c3302dd8171c47ba89523123cbb7a0de0588971f
   1#!/usr/bin/perl
   2
   3use warnings FATAL => 'all';
   4use strict;
   5
   6# Highlight by reversing foreground and background. You could do
   7# other things like bold or underline if you prefer.
   8my $HIGHLIGHT   = "\x1b[7m";
   9my $UNHIGHLIGHT = "\x1b[27m";
  10my $COLOR = qr/\x1b\[[0-9;]*m/;
  11
  12my @window;
  13
  14while (<>) {
  15        # We highlight only single-line changes, so we need
  16        # a 4-line window to make a decision on whether
  17        # to highlight.
  18        push @window, $_;
  19        next if @window < 4;
  20        if ($window[0] =~ /^$COLOR*(\@| )/ &&
  21            $window[1] =~ /^$COLOR*-/ &&
  22            $window[2] =~ /^$COLOR*\+/ &&
  23            $window[3] !~ /^$COLOR*\+/) {
  24                print shift @window;
  25                show_pair(shift @window, shift @window);
  26        }
  27        else {
  28                print shift @window;
  29        }
  30
  31        # Most of the time there is enough output to keep things streaming,
  32        # but for something like "git log -Sfoo", you can get one early
  33        # commit and then many seconds of nothing. We want to show
  34        # that one commit as soon as possible.
  35        #
  36        # Since we can receive arbitrary input, there's no optimal
  37        # place to flush. Flushing on a blank line is a heuristic that
  38        # happens to match git-log output.
  39        if (!length) {
  40                local $| = 1;
  41        }
  42}
  43
  44# Special case a single-line hunk at the end of file.
  45if (@window == 3 &&
  46    $window[0] =~ /^$COLOR*(\@| )/ &&
  47    $window[1] =~ /^$COLOR*-/ &&
  48    $window[2] =~ /^$COLOR*\+/) {
  49        print shift @window;
  50        show_pair(shift @window, shift @window);
  51}
  52
  53# And then flush any remaining lines.
  54while (@window) {
  55        print shift @window;
  56}
  57
  58exit 0;
  59
  60sub show_pair {
  61        my @a = split_line(shift);
  62        my @b = split_line(shift);
  63
  64        # Find common prefix, taking care to skip any ansi
  65        # color codes.
  66        my $seen_plusminus;
  67        my ($pa, $pb) = (0, 0);
  68        while ($pa < @a && $pb < @b) {
  69                if ($a[$pa] =~ /$COLOR/) {
  70                        $pa++;
  71                }
  72                elsif ($b[$pb] =~ /$COLOR/) {
  73                        $pb++;
  74                }
  75                elsif ($a[$pa] eq $b[$pb]) {
  76                        $pa++;
  77                        $pb++;
  78                }
  79                elsif (!$seen_plusminus && $a[$pa] eq '-' && $b[$pb] eq '+') {
  80                        $seen_plusminus = 1;
  81                        $pa++;
  82                        $pb++;
  83                }
  84                else {
  85                        last;
  86                }
  87        }
  88
  89        # Find common suffix, ignoring colors.
  90        my ($sa, $sb) = ($#a, $#b);
  91        while ($sa >= $pa && $sb >= $pb) {
  92                if ($a[$sa] =~ /$COLOR/) {
  93                        $sa--;
  94                }
  95                elsif ($b[$sb] =~ /$COLOR/) {
  96                        $sb--;
  97                }
  98                elsif ($a[$sa] eq $b[$sb]) {
  99                        $sa--;
 100                        $sb--;
 101                }
 102                else {
 103                        last;
 104                }
 105        }
 106
 107        print highlight(\@a, $pa, $sa);
 108        print highlight(\@b, $pb, $sb);
 109}
 110
 111sub split_line {
 112        local $_ = shift;
 113        return map { /$COLOR/ ? $_ : (split //) }
 114               split /($COLOR*)/;
 115}
 116
 117sub highlight {
 118        my ($line, $prefix, $suffix) = @_;
 119
 120        return join('',
 121                @{$line}[0..($prefix-1)],
 122                $HIGHLIGHT,
 123                @{$line}[$prefix..$suffix],
 124                $UNHIGHLIGHT,
 125                @{$line}[($suffix+1)..$#$line]
 126        );
 127}