fmt-merge-msg: show summary of what is merged.

In addition to the branch names, populate the log message with
one-line description from actual commits that are being merged.

This was prompted by Len's 12-way octopus.  You need to have
'merge.summary' in the configuration file to enable it:

	$ git repo-config merge.summary yes

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/git-fmt-merge-msg.perl b/git-fmt-merge-msg.perl
index 778388e..0467a38 100755 (executable)
--- a/git-fmt-merge-msg.perl
+++ b/git-fmt-merge-msg.perl
@@ -27,10 +27,47 @@ sub andjoin {
        return ($m);
 }
 
+sub repoconfig {
+       my $fh;
+       my $val;
+       eval {
+               open $fh, '-|', 'git-repo-config', '--get', 'merge.summary'
+                   or die "$!";
+               ($val) = <$fh>;
+               close $fh;
+       };
+       return $val;
+}
+
+sub mergebase {
+       my ($other) = @_;
+       my $fh;
+       open $fh, '-|', 'git-merge-base', '--all', 'HEAD', $other or die "$!";
+       my (@mb) = map { chomp; $_ } <$fh>;
+       close $fh or die "$!";
+       return @mb;
+}
+
+sub shortlog {
+       my ($tip, $limit, @base) = @_;
+       my ($fh, @result);
+       open $fh, '-|', ('git-log', "--max-count=$limit", '--topo-order',
+                        '--pretty=oneline', $tip, map { "^$_" } @base)
+           or die "$!";
+       while (<$fh>) {
+               s/^[0-9a-f]{40}\s+//;
+               push @result, $_;
+       }
+       close $fh or die "$!";
+       return @result;
+}
+
+my @origin = ();
 while (<>) {
-       my ($bname, $tname, $gname, $src);
+       my ($bname, $tname, $gname, $src, $sha1, $origin);
        chomp;
-       s/^[0-9a-f]*    //;
+       s/^([0-9a-f]*)  //;
+       $sha1 = $1;
        next if (/^not-for-merge/);
        s/^     //;
        if (s/ of (.*)$//) {
@@ -52,19 +89,30 @@ while (<>) {
                };
        }
        if (/^branch (.*)$/) {
+               $origin = $1;
                push @{$src{$src}{BRANCH}}, $1;
                $src{$src}{HEAD_STATUS} |= 2;
        }
        elsif (/^tag (.*)$/) {
+               $origin = $_;
                push @{$src{$src}{TAG}}, $1;
                $src{$src}{HEAD_STATUS} |= 2;
        }
        elsif (/^HEAD$/) {
+               $origin = $src;
                $src{$src}{HEAD_STATUS} |= 1;
        }
        else {
                push @{$src{$src}{GENERIC}}, $_;
                $src{$src}{HEAD_STATUS} |= 2;
+               $origin = $src;
+       }
+       if ($src eq '.' || $src eq $origin) {
+               $origin =~ s/^'(.*)'$/$1/;
+               push @origin, [$sha1, "$origin"];
+       }
+       else {
+               push @origin, [$sha1, "$origin of $src"];
        }
 }
 
@@ -93,3 +141,30 @@ for my $src (@src) {
        push @msg, $this;
 }
 print "Merge ", join("; ", @msg), "\n";
+
+if (!repoconfig) {
+       exit(0);
+}
+
+# We limit the merge message to the latst 20 or so per each branch.
+my $limit = 20;
+
+for (@origin) {
+       my ($sha1, $name) = @$_;
+       my @mb = mergebase($sha1);
+       my @log = shortlog($sha1, $limit + 1, @mb);
+       if ($limit + 1 <= @log) {
+               print "\n* $name: (" . scalar(@log) . " commits)\n";
+       }
+       else {
+               print "\n* $name:\n";
+       }
+       my $cnt = 0;
+       for my $log (@log) {
+               if ($limit < ++$cnt) {
+                       print "  ...\n";
+                       last;
+               }
+               print "  $log";
+       }
+}