Re: [PATCH] [RFC][GSoC][PATCH] attr: use local repository state in read_attr

[Junio C Hamano <gitster@pobox.com>]

Tian Yuchen <a3205153416@gmail.com> writes:

> Junio C Hamano <gitster@pobox.com> writes:
>
>  >The codepath read_attr() is in is usually not that hot but it is not
>  >cheap.
>
> I'm a bit curious—under what circumstances would calling this method 
> result in significant performance regression?

Significant?  I dunno.

And quite honestly, I do not care about significance very much in a
case like this.  Doing things that do not make sense, like checking
the same configuration variable again and again when you _know_ that
you never switched to a different repository since you last checked,
is simply wrong.  It burdens the readers with unnecessary cognitive
load by making them wonder why you do such a nonsensical thing.

The read_attr() is called during an attr stack construction, which
traverses the directory hierarchy of a single repositry's working
tree (we do not traverse across submodule boundaries), and the same
istate (i.e., index contents) structure is passed around throughout
the callchain.  The repository instance at istate->repo may be a
good place to store "am I bare?" bit that is computed just once and
reused whenever we need to know, like in the funcion under
discussion.