service: handle string run cmd

This was not handled at all during deserialization.
The string argument gets turned into an array internally
but we skip that to preserve all args in the @run_params
variable. That means that we have to handle strings when
deserializing too.

Library/Homebrew/service.rb

@@ -46,8 +46,11 @@ module Homebrew
     }
     def run(command = nil, macos: nil, linux: nil)
       # Save parameters for serialization
-      @run_params ||= command
-      @run_params ||= { macos: macos, linux: linux }.compact
+      if command
+        @run_params = command
+      elsif macos || linux
+        @run_params = { macos: macos, linux: linux }.compact
+      end
 
       command ||= on_system_conditional(macos: macos, linux: linux)
       case T.unsafe(command)
@@ -551,15 +554,22 @@ module Homebrew
       hash = {}
       hash[:run] =
         case api_hash["run"]
-        when Hash
-          api_hash["run"].to_h do |key, array|
-            [
-              key.to_sym,
-              array.map(&method(:replace_placeholders)),
-            ]
-          end
+        when String
+          replace_placeholders(api_hash["run"])
         when Array
           api_hash["run"].map(&method(:replace_placeholders))
+        when Hash
+          api_hash["run"].to_h do |key, elem|
+            run_cmd = if elem.is_a?(Array)
+              elem.map(&method(:replace_placeholders))
+            else
+              replace_placeholders(elem)
+            end
+
+            [key.to_sym, run_cmd]
+          end
+        else
+          raise ArgumentError, "Unexepected run command: #{api_hash["run"]}"
         end
 
       hash[:keep_alive] = api_hash["keep_alive"].transform_keys(&:to_sym) if api_hash.key?("keep_alive")

Library/Homebrew/test/service_spec.rb

@@ -975,5 +975,37 @@ describe Homebrew::Service do
     it "replaces placeholders with local paths" do
       expect(described_class.deserialize(serialized_hash)).to eq(deserialized_hash)
     end
+
+    describe "run command" do
+      it "handles String argument correctly" do
+        expect(described_class.deserialize({
+          "run" => "$HOMEBREW_PREFIX/opt/formula_name/bin/beanstalkd",
+        })).to eq({
+          run: "#{HOMEBREW_PREFIX}/opt/formula_name/bin/beanstalkd",
+        })
+      end
+
+      it "handles Array argument correctly" do
+        expect(described_class.deserialize({
+          "run" => ["$HOMEBREW_PREFIX/opt/formula_name/bin/beanstalkd", "--option"],
+        })).to eq({
+          run: ["#{HOMEBREW_PREFIX}/opt/formula_name/bin/beanstalkd", "--option"],
+        })
+      end
+
+      it "handles Hash argument correctly" do
+        expect(described_class.deserialize({
+          "run" => {
+            "linux" => "$HOMEBREW_PREFIX/opt/formula_name/bin/beanstalkd",
+            "macos" => ["$HOMEBREW_PREFIX/opt/formula_name/bin/beanstalkd", "--option"],
+          },
+        })).to eq({
+          run: {
+            linux: "#{HOMEBREW_PREFIX}/opt/formula_name/bin/beanstalkd",
+            macos: ["#{HOMEBREW_PREFIX}/opt/formula_name/bin/beanstalkd", "--option"],
+          },
+        })
+      end
+    end
   end
 end