Date: 27 Nov 89  2305 PST
From: Don Knuth <DEK@SAIL.Stanford.EDU>
Subject: TeX: a new bug 
Keywords: TeX, bug

I just received a message from Rainer Sch\"opf and Frank Mittelbach
in Gutenberg's city (Mainz) that they've done it again, found another
subtle bug. This one is especially unique because it will not be
detected in the TRIP test; it only occurs in the system-dependent code
that figures out the "area" and "extension" part of a file name.

As far as I know, the error occurs only when you try to combine
\csname somehow with file name specification; for example,
        \input area:file.ext\csname xyz\endcsname
will fail on many systems. (Reason: TeX may have to store the
control sequence name xyz, while it's looking for the token following
"ext". This moves things in the string pool; but the present TeX doesn't
move the area and extension pointers, so they might point to garbage.)

This bug will be corrected in version 2.993, but I decided to use
TeXhax to let installers get a head start, since this bug affects
nearly everybody's system-dependent code! The changes are simple---
so simple I haven't even felt the need to test them yet---but they
should be made, and you can get a head start by putting them into
your change files before you get a new TEX.WEB file.

Here are the changes I'll be making to TEX.WEB (unless there's
an error here, which cannot be:)

%---- an excerpt from the next version of tex82.bug --------------------