[PATCH v2 4/6] t3650: document bug when directory renames are turned off

From: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Date: Mar 13, 2025, 02:46 UTC
Message-ID: <fefda4add11074288811752f922c309963c57eea.1741834001.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1875.v2.git.1741834001.gitgitgadget@gmail.com>

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

There is a bug in the way renames are cached that rears its head when `merge.directoryRenames` is set to false; it results in the following message:

    merge-ort.c:3002: process_renames: Assertion `newinfo && !newinfo->merged.clean' failed.
    Aborted

It is quite a curious bug: the same test case will succeed, without any assertion, if instead run with `merge.directoryRenames=true`.

Further, the assertion does not manifest while replaying the first commit, it manifests while replaying the _second_ commit of the commit range. But it does _not_ manifest when the second commit is replayed individually.

This would indicate that there is an incomplete rename cache left-over from the first replayed commit which is being reused for the second commit, and if directory rename detection is enabled, the missing paths are somehow regenerated.

Incidentally, the same bug can by triggered by modifying t6429 to switch from merge.directoryRenames=true to merge.directoryRenames=false.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
[en: tweaked the commit message slightly, including adjusting the
 line number of the assertion to the latest version, and the much
 later discovery that a simple t6429 tweak would also display the
 issue.]
Signed-off-by: Elijah Newren <newren@gmail.com>
---
 t/t3650-replay-basics.sh | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/t/t3650-replay-basics.sh b/t/t3650-replay-basics.sh
index 389670262e4..cade7930765 100755
--- a/t/t3650-replay-basics.sh
+++ b/t/t3650-replay-basics.sh
@@ -195,4 +195,26 @@ test_expect_success 'using replay on bare repo to rebase multiple divergent bran
 	done
 '
 
+test_expect_failure 'merge.directoryRenames=false' '
+	# create a test case that stress-tests the rename caching
+	git switch -c rename-onto &&
+
+	mkdir -p to-rename &&
+	test_commit to-rename/move &&
+
+	mkdir -p renamed-directory &&
+	git mv to-rename/move* renamed-directory/ &&
+	test_tick &&
+	git commit -m renamed-directory &&
+
+	git switch -c rename-from HEAD^ &&
+	test_commit to-rename/add-a-file &&
+	echo modified >to-rename/add-a-file.t &&
+	test_tick &&
+	git commit -m modified to-rename/add-a-file.t &&
+
+	git -c merge.directoryRenames=false replay \
+		--onto rename-onto rename-onto..rename-from
+'
+
 test_done

-- 
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