feat: Add destinations command

lib/kamal/cli/main.rb

@@ -15,6 +15,26 @@ def setup
     end
   end
 
+  desc "destinations", "List available destinations"
+  option :json, aliases: "-j", type: :boolean, default: false, desc: "Output as JSON"
+  def destinations
+    pattern = if options[:config_file].end_with? ".erb"
+                options[:config_file].gsub(/\.yml\.erb/, ".*.yml.erb")
+              else
+                options[:config_file].gsub(/\.yml/, ".*.yml")
+              end
+
+    list = Dir.glob(pattern).map do |f|
+      File.basename(f, ".yml.erb").gsub(/\.yml\.erb/, "").gsub(/\.yml/, "").gsub(/^\w*\./, "")
+    end
+
+    if options[:json]
+      puts list.to_json
+    else
+      puts list
+    end
+  end
+
   desc "deploy", "Deploy app to servers"
   option :skip_push, aliases: "-P", type: :boolean, default: false, desc: "Skip image build and push"
   def deploy

test/cli/main_test.rb

@@ -10,6 +10,22 @@ class CliMainTest < CliTestCase
     run_command("setup")
   end
 
+  test "destinations" do
+    run_command("destinations", config_file: "deploy_for_dest").tap do |output|
+      assert_equal "mars\nworld", output
+    end
+  end
+
+  test "destinations --json" do
+    run_command("destinations", "--json", config_file: "deploy_for_dest").tap do |output|
+      assert_equal '["mars","world"]', output
+    end
+
+    run_command("destinations", "-j", config_file: "deploy_for_dest").tap do |output|
+      assert_equal '["mars","world"]', output
+    end
+  end
+
   test "deploy" do
     invoke_options = { "config_file" => "test/fixtures/deploy_simple.yml", "version" => "999", "skip_hooks" => false }