Help figuring out origin of error: "ERROR in parse_header: buffer was .. client: reader got error Success"

Help figuring out origin of error: "ERROR in parse_header: buffer was .. client: reader got error Success"

[Kaushal Modi]

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Hello,

I have ended up with an unusual regression scenario on emacs master, which
I can reproduce only with the combination of M-x shell-command-on-region
and the par[1] CLI utility.

I don't see the issue on emacs 26.1.

The issue is that when I select a region of text and do `M-| par`, I get
this error:

ERROR in parse_header: buffer was ';; This buffer is for te'
error: client: reader got error Success

I got that error by launching emacs -Q (master branch), selecting the text
in the scratch buffer and doing `M-| par`. Interestingly that error doesn't
happen on running `od', or `cat' or any other command via M-|.

I contacted the par author Adam Costello, and he had this to say:

> > I grepped Emacs source and par source and none contain any part of
> > that error string.

> Emacs versions earlier than 24 have a lib-src/fakemail.c that contains a
> parse_header() function.  Could that be involved?

But I don't know .. this is a very recent regression .. some time after
26.1 release.

I have already reported this bug at
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=34174. I am emailing in this
mailing list to see if anyone here can connect the dots between that error
and specifically using par.

Thoughts?


[1]: http://www.nicemice.net/par/

--
Kaushal Modi

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