cat-file: handle content request for --batch-command without type

The batch mode of cat-file needs to know the object's type in order to print the contents (because it decides whether to stream or not based on object type). The default batch output contains %(objecttype), so we get the type info automatically. But when it doesn't, we have to ask for it explicitly. In the --batch code path, we check while setting up the object_info struct whether we will print the contents, and if so set "typep" to get the value. This comes from 6554dfa97a (cat-file: handle --batch format with missing type/size, 2013-12-12). But later we added a --batch-command mode, which does not do the same trick. The decision about whether to retrieve the contents is made per-command (a "contents" vs "info" command), so we can't decide when building the object_info originally. As a result, asking for: echo "contents HEAD" | git cat-file --batch-command="%(objectname)" will fail the assertion in print_object_or_die() that the type was actually filled in. We can fix it by tweaking the object_info on the fly as we receive each command. But we should be careful to restore it afterwards; otherwise a sequence of commands like: contents $one info $two info $three will pay the type-lookup price for $two and $three when it does not need to. This wouldn't be incorrect, but just slightly inefficient (and hence there are no tests for that part, because the externally-visible behavior is the same). Reported-by: Alan Stokes <alan@source.dev> Helped-by: Pablo Sabater <pabloosabaterr@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>