Re: [PATCH v1 8/9] diff --color-moved-ws: modify allow-indentation-change

[Phillip Wood <phillip.wood@talktalk.net>]

Hi Stefan

On 16/11/2018 21:47, Stefan Beller wrote:
> On Fri, Nov 16, 2018 at 3:04 AM Phillip Wood <phillip.wood@talktalk.net> wrote:
>>
>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>
>> Currently diff --color-moved-ws=allow-indentation-change does not
>> support indentation that contains a mix of tabs and spaces. For
>> example in commit 546f70f377 ("convert.h: drop 'extern' from function
>> declaration", 2018-06-30) the function parameters in the following
>> lines are not colored as moved [1].
>>
>> -extern int stream_filter(struct stream_filter *,
>> -                        const char *input, size_t *isize_p,
>> -                        char *output, size_t *osize_p);
>> +int stream_filter(struct stream_filter *,
>> +                 const char *input, size_t *isize_p,
>> +                 char *output, size_t *osize_p);
>>
>> This commit changes the way the indentation is handled to track the
>> visual size of the indentation rather than the characters in the
>> indentation. This has they benefit that any whitespace errors do not
> 
> s/they/the/

Thanks, well spotted

> 
>> interfer with the move detection (the whitespace errors will still be
>> highlighted according to --ws-error-highlight). During the discussion
>> of this feature there were concerns about the correct detection of
>> indentation for python. However those concerns apply whether or not
>> we're detecting moved lines so no attempt is made to determine if the
>> indentation is 'pythonic'.
>>
>> [1] Note that before the commit to fix the erroneous coloring of moved
>>      lines each line was colored as a different block, since that commit
>>      they are uncolored.
>>
>> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>> ---
>>
>> Notes:
>>      Changes since rfc:
>>       - It now replaces the existing implementation rather than adding a new
>>         mode.
>>       - The indentation deltas are now calculated once for each line and
>>         cached.
>>       - Optimized the whitespace delta comparison to compare string lengths
>>         before comparing the actual strings.
>>       - Modified the calculation of tabs as suggested by Stefan.
>>       - Split out the blank line handling into a separate commit as suggest
>>         by Stefan.
>>       - Fixed some comments pointed out by Stefan.
>>
>>   diff.c                     | 130 +++++++++++++++++++++----------------
>>   t/t4015-diff-whitespace.sh |  56 ++++++++++++++++
>>   2 files changed, 129 insertions(+), 57 deletions(-)
>>
>> diff --git a/diff.c b/diff.c
>> index c378ce3daf..89559293e7 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -750,6 +750,8 @@ struct emitted_diff_symbol {
>>          const char *line;
>>          int len;
>>          int flags;
>> +       int indent_off;
>> +       int indent_width;
> 
> So this is the trick how we compute the ws related
> data only once per line. :-)
> 
> On the other hand, we do not save memory by disabling
> the ws detection, but I guess that is not a problem for now.

I did wonder about that, but decided the increase was small compared to 
all the strings that are copied when creating the emitted_diff_symbols. 
If we want to save memory then we should stop struct 
emitted_diff_symbol() from carrying a copy of all the strings.

> Would it make sense to have the new variables be
> unsigned? (Also a comment on what they are, I
> needed to read the code to understand off to be
> offset into the line, where the content starts, and
> width to be the visual width, as I did not recall
> the RFC.)

Yes a comment would make sense. I don't think I have a strong preference 
for signed/unsigned, I can change it if you want.

Thanks for looking at these so promptly

Best Wishes

Phillip
>> +static void fill_es_indent_data(struct emitted_diff_symbol *es)
>> [...]
> 
>> +               if (o->color_moved_ws_handling &
>> +                   COLOR_MOVED_WS_ALLOW_INDENTATION_CHANGE)
>> +                       fill_es_indent_data(&o->emitted_symbols->buf[n]);
> 
> Nice.
> 
> By reducing the information kept around to ints, we also do not need
> to alloc/free
> memory for each line.
> 
>> +++ b/t/t4015-diff-whitespace.sh
>> @@ -1901,4 +1901,60 @@ test_expect_success 'compare whitespace delta incompatible with other space opti
>>          test_i18ngrep allow-indentation-change err
>>   '
>>
>> +test_expect_success 'compare mixed whitespace delta across moved blocks' '
> 
> Looks good,
> 
> Thanks!
> Stefan
>