Somewhat surprising behaviour of \scantokens after \endinput

[jfbu]

Hi,

I have encountered a phenomenon with \scantokens executed after \endinput:

---
% execute this file testscan.tex with etex on command line
\def\test{%
    \begingroup
    \endlinechar-1\everyeof{\noexpand}%
    \edef\foo{\scantokens{}}%
    \endgroup
}%
\test % ok
% \test\endinput % would be ok
\endinput\test % not ok
---

executing "etex testscan" (or pdftex, xetex, luatex, eptex) gives this:

Runaway definition?
->
! File ended while scanning definition of \foo.
<inserted text> 
                }
\test ...of {\noexpand }\edef \foo {\scantokens {}
                                                  }\endgroup 
l.12 \endinput\test
                    % not ok^^M
? X

I would be curious if some expert could elucidate.

It seems the \noexpand which is usual trick to
be able to use \scantokens inside an \edef
fails here, 

and this is caused by the \scantokens being executed
after the \endinput token was already encountered

I have not looked at the sources and I can't
say a priori if this is to be expected or is
a problem with \scantokens

All I remember from whatever TeX documentation
I have read in the past
is that TeX executes the macros on the same
line as \endinput

And that a priori, it is unexpected behaviour
if one does not know the innards of \scantokens

I looked at https://tug.org/mailman/listinfo
but did not find an eTeX specific list,
so posting here as it is not pdftex specific either

Best,

Please CC my address if replying

Jean-François