[tex-k] Uninterruptible loop in web2c TeX

[Paul Vojta]

On Thu, Aug 20, 2020 at 05:04:55AM +0200, Reinhard Kotucha wrote:
> On 2020-08-20 at 08:40:54 +0700, Igor Liferenko wrote:
> 
>  > Hi Reinhard ,
>  >
>  > > after pressing Ctrl+C, did you do what the message said?
>  >
>  > Here is the full transcript:
>  >
>  > $ tex
>  > This is TeX, Version 3.14159265 (TeX Live 2020/Debian) (preloaded format=tex)
>  > **\relax
>  >
>  > *^C! Interruption.
>  > <*>
>  >
>  > ? (Please type a command or say `\end')
>  > *(Please type a command or say `\end')
>  > *(Please type a command or say `\end')
>  > *(Please type a command or say `\end')
>  > <ad infinitum>
>  >
>  > >  Did you enter "\end"?
>  >
>  > It does not allow me to enter `\end' because it seems it always reads
>  > EOF from stdin.
>  >
>  > > Please try
>  > >
>  > >   1) run `tex'
>  > >   2) type `\relax' and <return>
>  > >   3) press Ctrl+C
>  > >   4) type \end
>  > >
>  > > Does this work?
>  >
>  > It is not supposed to work, because after Ctrl+C I get the `?' prompt,
>  > and `\end' can be entered only in `*' prompt.
> 
> But if you press <return> you get the message
> 
>   (Please type a command or say `\end')
> 
> and you can abort with \end.
> 
> Regards,
>   Reinhard

I am able to reproduce Igor's bug report.

If I press <return> I get no change in the infinite loop, nor does
ignoring the output and typing `\end' cause it to stop.

I am running a self-compiled copy of TeX, based on sources fetched
on or about August 7.

Paul Vojta, vojta <at> math <dot> berkeley |dot| edu