Re: [PATCH 4/7] commit-graph: fix bogus counter in "Scanning merged commits" progress line

Am 21.06.21 um 22:08 schrieb Ævar Arnfjörð Bjarmason:

On Mon, Jun 21 2021, René Scharfe wrote:

quoted

Am 21.06.21 um 00:13 schrieb Ævar Arnfjörð Bjarmason:

quoted

On Sun, Jun 20 2021, SZEDER Gábor wrote:

quoted

The final value of the counter of the "Scanning merged commits"
progress line is always one less than its expected total, e.g.:

  Scanning merged commits:  83% (5/6), done.

This happens because while iterating over an array the loop variable
is passed to display_progress() as-is, but while C arrays (and thus
the loop variable) start at 0 and end at N-1, the progress counter
must end at N.  This causes the failures of the tests
'fetch.writeCommitGraph' and 'fetch.writeCommitGraph with submodules'
in 't5510-fetch.sh' when run with GIT_TEST_CHECK_PROGRESS=1.

Fix this by passing 'i + 1' to display_progress(), like most other
callsites do.

Signed-off-by: SZEDER Gábor <redacted>
---
 commit-graph.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/commit-graph.c b/commit-graph.c
index 2bcb4e0f89..3181906368 100644
--- a/commit-graph.c
+++ b/commit-graph.c

@@ -2096,7 +2096,7 @@ static void sort_and_scan_merged_commits(struct write_commit_graph_context *ctx)

 	ctx->num_extra_edges = 0;
 	for (i = 0; i < ctx->commits.nr; i++) {
-		display_progress(ctx->progress, i);
+		display_progress(ctx->progress, i + 1);

 		if (i && oideq(&ctx->commits.list[i - 1]->object.oid,
 			  &ctx->commits.list[i]->object.oid)) {

I think this fix makes sense, but FWIW there's a large thread starting
at [1] where René disagrees with me, and thinks the fix for this sort of
thing would be to display_progress(..., i + 1) at the end of that
for-loop, or just before the stop_progress().

I don't agree, but just noting the disagreement, and that if that
argument wins then a patch like this would involve changing the other
20-some calls to display_progress() in commit-graph.c to work
differently (and to be more complex, we'd need to deal with loop
break/continue etc.).

1. https://lore.kernel.org/git/patch-2.2-042f598826-20210607T144206Z-avarab@gmail.com/ (local)

*sigh*  (And sorry, Ævar.)

Before an item is done, it should be reported as not done.  After an
item is done, it should be reported as done.  One loop iteration
finishes one item.  Thus the number of items to report at the bottom of
the loop is one higher than at the top.  i is the correct number to
report at the top of a zero-based loop, i+1 at the bottom.

Anyone with more time than sense can go and read over our linked back &
forth thread where we're disagreeing on that point :). I think the pattern
in commit-graph.c makes sense, you don't.

Thanks for this comment, I think I got it now: Work doesn't count in the
commit-graph.c model of measuring progress, literally.  I.e. progress is
the same before and after one item of work.  Instead it counts the
number of loop iterations.  The model I describe above counts finished
work items instead.  The results of the two models differ by at most one
despite their inverted axiom regarding the value of work.

Phew, that took me a while.

Anyway, aside from that. I think, and I really would be advocating this
too, even if our respective positions were reversed, that *in this case*
it makes sense to just take something like SZEDER's patch here
as-is. Because in that file there's some dozen occurrences of that exact
pattern.

The code without the patch either forgets to report the last work item
in the count-work-items model or is one short in the count-iterations
model, so a fix is needed either way.

The number of the other occurrences wouldn't matter if they were
buggy, but in this case they indicate that Stolee consistently used
the count-iterations model.  Thus using it in the patch as well makes
sense.

Let's just bring this one case in line with the rest, if we then want to
argue that one or the other use of the progress.c API is wrong as a
general thing, I think it makes more sense to discuss that as some
follow-up series that changes these various API uses en-masse than
holding back isolated fixes that leave the state of the progress bar it
!= 100%.

Agreed.

René