Tests and more fixes for submodule diffs

This adds tests for diffs with submodules in them and (perhaps
unsurprisingly) requires further fixes to be made.  Specifically,
this fixes:

- when considering if a submodule is dirty in the workdir, it was
  being treated as dirty even if only the index was dirty.
- git_diff_patch_to_str (and git_diff_patch_print) were "printing"
  the headers for files (and submodules) that were unmodified or
  had no meaningful content.
- added comment to previous fix and removed unneeded parens.

1 files changed, 20 insertions, 3 deletions

diff --git a/include/git2/submodule.h b/include/git2/submodule.h
index 1abd33e79..40934b3ed 100644
--- a/include/git2/submodule.h
+++ b/include/git2/submodule.h
@@ -119,11 +119,28 @@ typedef enum {
 	 GIT_SUBMODULE_STATUS_WD_UNTRACKED      = (1u << 13),
 } git_submodule_status_t;
 
-#define GIT_SUBMODULE_STATUS_IS_UNMODIFIED(S) \
-	(((S) & ~(GIT_SUBMODULE_STATUS_IN_HEAD | \
+#define GIT_SUBMODULE_STATUS__IN_FLAGS \
+	(GIT_SUBMODULE_STATUS_IN_HEAD | \
 	GIT_SUBMODULE_STATUS_IN_INDEX | \
 	GIT_SUBMODULE_STATUS_IN_CONFIG | \
-	GIT_SUBMODULE_STATUS_IN_WD)) == 0)
+	GIT_SUBMODULE_STATUS_IN_WD)
+
+#define GIT_SUBMODULE_STATUS__INDEX_FLAGS \
+	(GIT_SUBMODULE_STATUS_INDEX_ADDED | \
+	GIT_SUBMODULE_STATUS_INDEX_DELETED | \
+	GIT_SUBMODULE_STATUS_INDEX_MODIFIED)
+
+#define GIT_SUBMODULE_STATUS__WD_FLAGS \
+	~(GIT_SUBMODULE_STATUS__IN_FLAGS | GIT_SUBMODULE_STATUS__INDEX_FLAGS)
+
+#define GIT_SUBMODULE_STATUS_IS_UNMODIFIED(S) \
+	(((S) & ~GIT_SUBMODULE_STATUS__IN_FLAGS) == 0)
+
+#define GIT_SUBMODULE_STATUS_IS_INDEX_UNMODIFIED(S) \
+	(((S) & GIT_SUBMODULE_STATUS__INDEX_FLAGS) == 0)
+
+#define GIT_SUBMODULE_STATUS_IS_WD_UNMODIFIED(S) \
+	(((S) & GIT_SUBMODULE_STATUS__WD_FLAGS) == 0)
 
 #define GIT_SUBMODULE_STATUS_IS_WD_DIRTY(S) \
 	(((S) & (GIT_SUBMODULE_STATUS_WD_INDEX_MODIFIED | \