Re: [PATCH] diff: add --ignore-blank-lines option

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 17, 2013, 19:52 UTC
Message-ID: <7vd2rkcy6r.fsf@alter.siamese.dyndns.org>
In-Reply-To: <CALWbr2zM=rD3GE9a=Xyrvz0E5mAMsDesJu8-Zs7JH7W4U4AbeA@mail.gmail.com>

Antoine Pelisse <apelisse@gmail.com> writes:

Show 10 quoted lines

>>> +     unsigned long changes = ULONG_MAX;
>
> Let me explain what "changes" means, as I know it will help the rest
> of the message:
> It counts the number of *added* blank lines we have ignored since
> "lxch" (needed to calculate the distance between lxch and xch)
> It also has the meaning of what was called "interesting" before.
> If changes == ULONG_MAX, we are still in interesting zone, otherwise
> it means we have ignored "changes" *added* blank lines (0 being a
> valid value).

OK.  That deserves a comment next to this variable.

> (Actually, After rereading this part, it looks like I could check that
> lxch == xchp rather than setting changes to ULONG_MAX).

Yeah, I think so.

Show 9 quoted lines

>>> +             if (distance < max_ignorable &&
>>> +                 (!xch->ignore || changes == ULONG_MAX)) {
>>> +                     lxch = xch;
>>> +                     changes = ULONG_MAX;
>>
> - If we are still in interesting zone, we take it, even if it's
> ignorable change. Because it's close enough.
> - Otherwise, only take real changes. We are close to another change,
> and we are still in the loop, so it must be interesting.

OK.

Show 10 quoted lines

>>> +             } else if (changes != ULONG_MAX &&
>>> +                        xch->i1 + changes - (lxch->i1 + lxch->chg1) > max_common) {
>>> +                     break;
>
> If we are no longer in "interesting zone" (changes != ULONG_MAX), it
> means we will stop if the distance is too big.
> "changes" is used in the calculation to consider the changes we have
> already ignored (xch->i1 - (lxch->i1 + lxch->chg1) will only work if
> xch and lxch are consecutive, we need to add the blank lines we
> ignored).

And this uses max_common that is much larger than max_ignorable because...?

The last interesting change, with its post context and inter hunk gap, together with precontext for this one, is close enough to the beginning of this one. So it is understandable if xch by itself is intereseting to use max_common. Even an interesting one, if that is so far from the last interesting one, should not be part of this hunk.

However, if the current one is by itself uninteresting, should we
still use the max_common, or should this be compared with
max_ignorable?

Show 21 quoted lines

>> Could you add comment to the "changes" variable and explain what the
>> variable means?
>>
>>> +             } else if (!xch->ignore) {
>>> +                     lxch = xch;
>>> +                     changes = ULONG_MAX;
>>
>> When this change by itself is interesting, it becomes the "last
>> interesting one" and the hunk continues.
>
> Exactly, and changes goes back to "interesting".
>
>>> +             } else {
>>> +                     if (changes == ULONG_MAX)
>>> +                             changes = 0;
>>> +                     changes += xch->chg2;
>>
>> Puzzled beyond guessing.  Also it is curious why here and only here
>> we look at chg2 side of the things, not i1/chg1 in this whole thing.
>
> chg2 being the number of blank line *additions*.

This is on the else side of if (!xch->ignore), so we are looking at ignored hunk, which means there is only blank line change. Can chg2 be 0 while chg1 is not zero, i.e. xch being a blank line removal?

What should happen in that case? Don't we want to show it, for the same reason we want to keep removal, as long as it is close enough to the interesting zone?

> Hope that makes things clearer,

Yes, it helped quite a bit.