In later patches we introduce the options and flag for commands
that modify the working directory, e.g. git-checkout.

This piece of code will be used universally for
all these working tree modifications as it
* supports dry run to answer the question:
  "Is it safe to change the submodule to this new state?"
  e.g. is it overwriting untracked files or are there local
  changes that would be overwritten?
* supports a force flag that can be used for resetting
  the tree.

Signed-off-by: Stefan Beller <redacted>
---
 submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 submodule.h |   7 ++++
 2 files changed, 142 insertions(+)

diff --git a/submodule.c b/submodule.c
index 0b2596e88a..a2cf8c9376 100644
--- a/submodule.c
+++ b/submodule.c

@@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
 	return ret;
 }
 
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
+
+	cp.git_cmd = 1;
+	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
+					"--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die("could not recurse into submodule '%s'", sub->path);
+
+	return finish_command(&cp);
+}
+
+void submodule_reset_index(const char *path)