bug#35046: [PATCH] factor: check the standard output instead of the standard input

[Shugo Maeda]

* src/factor.c (lbuf_putc): Use line buffered mode if the standard
output (not the standard input) is a terminal in the same way as the
stdio library.  User programs might use pty only for the standard out
like the example of Ruby's PTY module:
https://docs.ruby-lang.org/en/2.6.0/PTY.html#module-PTY-label-Example
---
 src/factor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/factor.c b/src/factor.c
index 39e8918ff..173774045 100644
--- a/src/factor.c
+++ b/src/factor.c
@@ -2403,7 +2403,7 @@ lbuf_putc (char c)
       /* Provide immediate output for interactive input.  */
       static int line_buffered = -1;
       if (line_buffered == -1)
-        line_buffered = isatty (STDIN_FILENO);
+        line_buffered = isatty (STDOUT_FILENO);
       if (line_buffered)
         lbuf_flush ();
       else if (buffered >= FACTOR_PIPE_BUF)
-- 
2.11.0