[PATCH] progress: treat "no terminal" as being in the foreground

On Tue, May 19, 2015 at 01:17:52AM -0400, Jeff King wrote:

One reasonable fix (I think) would be to treat an error return from
tcgetpgrp() as "yes, we are the foreground", like:

I think I convinced myself this is the right fix. So here it is, all
wrapped up with a commit message. I'd love to hear confirmation, though.
:)

-- >8 --
progress: treat "no terminal" as being in the foreground

Commit 85cb890 (progress: no progress in background,
2015-04-13) avoids sending progress from background
processes by checking that the process group id of the
current process is the same as that of the controlling
terminal.

If we don't have a terminal, however, this check never
succeeds, and we print no progress at all (until the final
"done" message). This can be seen when cloning a large
repository; instead of getting progress updates for
"counting objects", it will appear to hang then print the
final count.

We can fix this by treating an error return from tcgetpgrp()
as a signal to show the progress.

Signed-off-by: Jeff King <redacted>
---
 progress.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/progress.c b/progress.c
index 43d9228..2e31bec 100644
--- a/progress.c
+++ b/progress.c

@@ -74,7 +74,8 @@ static void clear_progress_signal(void)
 
 static int is_foreground_fd(int fd)
 {
-	return getpgid(0) == tcgetpgrp(fd);
+	int tpgrp = tcgetpgrp(fd);
+	return tpgrp < 0 || tpgrp == getpgid(0);
 }
 
 static int display(struct progress *progress, unsigned n, const char *done)

-- 
2.4.1.396.g7ba6d7b