bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

[David M. Koppelman]

Execute:

 (read-char-from-minibuffer "Answer y or n" '(?y ?n))

and press Enter. The form returns Enter (13) rather than re-prompting
for a y or n.

This causes a dataloss threat due to read-char-from-minibuffer being
called through ask-user-about-supersession-threat.

Even if the read-char-from-minibuffer bug is quickly fixed, I'd
sleep better if the following patch were applied to userlock.el:

@@ -194,7 +194,9 @@ ask-user-about-supersession-threat
 		       (list "File reverted" filename)))
 	      ((eq answer ?n)
 	       (signal 'file-supersession
-		       (list "File changed on disk" filename)))))
+		       (list "File changed on disk" filename)))
+              ((eq answer ?y))
+              (t (setq answer nil))))
       (message
        "File on disk now will become a backup file if you save these changes.")
       (setq buffer-backed-up nil))))


In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.17.4)
 of 2021-10-08 built on dmk-laptop-21
Repository revision: e73c9ac4ed4ce0a4b423dae6acbfb384c1afbce0
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101002
System Description: Fedora Linux 35 (KDE Plasma Prerelease)

Configured using:
 'configure 'CFLAGS=-O3 -march=native' --without-pop
 --with-native-compilation'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
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NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
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Memory information:
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bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

[Lars Ingebrigtsen]

"David M. Koppelman" <koppel@ece.lsu.edu> writes:

> Execute:
>
>  (read-char-from-minibuffer "Answer y or n" '(?y ?n))
>
> and press Enter. The form returns Enter (13) rather than re-prompting
> for a y or n.

It seems undocumented what RET is supposed to do in this function --
I've added Juri to the CCs, perhaps he has some comments.

> This causes a dataloss threat due to read-char-from-minibuffer being
> called through ask-user-about-supersession-threat.
>
> Even if the read-char-from-minibuffer bug is quickly fixed, I'd
> sleep better if the following patch were applied to userlock.el:
>
> @@ -194,7 +194,9 @@ ask-user-about-supersession-threat
>  		       (list "File reverted" filename)))
>  	      ((eq answer ?n)
>  	       (signal 'file-supersession
> -		       (list "File changed on disk" filename)))))
> +		       (list "File changed on disk" filename)))
> +              ((eq answer ?y))
> +              (t (setq answer nil))))

But I think ask-user-about-supersession-threat is working correctly here
already (almost by chance).  RET means "yes" in functions like
`y-or-n-p', which this is basically an extended version of, so it should
work as "yes" here, too.

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

bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

[David Koppelman]

> But I think ask-user-about-supersession-threat is working correctly here
> already (almost by chance).  RET means "yes" in functions like
> `y-or-n-p', which this is basically an extended version of, so it should
> work as "yes" here, too.

That might make sense if someone were expecting a prompt, but this
prompt appears totally unexpectedly when one tries to enter text into
a buffer, often that text includes enter. It would be easy to overlook
the prompt and so suffer dataloss.

David



Lars Ingebrigtsen <larsi@gnus.org> writes:

> "David M. Koppelman" <koppel@ece.lsu.edu> writes:
>
>> Execute:
>>
>>  (read-char-from-minibuffer "Answer y or n" '(?y ?n))
>>
>> and press Enter. The form returns Enter (13) rather than re-prompting
>> for a y or n.
>
> It seems undocumented what RET is supposed to do in this function --
> I've added Juri to the CCs, perhaps he has some comments.
>
>> This causes a dataloss threat due to read-char-from-minibuffer being
>> called through ask-user-about-supersession-threat.
>>
>> Even if the read-char-from-minibuffer bug is quickly fixed, I'd
>> sleep better if the following patch were applied to userlock.el:
>>
>> @@ -194,7 +194,9 @@ ask-user-about-supersession-threat
>>  		       (list "File reverted" filename)))
>>  	      ((eq answer ?n)
>>  	       (signal 'file-supersession
>> -		       (list "File changed on disk" filename)))))
>> +		       (list "File changed on disk" filename)))
>> +              ((eq answer ?y))
>> +              (t (setq answer nil))))
>
> But I think ask-user-about-supersession-threat is working correctly here
> already (almost by chance).  RET means "yes" in functions like
> `y-or-n-p', which this is basically an extended version of, so it should
> work as "yes" here, too.

bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

[Juri Linkov]

close 51101 28.0.60
quit

>> Execute:
>>
>>  (read-char-from-minibuffer "Answer y or n" '(?y ?n))
>>
>> and press Enter. The form returns Enter (13) rather than re-prompting
>> for a y or n.
>
> It seems undocumented what RET is supposed to do in this function --
> I've added Juri to the CCs, perhaps he has some comments.

RET is supposed to do exactly the same what it did in
read-char-choice-with-read-key, or when these variables are non-nil:
read-char-choice-use-read-key and y-or-n-p-use-read-key,
i.e. to ignore RET and read the character again.

So this is fixed accordingly now in 28.0.

>> This causes a dataloss threat due to read-char-from-minibuffer being
>> called through ask-user-about-supersession-threat.
>>
>> Even if the read-char-from-minibuffer bug is quickly fixed, I'd
>> sleep better if the following patch were applied to userlock.el:
>>
>> @@ -194,7 +194,9 @@ ask-user-about-supersession-threat
>>  		       (list "File reverted" filename)))
>>  	      ((eq answer ?n)
>>  	       (signal 'file-supersession
>> -		       (list "File changed on disk" filename)))))
>> +		       (list "File changed on disk" filename)))
>> +              ((eq answer ?y))
>> +              (t (setq answer nil))))

I installed the patch provided by David as well.

> But I think ask-user-about-supersession-threat is working correctly here
> already (almost by chance).  RET means "yes" in functions like
> `y-or-n-p', which this is basically an extended version of, so it should
> work as "yes" here, too.

Maybe it works here because ask-user-about-supersession-threat
is called from C with some flag that disables signaling 'quit'.
But when trying to type RET after (y-or-n-p "Answer y or n: ")
it terminates with the 'quit' signal.  And indeed in the map
used by y-or-n-p, RET is bound to 'exit':

    (define-key query-replace-map "\r" 'exit)

I noticed the recent commit ec9f25bd356c7c81d94c78f11100b97d6d52ce97
saying that RET means "yes" in y-or-n-p.  But anyway since RET
now does the same that read-char-choice-with-read-key does,
so I removed mentions of RET from the doc string.  Or should
the fixed behavior be mentioned?

bug#51101: 29.0.50; read-char-from-minibuffer accepts Enter even when not a choice.

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> Maybe it works here because ask-user-about-supersession-threat
> is called from C with some flag that disables signaling 'quit'.
> But when trying to type RET after (y-or-n-p "Answer y or n: ")
> it terminates with the 'quit' signal.  And indeed in the map
> used by y-or-n-p, RET is bound to 'exit':
>
>     (define-key query-replace-map "\r" 'exit)

I must have tested this in the wrong version of Emacs -- I thought I was
testing y-or-n-p in Emacs 26.3 to see what it did there, but I must have
started a more recent version instead.

> I noticed the recent commit ec9f25bd356c7c81d94c78f11100b97d6d52ce97
> saying that RET means "yes" in y-or-n-p.  But anyway since RET
> now does the same that read-char-choice-with-read-key does,
> so I removed mentions of RET from the doc string.  Or should
> the fixed behavior be mentioned?

No, that's fine.

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