ask why the feature was nuked rather than handling it
> like file variables
> (https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Variables.html).

It wasn't nuked, you are reading too much into that NEWS entry.  Only
the dangerous part was disabled, and even that can be enabled if you
trust the source of the file.

Re: saving/restoring text and overlays

[Leo Butler]

Eli Zaretskii <eliz@gnu.org> writes:

> ********************************************************
> Caution: This message was sent from outside the University of Manitoba.
> ********************************************************
>
>> From: Leo Butler <leo.butler@umanitoba.ca>
>> Date: Sun, 29 Mar 2020 15:21:39 -0500
>> Cc: help-gnu-emacs@gnu.org
>> 
>> So it appears that enriched text mode did do what I want, but the way
>> Emacs handles display properties is too permissive...
>> 
>> This leads me to ask why the feature was nuked rather than handling it
>> like file variables
>> (https://www.gnu.org/software/emacs/manual/html_node/emacs/File-Variables.html).
>
> It wasn't nuked, you are reading too much into that NEWS entry.  Only
> the dangerous part was disabled, and even that can be enabled if you
> trust the source of the file.

You are right.

After more investigation, I find that Emacs 25.2.2 on Ubuntu 18.04
is not saving the x-display properties while Emacs 26.1 on Debian
testing does.

Inspection of enriched.el on each system shows that on Ubuntu
enriched-translations is missing the portions

    (FUNCTION      (enriched-decode-foreground "x-color")
		   (enriched-decode-background "x-bg-color")
		   (enriched-decode-display-prop "x-display"))
    (display	   (nil		enriched-handle-display-prop))

Sigh.

Apologies, I should have looked more carefully.

Leo