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From: Junio C Hamano <>
To: ZheNing Hu <>
Cc: ZheNing Hu via GitGitGadget <>,
	Git List <>,
	Johannes Schindelin <>
Subject: Re: [PATCH] [GSOC] ref-filter: solve bugs caused by enumeration
Date: Thu, 06 May 2021 14:35:56 +0900	[thread overview]
Message-ID: <xmqqk0oczao3.fsf@gitster.g> (raw)
In-Reply-To: <> (ZheNing Hu's message of "Thu, 6 May 2021 13:02:51 +0800")

ZheNing Hu <> writes:

>> Is it that a check refers to one member of a union without making
>> sure that member is the one in effect in the union?  I am most
>> puzzled by the mention of "enumeration" when there does not appear
>> to be any enum involved.
> Sorry, I didn't make it clear. I re-describe the problem first, and then
> modify the commit messages.
> Suppose we are dealing with "%(notes)", the name member of our
> `used_atom` item at this time is "notes", and its member union `u` uses
> a `struct notes_option`, we fill some values in `used_atom.u.notes_option`,
> When we traverse in `used_atom` array in `populate_value()` and previous
> judgement like "if (starts_with(name, "refname"))" will failed, because we
> are dealing with atom "notes", but in judgement "else if
> (atom->u.remote_ref.push)",
> The value we fill in `used_atom.u.notes_option` just makes
> `used_atom.u.remote_ref.push` non-zero. This leads us into the wrong case.
> Is this clearer?

This time you avoided the word enumeration, and it made it clearer.
The word commonly used is "condition" where you said "judgment", I
think, and wit that it would probably be even more clear.

used_atom.u is an union, and it has different members depending on
what atom the auxiliary data the union part of the "struct
used_atom" wants to record.  At most only one of the members can be
valid at any one time.  Since the code checks u.remote_ref without
even making sure if the atom is "push" or "push:" (which are only
two cases that u.remote_ref.push becomes valid), but u.remote_ref
shares the same storage for other members of the union, the check
was reading from an invalid member, which was the bug.

So the fix was to see what atom it is by checking its name member?
Is starts_with() a reliable test?  A fictitious atom "pushe" will be
different from "push" or "push:<something>", but will still pass
that test, so from the point of view of future-proofing the tests,
shouldn't it do the same check as the one at the beginning of


  reply	other threads:[~2021-05-06  5:36 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-05 15:31 [PATCH] [GSOC] ref-filter: solve bugs caused by enumeration ZheNing Hu via GitGitGadget
2021-05-06  1:53 ` Junio C Hamano
2021-05-06  5:02   ` ZheNing Hu
2021-05-06  5:35     ` Junio C Hamano [this message]
2021-05-06 10:39       ` ZheNing Hu
2021-05-06 11:20         ` Junio C Hamano
2021-05-06 11:52           ` ZheNing Hu
2021-05-06 21:20             ` Junio C Hamano
2021-05-07  4:32               ` ZheNing Hu
2021-05-07  4:49                 ` Junio C Hamano
2021-05-07  5:09                   ` ZheNing Hu
2021-05-06 16:31 ` [PATCH v2] [GSOC] ref-filter: fix read invalid union member bug ZheNing Hu via GitGitGadget
2021-05-08 15:26   ` [PATCH v3] " ZheNing Hu via GitGitGadget
2021-05-10  7:21     ` Junio C Hamano
2021-05-10 12:35       ` ZheNing Hu
2021-05-10  7:27     ` Junio C Hamano
2021-05-10 12:51       ` ZheNing Hu
2021-05-10 15:01     ` [PATCH v4] " ZheNing Hu via GitGitGadget
2021-05-11  2:29       ` Junio C Hamano
2021-05-11  6:28         ` ZheNing Hu
2021-05-11  9:30           ` Junio C Hamano
2021-05-11 11:47             ` ZheNing Hu
2021-05-11 13:12               ` Junio C Hamano
2021-05-11 13:31                 ` ZheNing Hu
2021-05-11 15:35       ` [PATCH v5] " ZheNing Hu via GitGitGadget
2021-05-12  1:36         ` Junio C Hamano
2021-05-12 10:37           ` ZheNing Hu
2021-05-12 12:12         ` [PATCH v6] " ZheNing Hu via GitGitGadget
2021-05-12 23:24           ` Junio C Hamano
2021-05-13  9:29             ` ZheNing Hu
2021-05-13 15:13           ` [PATCH v7] " ZheNing Hu via GitGitGadget

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