send-email: support validate hook

Currently, send-email has support for rudimentary e-mail validation.
Allow the user to add support for more validation by providing a
sendemail-validate hook.

Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-send-email.txt

@@ -377,6 +377,7 @@ have been specified, in which case default to 'compose'.
 	Currently, validation means the following:
 +
 --
+		*	Invoke the sendemail-validate hook if present (see linkgit:githooks[5]).
 		*	Warn of patches that contain lines longer than 998 characters; this
 			is due to SMTP limits as described by http://www.ietf.org/rfc/rfc2821.txt.
 --

Documentation/githooks.txt

@@ -447,6 +447,14 @@ rebase::
 The commits are guaranteed to be listed in the order that they were
 processed by rebase.
 
+sendemail-validate
+~~~~~~~~~~~~~~~~~~
+
+This hook is invoked by 'git send-email'.  It takes a single parameter,
+the name of the file that holds the e-mail to be sent.  Exiting with a
+non-zero status causes 'git send-email' to abort before sending any
+e-mails.
+
 
 GIT
 ---

git-send-email.perl

@@ -25,8 +25,9 @@
 use Text::ParseWords;
 use Term::ANSIColor;
 use File::Temp qw/ tempdir tempfile /;
-use File::Spec::Functions qw(catfile);
+use File::Spec::Functions qw(catdir catfile);
 use Error qw(:try);
+use Cwd qw(abs_path cwd);
 use Git;
 use Git::I18N;
 
@@ -1737,6 +1738,23 @@ sub unique_email_list {
 
 sub validate_patch {
 	my $fn = shift;
+
+	my $validate_hook = catfile(catdir($repo->repo_path(), 'hooks'),
+				    'sendemail-validate');
+	my $hook_error;
+	if (-x $validate_hook) {
+		my $target = abs_path($fn);
+		# The hook needs a correct cwd and GIT_DIR.
+		my $cwd_save = cwd();
+		chdir($repo->wc_path() or $repo->repo_path())
+			or die("chdir: $!");
+		local $ENV{"GIT_DIR"} = $repo->repo_path();
+		$hook_error = "rejected by sendemail-validate hook"
+			if system($validate_hook, $target);
+		chdir($cwd_save) or die("chdir: $!");
+	}
+	return $hook_error if $hook_error;
+
 	open(my $fh, '<', $fn)
 		or die sprintf(__("unable to open %s: %s\n"), $fn, $!);
 	while (my $line = <$fh>) {

t/t9001-send-email.sh

@@ -1913,4 +1913,44 @@ test_expect_success $PREREQ 'leading and trailing whitespaces are removed' '
 	test_cmp expected-list actual-list
 '
 
+test_expect_success $PREREQ 'invoke hook' '
+	mkdir -p .git/hooks &&
+
+	write_script .git/hooks/sendemail-validate <<-\EOF &&
+	# test that we have the correct environment variable, pwd, and
+	# argument
+	case "$GIT_DIR" in
+	*.git)
+		true
+		;;
+	*)
+		false
+		;;
+	esac &&
+	test -f 0001-add-master.patch &&
+	grep "add master" "$1"
+	EOF
+
+	mkdir subdir &&
+	(
+		# Test that it works even if we are not at the root of the
+		# working tree
+		cd subdir &&
+		git send-email \
+			--from="Example <nobody@example.com>" \
+			--to=nobody@example.com \
+			--smtp-server="$(pwd)/../fake.sendmail" \
+			../0001-add-master.patch &&
+
+		# Verify error message when a patch is rejected by the hook
+		sed -e "s/add master/x/" ../0001-add-master.patch >../another.patch &&
+		git send-email \
+			--from="Example <nobody@example.com>" \
+			--to=nobody@example.com \
+			--smtp-server="$(pwd)/../fake.sendmail" \
+			../another.patch 2>err
+		test_i18ngrep "rejected by sendemail-validate hook" err
+	)
+'
+
 test_done