submodule: support reading .gitmodules when it's not in the working tree

diff --git a/submodule.c b/submodule.c
index 2e97032f864a20174657f477045d9855c9afe44d..2b7082b2dbba735d81998dd4a31b1dbe9ab6b14f 100644 (file)
--- a/submodule.c
+++ b/submodule.c
@@ -50,6 +50,24 @@ int is_gitmodules_unmerged(const struct index_state *istate)
        return 0;
 }
 
+/*
+ * Check if the .gitmodules file is safe to write.
+ *
+ * Writing to the .gitmodules file requires that the file exists in the
+ * working tree or, if it doesn't, that a brand new .gitmodules file is going
+ * to be created (i.e. it's neither in the index nor in the current branch).
+ *
+ * It is not safe to write to .gitmodules if it's not in the working tree but
+ * it is in the index or in the current branch, because writing new values
+ * (and staging them) would blindly overwrite ALL the old content.
+ */
+int is_writing_gitmodules_ok(void)
+{
+       struct object_id oid;
+       return file_exists(GITMODULES_FILE) ||
+               (get_oid(GITMODULES_INDEX, &oid) < 0 && get_oid(GITMODULES_HEAD, &oid) < 0);
+}
+
 /*
  * Check if the .gitmodules file has unstaged modifications.  This must be
  * checked before allowing modifications to the .gitmodules file with the