Re: [PATCH 18/25] progress.c: emit progress on first signal, show "stalled"

Ever since the progress.c code was added in 96a02f8f6d2 (common
progress display support, 2007-04-18) we have been driven purely by
calls to the display() function (via the public display_progress()),
or via stop_progress(). Even though we got a signal and invoked
progress_interval() that function would not actually emit progress
output for us.

Thus in cases like "git gc" we don't emit any "Enumerating Objects"
output until we get past the setup code, and start enumerating
objects, we'll now (at least on my laptop) show output earlier, and
emit a "stalled" message before we start the count.

But more generally, this is a first step towards never showing a
hanging progress bar from the user's perspective. If we're truly
taking a very long time with one item we can show some spinner that we
update every time we get a signal. We don't right now, and only
special-case the most common case of hanging before we get to the
first item.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 progress.c                  |  7 +++++
 t/t0500-progress-display.sh | 63 ++++++++++++++++++++++++++++++++++---
 2 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/progress.c b/progress.c
index 6c4038df791..35847d3a7f2 100644
--- a/progress.c
+++ b/progress.c

@@ -255,6 +255,13 @@ void display_progress(struct progress *progress, uint64_t n)
 static void progress_interval(int signum)
 {
 	progress_update = 1;
+
+	if (global_progress->last_value != -1)
+		return;
+
+	display(global_progress, 0, _(", stalled."), 0);