[PATCH 4/5] unpack-trees: Fix same() for submodules

[Stefan Beller <sbeller@google.com>]

The function same(a, b) is used to check if two entries a and b are the
same.  As the index contains the staged files the same() function can be
used to check if files between a given revision and the index are the same.

In case of submodules, the gitlink entry is showing up as not modified
despite potential changes inside the submodule.

Fix the function to examine submodules by looking inside the submodule.
This patch alone doesn't affect any correctness garantuees, but in
combination with the next patch this fixes the new test introduced
earlier in this series.

This may be a slight performance regression as now we have to
inspect any submodule thouroughly.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 unpack-trees.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/unpack-trees.c b/unpack-trees.c
index bf8b602901..4d839e8edb 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1427,6 +1427,8 @@ static int same(const struct cache_entry *a, const struct cache_entry *b)
 		return 1;
 	if ((a->ce_flags | b->ce_flags) & CE_CONFLICTED)
 		return 0;
+	if (S_ISGITLINK(b->ce_mode) && should_update_submodules())
+		return !oidcmp(&a->oid, &b->oid) && !is_submodule_modified(b->name, 0);
 	return a->ce_mode == b->ce_mode &&
 	       !oidcmp(&a->oid, &b->oid);
 }
-- 
2.15.1.620.gb9897f4670-goog