Re: [PATCH 7/7] diff.c: add --color-moved-ignore-space-delta option

[Stefan Beller <sbeller@google.com>]

On Mon, Apr 2, 2018 at 5:41 PM, Jonathan Tan <jonathantanmy@google.com> wrote:
> On Mon,  2 Apr 2018 15:48:54 -0700
> Stefan Beller <sbeller@google.com> wrote:
>
>> +struct ws_delta {
>> +     int deltachars;
>> +     char firstchar;
>> +};
>
> I'll just make some overall design comments.
>
> Shouldn't this be a string of characters (or a char* and len) and
> whether it was added or removed? If you're only checking the first
> character, this would not work if the other characters were different.

I considered diving into this, but it seemed to be too complicated for
>95 % of the use cases, which can be approximated in change of the
first character.

Because if we take a string of characters, we'd also need to take care of
tricky conversions (e.g. Are 8 white spaces equal to a tab, and if so do
we break blocks if one line converts 8 ws to a tab?)

So I would definitely pursue the string instead of change of first
character, but what are all the heuristics to put in?

Just to be clear: The string would contain only the change in
white space up front, or would we also somehow store white space
in other parts?

- # This is a sample comment
- # across multiple lines
- # maybe even a license header
+ #     This is a sample comment
+ #     across multiple lines
+ #     maybe even a license header

How about this?


>
>> @@ -717,10 +752,20 @@ static int moved_entry_cmp(const void *hashmap_cmp_fn_data,
>>       const struct diff_options *diffopt = hashmap_cmp_fn_data;
>>       const struct moved_entry *a = entry;
>>       const struct moved_entry *b = entry_or_key;
>> +     unsigned flags = diffopt->color_moved & XDF_WHITESPACE_FLAGS;
>> +
>> +     if (diffopt->color_moved & COLOR_MOVED_DELTA_WHITESPACES)
>> +             /*
>> +              * As there is not specific white space config given,
>> +              * we'd need to check for a new block, so ignore all
>> +              * white space. The setup of the white space
>> +              * configuration for the next block is done else where
>> +              */
>> +             flags |= XDF_IGNORE_WHITESPACE;
>>
>>       return !xdiff_compare_lines(a->es->line, a->es->len,
>>                                   b->es->line, b->es->len,
>> -                                 diffopt->color_moved & XDF_WHITESPACE_FLAGS);
>> +                                 flags);
>>  }
>
> I think we should just prohibit combining this with any of the
> whitespace ignoring flags except for the space-at-eol one. They seem to
> contradict anyway.

ok, we can narrow this one down to ignore all white space.

>
>> +test_expect_success 'compare whitespace delta across moved blocks' '
>> +
>> +     git reset --hard &&
>> +     q_to_tab <<-\EOF >text.txt &&
>> +     QIndented
>> +     QText
>> +     Qacross
>> +     Qfive
>> +     Qlines
>> +     QBut!
>> +     Qthis
>> +     QQone
>> +     Qline
>> +     QQdid
>> +     Qnot
>> +     QQadjust
>> +     EOF
>
> Do we need 5 lines? I thought 2 would suffice. (It's the ALNUM_COUNT
> that matters, as far as I know.) This makes it hard to see that the
> "But!" line is the one that counts.

I did not want to go with the bare minimum as then adjusting the minimum
would be a pain as these unrelated (to the minimum) test cases would
break.

>
>> +test_expect_success 'compare whitespace delta across moved blocks with multiple indentation levels' '

>> +     EOF
>
> If the objective it just to show that the functions f and g are treated
> as one unit despite their lines being of multiple indentation levels,
> the test file could be much shorter.

yeah, I noticed that we already test that in the test above where we
have that test after the "But!", where lines ziggy-zag. Will drop this test.