text: // sample code from commit.c of the Git repository (https://github.com/git)
  
  struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name)
  {
  	struct commit *c = lookup_commit_reference(sha1);
  	if (!c)
  		die(_("could not parse %s"), ref_name);
  	if (hashcmp(sha1, c->object.sha1)) {
  		warning(_("%s %s is not a commit!"),
  			ref_name, sha1_to_hex(sha1));
  	}
  	return c;
  }
  