Re: [PATCH] [GSOC] ref-filter: solve bugs caused by enumeration

[ZheNing Hu <adlternative@gmail.com>]

Junio C Hamano <gitster@pobox.com> 于2021年5月6日周四 上午9:53写道：
>
> "ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: ZheNing Hu <adlternative@gmail.com>
> >
> > Johannes Schindelin seems to have introduced a bug in
> > cc72385f(for-each-ref: let upstream/push optionally
> > report the remote name), it use `atom->u.remote_ref.option`
> > which is a member of enumeration in the judgment statement.
>
> Sorry but I am not sure if our readers would understand what "a
> member of enumeration in the judgment statement" is (I certainly do
> not), and even more importantly, "bugs caused by enumeration" on the
> title does not hint much about what problem the patch is trying to
> solve.
>
> > When we use other members in the enumeration `used_atom.u`,
> > and it happened to fill in `remote_ref.push`, this judgment
> > may still be established and produces errors. So replace the
> > judgment statement with `starts_with(name, "push")` to fix
> > the error.
>
> And this paragraph does not enlighten all that much, unfortunately.
>
> 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?

Thanks.
--
ZheNing Hu