\show crashes MiKTeX

[T-F-S]

After last MiKTeX update, the \show command crashes MiKTeX on Windows 10.

Consider the following MWE:

\documentclass{article}

\def\foo{Hello World}

\begin{document}

\show\foo

\foo

\end{document}

Compiling with pdflatex does NOT ask for interaction, but does immediately display the following (no stop at ?):

c:\temp>pdflatex dummy.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.21 (MiKTeX 20.6)
entering extended mode
(dummy.tex
LaTeX2e <2020-02-02> patch level 5
L3 programming layer <2020-06-18>
("C:\Program Files\MiKTeX 2.9\tex/latex/base\article.cls"
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class
("C:\Program Files\MiKTeX 2.9\tex/latex/base\size10.clo"))
("C:\Program Files\MiKTeX 2.9\tex/latex/l3backend\l3backend-pdfmode.def")
(dummy.aux)
> \foo=macro:
->Hello World.
l.8 \show\foo

?
Sorry, but pdflatex did not succeed.

The log file hopefully contains the information to get MiKTeX going again:

  C:\Users\Thomas\AppData\Local\MiKTeX\2.9\miktex\log\pdflatex.log

The pdflatex.log shows:

2020-06-29 16:46:15,532+0200 INFO  pdflatex - this process (5708) started by 'cmd' with command line: pdflatex dummy.tex
2020-06-29 16:46:15,539+0200 INFO  pdflatex - allowing known shell commands
2020-06-29 16:46:15,539+0200 INFO  pdflatex - enabling input (output) from (to) processes
2020-06-29 16:46:15,637+0200 FATAL pdflatex.core - MiKTeX encountered an internal error.
2020-06-29 16:46:15,637+0200 FATAL pdflatex.core - Data: 
2020-06-29 16:46:15,637+0200 FATAL pdflatex.core - Source: Libraries\MiKTeX\TeXAndFriends\inputline.cpp:627
2020-06-29 16:46:15,638+0200 FATAL pdflatex - MiKTeX encountered an internal error.
2020-06-29 16:46:15,638+0200 FATAL pdflatex - Info: 
2020-06-29 16:46:15,638+0200 FATAL pdflatex - Source: Libraries\MiKTeX\TeXAndFriends\inputline.cpp
2020-06-29 16:46:15,638+0200 FATAL pdflatex - Line: 627
2020-06-29 16:46:15,640+0200 INFO  pdflatex - this process (5708) finishes with exit code 1
2020-06-29 16:46:15,640+0200 WARN  miktex.core - still open: dummy.tex
2020-06-29 16:46:15,640+0200 WARN  miktex.core - still open: dummy.aux
2020-06-29 16:46:15,640+0200 WARN  miktex.core - still open: dummy.log

This error was confirmed on https://tex.stackexchange.com/questions/551592/show-crashes-miktex by other users.

• I have read the MiKTeX Contributing Guidelines

[edocevoli]

Thank you. This will be fixed with the next update.

[crecapet]

I confirm this recent issue (Windows 10).

[edocevoli]

This has been fixed.