[PATCH 2/7] progress: catch nested/overlapping progresses with GIT_TEST_CHECK_PROGRESS

We had to fix two buggy progress lines in the past, where
stop_progress calls were added at the wrong place [1], resulting in
"done" progress lines appearing in the wrong order.

Extend GIT_TEST_CHECK_PROGRESS to catch these cases as well, i.e.
trigger a BUG() when a progress has already been running when
start_progress() or one of its variants is called to start a new one.

Running the test suite with GIT_TEST_CHECK_PROGRESS enabled doesn't
reveal any new issues [2].

Note that this will trigger even in cases where the output is not
visibly wrong, e.g. consider this simplified sequence of calls:

  progress1 = start_delayed_progress();
  progress2 = start_delayed_progress();
  for (i = 0; ...)
      display_progress(progress2, i + 1);
  stop_progres(&progress2);
  for (j = 0; ...)
      display_progress(progress1, j + 1);
  stop_progres(&progress1);

This doesn't produce bogus output like what is shown in those two
fixes [1], because 'progress2' is already "done" before the first
display_progress(progress1, ...) call.  Btw, this is not just a
pathological example, we do have two progress lines arranged like
this, but they are only shown when standard error is a terminal, and
thus aren't caught by GIT_TEST_CHECK_PROGRESS in its current form.

[1] 6f9d5f2fda (commit-graph: fix progress of reachable commits,
                2020-07-09)
    862aead24e (commit-graph: fix "Collecting commits from input"
                progress line, 2020-07-10)

[2] This patch series applies with a minor conflict on top of
    6f9d5f2fda^, and makes 37 tests fail because of that bug.

Signed-off-by: SZEDER Gábor <redacted>
---
 progress.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/progress.c b/progress.c
index 255995406f..549e8d1fe7 100644
--- a/progress.c
+++ b/progress.c

@@ -48,6 +48,8 @@ struct progress {
 static volatile sig_atomic_t progress_update;
 
 static int test_check_progress;
+/* Used to catch nested/overlapping progresses with GIT_TEST_CHECK_PROGRESS. */
+static struct progress *current_progress = NULL;
 
 /*
  * These are only intended for testing the progress output, i.e. exclusively

@@ -258,8 +260,12 @@ static struct progress *start_progress_delay(const char *title, uint64_t total,
 	struct progress *progress;
 
 	test_check_progress = git_env_bool("GIT_TEST_CHECK_PROGRESS", 0);
+	if (test_check_progress && current_progress)
+		BUG("progress \"%s\" is still active when starting new progress \"%s\"",
+		    current_progress->title, title);
 
 	progress = xmalloc(sizeof(*progress));
+	current_progress = progress;
 	progress->title = title;
 	progress->total = total;
 	progress->last_value = -1;

@@ -383,6 +389,7 @@ void stop_progress_msg(struct progress **p_progress, const char *msg)
 	strbuf_release(&progress->counters_sb);
 	if (progress->throughput)
 		strbuf_release(&progress->throughput->display);
+	current_progress = NULL;
 	free(progress->throughput);
 	free(progress);
 }

-- 
2.32.0.289.g44fbea0957