Re: [PATCH] attr: do not mark queried macros as unset

[Jeff King <peff@peff.net>]

On Fri, Jan 18, 2019 at 02:19:55PM -0800, Stefan Beller wrote:

> > I dunno. This is why I submitted the initial patch as the simplest fix. ;)
> >
> 
> The first patch is
> Reviewed-by: Stefan Beller <sbeller@google.com>

Thanks!

> Diffing across both patches, this seems to be the relevant part:
> [...]
> 
> ---8<---
> @@ -1111,14 +1116,13 @@ static void collect_some_attrs(const struct
> index_state *istate,
> 
>         prepare_attr_stack(istate, path, dirlen, &check->stack);
>         all_attrs_init(&g_attr_hashmap, check);
> -       determine_macros(check->all_attrs, check->stack);
> 
>         if (check->nr) {
>                 rem = 0;
>                 for (i = 0; i < check->nr; i++) {
>                         int n = check->items[i].attr->attr_nr;
>                         struct all_attrs_item *item = &check->all_attrs[n];
> -                       if (item->macro) {
> +                       if (!item->attr->in_stack) {
>                                 item->value = ATTR__UNSET;
>                                 rem++;
>                         }
> @@ -1127,6 +1131,8 @@ static void collect_some_attrs(const struct
> index_state *istate,
>                         return;
>         }
> 
> +       determine_macros(check->all_attrs, check->stack);
> +
>         rem = check->all_attrs_nr;
>         fill(path, pathlen, basename_offset, check->stack,
> check->all_attrs, rem);
>  }
> ---8<---
> 
> which I think is correct.

Yes, that's the interesting part. I think I've convinced myself, too,
that it doesn't do the _wrong_ thing ever. But I think it misses the
point of the original, which is that you want common ones like "diff"
not to trigger in_stack if nobody has actually used them. And doing that
really does mean marking in_stack not just when a macro mentions it
(because clearly "binary" is going to mention it for every repo), but
waiting to see if anybody mentions that macro.

Which means we must call determine_macros(), and then propagate the
macro's in_stack to its expansion (if it's indeed called at all).

I don't think that would be _too_ hard to do. But I also wonder if
there's much point. We are trying to avoid fill(), but I think that
determine_macros() is of roughly the same complexity (look at all
matches of all stacks). I guess it does avoid path_matches(), which is a
bit more expensive. And in theory it could be cached for a particular
stack top, so the work is amortized across many path lookups (though I
think that gets even more tricky).

-Peff