bug#22096: 25.0.50; reading from fifo breaks display

[Mark Oteiza]

I suppose this is two issues, really. I am trying to read from a FIFO,
specifically one written to by mpd, configured in mpd.conf with

audio_output {
  type "fifo"
  name "FIFO"
  path "/tmp/mpd.fifo"
  format "44100:16:2"
}

With mpd running I can see that the FIFO is there and I can read from it
with other tools/mpd clients.

(info "(elisp) Reading from Files") suggests I should be able to read
from a FIFO. From emacs -Q, insert the following into the scratch buffer:

(insert-file-contents "/tmp/mpd.fifo" nil 0 10 nil)

First issue: evaluating this yields

(file-error "not a regular file" "/tmp/mpd.fifo")

Second issue: changing the VISIT argument to t and evaluating:

(insert-file-contents "/tmp/mpd.fifo" t 0 10 nil)

breaks the display engine. "nil)" becomes invisible, the last "r" in the
scratch buffer message becomes fontified as a matching paren, and
hitting C-a at the end of the form takes me to the aforementioned "r".
I have attached an image.

fifodisplay.png
Description: broken display

In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2015-12-03
Repository revision: eaa1fd6dbff8346eb38485de5ebf0fbfacf374d9
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=generic -O0 -pipe
 -fstack-protector-strong --param=ssp-buffer-size=4 -g
 -fvar-tracking-assignments -g -fvar-tracking-assignments'
 LDFLAGS=-Wl,-O0,--sort-common,--as-needed,-z,relro'

Configured features:
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ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
LUCID X11 MODULES

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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Recent messages:
Loading /home/mvo/.local/share/emacs/custom.el (source)...done
For information about GNU Emacs and the GNU system, type C-h C-a.
delete-backward-char: Text is read-only

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/home/mvo/.emacs.d/site-lisp/twitch
/home/mvo/.emacs.d/elpa/kv-0.0.19/kv hides 
/home/mvo/.emacs.d/site-lisp/emacs-kv/kv
/home/mvo/.emacs.d/elpa/kv-0.0.19/kv-tests hides 
/home/mvo/.emacs.d/site-lisp/emacs-kv/kv-tests
/home/mvo/.emacs.d/elpa/esxml-0.3.1/esxml hides 
/home/mvo/.emacs.d/site-lisp/esxml/esxml

Features:
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Memory information:
((conses 16 161562 101461)
 (symbols 48 24795 25)
 (miscs 40 58 179)
 (strings 32 40408 74230)
 (string-bytes 1 1128413)
 (vectors 16 17014)
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 (buffers 976 11)
 (heap 1024 33756 9289))