[PATCH] submodule: Demonstrate known breakage during recursive merge

From: Brad King <brad.king@kitware.com>
Date: Aug 24, 2011, 13:59 UTC
Message-ID: <680d2679c3275c01152500760311b5f96a93ea62.1314193375.git.brad.king@kitware.com>

Since commit 68d03e4a (Implement automatic fast-forward merge for submodules, 2010-07-07) we try to suggest submodule commits that resolve a conflict. Consider a true recursive merge case

    b---bc
   / \ /
  o   X
   \ / \
    c---cb

in which the two heads themselves (bc,cb) had resolved a submodule conflict (i.e. reference different commits than their parents). The submodule merge search runs during the temporary merge of the two merge bases (b,c) and prints out a suggestion that is not meaningful to the user. Then during the main merge the submodule merge search runs again but dies with the message

  fatal: --ancestry-path given but there are no bottom commits

while trying to enumerate candidates. Demonstrate this known breakage with a new test in t7405-submodule-merge covering the case.

Signed-off-by: Brad King <brad.king@kitware.com>
---
Hi folks,

A co-worker encountered this problem last week in a real project. The merge dies and does not leave the submodule conflict in the index. We were able to work around it by moving the submodule out of the way and resolving the conflict by hand. Then I ran the merge again to debug the problem and narrowed it down to this case.

BTW, if one adds the line

  rm -rf sub && mkdir sub &&

just above the line

  test_must_fail git merge top-bc

then the test passes because no submodule merge search runs. Therefore this test can be switched to expect success when the problem is fixed.

Brad

 t/t7405-submodule-merge.sh |   51 ++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/t/t7405-submodule-merge.sh b/t/t7405-submodule-merge.sh
index a8fb30b..8f6f2d6 100755
--- a/t/t7405-submodule-merge.sh
+++ b/t/t7405-submodule-merge.sh
@@ -228,4 +228,55 @@ test_expect_success 'merging with a modify/modify conflict between merge bases'
 	git merge d
 '
 
+# canonical criss-cross history in top and submodule
+test_expect_success 'setup for recursive merge with submodule' '
+	mkdir merge-recursive &&
+	(cd merge-recursive &&
+	 git init &&
+	 mkdir sub &&
+	 (cd sub &&
+	  git init &&
+	  test_commit a &&
+	  git checkout -b sub-b master &&
+	  test_commit b &&
+	  git checkout -b sub-c master &&
+	  test_commit c &&
+	  git checkout -b sub-bc sub-b &&
+	  git merge sub-c &&
+	  git checkout -b sub-cb sub-c &&
+	  git merge sub-b &&
+	  git checkout master) &&
+	 git add sub &&
+	 git commit -m a &&
+	 git checkout -b top-b master &&
+	 (cd sub && git checkout sub-b) &&
+	 git add sub &&
+	 git commit -m b &&
+	 git checkout -b top-c master &&
+	 (cd sub && git checkout sub-c) &&
+	 git add sub &&
+	 git commit -m c &&
+	 git checkout -b top-bc top-b &&
+	 git merge -s ours -n top-c &&
+	 (cd sub && git checkout sub-bc) &&
+	 git add sub &&
+	 git commit -m bc &&
+	 git checkout -b top-cb top-c &&
+	 git merge -s ours -n top-b &&
+	 (cd sub && git checkout sub-cb) &&
+	 git add sub &&
+	 git commit -m cb)
+'
+
+# merge should leave submodule unmerged in index
+test_expect_failure 'recursive merge with submodule' '
+	(cd merge-recursive &&
+	 test_must_fail git merge top-bc &&
+	 echo "160000 $(git rev-parse top-cb:sub) 2	sub" > expect2 &&
+	 echo "160000 $(git rev-parse top-bc:sub) 3	sub" > expect3 &&
+	 git ls-files -u > actual &&
+	 grep "$(cat expect2)" actual > /dev/null &&
+	 grep "$(cat expect3)" actual > /dev/null)
+'
+
 test_done

-- 
1.7.4.4