From 63babecba745460543d129fc94bedebe7f8e40a4 Mon Sep 17 00:00:00 2001
From: Matthew Kent <matthew@37signals.com>
Date: Fri, 24 Nov 2023 21:18:06 -0800
Subject: [PATCH] Raise an error when either the filtered hosts or roles are
 empty.

Keeps us confusingly running things on the primary_host when nothing
matches.
---
 lib/kamal/commander.rb | 20 ++++++++++++++++++--
 test/commander_test.rb | 17 +++++++++++++----
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/lib/kamal/commander.rb b/lib/kamal/commander.rb
index ded958eb..0a4f4b92 100644
--- a/lib/kamal/commander.rb
+++ b/lib/kamal/commander.rb
@@ -28,11 +28,27 @@ class Kamal::Commander
   end
 
   def specific_roles=(role_names)
-    @specific_roles = Kamal::Utils.filter_specific_items(role_names, config.roles) if role_names.present?
+    if role_names.present?
+      @specific_roles = Kamal::Utils.filter_specific_items(role_names, config.roles)
+
+      if @specific_roles.empty?
+        raise ArgumentError, "No --roles match for #{role_names.join(',')}"
+      end
+
+      @specific_roles
+    end
   end
 
   def specific_hosts=(hosts)
-    @specific_hosts = Kamal::Utils.filter_specific_items(hosts, config.all_hosts) if hosts.present?
+    if hosts.present?
+      @specific_hosts = Kamal::Utils.filter_specific_items(hosts, config.all_hosts)
+
+      if @specific_hosts.empty?
+        raise ArgumentError, "No --hosts match for #{hosts.join(',')}"
+      end
+
+      @specific_hosts
+    end
   end
 
   def primary_host
diff --git a/test/commander_test.rb b/test/commander_test.rb
index d9802668..4e848a4b 100644
--- a/test/commander_test.rb
+++ b/test/commander_test.rb
@@ -24,8 +24,10 @@ class CommanderTest < ActiveSupport::TestCase
     @kamal.specific_hosts = [ "*" ]
     assert_equal [ "1.1.1.1", "1.1.1.2", "1.1.1.3", "1.1.1.4" ], @kamal.hosts
 
-    @kamal.specific_hosts = [ "*miss" ]
-    assert_equal [], @kamal.hosts
+    exception = assert_raises(ArgumentError) do
+      @kamal.specific_hosts = [ "*miss" ]
+    end
+    assert_match /hosts match for \*miss/, exception.message
   end
 
   test "filtering hosts by filtering roles" do
@@ -33,6 +35,11 @@ class CommanderTest < ActiveSupport::TestCase
 
     @kamal.specific_roles = [ "web" ]
     assert_equal [ "1.1.1.1", "1.1.1.2" ], @kamal.hosts
+
+    exception = assert_raises(ArgumentError) do
+      @kamal.specific_roles = [ "*miss" ]
+    end
+    assert_match /roles match for \*miss/, exception.message
   end
 
   test "filtering roles" do
@@ -50,8 +57,10 @@ class CommanderTest < ActiveSupport::TestCase
     @kamal.specific_roles = [ "*" ]
     assert_equal [ "web", "workers" ], @kamal.roles.map(&:name)
 
-    @kamal.specific_roles = [ "*miss" ]
-    assert_equal [], @kamal.roles.map(&:name)
+    exception = assert_raises(ArgumentError) do
+      @kamal.specific_roles = [ "*miss" ]
+    end
+    assert_match /roles match for \*miss/, exception.message
   end
 
   test "filtering roles by filtering hosts" do