bug#56025: 29.0.50; em-extpipe-test-2 times out on EMBA and Cygwin

[Ken Brown <kbrown@cornell.edu>]

On 6/17/2022 10:07 PM, Ken Brown wrote:
> On 6/17/2022 8:57 PM, Sean Whitton wrote:
>> On Fri 17 Jun 2022 at 09:39am -04, Ken Brown wrote:
>>> I just tried a different experiment: In an interactive emacs-29 session, I
>>> started eshell and typed
>>>
>>>     echo \"bar\" | rev *>temp
>>>
>>> Nothing visible happens until I type 'C-c C-c'.  Then a prompt appears again,
>>> and 'ls -l' shows that temp exists and is empty.
>>>
>>> Prior to typing 'C-c C-c', 'M-x list-processes' (or 'C-c C-s') shows a bash
>>> process running but it doesn't show 'rev'.  But running 'ps' outside of emacs
>>> shows both 'rev' and its parent 'bash' process.
>>>
>>> It does seem that there's an actual bug here, not just a test that should be
>>> skipped because it times out.  It could be a Cygwin bug, of course, but that
>>> doesn't explain the EMBA failure.
>>
>> Could you see if the same thing happens if you type
>>
>>      echo "bar" | sh -c "rev >temp"
>>
>> into an interactive session, please?
>>
>> If it's the same then extpipe has uncovered a general Eshell bug.
> 
> Yes, it's the same.  And it's even the same if I remove the quotation marks 
> around "rev >temp".

And it's also the same if remove the output redirection, i.e., if I type 'echo 
bar | sh -c rev'.  On the other hand, if I type 'echo bar | rev', then I see the 
output 'rab'; but rev doesn't exit, and I don't get the eshell prompt, until I 
type 'C-c C-c'.  On the third hand, 'echo bar | cat' almost works; I see the 
output 'bar' followed immediately by the eshell prompt (with no newline after 
'bar').  Is eshell stripping newlines in some circumstances?  If so, I wonder if 
this accounts for the failure of rev to exit in some of the earlier examples, 
since it operates on lines?

Ken