Re: [PATCH 00/12] Remove more index compatibility macros

[Eric Sunshine <sunshine@sunshineco.com>]

On Fri, Jan 1, 2021 at 8:09 AM Derrick Stolee via GitGitGadget
<gitgitgadget@gmail.com> wrote:
> My strategy for update-index was to create static globals "repo" and
> "istate" that point to the_repository and the_index, respectively. Then, I
> was able to remove macros one-by-one without changing method prototypes
> within the file.
>
> I had started trying to keep everything local to the method signatures, but
> I hit a snag when reaching the command-line parsing callbacks, which I could
> not modify their call signature. [...]

You should be able to do this, not by modifying the callback
signature, but by taking advantage of the `extra` member of `struct
option` which is available to callback functions or arbitrary use. If
you need to access the index in a callback, then assign a `struct
index_state *` to `extra`; likewise assign a `struct repository *` to
`extra` to access the repository. If you need access to both the index
and the repository, then just store the repository in `extra` since
the repository has an `index` field.

You won't be able to use any of the canned OPT_FOO() macros to
initialize an entry in the update-index.c `options[]` array which
needs `extra`-initialization since the macros don't let you specify
`extra`, but you can easily bypass the macro and initialize the
`struct option` manually. (After all, the macros exist for
convenience; they are not a hard requirement.)

Within the callback, extract the `repository` or `index_state` as you
would any other field. For instance:

    const struct repository *repo = opt->extra;

This should allow you to get rid of the globals introduced by patch
[4/12] (assuming passing the index and repo arguments around
everywhere doesn't get overly hairy).