[bug-gawk] coprocess pseudo-tty bug

[Andrew J. Schorr]

Hi,

A discussion in comp.lang.awk about coprocess deadlock and pseudo-ttys has
revealed what appears to be a bug, although I do not yet understand what
is going wrong.

https://groups.google.com/forum/#!topic/comp.lang.awk/pz4gmSw0uas

bash-4.2$ cat /tmp/pty.awk 
BEGIN {
   cmd = "tr A-Z a-z"
   PROCINFO[cmd, "pty"] = 1
   input = "ABCD"
   print input |& cmd
   cmd |& getline x
   print x
}

This works correctly in gawk 4.1.2:

bash-4.2$ ./gawk --version | head -1
GNU Awk 4.1.2, API: 1.1 (GNU MPFR 3.1.1, GNU MP 6.0.0)
bash-4.2$ ./gawk -f /tmp/pty.awk 
abcd
bash-4.2$ ./gawk -f /tmp/pty.awk  | od -c
0000000   a   b   c   d  \n
0000005

By 4.1.4, it is broken:
bash-4.2$ cd ../gawk-4.1.4
bash-4.2$ ./gawk --version | head -1
GNU Awk 4.1.4, API: 1.1 (GNU MPFR 3.1.1, GNU MP 6.0.0)
bash-4.2$ ./gawk -f /tmp/pty.awk 
ABCD
bash-4.2$ ./gawk -f /tmp/pty.awk  | od -c
0000000   A   B   C   D  \r  \n
0000006

And it is still broken in the gawk-4.2-stable branch:

bash-4.2$ ./gawk --version | head -1
GNU Awk 4.2.0b, API: 2.0 (GNU MPFR 3.1.1, GNU MP 6.0.0)
bash-4.2$ ./gawk -f /tmp/pty.awk 
ABCD
bash-4.2$ ./gawk -f /tmp/pty.awk  | od -c
0000000   A   B   C   D  \r  \n
0000006

I have not had a chance to chase this down yet. I guess "git bisect" is
the way to go.

Regards,
Andy