send-email: automatic envelope sender

This adds the option to specify the envelope sender as "auto" which
would pick the 'from' address. This is good because now we can specify
the address only in one place in $HOME/.gitconfig and change it easily.

[jc: added tests]

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-send-email.txt

@@ -108,9 +108,10 @@ Sending
 --envelope-sender=<address>::
 	Specify the envelope sender used to send the emails.
 	This is useful if your default address is not the address that is
-	subscribed to a list. If you use the sendmail binary, you must have
-	suitable privileges for the -f parameter. Default is the value of
-	the 'sendemail.envelopesender' configuration variable; if that is
+	subscribed to a list. In order to use the 'From' address, set the
+	value to "auto". If you use the sendmail binary, you must have
+	suitable privileges for the -f parameter.  Default is the value of the
+	'sendemail.envelopesender' configuration variable; if that is
 	unspecified, choosing the envelope sender is left to your MTA.
 
 --smtp-encryption=<encryption>::

git-send-email.perl

@@ -861,7 +861,9 @@ sub send_message
 
 	my @sendmail_parameters = ('-i', @recipients);
 	my $raw_from = $sanitized_sender;
-	$raw_from = $envelope_sender if (defined $envelope_sender);
+	if (defined $envelope_sender && $envelope_sender ne "auto") {
+		$raw_from = $envelope_sender;
+	}
 	$raw_from = extract_valid_address($raw_from);
 	unshift (@sendmail_parameters,
 			'-f', $raw_from) if(defined $envelope_sender);

t/t9001-send-email.sh

@@ -112,6 +112,23 @@ test_expect_success \
     'Verify commandline' \
     'test_cmp expected commandline1'
 
+test_expect_success 'Send patches with --envelope-sender=auto' '
+    clean_fake_sendmail &&
+     git send-email --envelope-sender=auto --suppress-cc=sob --from="Example <nobody@example.com>" --to=nobody@example.com --smtp-server="$(pwd)/fake.sendmail" $patches 2>errors
+'
+
+cat >expected <<\EOF
+!nobody@example.com!
+!-i!
+!nobody@example.com!
+!author@example.com!
+!one@example.com!
+!two@example.com!
+EOF
+test_expect_success \
+    'Verify commandline' \
+    'test_cmp expected commandline1'
+
 cat >expected-show-all-headers <<\EOF
 0001-Second.patch
 (mbox) Adding cc: A <author@example.com> from line 'From: A <author@example.com>'