Subject: [PATCH v4] git-send-email: use ! to indicate relative path to command

From: Gregory Anders <[email-masked]>
Date: Tue, 11 May 2021 14:40:44 -0600

Presently, the smtpServer config option can use a sendmail-like program
by providing an absolute path to the program as the value for this
option. However, an absolute path is not always portable and it is often
preferable to simply specify a program name and have `git-send-email`
find that program on $PATH.

For example, if a user wishes to use msmtp to send emails, they might
be able to simply use

    [sendemail]
            smtpServer = !msmtp

instead of using the full path. This is particularly useful when a
common git config file is used across multiple systems where the
absolute path to a given program may differ.

To that end, this patch allows the smtpServer config option to be
prefixed with a ! character that implements the above behavior; namely,
the specified value (sans the ! character) is used as if the user had
entered it directly on the command line.

See also https://lore.kernel.org/git/[email-masked]/.

Signed-off-by: Gregory Anders <[email-masked]>
---
 Documentation/git-send-email.txt | 13 +++++++------
 git-send-email.perl              |  7 +++++--
 t/t9001-send-email.sh            | 10 ++++++++++
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index 93708aefea..418e66c703 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -212,12 +212,13 @@ a password is obtained using 'git-credential'.
 --smtp-server=<host>::
 	If set, specifies the outgoing SMTP server to use (e.g.
 	`smtp.example.com` or a raw IP address).  Alternatively it can
-	specify a full pathname of a sendmail-like program instead;
-	the program must support the `-i` option.  Default value can
-	be specified by the `sendemail.smtpServer` configuration
-	option; the built-in default is to search for `sendmail` in
-	`/usr/sbin`, `/usr/lib` and $PATH if such program is
-	available, falling back to `localhost` otherwise.
+	specify a sendmail-like program instead, either by a full
+	path-name or by prefixing the program name with `!`.  The
+	program must support the `-i` option.  Default value can be
+	specified by the `sendemail.smtpServer` configuration option;
+	the built-in default is to search for `sendmail` in `/usr/sbin`,
+	`/usr/lib` and $PATH if such program is available, falling back
+	to `localhost` otherwise.
 
 --smtp-server-port=<port>::
 	Specifies a port different from the default port (SMTP
diff --git a/git-send-email.perl b/git-send-email.perl
index 175da07d94..022dcf0999 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1492,11 +1492,14 @@ sub send_message {
 
 	if ($dry_run) {
 		# We don't want to send the email.
-	} elsif (file_name_is_absolute($smtp_server)) {
+	} elsif (file_name_is_absolute($smtp_server) || $smtp_server =~ /^!/) {
+		my $prog = $smtp_server;
+		$prog =~ s/^!//;
+
 		my $pid = open my $sm, '|-';
 		defined $pid or die $!;
 		if (!$pid) {
-			exec($smtp_server, @sendmail_parameters) or die $!;
+			exec($prog, @sendmail_parameters) or die $!;
 		}
 		print $sm "$header\n$message";
 		close $sm or die $!;
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 65b3035371..14cc61ace7 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -2225,4 +2225,14 @@ test_expect_success $PREREQ 'test forbidSendmailVariables behavior override' '
 		HEAD^
 '
 
+test_expect_success $PREREQ 'test using a command for smtpServer with !' '
+	clean_fake_sendmail &&
+	PATH="$(pwd):$PATH" \
+	git send-email \
+		--from="Example <[email-masked]>" \
+		--to=[email-masked] \
+		--smtp-server="!fake.sendmail" \
+		$patches 2>errors
+'
+
 test_done
-- 
2.31.1.576.g2f8a831619