Re: [PATCH 1/2] [GSOC] cat-file: fix --batch report changed-type bug

From: ZheNing Hu <adlternative@gmail.com>
To: Jeff King <peff@peff.net>
Cc: ZheNing Hu via GitGitGadget <gitgitgadget@gmail.com>,
	Git List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>,
	Christian Couder <christian.couder@gmail.com>,
	Hariom Verma <hariom18599@gmail.com>,
	Felipe Contreras <felipe.contreras@gmail.com>
Subject: Re: [PATCH 1/2] [GSOC] cat-file: fix --batch report changed-type bug
Date: Thu, 3 Jun 2021 15:18:43 +0800	[thread overview]
Message-ID: <CAOLTT8QMpMV=7A4ZP2k5YUrqjznBwh_uDv+qvC7Meq3pwvZt1g@mail.gmail.com> (raw)
In-Reply-To: <YLfjexczp1/HILWj@coredump.intra.peff.net>

Jeff King <peff@peff.net> 于2021年6月3日周四 上午4:01写道：
>
>   This assumption was broken by 845de33a5b (cat-file: avoid noop calls
>   to sha1_object_info_extended, 2016-05-18). That commit skips the call
>   to oid_object_info_extended() entirely when --batch-all-objects is in
>   use, and the custom format does not include any placeholders that
>   require calling it.
>

Or when the custom format only include placeholders like %(objectname) or
%(rest), oid_object_info_extended() will not get the type of the object.

>   This results in an error when we try to confirm that the type didn't
>   change:
>
>     $ git cat-file --batch=batman --batch-all-objects
>     batman
>     fatal: object 000023961a0c02d6e21dc51ea3484ff71abf1c74 changed type!?
>
>   and also has other subtle effects (e.g., we'd fail to stream a blob,
>   since we don't realize it's a blog in the first place).
>
>   We can fix this by flipping the order of the setup. The check for "do
>   we need to get the object info" must come _after_ we've decided
>   whether we need to look up the type.
>
> -Peff

--
ZheNing Hu