[PATCH v5 6/6] grep: search history of moved submodules

[Brandon Williams <bmwill@google.com>]

If a submodule was renamed at any point since it's inception then if you
were to try and grep on a commit prior to the submodule being moved, you
wouldn't be able to find a working directory for the submodule since the
path in the past is different from the current path.

This patch teaches grep to find the .git directory for a submodule in
the parents .git/modules/ directory in the event the path to the
submodule in the commit that is being searched differs from the state of
the currently checked out commit.  If found, the child process that is
spawned to grep the submodule will chdir into its gitdir instead of a
working directory.

In order to override the explicit setting of submodule child process's
gitdir environment variable (which was introduced in '10f5c526')
`GIT_DIR_ENVIORMENT` needs to be pushed onto child process's env_array.
This allows the searching of history from a submodule's gitdir, rather
than from a working directory.

Signed-off-by: Brandon Williams <bmwill@google.com>
---
 builtin/grep.c                     | 20 +++++++++++++++++--
 t/t7814-grep-recurse-submodules.sh | 41 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/builtin/grep.c b/builtin/grep.c
index 5918a26..2c727ef 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -547,6 +547,7 @@ static int grep_submodule_launch(struct grep_opt *opt,
 		name = gs->name;
 
 	prepare_submodule_repo_env(&cp.env_array);
+	argv_array_push(&cp.env_array, GIT_DIR_ENVIRONMENT);
 
 	/* Add super prefix */
 	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
@@ -615,8 +616,23 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 {
 	if (!is_submodule_initialized(path))
 		return 0;
-	if (!is_submodule_populated(path))
-		return 0;
+	if (!is_submodule_populated(path)) {
+		/*
+		 * If searching history, check for the presense of the
+		 * submodule's gitdir before skipping the submodule.
+		 */
+		if (sha1) {
+			const struct submodule *sub =
+					submodule_from_path(null_sha1, path);
+			if (sub)
+				path = git_path("modules/%s", sub->name);
+
+			if (!(is_directory(path) && is_git_directory(path)))
+				return 0;
+		} else {
+			return 0;
+		}
+	}
 
 #ifndef NO_PTHREADS
 	if (num_threads) {
diff --git a/t/t7814-grep-recurse-submodules.sh b/t/t7814-grep-recurse-submodules.sh
index 9e93fe7..0507771 100755
--- a/t/t7814-grep-recurse-submodules.sh
+++ b/t/t7814-grep-recurse-submodules.sh
@@ -186,6 +186,47 @@ test_expect_success 'grep recurse submodule colon in name' '
 	test_cmp expect actual
 '
 
+test_expect_success 'grep history with moved submoules' '
+	git init parent &&
+	test_when_finished "rm -rf parent" &&
+	echo "foobar" >parent/file &&
+	git -C parent add file &&
+	git -C parent commit -m "add file" &&
+
+	git init sub &&
+	test_when_finished "rm -rf sub" &&
+	echo "foobar" >sub/file &&
+	git -C sub add file &&
+	git -C sub commit -m "add file" &&
+
+	git -C parent submodule add ../sub dir/sub &&
+	git -C parent commit -m "add submodule" &&
+
+	cat >expect <<-\EOF &&
+	dir/sub/file:foobar
+	file:foobar
+	EOF
+	git -C parent grep -e "foobar" --recurse-submodules >actual &&
+	test_cmp expect actual &&
+
+	git -C parent mv dir/sub sub-moved &&
+	git -C parent commit -m "moved submodule" &&
+
+	cat >expect <<-\EOF &&
+	file:foobar
+	sub-moved/file:foobar
+	EOF
+	git -C parent grep -e "foobar" --recurse-submodules >actual &&
+	test_cmp expect actual &&
+
+	cat >expect <<-\EOF &&
+	HEAD^:dir/sub/file:foobar
+	HEAD^:file:foobar
+	EOF
+	git -C parent grep -e "foobar" --recurse-submodules HEAD^ >actual &&
+	test_cmp expect actual
+'
+
 test_incompatible_with_recurse_submodules ()
 {
 	test_expect_success "--recurse-submodules and $1 are incompatible" "
-- 
2.8.0.rc3.226.g39d4020