merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 770 insertions, 0 deletions

diff --git a/third_party/git/t/t6430-merge-recursive.sh b/third_party/git/t/t6430-merge-recursive.sh
new file mode 100755
index 000000000000..a328260d4264
--- /dev/null
+++ b/third_party/git/t/t6430-merge-recursive.sh
@@ -0,0 +1,770 @@
+#!/bin/sh
+
+test_description='merge-recursive backend test'
+
+. ./test-lib.sh
+
+test_expect_success 'setup 1' '
+
+	echo hello >a &&
+	o0=$(git hash-object a) &&
+	cp a b &&
+	cp a c &&
+	mkdir d &&
+	cp a d/e &&
+
+	test_tick &&
+	git add a b c d/e &&
+	git commit -m initial &&
+	c0=$(git rev-parse --verify HEAD) &&
+	git branch side &&
+	git branch df-1 &&
+	git branch df-2 &&
+	git branch df-3 &&
+	git branch remove &&
+	git branch submod &&
+	git branch copy &&
+	git branch rename &&
+	git branch rename-ln &&
+
+	echo hello >>a &&
+	cp a d/e &&
+	o1=$(git hash-object a) &&
+
+	git add a d/e &&
+
+	test_tick &&
+	git commit -m "master modifies a and d/e" &&
+	c1=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o1	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o1	d/e" &&
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup 2' '
+
+	rm -rf [abcd] &&
+	git checkout side &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	echo goodbye >>a &&
+	o2=$(git hash-object a) &&
+
+	git add a &&
+
+	test_tick &&
+	git commit -m "side modifies a" &&
+	c2=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o2	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o2 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup 3' '
+
+	rm -rf [abcd] &&
+	git checkout df-1 &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	rm -f b && mkdir b && echo df-1 >b/c && git add b/c &&
+	o3=$(git hash-object b/c) &&
+
+	test_tick &&
+	git commit -m "df-1 makes b/c" &&
+	c3=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o3	b/c" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o3 0	b/c" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup 4' '
+
+	rm -rf [abcd] &&
+	git checkout df-2 &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	rm -f a && mkdir a && echo df-2 >a/c && git add a/c &&
+	o4=$(git hash-object a/c) &&
+
+	test_tick &&
+	git commit -m "df-2 makes a/c" &&
+	c4=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o4	a/c" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o4 0	a/c" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup 5' '
+
+	rm -rf [abcd] &&
+	git checkout remove &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	rm -f b &&
+	echo remove-conflict >a &&
+
+	git add a &&
+	git rm b &&
+	o5=$(git hash-object a) &&
+
+	test_tick &&
+	git commit -m "remove removes b and modifies a" &&
+	c5=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o5	a" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o5 0	a" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'setup 6' '
+
+	rm -rf [abcd] &&
+	git checkout df-3 &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	rm -fr d && echo df-3 >d && git add d &&
+	o6=$(git hash-object d) &&
+
+	test_tick &&
+	git commit -m "df-3 makes d" &&
+	c6=$(git rev-parse --verify HEAD) &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o6	d" &&
+		echo "100644 $o0 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o6 0	d"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'setup 7' '
+
+	git checkout submod &&
+	git rm d/e &&
+	test_tick &&
+	git commit -m "remove d/e" &&
+	git update-index --add --cacheinfo 160000 $c1 d &&
+	test_tick &&
+	git commit -m "make d/ a submodule"
+'
+
+test_expect_success 'setup 8' '
+	git checkout rename &&
+	git mv a e &&
+	git add e &&
+	test_tick &&
+	git commit -m "rename a->e" &&
+	c7=$(git rev-parse --verify HEAD) &&
+	git checkout rename-ln &&
+	git mv a e &&
+	test_ln_s_add e a &&
+	test_tick &&
+	git commit -m "rename a->e, symlink a->e" &&
+	oln=$(printf e | git hash-object --stdin)
+'
+
+test_expect_success 'setup 9' '
+	git checkout copy &&
+	cp a e &&
+	git add e &&
+	test_tick &&
+	git commit -m "copy a->e"
+'
+
+test_expect_success 'merge-recursive simple' '
+
+	rm -fr [abcd] &&
+	git checkout -f "$c2" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c2" "$c1"
+'
+
+test_expect_success 'merge-recursive result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o0 1	a" &&
+		echo "100644 $o2 2	a" &&
+		echo "100644 $o1 3	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'fail if the index has unresolved entries' '
+
+	rm -fr [abcd] &&
+	git checkout -f "$c1" &&
+
+	test_must_fail git merge "$c5" &&
+	test_must_fail git merge "$c5" 2> out &&
+	test_i18ngrep "not possible because you have unmerged files" out &&
+	git add -u &&
+	test_must_fail git merge "$c5" 2> out &&
+	test_i18ngrep "You have not concluded your merge" out &&
+	rm -f .git/MERGE_HEAD &&
+	test_must_fail git merge "$c5" 2> out &&
+	test_i18ngrep "Your local changes to the following files would be overwritten by merge:" out
+'
+
+test_expect_success 'merge-recursive remove conflict' '
+
+	rm -fr [abcd] &&
+	git checkout -f "$c1" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c1" "$c5"
+'
+
+test_expect_success 'merge-recursive remove conflict' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o0 1	a" &&
+		echo "100644 $o1 2	a" &&
+		echo "100644 $o5 3	a" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive d/f simple' '
+	rm -fr [abcd] &&
+	git reset --hard &&
+	git checkout -f "$c1" &&
+
+	git merge-recursive "$c0" -- "$c1" "$c3"
+'
+
+test_expect_success 'merge-recursive result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o3 0	b/c" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive d/f conflict' '
+
+	rm -fr [abcd] &&
+	git reset --hard &&
+	git checkout -f "$c1" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c1" "$c4"
+'
+
+test_expect_success 'merge-recursive d/f conflict result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o0 1	a" &&
+		echo "100644 $o1 2	a" &&
+		echo "100644 $o4 0	a/c" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive d/f conflict the other way' '
+
+	rm -fr [abcd] &&
+	git reset --hard &&
+	git checkout -f "$c4" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c4" "$c1"
+'
+
+test_expect_success 'merge-recursive d/f conflict result the other way' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o0 1	a" &&
+		echo "100644 $o1 3	a" &&
+		echo "100644 $o4 0	a/c" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive d/f conflict' '
+
+	rm -fr [abcd] &&
+	git reset --hard &&
+	git checkout -f "$c1" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c1" "$c6"
+'
+
+test_expect_success 'merge-recursive d/f conflict result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o6 3	d" &&
+		echo "100644 $o0 1	d/e" &&
+		echo "100644 $o1 2	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive d/f conflict' '
+
+	rm -fr [abcd] &&
+	git reset --hard &&
+	git checkout -f "$c6" &&
+
+	test_expect_code 1 git merge-recursive "$c0" -- "$c6" "$c1"
+'
+
+test_expect_success 'merge-recursive d/f conflict result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o6 2	d" &&
+		echo "100644 $o0 1	d/e" &&
+		echo "100644 $o1 3	d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success SYMLINKS 'dir in working tree with symlink ancestor does not produce d/f conflict' '
+	git init sym &&
+	(
+		cd sym &&
+		ln -s . foo &&
+		mkdir bar &&
+		>bar/file &&
+		git add foo bar/file &&
+		git commit -m "foo symlink" &&
+
+		git checkout -b branch1 &&
+		git commit --allow-empty -m "empty commit" &&
+
+		git checkout master &&
+		git rm foo &&
+		mkdir foo &&
+		>foo/bar &&
+		git add foo/bar &&
+		git commit -m "replace foo symlink with real foo dir and foo/bar file" &&
+
+		git checkout branch1 &&
+
+		git cherry-pick master &&
+		test_path_is_dir foo &&
+		test_path_is_file foo/bar
+	)
+'
+
+test_expect_success 'reset and 3-way merge' '
+
+	git reset --hard "$c2" &&
+	git read-tree -m "$c0" "$c2" "$c1"
+
+'
+
+test_expect_success 'reset and bind merge' '
+
+	git reset --hard master &&
+	git read-tree --prefix=M/ master &&
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	M/a" &&
+		echo "100644 $o0 0	M/b" &&
+		echo "100644 $o0 0	M/c" &&
+		echo "100644 $o1 0	M/d/e" &&
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	git read-tree --prefix=a1/ master &&
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	M/a" &&
+		echo "100644 $o0 0	M/b" &&
+		echo "100644 $o0 0	M/c" &&
+		echo "100644 $o1 0	M/d/e" &&
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o1 0	a1/a" &&
+		echo "100644 $o0 0	a1/b" &&
+		echo "100644 $o0 0	a1/c" &&
+		echo "100644 $o1 0	a1/d/e" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e"
+	) >expected &&
+	test_cmp expected actual &&
+
+	git read-tree --prefix=z/ master &&
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o1 0	M/a" &&
+		echo "100644 $o0 0	M/b" &&
+		echo "100644 $o0 0	M/c" &&
+		echo "100644 $o1 0	M/d/e" &&
+		echo "100644 $o1 0	a" &&
+		echo "100644 $o1 0	a1/a" &&
+		echo "100644 $o0 0	a1/b" &&
+		echo "100644 $o0 0	a1/c" &&
+		echo "100644 $o1 0	a1/d/e" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o1 0	d/e" &&
+		echo "100644 $o1 0	z/a" &&
+		echo "100644 $o0 0	z/b" &&
+		echo "100644 $o0 0	z/c" &&
+		echo "100644 $o1 0	z/d/e"
+	) >expected &&
+	test_cmp expected actual
+
+'
+
+test_expect_success 'merge-recursive w/ empty work tree - ours has rename' '
+	(
+		GIT_WORK_TREE="$PWD/ours-has-rename-work" &&
+		export GIT_WORK_TREE &&
+		GIT_INDEX_FILE="$PWD/ours-has-rename-index" &&
+		export GIT_INDEX_FILE &&
+		mkdir "$GIT_WORK_TREE" &&
+		git read-tree -i -m $c7 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git update-index --ignore-missing --refresh 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git merge-recursive $c0 -- $c7 $c3 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git ls-files -s >actual-files 2>actual-err &&
+		test_must_be_empty actual-err
+	) &&
+	cat >expected-files <<-EOF &&
+	100644 $o3 0	b/c
+	100644 $o0 0	c
+	100644 $o0 0	d/e
+	100644 $o0 0	e
+	EOF
+	test_cmp expected-files actual-files
+'
+
+test_expect_success 'merge-recursive w/ empty work tree - theirs has rename' '
+	(
+		GIT_WORK_TREE="$PWD/theirs-has-rename-work" &&
+		export GIT_WORK_TREE &&
+		GIT_INDEX_FILE="$PWD/theirs-has-rename-index" &&
+		export GIT_INDEX_FILE &&
+		mkdir "$GIT_WORK_TREE" &&
+		git read-tree -i -m $c3 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git update-index --ignore-missing --refresh 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git merge-recursive $c0 -- $c3 $c7 2>actual-err &&
+		test_must_be_empty actual-err &&
+		git ls-files -s >actual-files 2>actual-err &&
+		test_must_be_empty actual-err
+	) &&
+	cat >expected-files <<-EOF &&
+	100644 $o3 0	b/c
+	100644 $o0 0	c
+	100644 $o0 0	d/e
+	100644 $o0 0	e
+	EOF
+	test_cmp expected-files actual-files
+'
+
+test_expect_success 'merge removes empty directories' '
+
+	git reset --hard master &&
+	git checkout -b rm &&
+	git rm d/e &&
+	git commit -mremoved-d/e &&
+	git checkout master &&
+	git merge -s recursive rm &&
+	test_path_is_missing d
+'
+
+test_expect_success 'merge-recursive simple w/submodule' '
+
+	git checkout submod &&
+	git merge remove
+'
+
+test_expect_success 'merge-recursive simple w/submodule result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o5 0	a" &&
+		echo "100644 $o0 0	c" &&
+		echo "160000 $c1 0	d"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'merge-recursive copy vs. rename' '
+	git checkout -f copy &&
+	git merge rename &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 blob $o0	e" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e" &&
+		echo "100644 $o0 0	e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_failure 'merge-recursive rename vs. rename/symlink' '
+
+	git checkout -f rename &&
+	git merge rename-ln &&
+	( git ls-tree -r HEAD && git ls-files -s ) >actual &&
+	(
+		echo "120000 blob $oln	a" &&
+		echo "100644 blob $o0	b" &&
+		echo "100644 blob $o0	c" &&
+		echo "100644 blob $o0	d/e" &&
+		echo "100644 blob $o0	e" &&
+		echo "120000 $oln 0	a" &&
+		echo "100644 $o0 0	b" &&
+		echo "100644 $o0 0	c" &&
+		echo "100644 $o0 0	d/e" &&
+		echo "100644 $o0 0	e"
+	) >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'merging with triple rename across D/F conflict' '
+	git reset --hard HEAD &&
+	git checkout -b topic &&
+	git rm -rf . &&
+
+	echo "just a file" >sub1 &&
+	mkdir -p sub2 &&
+	echo content1 >sub2/file1 &&
+	echo content2 >sub2/file2 &&
+	echo content3 >sub2/file3 &&
+	mkdir simple &&
+	echo base >simple/bar &&
+	git add -A &&
+	test_tick &&
+	git commit -m base &&
+
+	git checkout -b other &&
+	echo more >>simple/bar &&
+	test_tick &&
+	git commit -a -m changesimplefile &&
+
+	git checkout topic &&
+	git rm sub1 &&
+	git mv sub2 sub1 &&
+	test_tick &&
+	git commit -m changefiletodir &&
+
+	test_tick &&
+	git merge other
+'
+
+test_expect_success 'merge-recursive remembers the names of all base trees' '
+	git reset --hard HEAD &&
+
+	# make the index match $c1 so that merge-recursive below does not
+	# fail early
+	git diff --binary HEAD $c1 -- | git apply --cached &&
+
+	# more trees than static slots used by oid_to_hex()
+	for commit in $c0 $c2 $c4 $c5 $c6 $c7
+	do
+		git rev-parse "$commit^{tree}"
+	done >trees &&
+
+	# ignore the return code; it only fails because the input is weird...
+	test_must_fail git -c merge.verbosity=5 merge-recursive $(cat trees) -- $c1 $c3 >out &&
+
+	# ...but make sure it fails in the expected way
+	test_i18ngrep CONFLICT.*rename/rename out &&
+
+	# merge-recursive prints in reverse order, but we do not care
+	sort <trees >expect &&
+	sed -n "s/^virtual //p" out | sort >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'merge-recursive internal merge resolves to the sameness' '
+	git reset --hard HEAD &&
+
+	# We are going to create a history leading to two criss-cross
+	# branches A and B.  The common ancestor at the bottom, O0,
+	# has two child commits O1 and O2, both of which will be merge
+	# base between A and B, like so:
+	#
+	#       O1---A
+	#      /  \ /
+	#    O0    .
+	#      \  / \
+	#       O2---B
+	#
+	# The recently added "check to see if the index is different from
+	# the tree into which something else is getting merged" check must
+	# NOT kick in when an inner merge between O1 and O2 is made.  Both
+	# O1 and O2 happen to have the same tree as O0 in this test to
+	# trigger the bug---whether the inner merge is made by merging O2
+	# into O1 or O1 into O2, their common ancestor O0 and the branch
+	# being merged have the same tree.  We should not trigger the "is
+	# the index dirty?" check in this case.
+
+	echo "zero" >file &&
+	git add file &&
+	test_tick &&
+	git commit -m "O0" &&
+	O0=$(git rev-parse HEAD) &&
+
+	test_tick &&
+	git commit --allow-empty -m "O1" &&
+	O1=$(git rev-parse HEAD) &&
+
+	git reset --hard $O0 &&
+	test_tick &&
+	git commit --allow-empty -m "O2" &&
+	O2=$(git rev-parse HEAD) &&
+
+	test_tick &&
+	git merge -s ours $O1 &&
+	B=$(git rev-parse HEAD) &&
+
+	git reset --hard $O1 &&
+	test_tick &&
+	git merge -s ours $O2 &&
+	A=$(git rev-parse HEAD) &&
+
+	git merge $B
+'
+
+test_done