merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

1 files changed, 1797 insertions, 0 deletions

diff --git a/third_party/git/t/t6036-recursive-corner-cases.sh b/third_party/git/t/t6036-recursive-corner-cases.sh
new file mode 100755
index 000000000000..d23b948f27f1
--- /dev/null
+++ b/third_party/git/t/t6036-recursive-corner-cases.sh
@@ -0,0 +1,1797 @@
+#!/bin/sh
+
+test_description='recursive merge corner cases involving criss-cross merges'
+
+. ./test-lib.sh
+
+#
+#  L1  L2
+#   o---o
+#  / \ / \
+# o   X   ?
+#  \ / \ /
+#   o---o
+#  R1  R2
+#
+
+test_expect_success 'setup basic criss-cross + rename with no modifications' '
+	test_create_repo basic-rename &&
+	(
+		cd basic-rename &&
+
+		ten="0 1 2 3 4 5 6 7 8 9" &&
+		for i in $ten
+		do
+			echo line $i in a sample file
+		done >one &&
+		for i in $ten
+		do
+			echo line $i in another sample file
+		done >two &&
+		git add one two &&
+		test_tick && git commit -m initial &&
+
+		git branch L1 &&
+		git checkout -b R1 &&
+		git mv one three &&
+		test_tick && git commit -m R1 &&
+
+		git checkout L1 &&
+		git mv two three &&
+		test_tick && git commit -m L1 &&
+
+		git checkout L1^0 &&
+		test_tick && git merge -s ours R1 &&
+		git tag L2 &&
+
+		git checkout R1^0 &&
+		test_tick && git merge -s ours L1 &&
+		git tag R2
+	)
+'
+
+test_expect_success 'merge simple rename+criss-cross with no modifications' '
+	(
+		cd basic-rename &&
+
+		git reset --hard &&
+		git checkout L2^0 &&
+
+		test_must_fail git merge -s recursive R2^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect       \
+			L2:three   R2:three &&
+		git rev-parse   >actual     \
+			:2:three   :3:three &&
+		test_cmp expect actual
+	)
+'
+
+#
+# Same as before, but modify L1 slightly:
+#
+#  L1m L2
+#   o---o
+#  / \ / \
+# o   X   ?
+#  \ / \ /
+#   o---o
+#  R1  R2
+#
+
+test_expect_success 'setup criss-cross + rename merges with basic modification' '
+	test_create_repo rename-modify &&
+	(
+		cd rename-modify &&
+
+		ten="0 1 2 3 4 5 6 7 8 9" &&
+		for i in $ten
+		do
+			echo line $i in a sample file
+		done >one &&
+		for i in $ten
+		do
+			echo line $i in another sample file
+		done >two &&
+		git add one two &&
+		test_tick && git commit -m initial &&
+
+		git branch L1 &&
+		git checkout -b R1 &&
+		git mv one three &&
+		echo more >>two &&
+		git add two &&
+		test_tick && git commit -m R1 &&
+
+		git checkout L1 &&
+		git mv two three &&
+		test_tick && git commit -m L1 &&
+
+		git checkout L1^0 &&
+		test_tick && git merge -s ours R1 &&
+		git tag L2 &&
+
+		git checkout R1^0 &&
+		test_tick && git merge -s ours L1 &&
+		git tag R2
+	)
+'
+
+test_expect_success 'merge criss-cross + rename merges with basic modification' '
+	(
+		cd rename-modify &&
+
+		git checkout L2^0 &&
+
+		test_must_fail git merge -s recursive R2^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect       \
+			L2:three   R2:three &&
+		git rev-parse   >actual     \
+			:2:three   :3:three &&
+		test_cmp expect actual
+	)
+'
+
+#
+# For the next test, we start with three commits in two lines of development
+# which setup a rename/add conflict:
+#   Commit A: File 'a' exists
+#   Commit B: Rename 'a' -> 'new_a'
+#   Commit C: Modify 'a', create different 'new_a'
+# Later, two different people merge and resolve differently:
+#   Commit D: Merge B & C, ignoring separately created 'new_a'
+#   Commit E: Merge B & C making use of some piece of secondary 'new_a'
+# Finally, someone goes to merge D & E.  Does git detect the conflict?
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+
+test_expect_success 'setup differently handled merges of rename/add conflict' '
+	test_create_repo rename-add &&
+	(
+		cd rename-add &&
+
+		printf "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n" >a &&
+		git add a &&
+		test_tick && git commit -m A &&
+
+		git branch B &&
+		git checkout -b C &&
+		echo 10 >>a &&
+		test_write_lines 0 1 2 3 4 5 6 7 foobar >new_a &&
+		git add a new_a &&
+		test_tick && git commit -m C &&
+
+		git checkout B &&
+		git mv a new_a &&
+		test_tick && git commit -m B &&
+
+		git checkout B^0 &&
+		test_must_fail git merge C &&
+		git show :2:new_a >new_a &&
+		git add new_a &&
+		test_tick && git commit -m D &&
+		git tag D &&
+
+		git checkout C^0 &&
+		test_must_fail git merge B &&
+		test_write_lines 0 1 2 3 4 5 6 7 bad_merge >new_a &&
+		git add -u &&
+		test_tick && git commit -m E &&
+		git tag E
+	)
+'
+
+test_expect_success 'git detects differently handled merges conflict' '
+	(
+		cd rename-add &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect       \
+			C:new_a  D:new_a  E:new_a &&
+		git rev-parse   >actual     \
+			:1:new_a :2:new_a :3:new_a &&
+		test_cmp expect actual &&
+
+		# Test that the two-way merge in new_a is as expected
+		git cat-file -p D:new_a >ours &&
+		git cat-file -p E:new_a >theirs &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "E^0" \
+			ours empty theirs &&
+		sed -e "s/^\([<=>]\)/\1\1\1/" ours >expect &&
+		git hash-object new_a >actual &&
+		git hash-object ours  >expect &&
+		test_cmp expect actual
+	)
+'
+
+# Repeat the above testcase with precisely the same setup, other than with
+# the two merge bases having different orderings of commit timestamps so
+# that they are reversed in the order they are provided to merge-recursive,
+# so that we can improve code coverage.
+test_expect_success 'git detects differently handled merges conflict, swapped' '
+	(
+		cd rename-add &&
+
+		# Difference #1: Do cleanup from previous testrun
+		git reset --hard &&
+		git clean -fdqx &&
+
+		# Difference #2: Change commit timestamps
+		btime=$(git log --no-walk --date=raw --format=%cd B | awk "{print \$1}") &&
+		ctime=$(git log --no-walk --date=raw --format=%cd C | awk "{print \$1}") &&
+		newctime=$(($btime+1)) &&
+		git fast-export --no-data --all | sed -e s/$ctime/$newctime/ | git fast-import --force --quiet &&
+		# End of differences; rest is copy-paste of last test
+
+		git checkout D^0 &&
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect       \
+			C:new_a  D:new_a  E:new_a &&
+		git rev-parse   >actual     \
+			:1:new_a :2:new_a :3:new_a &&
+		test_cmp expect actual &&
+
+		# Test that the two-way merge in new_a is as expected
+		git cat-file -p D:new_a >ours &&
+		git cat-file -p E:new_a >theirs &&
+		>empty &&
+		test_must_fail git merge-file \
+			-L "HEAD" \
+			-L "" \
+			-L "E^0" \
+			ours empty theirs &&
+		sed -e "s/^\([<=>]\)/\1\1\1/" ours >expect &&
+		git hash-object new_a >actual &&
+		git hash-object ours  >expect &&
+		test_cmp expect actual
+	)
+'
+
+#
+# criss-cross + modify/delete:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: file with contents 'A\n'
+#   Commit B: file with contents 'B\n'
+#   Commit C: file not present
+#   Commit D: file with contents 'B\n'
+#   Commit E: file not present
+#
+# Merging commits D & E should result in modify/delete conflict.
+
+test_expect_success 'setup criss-cross + modify/delete resolved differently' '
+	test_create_repo modify-delete &&
+	(
+		cd modify-delete &&
+
+		echo A >file &&
+		git add file &&
+		test_tick &&
+		git commit -m A &&
+
+		git branch B &&
+		git checkout -b C &&
+		git rm file &&
+		test_tick &&
+		git commit -m C &&
+
+		git checkout B &&
+		echo B >file &&
+		git add file &&
+		test_tick &&
+		git commit -m B &&
+
+		git checkout B^0 &&
+		test_must_fail git merge C &&
+		echo B >file &&
+		git add file &&
+		test_tick &&
+		git commit -m D &&
+		git tag D &&
+
+		git checkout C^0 &&
+		test_must_fail git merge B &&
+		git rm file &&
+		test_tick &&
+		git commit -m E &&
+		git tag E
+	)
+'
+
+test_expect_success 'git detects conflict merging criss-cross+modify/delete' '
+	(
+		cd modify-delete &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+
+		git rev-parse >expect       \
+			master:file  B:file &&
+		git rev-parse   >actual      \
+			:1:file      :2:file &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'git detects conflict merging criss-cross+modify/delete, reverse direction' '
+	(
+		cd modify-delete &&
+
+		git reset --hard &&
+		git checkout E^0 &&
+
+		test_must_fail git merge -s recursive D^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+
+		git rev-parse >expect       \
+			master:file  B:file &&
+		git rev-parse   >actual      \
+			:1:file      :3:file &&
+		test_cmp expect actual
+	)
+'
+
+#      SORRY FOR THE SUPER LONG DESCRIPTION, BUT THIS NEXT ONE IS HAIRY
+#
+# criss-cross + d/f conflict via add/add:
+#   Commit A: Neither file 'a' nor directory 'a/' exists.
+#   Commit B: Introduce 'a'
+#   Commit C: Introduce 'a/file'
+#   Commit D1: Merge B & C, keeping 'a'    and deleting 'a/'
+#   Commit E1: Merge B & C, deleting 'a' but keeping 'a/file'
+#
+#      B   D1 or D2
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E1 or E2 or E3
+#
+# I'll describe D2, E2, & E3 (which are alternatives for D1 & E1) more below...
+#
+# Merging D1 & E1 requires we first create a virtual merge base X from
+# merging A & B in memory.  There are several possibilities for the merge-base:
+#   1: Keep both 'a' and 'a/file' (assuming crazy filesystem allowing a tree
+#      with a directory and file at same path): results in merge of D1 & E1
+#      being clean with both files deleted.  Bad (no conflict detected).
+#   2: Keep 'a' but not 'a/file': Merging D1 & E1 is clean and matches E1.  Bad.
+#   3: Keep 'a/file' but not 'a': Merging D1 & E1 is clean and matches D1.  Bad.
+#   4: Keep neither file: Merging D1 & E1 reports the D/F add/add conflict.
+#
+# So 4 sounds good for this case, but if we were to merge D1 & E3, where E3
+# is defined as:
+#   Commit E3: Merge B & C, keeping modified a, and deleting a/
+# then we'd get an add/add conflict for 'a', which seems suboptimal.  A little
+# creativity leads us to an alternate choice:
+#   5: Keep 'a' as 'a~$UNIQUE' and a/file; results:
+#        Merge D1 & E1: rename/delete conflict for 'a'; a/file silently deleted
+#        Merge D1 & E3 is clean, as expected.
+#
+# So choice 5 at least provides some kind of conflict for the original case,
+# and can merge cleanly as expected with D1 and E3.  It also made things just
+# slightly funny for merging D1 and e$, where E4 is defined as:
+#   Commit E4: Merge B & C, modifying 'a' and renaming to 'a2', and deleting 'a/'
+# in this case, we'll get a rename/rename(1to2) conflict because a~$UNIQUE
+# gets renamed to 'a' in D1 and to 'a2' in E4.  But that's better than having
+# two files (both 'a' and 'a2') sitting around without the user being notified
+# that we could detect they were related and need to be merged.  Also, choice
+# 5 makes the handling of 'a/file' seem suboptimal.  What if we were to merge
+# D2 and E4, where D2 is:
+#   Commit D2: Merge B & C, renaming 'a'->'a2', keeping 'a/file'
+# This would result in a clean merge with 'a2' having three-way merged
+# contents (good), and deleting 'a/' (bad) -- it doesn't detect the
+# conflict in how the different sides treated a/file differently.
+# Continuing down the creative route:
+#   6: Keep 'a' as 'a~$UNIQUE1' and keep 'a/' as 'a~$UNIQUE2/'; results:
+#        Merge D1 & E1: rename/delete conflict for 'a' and each path under 'a/'.
+#        Merge D1 & E3: clean, as expected.
+#        Merge D1 & E4: rename/rename(1to2) conflict on 'a' vs 'a2'.
+#        Merge D2 & E4: clean for 'a2', rename/delete for a/file
+#
+# Choice 6 could cause rename detection to take longer (providing more targets
+# that need to be searched).  Also, the conflict message for each path under
+# 'a/' might be annoying unless we can detect it at the directory level, print
+# it once, and then suppress it for individual filepaths underneath.
+#
+#
+# As of time of writing, git uses choice 5.  Directory rename detection and
+# rename detection performance improvements might make choice 6 a desirable
+# improvement.  But we can at least document where we fall short for now...
+#
+#
+# Historically, this testcase also used:
+#   Commit E2: Merge B & C, deleting 'a' but keeping slightly modified 'a/file'
+# The merge of D1 & E2 is very similar to D1 & E1 -- it has similar issues for
+# path 'a', but should always result in a modify/delete conflict for path
+# 'a/file'.  These tests ran the two merges
+#   D1 & E1
+#   D1 & E2
+# in both directions, to check for directional issues with D/F conflict
+# handling. Later we added
+#   D1 & E3
+#   D1 & E4
+#   D2 & E4
+# for good measure, though we only ran those one way because we had pretty
+# good confidence in merge-recursive's directional handling of D/F issues.
+#
+# Just to summarize all the intermediate merge commits:
+#   Commit D1: Merge B & C, keeping a    and deleting a/
+#   Commit D2: Merge B & C, renaming a->a2, keeping a/file
+#   Commit E1: Merge B & C, deleting a but keeping a/file
+#   Commit E2: Merge B & C, deleting a but keeping slightly modified a/file
+#   Commit E3: Merge B & C, keeping modified a, and deleting a/
+#   Commit E4: Merge B & C, modifying 'a' and renaming to 'a2', and deleting 'a/'
+#
+
+test_expect_success 'setup differently handled merges of directory/file conflict' '
+	test_create_repo directory-file &&
+	(
+		cd directory-file &&
+
+		>ignore-me &&
+		git add ignore-me &&
+		test_tick &&
+		git commit -m A &&
+		git tag A &&
+
+		git branch B &&
+		git checkout -b C &&
+		mkdir a &&
+		test_write_lines a b c d e f g >a/file &&
+		git add a/file &&
+		test_tick &&
+		git commit -m C &&
+
+		git checkout B &&
+		test_write_lines 1 2 3 4 5 6 7 >a &&
+		git add a &&
+		test_tick &&
+		git commit -m B &&
+
+		git checkout B^0 &&
+		git merge -s ours -m D1 C^0 &&
+		git tag D1 &&
+
+		git checkout B^0 &&
+		test_must_fail git merge C^0 &&
+		git clean -fd &&
+		git rm -rf a/ &&
+		git rm a &&
+		git cat-file -p B:a >a2 &&
+		git add a2 &&
+		git commit -m D2 &&
+		git tag D2 &&
+
+		git checkout C^0 &&
+		git merge -s ours -m E1 B^0 &&
+		git tag E1 &&
+
+		git checkout C^0 &&
+		git merge -s ours -m E2 B^0 &&
+		test_write_lines a b c d e f g h >a/file &&
+		git add a/file &&
+		git commit --amend -C HEAD &&
+		git tag E2 &&
+
+		git checkout C^0 &&
+		test_must_fail git merge B^0 &&
+		git clean -fd &&
+		git rm -rf a/ &&
+		test_write_lines 1 2 3 4 5 6 7 8 >a &&
+		git add a &&
+		git commit -m E3 &&
+		git tag E3 &&
+
+		git checkout C^0 &&
+		test_must_fail git merge B^0 &&
+		git clean -fd &&
+		git rm -rf a/ &&
+		git rm a &&
+		test_write_lines 1 2 3 4 5 6 7 8 >a2 &&
+		git add a2 &&
+		git commit -m E4 &&
+		git tag E4
+	)
+'
+
+test_expect_success 'merge of D1 & E1 fails but has appropriate contents' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout D1^0 &&
+
+		test_must_fail git merge -s recursive E1^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 1 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect    \
+			A:ignore-me  B:a &&
+		git rev-parse   >actual   \
+			:0:ignore-me :2:a &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'merge of E1 & D1 fails but has appropriate contents' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout E1^0 &&
+
+		test_must_fail git merge -s recursive D1^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 1 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect    \
+			A:ignore-me  B:a &&
+		git rev-parse   >actual   \
+			:0:ignore-me :3:a &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'merge of D1 & E2 fails but has appropriate contents' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout D1^0 &&
+
+		test_must_fail git merge -s recursive E2^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 4 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 2 out &&
+
+		git rev-parse >expect    \
+			B:a   E2:a/file  C:a/file   A:ignore-me &&
+		git rev-parse   >actual   \
+			:2:a  :3:a/file  :1:a/file  :0:ignore-me &&
+		test_cmp expect actual &&
+
+		test_path_is_file a~HEAD
+	)
+'
+
+test_expect_success 'merge of E2 & D1 fails but has appropriate contents' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout E2^0 &&
+
+		test_must_fail git merge -s recursive D1^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 4 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 2 out &&
+
+		git rev-parse >expect    \
+			B:a   E2:a/file  C:a/file   A:ignore-me &&
+		git rev-parse   >actual   \
+			:3:a  :2:a/file  :1:a/file  :0:ignore-me &&
+		test_cmp expect actual &&
+
+		test_path_is_file a~D1^0
+	)
+'
+
+test_expect_success 'merge of D1 & E3 succeeds' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout D1^0 &&
+
+		git merge -s recursive E3^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 0 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect    \
+			A:ignore-me  E3:a &&
+		git rev-parse   >actual   \
+			:0:ignore-me :0:a &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'merge of D1 & E4 notifies user a and a2 are related' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout D1^0 &&
+
+		test_must_fail git merge -s recursive E4^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 4 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect                  \
+			A:ignore-me  B:a   D1:a  E4:a2 &&
+		git rev-parse   >actual                \
+			:0:ignore-me :1:a~Temporary\ merge\ branch\ 2  :2:a  :3:a2 &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_failure 'merge of D2 & E4 merges a2s & reports conflict for a/file' '
+	test_when_finished "git -C directory-file reset --hard" &&
+	test_when_finished "git -C directory-file clean -fdqx" &&
+	(
+		cd directory-file &&
+
+		git checkout D2^0 &&
+
+		test_must_fail git merge -s recursive E4^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 1 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect                 \
+			A:ignore-me  E4:a2  D2:a/file &&
+		git rev-parse   >actual               \
+			:0:ignore-me :0:a2  :2:a/file &&
+		test_cmp expect actual
+	)
+'
+
+#
+# criss-cross with rename/rename(1to2)/modify followed by
+# rename/rename(2to1)/modify:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: new file: a
+#   Commit B: rename a->b, modifying by adding a line
+#   Commit C: rename a->c
+#   Commit D: merge B&C, resolving conflict by keeping contents in newname
+#   Commit E: merge B&C, resolving conflict similar to D but adding another line
+#
+# There is a conflict merging B & C, but one of filename not of file
+# content.  Whoever created D and E chose specific resolutions for that
+# conflict resolution.  Now, since: (1) there is no content conflict
+# merging B & C, (2) D does not modify that merged content further, and (3)
+# both D & E resolve the name conflict in the same way, the modification to
+# newname in E should not cause any conflicts when it is merged with D.
+# (Note that this can be accomplished by having the virtual merge base have
+# the merged contents of b and c stored in a file named a, which seems like
+# the most logical choice anyway.)
+#
+# Comment from Junio: I do not necessarily agree with the choice "a", but
+# it feels sound to say "B and C do not agree what the final pathname
+# should be, but we know this content was derived from the common A:a so we
+# use one path whose name is arbitrary in the virtual merge base X between
+# D and E" and then further let the rename detection to notice that that
+# arbitrary path gets renamed between X-D to "newname" and X-E also to
+# "newname" to resolve it as both sides renaming it to the same new
+# name. It is akin to what we do at the content level, i.e. "B and C do not
+# agree what the final contents should be, so we leave the conflict marker
+# but that may cancel out at the final merge stage".
+
+test_expect_success 'setup rename/rename(1to2)/modify followed by what looks like rename/rename(2to1)/modify' '
+	test_create_repo rename-squared-squared &&
+	(
+		cd rename-squared-squared &&
+
+		printf "1\n2\n3\n4\n5\n6\n" >a &&
+		git add a &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git mv a b &&
+		echo 7 >>b &&
+		git add -u &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git mv a c &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge --no-commit -s ours C^0 &&
+		git mv b newname &&
+		git commit -m "Merge commit C^0 into HEAD" &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge --no-commit -s ours B^0 &&
+		git mv c newname &&
+		printf "7\n8\n" >>newname &&
+		git add -u &&
+		git commit -m "Merge commit B^0 into HEAD" &&
+		git tag E
+	)
+'
+
+test_expect_success 'handle rename/rename(1to2)/modify followed by what looks like rename/rename(2to1)/modify' '
+	(
+		cd rename-squared-squared &&
+
+		git checkout D^0 &&
+
+		git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 1 out &&
+		git ls-files -u >out &&
+		test_line_count = 0 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		test $(git rev-parse HEAD:newname) = $(git rev-parse E:newname)
+	)
+'
+
+#
+# criss-cross with rename/rename(1to2)/add-source + resolvable modify/modify:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: new file: a
+#   Commit B: rename a->b
+#   Commit C: rename a->c, add different a
+#   Commit D: merge B&C, keeping b&c and (new) a modified at beginning
+#   Commit E: merge B&C, keeping b&c and (new) a modified at end
+#
+# Merging commits D & E should result in no conflict; doing so correctly
+# requires getting the virtual merge base (from merging B&C) right, handling
+# renaming carefully (both in the virtual merge base and later), and getting
+# content merge handled.
+
+test_expect_success 'setup criss-cross + rename/rename/add-source + modify/modify' '
+	test_create_repo rename-rename-add-source &&
+	(
+		cd rename-rename-add-source &&
+
+		printf "lots\nof\nwords\nand\ncontent\n" >a &&
+		git add a &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git mv a b &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git mv a c &&
+		printf "2\n3\n4\n5\n6\n7\n" >a &&
+		git add a &&
+		git commit -m C &&
+
+		git checkout B^0 &&
+		git merge --no-commit -s ours C^0 &&
+		git checkout C -- a c &&
+		mv a old_a &&
+		echo 1 >a &&
+		cat old_a >>a &&
+		rm old_a &&
+		git add -u &&
+		git commit -m "Merge commit C^0 into HEAD" &&
+		git tag D &&
+
+		git checkout C^0 &&
+		git merge --no-commit -s ours B^0 &&
+		git checkout B -- b &&
+		echo 8 >>a &&
+		git add -u &&
+		git commit -m "Merge commit B^0 into HEAD" &&
+		git tag E
+	)
+'
+
+test_expect_failure 'detect rename/rename/add-source for virtual merge-base' '
+	(
+		cd rename-rename-add-source &&
+
+		git checkout D^0 &&
+
+		git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 0 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		printf "1\n2\n3\n4\n5\n6\n7\n8\n" >correct &&
+		git rev-parse >expect \
+			A:a   A:a     \
+			correct       &&
+		git rev-parse   >actual  \
+			:0:b  :0:c       &&
+		git hash-object >>actual \
+			a                &&
+		test_cmp expect actual
+	)
+'
+
+#
+# criss-cross with rename/rename(1to2)/add-dest + simple modify:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: new file: a
+#   Commit B: rename a->b, add c
+#   Commit C: rename a->c
+#   Commit D: merge B&C, keeping A:a and B:c
+#   Commit E: merge B&C, keeping A:a and slightly modified c from B
+#
+# Merging commits D & E should result in no conflict.  The virtual merge
+# base of B & C needs to not delete B:c for that to work, though...
+
+test_expect_success 'setup criss-cross+rename/rename/add-dest + simple modify' '
+	test_create_repo rename-rename-add-dest &&
+	(
+		cd rename-rename-add-dest &&
+
+		>a &&
+		git add a &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git mv a b &&
+		printf "1\n2\n3\n4\n5\n6\n7\n" >c &&
+		git add c &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git mv a c &&
+		git commit -m C &&
+
+		git checkout B^0 &&
+		git merge --no-commit -s ours C^0 &&
+		git mv b a &&
+		git commit -m "D is like B but renames b back to a" &&
+		git tag D &&
+
+		git checkout B^0 &&
+		git merge --no-commit -s ours C^0 &&
+		git mv b a &&
+		echo 8 >>c &&
+		git add c &&
+		git commit -m "E like D but has mod in c" &&
+		git tag E
+	)
+'
+
+test_expect_success 'virtual merge base handles rename/rename(1to2)/add-dest' '
+	(
+		cd rename-rename-add-dest &&
+
+		git checkout D^0 &&
+
+		git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 0 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		git rev-parse >expect \
+			A:a   E:c     &&
+		git rev-parse   >actual \
+			:0:a  :0:c      &&
+		test_cmp expect actual
+	)
+'
+
+#
+# criss-cross with modify/modify on a symlink:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: simple simlink fickle->lagoon
+#   Commit B: redirect fickle->disneyland
+#   Commit C: redirect fickle->home
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious modify/modify conflict for the symlink 'fickle'.  Can
+# git detect it?
+
+test_expect_success 'setup symlink modify/modify' '
+	test_create_repo symlink-modify-modify &&
+	(
+		cd symlink-modify-modify &&
+
+		test_ln_s_add lagoon fickle &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git rm fickle &&
+		test_ln_s_add disneyland fickle &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git rm fickle &&
+		test_ln_s_add home fickle &&
+		git add fickle &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check symlink modify/modify' '
+	(
+		cd symlink-modify-modify &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+#
+# criss-cross with add/add of a symlink:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: No symlink or path exists yet
+#   Commit B: set up symlink: fickle->disneyland
+#   Commit C: set up symlink: fickle->home
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious add/add conflict for the symlink 'fickle'.  Can
+# git detect it?
+
+test_expect_success 'setup symlink add/add' '
+	test_create_repo symlink-add-add &&
+	(
+		cd symlink-add-add &&
+
+		touch ignoreme &&
+		git add ignoreme &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		test_ln_s_add disneyland fickle &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		test_ln_s_add home fickle &&
+		git add fickle &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check symlink add/add' '
+	(
+		cd symlink-add-add &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+#
+# criss-cross with modify/modify on a submodule:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: simple submodule repo
+#   Commit B: update repo
+#   Commit C: update repo differently
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious modify/modify conflict for the submodule 'repo'.  Can
+# git detect it?
+
+test_expect_success 'setup submodule modify/modify' '
+	test_create_repo submodule-modify-modify &&
+	(
+		cd submodule-modify-modify &&
+
+		test_create_repo submod &&
+		(
+			cd submod &&
+			touch file-A &&
+			git add file-A &&
+			git commit -m A &&
+			git tag A &&
+
+			git checkout -b B A &&
+			touch file-B &&
+			git add file-B &&
+			git commit -m B &&
+			git tag B &&
+
+			git checkout -b C A &&
+			touch file-C &&
+			git add file-C &&
+			git commit -m C &&
+			git tag C
+		) &&
+
+		git -C submod reset --hard A &&
+		git add submod &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git -C submod reset --hard B &&
+		git add submod &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git -C submod reset --hard C &&
+		git add submod &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check submodule modify/modify' '
+	(
+		cd submodule-modify-modify &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+#
+# criss-cross with add/add on a submodule:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: nothing of note
+#   Commit B: introduce submodule repo
+#   Commit C: introduce submodule repo at different commit
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious add/add conflict for the submodule 'repo'.  Can
+# git detect it?
+
+test_expect_success 'setup submodule add/add' '
+	test_create_repo submodule-add-add &&
+	(
+		cd submodule-add-add &&
+
+		test_create_repo submod &&
+		(
+			cd submod &&
+			touch file-A &&
+			git add file-A &&
+			git commit -m A &&
+			git tag A &&
+
+			git checkout -b B A &&
+			touch file-B &&
+			git add file-B &&
+			git commit -m B &&
+			git tag B &&
+
+			git checkout -b C A &&
+			touch file-C &&
+			git add file-C &&
+			git commit -m C &&
+			git tag C
+		) &&
+
+		touch irrelevant-file &&
+		git add irrelevant-file &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git -C submod reset --hard B &&
+		git add submod &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		git -C submod reset --hard C &&
+		git add submod &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check submodule add/add' '
+	(
+		cd submodule-add-add &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+#
+# criss-cross with conflicting entry types:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: nothing of note
+#   Commit B: introduce submodule 'path'
+#   Commit C: introduce symlink 'path'
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious add/add conflict for 'path'.  Can git detect it?
+
+test_expect_success 'setup conflicting entry types (submodule vs symlink)' '
+	test_create_repo submodule-symlink-add-add &&
+	(
+		cd submodule-symlink-add-add &&
+
+		test_create_repo path &&
+		(
+			cd path &&
+			touch file-B &&
+			git add file-B &&
+			git commit -m B &&
+			git tag B
+		) &&
+
+		touch irrelevant-file &&
+		git add irrelevant-file &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		git -C path reset --hard B &&
+		git add path &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		rm -rf path/ &&
+		test_ln_s_add irrelevant-file path &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check conflicting entry types (submodule vs symlink)' '
+	(
+		cd submodule-symlink-add-add &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+#
+# criss-cross with regular files that have conflicting modes:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: nothing of note
+#   Commit B: introduce file source_me.bash, not executable
+#   Commit C: introduce file source_me.bash, executable
+#   Commit D: merge B&C, resolving in favor of B
+#   Commit E: merge B&C, resolving in favor of C
+#
+# This is an obvious add/add mode conflict.  Can git detect it?
+
+test_expect_success 'setup conflicting modes for regular file' '
+	test_create_repo regular-file-mode-conflict &&
+	(
+		cd regular-file-mode-conflict &&
+
+		touch irrelevant-file &&
+		git add irrelevant-file &&
+		git commit -m A &&
+		git tag A &&
+
+		git checkout -b B A &&
+		echo "command_to_run" >source_me.bash &&
+		git add source_me.bash &&
+		git commit -m B &&
+
+		git checkout -b C A &&
+		echo "command_to_run" >source_me.bash &&
+		git add source_me.bash &&
+		test_chmod +x source_me.bash &&
+		git commit -m C &&
+
+		git checkout -q B^0 &&
+		git merge -s ours -m D C^0 &&
+		git tag D &&
+
+		git checkout -q C^0 &&
+		git merge -s ours -m E B^0 &&
+		git tag E
+	)
+'
+
+test_expect_failure 'check conflicting modes for regular file' '
+	(
+		cd regular-file-mode-conflict &&
+
+		git checkout D^0 &&
+
+		test_must_fail git merge -s recursive E^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		git ls-files -o >out &&
+		test_line_count = 1 out
+	)
+'
+
+# Setup:
+#          L1---L2
+#         /  \ /  \
+#   master    X    ?
+#         \  / \  /
+#          R1---R2
+#
+# Where:
+#   master has two files, named 'b' and 'a'
+#   branches L1 and R1 both modify each of the two files in conflicting ways
+#
+#   L2 is a merge of R1 into L1; more on it later.
+#   R2 is a merge of L1 into R1; more on it later.
+#
+#   X is an auto-generated merge-base used when merging L2 and R2.
+#   since X is a merge of L1 and R1, it has conflicting versions of each file
+#
+#   More about L2 and R2:
+#     - both resolve the conflicts in 'b' and 'a' differently
+#     - L2 renames 'b' to 'm'
+#     - R2 renames 'a' to 'm'
+#
+#   In the end, in file 'm' we have four different conflicting files (from
+#   two versions of 'b' and two of 'a').  In addition, if
+#   merge.conflictstyle is diff3, then the base version also has
+#   conflict markers of its own, leading to a total of three levels of
+#   conflict markers.  This is a pretty weird corner case, but we just want
+#   to ensure that we handle it as well as practical.
+
+test_expect_success 'setup nested conflicts' '
+	test_create_repo nested_conflicts &&
+	(
+		cd nested_conflicts &&
+
+		# Create some related files now
+		for i in $(test_seq 1 10)
+		do
+			echo Random base content line $i
+		done >initial &&
+
+		cp initial b_L1 &&
+		cp initial b_R1 &&
+		cp initial b_L2 &&
+		cp initial b_R2 &&
+		cp initial a_L1 &&
+		cp initial a_R1 &&
+		cp initial a_L2 &&
+		cp initial a_R2 &&
+
+		test_write_lines b b_L1 >>b_L1 &&
+		test_write_lines b b_R1 >>b_R1 &&
+		test_write_lines b b_L2 >>b_L2 &&
+		test_write_lines b b_R2 >>b_R2 &&
+		test_write_lines a a_L1 >>a_L1 &&
+		test_write_lines a a_R1 >>a_R1 &&
+		test_write_lines a a_L2 >>a_L2 &&
+		test_write_lines a a_R2 >>a_R2 &&
+
+		# Setup original commit (or merge-base), consisting of
+		# files named "b" and "a"
+		cp initial b &&
+		cp initial a &&
+		echo b >>b &&
+		echo a >>a &&
+		git add b a &&
+		test_tick && git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Handle the left side
+		git checkout L &&
+		mv -f b_L1 b &&
+		mv -f a_L1 a &&
+		git add b a &&
+		test_tick && git commit -m "version L1 of files" &&
+		git tag L1 &&
+
+		# Handle the right side
+		git checkout R &&
+		mv -f b_R1 b &&
+		mv -f a_R1 a &&
+		git add b a &&
+		test_tick && git commit -m "verson R1 of files" &&
+		git tag R1 &&
+
+		# Create first merge on left side
+		git checkout L &&
+		test_must_fail git merge R1 &&
+		mv -f b_L2 b &&
+		mv -f a_L2 a &&
+		git add b a &&
+		git mv b m &&
+		test_tick && git commit -m "left merge, rename b->m" &&
+		git tag L2 &&
+
+		# Create first merge on right side
+		git checkout R &&
+		test_must_fail git merge L1 &&
+		mv -f b_R2 b &&
+		mv -f a_R2 a &&
+		git add b a &&
+		git mv a m &&
+		test_tick && git commit -m "right merge, rename a->m" &&
+		git tag R2
+	)
+'
+
+test_expect_success 'check nested conflicts' '
+	(
+		cd nested_conflicts &&
+
+		git clean -f &&
+		git checkout L2^0 &&
+
+		# Merge must fail; there is a conflict
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R2^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >out &&
+		test_line_count = 2 out &&
+		git ls-files -u >out &&
+		test_line_count = 2 out &&
+		# Ensure we have the correct number of untracked files
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		# Create a and b from virtual merge base X
+		git cat-file -p master:a >base &&
+		git cat-file -p L1:a >ours &&
+		git cat-file -p R1:a >theirs &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			ours  \
+			base  \
+			theirs &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >vmb_a &&
+
+		git cat-file -p master:b >base &&
+		git cat-file -p L1:b >ours &&
+		git cat-file -p R1:b >theirs &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			ours  \
+			base  \
+			theirs &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >vmb_b &&
+
+		# Compare :2:m to expected values
+		git cat-file -p L2:m >ours &&
+		git cat-file -p R2:b >theirs &&
+		test_must_fail git merge-file --diff3  \
+			-L "HEAD:m"                    \
+			-L "merged common ancestors:b" \
+			-L "R2^0:b"                    \
+			ours                           \
+			vmb_b                          \
+			theirs                         &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >m_stage_2 &&
+		git cat-file -p :2:m >actual &&
+		test_cmp m_stage_2 actual &&
+
+		# Compare :3:m to expected values
+		git cat-file -p L2:a >ours &&
+		git cat-file -p R2:m >theirs &&
+		test_must_fail git merge-file --diff3  \
+			-L "HEAD:a"                    \
+			-L "merged common ancestors:a" \
+			-L "R2^0:m"                    \
+			ours                           \
+			vmb_a                          \
+			theirs                         &&
+		sed -e "s/^\([<|=>]\)/\1\1/" ours >m_stage_3 &&
+		git cat-file -p :3:m >actual &&
+		test_cmp m_stage_3 actual &&
+
+		# Compare m to expected contents
+		>empty &&
+		cp m_stage_2 expected_final_m &&
+		test_must_fail git merge-file --diff3 \
+			-L "HEAD"                     \
+			-L "merged common ancestors"  \
+			-L "R2^0"                     \
+			expected_final_m              \
+			empty                         \
+			m_stage_3                     &&
+		test_cmp expected_final_m m
+	)
+'
+
+# Setup:
+#          L1---L2---L3
+#         /  \ /  \ /  \
+#   master    X1   X2   ?
+#         \  / \  / \  /
+#          R1---R2---R3
+#
+# Where:
+#   master has one file named 'content'
+#   branches L1 and R1 both modify each of the two files in conflicting ways
+#
+#   L<n> (n>1) is a merge of R<n-1> into L<n-1>
+#   R<n> (n>1) is a merge of L<n-1> into R<n-1>
+#   L<n> and R<n> resolve the conflicts differently.
+#
+#   X<n> is an auto-generated merge-base used when merging L<n+1> and R<n+1>.
+#   By construction, X1 has conflict markers due to conflicting versions.
+#   X2, due to using merge.conflictstyle=3, has nested conflict markers.
+#
+#   So, merging R3 into L3 using merge.conflictstyle=3 should show the
+#   nested conflict markers from X2 in the base version -- that means we
+#   have three levels of conflict markers.  Can we distinguish all three?
+
+test_expect_success 'setup virtual merge base with nested conflicts' '
+	test_create_repo virtual_merge_base_has_nested_conflicts &&
+	(
+		cd virtual_merge_base_has_nested_conflicts &&
+
+		# Create some related files now
+		for i in $(test_seq 1 10)
+		do
+			echo Random base content line $i
+		done >content &&
+
+		# Setup original commit
+		git add content &&
+		test_tick && git commit -m initial &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		echo left >>content &&
+		git add content &&
+		test_tick && git commit -m "version L1 of content" &&
+		git tag L1 &&
+
+		# Create R1
+		git checkout R &&
+		echo right >>content &&
+		git add content &&
+		test_tick && git commit -m "verson R1 of content" &&
+		git tag R1 &&
+
+		# Create L2
+		git checkout L &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge R1 &&
+		git checkout L1 content &&
+		test_tick && git commit -m "version L2 of content" &&
+		git tag L2 &&
+
+		# Create R2
+		git checkout R &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge L1 &&
+		git checkout R1 content &&
+		test_tick && git commit -m "version R2 of content" &&
+		git tag R2 &&
+
+		# Create L3
+		git checkout L &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge R2 &&
+		git checkout L1 content &&
+		test_tick && git commit -m "version L3 of content" &&
+		git tag L3 &&
+
+		# Create R3
+		git checkout R &&
+		test_must_fail git -c merge.conflictstyle=diff3 merge L2 &&
+		git checkout R1 content &&
+		test_tick && git commit -m "version R3 of content" &&
+		git tag R3
+	)
+'
+
+test_expect_success 'check virtual merge base with nested conflicts' '
+	(
+		cd virtual_merge_base_has_nested_conflicts &&
+
+		git checkout L3^0 &&
+
+		# Merge must fail; there is a conflict
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R3^0 &&
+
+		# Make sure the index has the right number of entries
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 3 out &&
+		# Ensure we have the correct number of untracked files
+		git ls-files -o >out &&
+		test_line_count = 1 out &&
+
+		# Compare :[23]:content to expected values
+		git rev-parse L1:content R1:content >expect &&
+		git rev-parse :2:content :3:content >actual &&
+		test_cmp expect actual &&
+
+		# Imitate X1 merge base, except without long enough conflict
+		# markers because a subsequent sed will modify them.  Put
+		# result into vmb.
+		git cat-file -p master:content >base &&
+		git cat-file -p L:content >left &&
+		git cat-file -p R:content >right &&
+		cp left merged-once &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			merged-once \
+			base        \
+			right       &&
+		sed -e "s/^\([<|=>]\)/\1\1\1/" merged-once >vmb &&
+
+		# Imitate X2 merge base, overwriting vmb.  Note that we
+		# extend both sets of conflict markers to make them longer
+		# with the sed command.
+		cp left merged-twice &&
+		test_must_fail git merge-file --diff3 \
+			-L "Temporary merge branch 1" \
+			-L "merged common ancestors"  \
+			-L "Temporary merge branch 2" \
+			merged-twice \
+			vmb          \
+			right        &&
+		sed -e "s/^\([<|=>]\)/\1\1\1/" merged-twice >vmb &&
+
+		# Compare :1:content to expected value
+		git cat-file -p :1:content >actual &&
+		test_cmp vmb actual &&
+
+		# Determine expected content in final outer merge, compare to
+		# what the merge generated.
+		cp -f left expect &&
+		test_must_fail git merge-file --diff3                      \
+			-L "HEAD"  -L "merged common ancestors"  -L "R3^0" \
+			expect     vmb                           right     &&
+		test_cmp expect content
+	)
+'
+
+test_done