send-email: lazily shell out to "git var"

Optimize git-send-email by only shelling out to "git var" if we need
to. This is easily done by re-inventing our own small version of
perl's Memoize module.

I suppose I could just use Memoize itself, but in a subsequent patch
I'll be micro-optimizing send-email's use of dependencies. Using
Memoize is a measly extra 5-10 milliseconds, but as we'll see that'll
end up mattering for us in the end.

This brings the runtime of a plain "send-email" from around ~160-170ms
to ~140m-150ms. The runtime of the tests is around the same, or around
~20s.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

git-send-email.perl

@@ -588,8 +588,18 @@ sub config_regexp {
 }
 
 my ($repoauthor, $repocommitter);
-($repoauthor) = Git::ident_person(@repo, 'author');
-($repocommitter) = Git::ident_person(@repo, 'committer');
+{
+	my %cache;
+	my ($author, $committer);
+	my $common = sub {
+		my ($what) = @_;
+		return $cache{$what} if exists $cache{$what};
+		($cache{$what}) = Git::ident_person(@repo, $what);
+		return $cache{$what};
+	};
+	$repoauthor = sub { $common->('author') };
+	$repocommitter = sub { $common->('committer') };
+}
 
 sub parse_address_line {
 	return map { $_->format } Mail::Address->parse($_[0]);
@@ -777,7 +787,7 @@ sub get_patch_subject {
 		or die sprintf(__("Failed to open for writing %s: %s"), $compose_filename, $!);
 
 
-	my $tpl_sender = $sender || $repoauthor || $repocommitter || '';
+	my $tpl_sender = $sender || $repoauthor->() || $repocommitter->() || '';
 	my $tpl_subject = $initial_subject || '';
 	my $tpl_in_reply_to = $initial_in_reply_to || '';
 	my $tpl_reply_to = $reply_to || '';
@@ -983,7 +993,7 @@ sub file_declares_8bit_cte {
 	$sender =~ s/^\s+|\s+$//g;
 	($sender) = expand_aliases($sender);
 } else {
-	$sender = $repoauthor || $repocommitter || '';
+	$sender = $repoauthor->() || $repocommitter->() || '';
 }
 
 # $sender could be an already sanitized address
@@ -1132,7 +1142,7 @@ sub make_message_id {
 	$uniq = "$message_id_stamp-$message_id_serial";
 
 	my $du_part;
-	for ($sender, $repocommitter, $repoauthor) {
+	for ($sender, $repocommitter->(), $repoauthor->()) {
 		$du_part = extract_valid_address(sanitize_address($_));
 		last if (defined $du_part and $du_part ne '');
 	}