[PATCH] git-add--interactive: Preserve diff heading when splitting hunks

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Change the display of hunks in hunk splitting mode to preserve the diff
heading, which hasn't been done ever since the hunk splitting was
initially added in v1.4.4.2-270-g835b2ae.

Splitting the first hunk of this patch will now result in:

    Stage this hunk [y,n,q,a,d,/,j,J,g,s,e,?]? s
    Split into 2 hunks.
    @@ -792,7 +792,7 @@ sub hunk_splittable {
    [...]

Instead of:

    Stage this hunk [y,n,q,a,d,/,j,J,g,s,e,?]? s
    Split into 2 hunks.
    @@ -792,7 +792,7 @@
    [...]

This makes it easier to use the tool when you're splitting some giant
hunk and can't remember in which function you are anymore.

The diff is somewhat larger than I initially expected because in order
to display the headings in the same color scheme as the output from
git-diff(1) itself I had to split up the code that would previously
color diff output that previously consisted entirely of the fraginfo,
but now consists of the fraginfo and the diff heading (the latter of
which isn't colored).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 git-add--interactive.perl | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index 1fadd69..ed1e564 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -792,11 +792,11 @@ sub hunk_splittable {
 
 sub parse_hunk_header {
 	my ($line) = @_;
-	my ($o_ofs, $o_cnt, $n_ofs, $n_cnt) =
-	    $line =~ /^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@/;
+	my ($o_ofs, $o_cnt, $n_ofs, $n_cnt, $heading) =
+	    $line =~ /^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@(.*)/;
 	$o_cnt = 1 unless defined $o_cnt;
 	$n_cnt = 1 unless defined $n_cnt;
-	return ($o_ofs, $o_cnt, $n_ofs, $n_cnt);
+	return ($o_ofs, $o_cnt, $n_ofs, $n_cnt, $heading);
 }
 
 sub split_hunk {
@@ -808,8 +808,7 @@ sub split_hunk {
 	# If there are context lines in the middle of a hunk,
 	# it can be split, but we would need to take care of
 	# overlaps later.
-
-	my ($o_ofs, undef, $n_ofs) = parse_hunk_header($text->[0]);
+	my ($o_ofs, undef, $n_ofs, undef, $heading) = parse_hunk_header($text->[0]);
 	my $hunk_start = 1;
 
       OUTER:
@@ -886,17 +885,26 @@ sub split_hunk {
 		my $o_cnt = $hunk->{OCNT};
 		my $n_cnt = $hunk->{NCNT};
 
-		my $head = ("@@ -$o_ofs" .
-			    (($o_cnt != 1) ? ",$o_cnt" : '') .
-			    " +$n_ofs" .
-			    (($n_cnt != 1) ? ",$n_cnt" : '') .
-			    " @@\n");
-		my $display_head = $head;
-		unshift @{$hunk->{TEXT}}, $head;
-		if ($diff_use_color) {
-			$display_head = colored($fraginfo_color, $head);
-		}
-		unshift @{$hunk->{DISPLAY}}, $display_head;
+		my $fraginfo = join(
+			"",
+			"@@ -$o_ofs",
+			(($o_cnt != 1) ? ",$o_cnt" : ''),
+			" +$n_ofs",
+			(($n_cnt != 1) ? ",$n_cnt" : ''),
+			" @@"
+		);
+		unshift @{$hunk->{TEXT}}, join(
+			"",
+			$fraginfo,
+			$heading,
+			"\n"
+		);
+		unshift @{$hunk->{DISPLAY}}, join(
+			"",
+			$diff_use_color ? colored($fraginfo_color, $fraginfo) : $fraginfo,
+			$heading,
+			"\n"
+		);
 	}
 	return @split;
 }
-- 
2.0.0.rc0