Merge pull request #1405 from mike-weiner/fix-1399-fail-exec-without-cmd

Raise an error to the user if the exec command parsed is blank

lib/kamal/cli/app.rb

@@ -112,6 +112,10 @@ class Kamal::Cli::App < Kamal::Cli::Base
       raise ArgumentError, "Detach is not compatible with #{incompatible_options.join(" or ")}"
     end
 
+    if cmd.empty?
+      raise ArgumentError, "No command provided. You must specify a command to execute."
+    end
+
     cmd = Kamal::Utils.join_commands(cmd)
     env = options[:env]
     detach = options[:detach]

test/cli/app_test.rb

@@ -312,6 +312,13 @@ class CliAppTest < CliTestCase
     end
   end
 
+  test "exec without command fails" do
+    error = assert_raises(ArgumentError, "Exec requires a command to be specified") do
+      run_command("exec")
+    end
+    assert_equal "No command provided. You must specify a command to execute.", error.message
+  end
+
   test "exec separate arguments" do
     run_command("exec", "ruby", " -v").tap do |output|
       assert_match "docker run --rm --network kamal --env-file .kamal/apps/app/env/roles/web.env --log-opt max-size=\"10m\" dhh/app:latest ruby -v", output