Add a RuboCop for shell command stubs

Library/Homebrew/rubocops/all.rb

@@ -11,6 +11,7 @@ require_relative "negate_include"
 require_relative "presence"
 require_relative "present"
 require_relative "safe_navigation_with_blank"
+require_relative "shell_command_stub"
 require_relative "shell_commands"
 require_relative "install_bundler_gems"
 

Library/Homebrew/rubocops/shell_command_stub.rb

@@ -0,0 +1,24 @@
+# typed: strict
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Homebrew
+      class ShellCommandStub < Base
+        MSG = "Shell command stubs must have a `.sh` counterpart."
+        RESTRICT_ON_SEND = [:include].freeze
+
+        sig { params(node: AST::SendNode).void }
+        def on_send(node)
+          return if node.first_argument&.const_name != "ShellCommand"
+
+          stub_path = Pathname.new(processed_source.file_path)
+          sh_cmd_path = Pathname.new("#{stub_path.dirname}/#{stub_path.basename(".rb")}.sh")
+          return if sh_cmd_path.exist?
+
+          add_offense(node)
+        end
+      end
+    end
+  end
+end