Re: [PATCH 3/2] dir.c: fix dir re-inclusion rules with "NODIR" and "MUSTBEDIR"

On Sat, Mar 19, 2016 at 1:00 AM, Junio C Hamano [off-list ref] wrote:

What is the ultimate goal of nd/exclusion-regression-fix topic over
the behaviour before 2.7.0 and after 2.7.1 (there was a regression
in 2.7.0 that was reverted in 2.7.1)?  From the cover letter of the
series:

    Take one was bad and reverted in commit 8c72236. Take two provides a
    more complete solution to the pair of rules

      exclude/this
      !exclude/this/except/this

    3/4 should do a better job at stopping regressions in take 1. 4/4
    provides the solution. I think I have tested (and wrote tests) for all
    the cases I can imagine.

"solution to the pair of rules" hints there are some problem in the
pair of rules, without stating what it is trying to solve.

Isn't the root cause of the issue that treat_one_path() when
deciding if it is worth descending into a directory check if the
directory itself is excluded and returns path_excluded, even if some
paths inside it may have a countermanding ! entries that would match
them?  What if we change that part smarter and allow it to descend?

That's the easy part, detecting a pair and continue descending. The
problem is after you descend, exclude engine may return contradicting
results on old patterns. It's the same thing that 3/2 describes (after
you change patterns from "!dir\ndir/file2" to "dir\n!dir/file2").
-- 
Duy