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From: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Duy Nguyen <pclouds@gmail.com>, Jeff King <peff@peff.net>,
	Junio C Hamano <gitster@pobox.com>,
	Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: [PATCH v3 3/3] repack -ad: prune the list of shallow commits
Date: Mon, 22 Oct 2018 15:05:40 -0700 (PDT)	[thread overview]
Message-ID: <1f9ff57d52a72e3795ac4a924e23a64b91b1f83e.1540245934.git.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.9.v3.git.gitgitgadget@gmail.com>

From: Johannes Schindelin <johannes.schindelin@gmx.de>

`git repack` can drop unreachable commits without further warning,
making the corresponding entries in `.git/shallow` invalid, which causes
serious problems when deepening the branches.

One scenario where unreachable commits are dropped by `git repack` is
when a `git fetch --prune` (or even a `git fetch` when a ref was
force-pushed in the meantime) can make a commit unreachable that was
reachable before.

Therefore it is not safe to assume that a `git repack -adlf` will keep
unreachable commits alone (under the assumption that they had not been
packed in the first place, which is an assumption at least some of Git's
code seems to make).

This is particularly important to keep in mind when looking at the
`.git/shallow` file: if any commits listed in that file become
unreachable, it is not a problem, but if they go missing, it *is* a
problem. One symptom of this problem is that a deepening fetch may now
fail with

	fatal: error in object: unshallow <commit-hash>

To avoid this problem, let's prune the shallow list in `git repack` when
the `-d` option is passed, unless `-A` is passed, too (which would force
the now-unreachable objects to be turned into loose objects instead of
being deleted). Additionally, we also need to take `--keep-reachable`
and `--unpack-unreachable=<date>` into account.

Note: an alternative solution discussed during the review of this patch
was to teach `git fetch` to simply ignore entries in .git/shallow if the
corresponding commits do not exist locally. A quick test, however,
revealed that the .git/shallow file is written during a shallow *clone*,
in which case the commits do not exist, either, but the "shallow" line
*does* need to be sent. Therefore, this approach would be a lot more
finicky than the approach presented by the this patch.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 builtin/repack.c         | 6 ++++++
 t/t5537-fetch-shallow.sh | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/builtin/repack.c b/builtin/repack.c
index c6a7943d5..9217fc832 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -549,6 +549,12 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 		if (!po_args.quiet && isatty(2))
 			opts |= PRUNE_PACKED_VERBOSE;
 		prune_packed_objects(opts);
+
+		if (!keep_unreachable &&
+		    (!(pack_everything & LOOSEN_UNREACHABLE) ||
+		     unpack_unreachable) &&
+		    is_repository_shallow(the_repository))
+			prune_shallow(0, 1);
 	}
 
 	if (!no_update_server_info)
diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index 2d0031703..777c9d1dc 100755
--- a/t/t5537-fetch-shallow.sh
+++ b/t/t5537-fetch-shallow.sh
@@ -186,7 +186,7 @@ EOF
 	test_cmp expect actual
 '
 
-test_expect_failure '.git/shallow is edited by repack' '
+test_expect_success '.git/shallow is edited by repack' '
 	git init shallow-server &&
 	test_commit -C shallow-server A &&
 	test_commit -C shallow-server B &&
-- 
gitgitgadget

  parent reply	other threads:[~2018-10-22 22:05 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-13 20:18 [PATCH 0/2] repack -ad: fix after `fetch --prune` in a shallow repository Johannes Schindelin via GitGitGadget
2018-07-11 22:17 ` [PATCH 1/2] repack: point out a bug handling stale shallow info Johannes Schindelin via GitGitGadget
2018-07-11 22:23 ` [PATCH 2/2] repack -ad: prune the list of shallow commits Johannes Schindelin via GitGitGadget
2018-07-13 20:31   ` Jeff King
2018-07-14 21:56     ` Johannes Schindelin
2018-07-16 17:36       ` Jeff King
2018-07-17 16:25         ` Junio C Hamano
2018-07-19 16:42           ` Johannes Schindelin
2018-07-19 20:49             ` Junio C Hamano
2018-07-20  9:30               ` Junio C Hamano
2018-07-20 19:31                 ` Jeff King
2018-07-17 17:28         ` Duy Nguyen
2018-07-17 19:41           ` Jeff King
2018-07-18 17:31             ` Duy Nguyen
2018-07-18 17:45               ` Jeff King
2018-07-18 17:48                 ` Duy Nguyen
2018-07-17 16:39   ` Duy Nguyen
2018-07-17 16:48     ` Duy Nguyen
2018-07-19 17:50       ` Johannes Schindelin
2018-07-17 13:51 ` [PATCH v2 0/2] repack -ad: fix after `fetch --prune` in a shallow repository Johannes Schindelin via GitGitGadget
2018-07-17 13:51   ` [PATCH v2 1/2] repack: point out a bug handling stale shallow info Johannes Schindelin via GitGitGadget
2018-07-17 13:51   ` [PATCH v2 2/2] repack -ad: prune the list of shallow commits Johannes Schindelin via GitGitGadget
2018-07-17 17:45     ` Eric Sunshine
2018-07-17 19:15   ` [PATCH v2 0/2] repack -ad: fix after `fetch --prune` in a shallow repository Jeff King
2018-07-17 19:20     ` Jeff King
2018-07-19 17:48       ` Johannes Schindelin
2018-10-22 22:05   ` [PATCH v3 0/3] repack -ad: fix after fetch --prune " Johannes Schindelin via GitGitGadget
2018-10-22 22:05     ` [PATCH v3 1/3] repack: point out a bug handling stale shallow info Johannes Schindelin via GitGitGadget
2018-10-24  3:39       ` Junio C Hamano
2018-10-24  8:12         ` Johannes Schindelin
2018-10-24  8:38           ` Johannes Schindelin
2018-10-22 22:05     ` [PATCH v3 2/3] shallow: offer to prune only non-existing entries Johannes Schindelin via GitGitGadget
2018-10-24  3:47       ` Junio C Hamano
2018-10-24  8:01         ` Johannes Schindelin
2018-10-24 15:56           ` Johannes Schindelin
2018-10-25 18:54             ` Jonathan Tan
2018-10-26  7:59               ` Johannes Schindelin
2018-10-26 20:49                 ` Jonathan Tan
2018-10-29 20:45                   ` Johannes Schindelin
2018-10-22 22:05     ` Johannes Schindelin via GitGitGadget [this message]
2018-10-24  3:56       ` [PATCH v3 3/3] repack -ad: prune the list of shallow commits Junio C Hamano
2018-10-24  8:02         ` Johannes Schindelin
2018-10-23 10:15     ` [PATCH v3 0/3] repack -ad: fix after fetch --prune in a shallow repository Johannes Schindelin
2018-10-24 15:56     ` [PATCH v4 " Johannes Schindelin via GitGitGadget
2018-10-24 15:56       ` [PATCH v4 1/3] repack: point out a bug handling stale shallow info Johannes Schindelin via GitGitGadget
2018-10-24 15:56       ` [PATCH v4 2/3] shallow: offer to prune only non-existing entries Johannes Schindelin via GitGitGadget
2018-10-24 15:56       ` [PATCH v4 3/3] repack -ad: prune the list of shallow commits Johannes Schindelin via GitGitGadget

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