send-email: address expansion for common mailers

mutt, gnus, pine, mailrc formats should be supported.

Testing and feedback for correctness and completeness of all formats
and support for additional formats would be good.

Nested expansions are also supported.

More than one alias file to be used.

All alias file formats must still of be the same type, though.

Two git repo-config keys are required for this
(as suggested by Ryan Anderson):

    sendemail.aliasesfile = <filename of aliases file>
    sendemail.aliasfiletype = (mutt|gnus|pine|mailrc)

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Acked-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-send-email.perl

@@ -89,6 +89,41 @@ sub gitvar_ident {
 my ($author) = gitvar_ident('GIT_AUTHOR_IDENT');
 my ($committer) = gitvar_ident('GIT_COMMITTER_IDENT');
 
+my %aliases;
+chomp(my @alias_files = `git-repo-config --get-all sendemail.aliasesfile`);
+chomp(my $aliasfiletype = `git-repo-config sendemail.aliasfiletype`);
+my %parse_alias = (
+	# multiline formats can be supported in the future
+	mutt => sub { my $fh = shift; while (<$fh>) {
+		if (/^alias\s+(\S+)\s+(.*)$/) {
+			my ($alias, $addr) = ($1, $2);
+			$addr =~ s/#.*$//; # mutt allows # comments
+			 # commas delimit multiple addresses
+			$aliases{$alias} = [ split(/\s*,\s*/, $addr) ];
+		}}},
+	mailrc => sub { my $fh = shift; while (<$fh>) {
+		if (/^alias\s+(\S+)\s+(.*)$/) {
+			# spaces delimit multiple addresses
+			$aliases{$1} = [ split(/\s+/, $2) ];
+		}}},
+	pine => sub { my $fh = shift; while (<$fh>) {
+		if (/^(\S+)\s+(.*)$/) {
+			$aliases{$1} = [ split(/\s*,\s*/, $2) ];
+		}}},
+	gnus => sub { my $fh = shift; while (<$fh>) {
+		if (/\(define-mail-alias\s+"(\S+?)"\s+"(\S+?)"\)/) {
+			$aliases{$1} = [ $2 ];
+		}}}
+);
+
+if (@alias_files && defined $parse_alias{$aliasfiletype}) {
+	foreach my $file (@alias_files) {
+		open my $fh, '<', $file or die "opening $file: $!\n";
+		$parse_alias{$aliasfiletype}->($fh);
+		close $fh;
+	}
+}
+
 my $prompting = 0;
 if (!defined $from) {
 	$from = $author || $committer;
@@ -112,6 +147,19 @@ if (!@to) {
 	$prompting++;
 }
 
+sub expand_aliases {
+	my @cur = @_;
+	my @last;
+	do {
+		@last = @cur;
+		@cur = map { $aliases{$_} ? @{$aliases{$_}} : $_ } @last;
+	} while (join(',',@cur) ne join(',',@last));
+	return @cur;
+}
+
+@to = expand_aliases(@to);
+@initial_cc = expand_aliases(@initial_cc);
+
 if (!defined $initial_subject && $compose) {
 	do {
 		$_ = $term->readline("What subject should the emails start with? ",