rubocops/service: add checks for custom service names

It now checks for two new edge cases.
1. Are the required methods defined in the block?
2. Is the `run` command defined if we're using methods other
   than `service_name` or `plist_name`?

It has also been updated to only get the list of method call nodes
once instead of doing it repeatedly for each cellar path check.

Library/Homebrew/rubocops/service.rb

@@ -21,15 +21,39 @@ module RuboCop
           share:    :opt_share,
         }.freeze
 
+        # These can be defined without using the `run` command.
+        RENAME_METHOD_CALLS = [:plist_name, :service_name].freeze
+
+        # At least one of these methods must be defined in a service block.
+        REQUIRED_METHOD_CALLS = [:run, *RENAME_METHOD_CALLS].freeze
+
         def audit_formula(_node, _class_node, _parent_class_node, body_node)
           service_node = find_block(body_node, :service)
           return if service_node.blank?
 
+          method_calls = service_node.each_descendant(:send).group_by(&:method_name)
+          method_calls.delete(:service)
+
+          # NOTE: Solving the first problem here might solve the second one too
+          # so we don't show both of them at the same time.
+          if (method_calls.keys & REQUIRED_METHOD_CALLS).empty?
+            offending_node(service_node)
+            problem "Service blocks require `run`, `plist_name` or `service_name` to be defined."
+          elsif !method_calls.key?(:run)
+            other_method_calls = method_calls.keys - RENAME_METHOD_CALLS
+            if other_method_calls.any?
+              offending_node(service_node)
+              problem "`run` must be defined to use methods other than " \
+                      "`service_name` and `plist_name` like #{other_method_calls}."
+            end
+          end
+
           # This check ensures that cellar paths like `bin` are not referenced
-          # because their `opt_` variants are more portable and work with the
+          # because their `opt_` variants are more portable and work with the API.
-          # API.
           CELLAR_PATH_AUDIT_CORRECTIONS.each do |path, opt_path|
-            find_every_method_call_by_name(service_node, path).each do |node|
+            next unless method_calls.key?(path)
+
+            method_calls.fetch(path).each do |node|
               offending_node(node)
               problem "Use `#{opt_path}` instead of `#{path}` in service blocks." do |corrector|
                 corrector.replace(node.source_range, opt_path)

Library/Homebrew/test/rubocops/service_spec.rb

@@ -5,6 +5,48 @@ require "rubocops/service"
 describe RuboCop::Cop::FormulaAudit::Service do
   subject(:cop) { described_class.new }
 
+  it "reports offenses when a service block is missing a required command" do
+    expect_offense(<<~RUBY)
+      class Foo < Formula
+        url "https://brew.sh/foo-1.0.tgz"
+
+        service do
+        ^^^^^^^^^^ FormulaAudit/Service: Service blocks require `run`, `plist_name` or `service_name` to be defined.
+          run_type :cron
+          working_dir "/tmp/example"
+        end
+      end
+    RUBY
+  end
+
+  it "reports no offenses when a service block only includes custom names" do
+    expect_no_offenses(<<~RUBY)
+      class Foo < Formula
+        url "https://brew.sh/foo-1.0.tgz"
+
+        service do
+          plist_name "custom.mcxl.foo"
+          service_name "custom.foo"
+        end
+      end
+    RUBY
+  end
+
+  it "reports offenses when a service block includes more than custom names and no run command" do
+    expect_offense(<<~RUBY)
+      class Foo < Formula
+        url "https://brew.sh/foo-1.0.tgz"
+
+        service do
+        ^^^^^^^^^^ FormulaAudit/Service: `run` must be defined to use methods other than `service_name` and `plist_name` like [:working_dir].
+          plist_name "custom.mcxl.foo"
+          service_name "custom.foo"
+          working_dir "/tmp/example"
+        end
+      end
+    RUBY
+  end
+
   it "reports offenses when a formula's service block uses cellar paths" do
     expect_offense(<<~RUBY)
       class Foo < Formula
@@ -31,7 +73,7 @@ describe RuboCop::Cop::FormulaAudit::Service do
     RUBY
   end
 
-  it "reports no offenses when a formula's service block only uses opt paths" do
+  it "reports no offenses when a service block only uses opt paths" do
     expect_no_offenses(<<~RUBY)
       class Bin < Formula
         url "https://brew.sh/foo-1.0.tgz"