GNU bug report logs - #54486
29.0.50; Eshell `escaped' string property can "leak" into output

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Package: emacs;

Reported by: Jim Porter <jporterbugs <at> gmail.com>

Date: Mon, 21 Mar 2022 03:53:02 UTC

Severity: normal

Found in version 29.0.50

Done: Jim Porter <jporterbugs <at> gmail.com>

Bug is archived. No further changes may be made.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Jim Porter <jporterbugs <at> gmail.com>
Subject: bug#54486: closed (Re: 29.0.50; Eshell `escaped' string property
 can "leak" into output)
Date: Sun, 24 Nov 2024 06:58:01 +0000
[Message part 1 (text/plain, inline)]
Your bug report

#54486: 29.0.50; Eshell `escaped' string property can "leak" into output

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 54486 <at> debbugs.gnu.org.

-- 
54486: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=54486
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems
[Message part 2 (message/rfc822, inline)]
From: Jim Porter <jporterbugs <at> gmail.com>
To: 54486-done <at> debbugs.gnu.org
Subject: Re: 29.0.50; Eshell `escaped' string property can "leak" into output
Date: Sat, 23 Nov 2024 22:56:54 -0800
On 3/20/2022 8:52 PM, Jim Porter wrote:
> When using Eshell, it's possible to inadvertently add an `escaped' 
> string property to strings, resulting in some pretty surprising 
> behavior. Starting from "emacs -Q --eval '(eshell)'":
> 
>    ~ $ setq var (list "foo" "bar")
>    ("foo" "bar")
>    ~ $ echo $var
>    ("foo" "bar")
>    ~ $ echo $var[0]
>    foo
>    ~ $ echo $var
>    (#("foo" 0 3
>       (escaped t))
>     "bar")

In the intervening years, I've improved Eshell's parser to prevent other 
bugs, which has resulted in the 'escaped' string property no longer 
being useful.

Instead, Eshell now propertizes text that has actual syntactic meaning: 
for example a globbing character like "*" gets the 'eshell-glob-char' 
text property. By marking *syntactic* characters with a text property, 
we ensure that Eshell only ever adds properties to text literally 
written into the Eshell buffer, which avoids the issue here.

As a result of all this, we can now remove the calls that added that 
property in Eshell. I've now made this change in b4655ff99b5, so closing 
this bug.

[Message part 3 (message/rfc822, inline)]
From: Jim Porter <jporterbugs <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.0.50; Eshell `escaped' string property can "leak" into output
Date: Sun, 20 Mar 2022 20:52:43 -0700
When using Eshell, it's possible to inadvertently add an `escaped' 
string property to strings, resulting in some pretty surprising 
behavior. Starting from "emacs -Q --eval '(eshell)'":

  ~ $ setq var (list "foo" "bar")
  ("foo" "bar")
  ~ $ echo $var
  ("foo" "bar")
  ~ $ echo $var[0]
  foo
  ~ $ echo $var
  (#("foo" 0 3
     (escaped t))
   "bar")

This happens because when the `$var[0]' argument is parsed in the third 
command, the function `eshell-interpolate-variable' wraps the 
code-to-be-called with `eshell-escape-arg'. That function adds an 
`escaped' property to any string passed into it.

The `escaped' property is used to indicate that the string should be 
treated literally (i.e. any special characters like "$" will no longer 
have any special meaning in Eshell). That's the right *behavior*, but 
ideally, there'd be a way to do so that doesn't involve manipulating the 
string like this. Eshell can't know the lifetime of the string, and it 
seems like a bad idea in general to go around messing with string 
properties just because you referenced that string somehow in Eshell.

I can't think of an obvious fix for this though. Any ideas?



This bug report was last modified 209 days ago.

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