t7405: add a directory/submodule conflict

For a directory/submodule conflict, we want contents from both the
directory and the submodule to be present for the user to use to resolve
the conflict, but we do not want paths under the directory being written
into the submodule and we do not want the merge being confused by paths
under the submodule being in the way.  Add testcases for these situations.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7405-submodule-merge.sh

@@ -333,4 +333,92 @@ test_expect_failure 'file/submodule conflict' '
 	)
 '
 
+# Directory/submodule conflict
+#   Commit O: <empty>
+#   Commit A: path (submodule), with sole tracked file named 'world'
+#   Commit B1: path/file
+#   Commit B2: path/world
+#
+#   Expected from merge of A & B1:
+#     Contents under path/ from commit B1 are renamed elsewhere; we do not
+#     want to write files from one of our tracked directories into a submodule
+#
+#   Expected from merge of A & B2:
+#     Similar to last merge, but with a slight twist: we don't want paths
+#     under the submodule to be treated as untracked or in the way.
+
+test_expect_success 'setup directory/submodule conflict' '
+	test_create_repo directory-submodule &&
+	(
+		cd directory-submodule &&
+
+		git commit --allow-empty -m O &&
+
+		git branch A &&
+		git branch B1 &&
+		git branch B2 &&
+
+		git checkout B1 &&
+		mkdir path &&
+		echo contents >path/file &&
+		git add path/file &&
+		git commit -m B1 &&
+
+		git checkout B2 &&
+		mkdir path &&
+		echo contents >path/world &&
+		git add path/world &&
+		git commit -m B2 &&
+
+		git checkout A &&
+		test_create_repo path &&
+		test_commit -C path hello world &&
+		git submodule add ./path &&
+		git commit -m A
+	)
+'
+
+test_expect_failure 'directory/submodule conflict; keep submodule clean' '
+	test_when_finished "git -C directory-submodule reset --hard" &&
+	(
+		cd directory-submodule &&
+
+		git checkout A^0 &&
+		test_must_fail git merge B1^0 &&
+
+		git ls-files -s >out &&
+		test_line_count = 3 out &&
+		git ls-files -u >out &&
+		test_line_count = 1 out &&
+
+		# path/ is still a submodule
+		test_path_is_dir path/.git &&
+
+		echo Checking if contents from B1:path/file showed up &&
+		# Would rather use grep -r, but that is GNU extension...
+		git ls-files -co | xargs grep -q contents 2>/dev/null &&
+
+		# However, B1:path/file should NOT have shown up at path/file,
+		# because we should not write into the submodule
+		test_path_is_missing path/file
+	)
+'
+
+test_expect_failure 'directory/submodule conflict; should not treat submodule files as untracked or in the way' '
+	test_when_finished "git -C directory-submodule/path reset --hard" &&
+	test_when_finished "git -C directory-submodule reset --hard" &&
+	(
+		cd directory-submodule &&
+
+		git checkout A^0 &&
+		test_must_fail git merge B2^0 >out 2>err &&
+
+		# We do not want files within the submodule to prevent the
+		# merge from starting; we should not be writing to such paths
+		# anyway.
+		test_i18ngrep ! "refusing to lose untracked file at" err
+
+	)
+'
+
 test_done