send-email: add sendmail email aliases format

Teach send-email to read aliases in the sendmail aliases format, i.e.

	<alias>: <address|alias>[, <address|alias>...]

Examples:

	alice: Alice W Land <awol@example.com>
	bob: Robert Bobbyton <bob@example.com>
	# this is a comment
	   # this is also a comment
	chloe: chloe@example.com
	abgroup: alice, bob
	bcgrp: bob, chloe, Other <o@example.com>

 - Quoted aliases and quoted addresses are not supported.
 - Line continuations are not supported.

Warnings are printed for explicitly unsupported constructs, and any
other lines that are not matched by the parser.

Signed-off-by: Allen Hubbe <allenbh@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-send-email.txt

@@ -383,7 +383,23 @@ sendemail.aliasesFile::
 
 sendemail.aliasFileType::
 	Format of the file(s) specified in sendemail.aliasesFile. Must be
-	one of 'mutt', 'mailrc', 'pine', 'elm', or 'gnus'.
+	one of 'mutt', 'mailrc', 'pine', 'elm', or 'gnus', or 'sendmail'.
++
+What an alias file in each format looks like can be found in
+the documentation of the email program of the same name. The
+differences and limitations from the standard formats are
+described below:
++
+--
+sendmail;;
+*	Quoted aliases and quoted addresses are not supported: lines that
+	contain a `"` symbol are ignored.
+*	Line continuations are not supported: lines that start with
+	whitespace characters, or end with a `\` symbol are ignored.
+*	Warnings are printed on the standard error output for any
+	explicitly unsupported constructs, and any other lines that are not
+	recognized by the parser.
+--
 
 sendemail.multiEdit::
 	If true (default), a single editor instance will be spawned to edit

git-send-email.perl

@@ -516,6 +516,31 @@ my %parse_alias = (
 			  }
 		      } },
 
+	sendmail => sub { my $fh = shift; while (<$fh>) {
+		# ignore blank lines and comment lines
+		if (/^\s*(?:#.*)?$/) { }
+
+		# warn on lines that contain quotes
+		elsif (/"/) {
+			print STDERR "sendmail alias with quotes is not supported: $_\n";
+		}
+
+		# warn on lines that continue
+		elsif (/^\s|\\$/) {
+			print STDERR "sendmail continuation line is not supported: $_\n";
+		}
+
+		# recognize lines that look like an alias
+		elsif (/^(\S+?)\s*:\s*(.+)$/) {
+			my ($alias, $addr) = ($1, $2);
+			$aliases{$alias} = [ split_addrs($addr) ];
+		}
+
+		# warn on lines that are not recognized
+		else {
+			print STDERR "sendmail line is not recognized: $_\n";
+		}}},
+
 	gnus => sub { my $fh = shift; while (<$fh>) {
 		if (/\(define-mail-alias\s+"(\S+?)"\s+"(\S+?)"\)/) {
 			$aliases{$1} = [ $2 ];

t/t9001-send-email.sh

@@ -1549,6 +1549,33 @@ test_expect_success $PREREQ 'sendemail.aliasfile=~/.mailrc' '
 	grep "^!someone@example\.org!$" commandline1
 '
 
+test_expect_success $PREREQ 'sendemail.aliasfiletype=sendmail' '
+	clean_fake_sendmail && rm -fr outdir &&
+	git format-patch -1 -o outdir &&
+	cat >>.tmp-email-aliases <<-\EOF &&
+	alice: Alice W Land <awol@example.com>
+	bob: Robert Bobbyton <bob@example.com>
+	# this is a comment
+	   # this is also a comment
+	chloe: chloe@example.com
+	abgroup: alice, bob
+	bcgrp: bob, chloe, Other <o@example.com>
+	EOF
+	git config --replace-all sendemail.aliasesfile \
+		"$(pwd)/.tmp-email-aliases" &&
+	git config sendemail.aliasfiletype sendmail &&
+	git send-email \
+		--from="Example <nobody@example.com>" \
+		--to=alice --to=bcgrp \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		outdir/0001-*.patch \
+		2>errors >out &&
+	grep "^!awol@example\.com!$" commandline1 &&
+	grep "^!bob@example\.com!$" commandline1 &&
+	grep "^!chloe@example\.com!$" commandline1 &&
+	grep "^!o@example\.com!$" commandline1
+'
+
 do_xmailer_test () {
 	expected=$1 params=$2 &&
 	git format-patch -1 &&