diff options
Diffstat (limited to 'contrib/diff-highlight')
| -rw-r--r-- | contrib/diff-highlight/README | 109 | ||||
| -rwxr-xr-x | contrib/diff-highlight/diff-highlight | 109 |
2 files changed, 181 insertions, 37 deletions
diff --git a/contrib/diff-highlight/README b/contrib/diff-highlight/README index 1b7b6df8eb..502e03b305 100644 --- a/contrib/diff-highlight/README +++ b/contrib/diff-highlight/README @@ -14,13 +14,15 @@ Instead, this script post-processes the line-oriented diff, finds pairs of lines, and highlights the differing segments. It's currently very simple and stupid about doing these tasks. In particular: - 1. It will only highlight a pair of lines if they are the only two - lines in a hunk. It could instead try to match up "before" and - "after" lines for a given hunk into pairs of similar lines. - However, this may end up visually distracting, as the paired - lines would have other highlighted lines in between them. And in - practice, the lines which most need attention called to their - small, hard-to-see changes are touching only a single line. + 1. It will only highlight hunks in which the number of removed and + added lines is the same, and it will pair lines within the hunk by + position (so the first removed line is compared to the first added + line, and so forth). This is simple and tends to work well in + practice. More complex changes don't highlight well, so we tend to + exclude them due to the "same number of removed and added lines" + restriction. Or even if we do try to highlight them, they end up + not highlighting because of our "don't highlight if the whole line + would be highlighted" rule. 2. It will find the common prefix and suffix of two lines, and consider everything in the middle to be "different". It could @@ -55,3 +57,96 @@ following in your git configuration: show = diff-highlight | less diff = diff-highlight | less --------------------------------------------- + +Bugs +---- + +Because diff-highlight relies on heuristics to guess which parts of +changes are important, there are some cases where the highlighting is +more distracting than useful. Fortunately, these cases are rare in +practice, and when they do occur, the worst case is simply a little +extra highlighting. This section documents some cases known to be +sub-optimal, in case somebody feels like working on improving the +heuristics. + +1. Two changes on the same line get highlighted in a blob. For example, + highlighting: + +---------------------------------------------- +-foo(buf, size); ++foo(obj->buf, obj->size); +---------------------------------------------- + + yields (where the inside of "+{}" would be highlighted): + +---------------------------------------------- +-foo(buf, size); ++foo(+{obj->buf, obj->}size); +---------------------------------------------- + + whereas a more semantically meaningful output would be: + +---------------------------------------------- +-foo(buf, size); ++foo(+{obj->}buf, +{obj->}size); +---------------------------------------------- + + Note that doing this right would probably involve a set of + content-specific boundary patterns, similar to word-diff. Otherwise + you get junk like: + +----------------------------------------------------- +-this line has some -{i}nt-{ere}sti-{ng} text on it ++this line has some +{fa}nt+{a}sti+{c} text on it +----------------------------------------------------- + + which is less readable than the current output. + +2. The multi-line matching assumes that lines in the pre- and post-image + match by position. This is often the case, but can be fooled when a + line is removed from the top and a new one added at the bottom (or + vice versa). Unless the lines in the middle are also changed, diffs + will show this as two hunks, and it will not get highlighted at all + (which is good). But if the lines in the middle are changed, the + highlighting can be misleading. Here's a pathological case: + +----------------------------------------------------- +-one +-two +-three +-four ++two 2 ++three 3 ++four 4 ++five 5 +----------------------------------------------------- + + which gets highlighted as: + +----------------------------------------------------- +-one +-t-{wo} +-three +-f-{our} ++two 2 ++t+{hree 3} ++four 4 ++f+{ive 5} +----------------------------------------------------- + + because it matches "two" to "three 3", and so forth. It would be + nicer as: + +----------------------------------------------------- +-one +-two +-three +-four ++two +{2} ++three +{3} ++four +{4} ++five 5 +----------------------------------------------------- + + which would probably involve pre-matching the lines into pairs + according to some heuristic. diff --git a/contrib/diff-highlight/diff-highlight b/contrib/diff-highlight/diff-highlight index d8938982e4..c4404d49c9 100755 --- a/contrib/diff-highlight/diff-highlight +++ b/contrib/diff-highlight/diff-highlight @@ -1,28 +1,37 @@ #!/usr/bin/perl +use warnings FATAL => 'all'; +use strict; + # Highlight by reversing foreground and background. You could do # other things like bold or underline if you prefer. my $HIGHLIGHT = "\x1b[7m"; my $UNHIGHLIGHT = "\x1b[27m"; my $COLOR = qr/\x1b\[[0-9;]*m/; +my $BORING = qr/$COLOR|\s/; -my @window; +my @removed; +my @added; +my $in_hunk; while (<>) { - # We highlight only single-line changes, so we need - # a 4-line window to make a decision on whether - # to highlight. - push @window, $_; - next if @window < 4; - if ($window[0] =~ /^$COLOR*(\@| )/ && - $window[1] =~ /^$COLOR*-/ && - $window[2] =~ /^$COLOR*\+/ && - $window[3] !~ /^$COLOR*\+/) { - print shift @window; - show_pair(shift @window, shift @window); + if (!$in_hunk) { + print; + $in_hunk = /^$COLOR*\@/; + } + elsif (/^$COLOR*-/) { + push @removed, $_; + } + elsif (/^$COLOR*\+/) { + push @added, $_; } else { - print shift @window; + show_hunk(\@removed, \@added); + @removed = (); + @added = (); + + print; + $in_hunk = /^$COLOR*[\@ ]/; } # Most of the time there is enough output to keep things streaming, @@ -38,23 +47,40 @@ while (<>) { } } -# Special case a single-line hunk at the end of file. -if (@window == 3 && - $window[0] =~ /^$COLOR*(\@| )/ && - $window[1] =~ /^$COLOR*-/ && - $window[2] =~ /^$COLOR*\+/) { - print shift @window; - show_pair(shift @window, shift @window); -} - -# And then flush any remaining lines. -while (@window) { - print shift @window; -} +# Flush any queued hunk (this can happen when there is no trailing context in +# the final diff of the input). +show_hunk(\@removed, \@added); exit 0; -sub show_pair { +sub show_hunk { + my ($a, $b) = @_; + + # If one side is empty, then there is nothing to compare or highlight. + if (!@$a || !@$b) { + print @$a, @$b; + return; + } + + # If we have mismatched numbers of lines on each side, we could try to + # be clever and match up similar lines. But for now we are simple and + # stupid, and only handle multi-line hunks that remove and add the same + # number of lines. + if (@$a != @$b) { + print @$a, @$b; + return; + } + + my @queue; + for (my $i = 0; $i < @$a; $i++) { + my ($rm, $add) = highlight_pair($a->[$i], $b->[$i]); + print $rm; + push @queue, $add; + } + print @queue; +} + +sub highlight_pair { my @a = split_line(shift); my @b = split_line(shift); @@ -101,8 +127,14 @@ sub show_pair { } } - print highlight(\@a, $pa, $sa); - print highlight(\@b, $pb, $sb); + if (is_pair_interesting(\@a, $pa, $sa, \@b, $pb, $sb)) { + return highlight_line(\@a, $pa, $sa), + highlight_line(\@b, $pb, $sb); + } + else { + return join('', @a), + join('', @b); + } } sub split_line { @@ -111,7 +143,7 @@ sub split_line { split /($COLOR*)/; } -sub highlight { +sub highlight_line { my ($line, $prefix, $suffix) = @_; return join('', @@ -122,3 +154,20 @@ sub highlight { @{$line}[($suffix+1)..$#$line] ); } + +# Pairs are interesting to highlight only if we are going to end up +# highlighting a subset (i.e., not the whole line). Otherwise, the highlighting +# is just useless noise. We can detect this by finding either a matching prefix +# or suffix (disregarding boring bits like whitespace and colorization). +sub is_pair_interesting { + my ($a, $pa, $sa, $b, $pb, $sb) = @_; + my $prefix_a = join('', @$a[0..($pa-1)]); + my $prefix_b = join('', @$b[0..($pb-1)]); + my $suffix_a = join('', @$a[($sa+1)..$#$a]); + my $suffix_b = join('', @$b[($sb+1)..$#$b]); + + return $prefix_a !~ /^$COLOR*-$BORING*$/ || + $prefix_b !~ /^$COLOR*\+$BORING*$/ || + $suffix_a !~ /^$BORING*$/ || + $suffix_b !~ /^$BORING*$/; +} |