[PATCH] Improve contrib/diff-highlight to highlight unevenly-sized hunks

From: Patrick Palka <patrick@parcs.ath.cx>
Date: Jun 15, 2015, 17:20 UTC
Message-ID: <1434388853-23915-1-git-send-email-patrick@parcs.ath.cx>

Currently the diff-highlight script does not try to highlight hunks that have different numbers of removed/added lines. But we can be a little smarter than that, without introducing much magic and complexity.

In the case of unevenly-sized hunks, we could still highlight the first few (lexicographical) add/remove pairs. It is not uncommon for hunks to have common "prefixes", and in such a case this change is very useful for spotting differences.

Signed-off-by: Patrick Palka <patrick@parcs.ath.cx>
---
 contrib/diff-highlight/diff-highlight | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/contrib/diff-highlight/diff-highlight b/contrib/diff-highlight/diff-highlight
index ffefc31..0dfbebd 100755
--- a/contrib/diff-highlight/diff-highlight
+++ b/contrib/diff-highlight/diff-highlight
@@ -88,22 +88,30 @@ sub show_hunk {
 		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;
-	}
+	# We match up the first MIN(a, b) lines on each side.
+	my $c = @$a < @$b ? @$a : @$b;
 
+	# Highlight each pair, and print each removed line of that pair.
 	my @queue;
-	for (my $i = 0; $i < @$a; $i++) {
+	for (my $i = 0; $i < $c; $i++) {
 		my ($rm, $add) = highlight_pair($a->[$i], $b->[$i]);
 		print $rm;
 		push @queue, $add;
 	}
+
+	# Print the remaining unmatched removed lines of the hunk.
+	for (my $i = $c; $i < @$a; $i++) {
+		print $a->[$i];
+	}
+
+	# Print the added lines of each highlighted pair.
 	print @queue;
+
+	# Print the remaining unmatched added lines of the hunk.
+	for (my $i = $c; $i < @$b; $i++) {
+		print $b->[$i];
+	}
+
 }
 
 sub highlight_pair {

-- 
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