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Re: [PATCH 6/8] gitweb: Highlight interesting parts of diff

From
Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Date
Feb 13, 2012, 21:09 UTC
Message-ID
<20120213220917.4cf14eb1@gmail.com>
In-Reply-To
<201202131944.50886.jnareb@gmail.com>
Jakub Narebski <jnareb@gmail.com> wrote:
Show 11 quoted lines
> On Mon, 13 Feb 2012, Michal Kiedrowicz wrote:
> > Jakub Narebski <jnareb@gmail.com> wrote:
> > > Michał Kiedrowicz <michal.kiedrowicz@gmail.com> writes:
> > I haven't found *examples* on GitHub and Trac sites, but what about
> > these ones:
> > 
> > https://github.com/gitster/git/commit/8cad4744ee37ebec1d9491a1381ec1771a1ba795
> > http://trac.edgewall.org/changeset/10973
> 
> Thanks.  That is what I meant by "good examples".  Perhaps they should
> be put in the commit message?
OK
Show 5 quoted lines
> 
> BTW GitHub is closed source, but we can check what algorithm does Trac
> use for diff refinement highlighting (highlighting changed portions of
> diff).
>

I think it's http://trac.edgewall.org/browser/trunk/trac/versioncontrol/diff.py (see markup intraline_changes()).

Show 11 quoted lines
> > > It doesn't implement LCS / diff
> > > algorithm like e.g. tkdiff does for its diff refinement highlighting,
> > > isn't it?
> > 
> > I doesn't. I share the Jeff's opinion that:
> > a) Jeff's approach is "good enough"
> > b) LCS on bytes could be very confusing if it marked few sets of
> > characters.
> 
> I wonder if we can use --diff-words for diff refinement highlighting,
> i.e. LCS on words.

I think we can try it, but I worry about performance of running `git diff` on every diff chunk.

Show 7 quoted lines
> 
> Anyway Jeff's approach is a bit limited, in that it would work only for
> change that does not involve adding newlines, for example splitting
> overly long line when changing something.
> 
> See for example line 1786 (in pre-image) in http://trac.edgewall.org/changeset/10973
>

Yes, I'm aware of that. I was thinking about improving it later ("Let's start with a simple refinment highlightning and maybe later add more sophisticated algorithms").

Show 6 quoted lines
> > > By completly different you mean that they do not have common prefix or
> > > common suffix (at least one of them), isn't it?
> 
> BTW. is it "at least one of prefix or suffix are non-empty" or "both prefix
> and suffix are non-empty"?
> 
At least one. See:
	-a = 42;
	+b = 42;
Here prefix is empty but suffix is not.
Show 6 quoted lines
> > I would also consider ignoring prefixes/suffixes with punctuation, like:
> > 
> > 	- * I like you.
> > 	+ * Alice had a little lamb.
> 
> But this patch doesn't implement this feature yet, isn't it?
No, but is a matter of adding
	-$prefix_is_space = 0 if ($r[$prefix] !~ /\s/);
	+$prefix_is_space = 0 if ($r[$prefix] !~ /\s|[[:punct:]]/);
(and the same for suffix)
> Well, here is another idea: do not highlight if sum of prefix and suffix
> lengths are less than some threshold, e.g. 2 characters not including 
> whitespace, or some percentage with respect to total line length.
> 
That might be a good idea.
Show 12 quoted lines
> > > Eeeeeek!  First you split into letters, in caller at that, then join?
> > > Why not pass striung ($str suggests string not array of characters),
> > > and use substr instead?
> > > 
> > > [Please disregard this and the next paragraph at first reading]
> > 
> > I will rename $str to something more self describing.
> 
> Please do.
> 
> BTW. don't you assume here that both common prefix and common suffix
> are non-empty?
Yes. The caller makes sure they are correct (at least
Show 7 quoted lines
> > > > +sub format_rem_add_line {
> > > > +	my ($rem, $add) = @_;
> > > > +	my @r = split(//, $rem);
> > > > +	my @a = split(//, $add);
> 
> BTW the name of variable can be just @add and @rem.
>

I know they are different scopes but I don't like it. It makes the code more confusing IMO. But I won't insist.

Show 10 quoted lines
> > > Shouldn't
> > > $prefix / $prefix_len start from 0, not from 1?
> > 
> > It starts from 1 because it skips first +/-. It should become obvious
> > after reading the comment from last patch :).
> > 
> > +	# In combined diff we must ignore two +/- characters.
> > +	$prefix = 2 if ($is_combined);
> 
> Anyway comment about that fact would be nice.
Will do.
Show 33 quoted lines
>  
> > > > +	my ($prefix_is_space, $suffix_is_space) = (1, 1);
> > > > +
> > > > +	while ($prefix < @r && $prefix < @a) {
> > > > +		last if ($r[$prefix] ne $a[$prefix]);
> > > > +
> > > > +		$prefix_is_space = 0 if ($r[$prefix] !~ /\s/);
> > > > +		$prefix++;
> > > > +	}
> > > 
> > > Ah, I see that it is easier to find common prefix by treating string
> > > as array of characters.
> > > 
> > > Though I wonder if it wouldn't be easier to use trick of XOR-ing two
> > > strings (see "Bitwise String Operators" in perlop(1)):
> > > 
> > >         my $xor = "$rem" ^ "$add";
> > > 
> > > and finding starting sequence of "\0", which denote common prefix.
> > > 
> > > 
> > > Though this and the following is a nice implementation of
> > > algorithm... as it would be implemented in C.  Nevermind, it might be
> > > good enough...
> > 
> > The splitting and comparing by characters is taken from diff-highlight.
> > I don't think it's worth changing here.
> 
> You are right.
> 
> I'll try to come with hacky algorithm using string bitwise xor and regexp,
> and benchmark it comparing to your C-like solution, but it can be left for
> later (simple is better than clever, usually).
If you have time :).
Show 18 quoted lines
> > > >  # HTML-format diff context, removed and added lines.
> > > >  sub format_ctx_rem_add_lines {
> > > > -	my ($ctx, $rem, $add) = @_;
> > > > +	my ($ctx, $rem, $add, $is_combined) = @_;
> > > >  	my (@new_ctx, @new_rem, @new_add);
> > > > +	my $num_add_lines = @$add;
> > > 
> > > Why is this temporary variable needed?  If you are not sure that ==
> > > operator enforces scalar context on both arguments you can always
> > > write
> > > 
> > >   scalar @$add == scalar @$rem
> > 
> > You read my mind.
> 
> BTW. the same comment applies to patch adding support for highlighting
> changed part in combined diff.
>
OK
Previous: Jakub NarebskiNext: Jakub Narebski
Message 54 of 67 in “gitweb: Highlight interesting parts of diff”
  1. 0/8 gitweb: Highlight interesting parts of diffMichał Kiedrowicz, Feb 10, 2012
  2. 1/8 gitweb: Extract print_sidebyside_diff_lines()Michał Kiedrowicz, Feb 10, 2012
  3. Jakub NarebskiFeb 11, 2012
  4. Michał KiedrowiczFeb 11, 2012
  5. 2/8 gitweb: Use print_diff_chunk() for both side-by-side and inline diffsMichał Kiedrowicz, Feb 10, 2012
  6. Jakub NarebskiFeb 11, 2012
  7. Michał KiedrowiczFeb 11, 2012
  8. Michał KiedrowiczFeb 25, 2012
  9. 3/8 gitweb: Move HTML-formatting diff line back to process_diff_line()Michał Kiedrowicz, Feb 10, 2012
  10. Jakub NarebskiFeb 11, 2012
  11. 4/8 gitweb: Push formatting diff lines to print_diff_chunk()Michał Kiedrowicz, Feb 10, 2012
  12. Jakub NarebskiFeb 11, 2012
  13. Michał KiedrowiczFeb 11, 2012
  14. Michał KiedrowiczFeb 11, 2012
  15. 5/8 gitweb: Format diff lines just before printingMichał Kiedrowicz, Feb 10, 2012
  16. Jakub NarebskiFeb 11, 2012
  17. Michał KiedrowiczFeb 11, 2012
  18. 6/8 gitweb: Highlight interesting parts of diffMichał Kiedrowicz, Feb 10, 2012
  19. Jakub NarebskiFeb 10, 2012
  20. Michał KiedrowiczFeb 10, 2012
  21. Jakub NarebskiFeb 10, 2012
  22. Michał KiedrowiczFeb 10, 2012
  23. Jakub NarebskiFeb 10, 2012
  24. Jeff KingFeb 10, 2012
  25. Michal KiedrowiczFeb 14, 2012
  26. Junio C HamanoFeb 14, 2012
  27. Jeff KingFeb 14, 2012
  28. Jeff KingFeb 10, 2012
  29. Michał KiedrowiczFeb 10, 2012
  30. Jeff KingFeb 10, 2012
  31. Michał KiedrowiczFeb 10, 2012
  32. diff-highlight: Work for multiline changes tooMichał Kiedrowicz, Feb 10, 2012
  33. Jeff KingFeb 13, 2012
  34. 1/5 diff-highlight: make perl strict and warnings fatalJeff King, Feb 13, 2012
  35. 2/5 diff-highlight: don't highlight whole linesJeff King, Feb 13, 2012
  36. Michal KiedrowiczFeb 14, 2012
  37. 3/5 diff-highlight: refactor to prepare for multi-line hunksJeff King, Feb 13, 2012
  38. 4/5 diff-highlight: match multi-line hunksJeff King, Feb 13, 2012
  39. 5/5 diff-highlight: document some non-optimal casesJeff King, Feb 13, 2012
  40. Michal KiedrowiczFeb 14, 2012
  41. Junio C HamanoFeb 14, 2012
  42. Jeff KingFeb 14, 2012
  43. Junio C HamanoFeb 14, 2012
  44. Jeff KingFeb 14, 2012
  45. Michal KiedrowiczFeb 14, 2012
  46. Jakub NarebskiFeb 10, 2012
  47. Jakub NarebskiFeb 11, 2012
  48. Jakub NarebskiFeb 12, 2012
  49. Michal KiedrowiczFeb 13, 2012
  50. Jakub NarebskiFeb 13, 2012
  51. Michał KiedrowiczFeb 13, 2012
  52. Michal KiedrowiczFeb 13, 2012
  53. Jakub NarebskiFeb 13, 2012
  54. Michał KiedrowiczFeb 13, 2012
  55. Jakub NarebskiFeb 14, 2012
  56. Michał KiedrowiczFeb 14, 2012
  57. Jeff KingFeb 14, 2012
  58. Michał KiedrowiczFeb 14, 2012
  59. Jeff KingFeb 14, 2012
  60. 7/8 gitweb: Use different colors to present marked changesMichał Kiedrowicz, Feb 10, 2012
  61. Jakub NarebskiFeb 12, 2012
  62. Michal KiedrowiczFeb 13, 2012
  63. 8/8 gitweb: Highlight combined diffsMichał Kiedrowicz, Feb 10, 2012
  64. Jakub NarebskiFeb 12, 2012
  65. Michal KiedrowiczFeb 13, 2012
  66. Jakub NarebskiFeb 11, 2012
  67. Michał KiedrowiczFeb 11, 2012

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