Skip generate_packs when shakapacker precompile hook configured

This change prevents react_on_rails from running generate_packs twice
when shakapacker has a precompile hook configured that already runs it.

Changes:
- Add PackerUtils.shakapacker_precompile_hook_configured? to detect hook
- Skip generate_packs in assets:precompile if hook is configured
- Skip generate_packs in bin/dev if hook is configured
- Add comprehensive test coverage for new behavior

This ensures generate_packs runs only once during both:
- Production asset precompilation (assets:precompile)
- Development server startup (bin/dev)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

lib/react_on_rails/configuration.rb

@@ -247,7 +247,11 @@ def adjust_precompile_task
       raise(ReactOnRails::Error, compile_command_conflict_message) if ReactOnRails::PackerUtils.precompile?
 
       precompile_tasks = lambda {
-        Rake::Task["react_on_rails:generate_packs"].invoke
+        # Skip generate_packs if shakapacker has a precompile hook configured
+        unless ReactOnRails::PackerUtils.shakapacker_precompile_hook_configured?
+          Rake::Task["react_on_rails:generate_packs"].invoke
+        end
+
         Rake::Task["react_on_rails:assets:webpack"].invoke
 
         # VERSIONS is per the shakacode/shakapacker clean method definition.

lib/react_on_rails/dev/pack_generator.rb

@@ -7,6 +7,12 @@ module Dev
     class PackGenerator
       class << self
         def generate(verbose: false)
+          # Skip if shakapacker has a precompile hook configured
+          if ReactOnRails::PackerUtils.shakapacker_precompile_hook_configured?
+            puts "⏭️  Skipping pack generation (handled by shakapacker precompile hook)" if verbose
+            return
+          end
+
           if verbose
             puts "📦 Generating React on Rails packs..."
             success = system "bundle exec rake react_on_rails:generate_packs"

lib/react_on_rails/packer_utils.rb

@@ -162,5 +162,21 @@ def self.raise_shakapacker_version_incompatible_for_basic_pack_generation
 
       raise ReactOnRails::Error, msg
     end
+
+    # Check if shakapacker.yml has a precompile hook configured
+    # This prevents react_on_rails from running generate_packs twice
+    def self.shakapacker_precompile_hook_configured?
+      return false unless defined?(::Shakapacker)
+
+      config_data = ::Shakapacker.config.send(:data)
+      hooks = config_data.dig("hooks", "precompile")
+
+      return false unless hooks
+
+      # Check if any hook contains the generate_packs rake task
+      Array(hooks).any? { |hook| hook.to_s.include?("react_on_rails:generate_packs") }
+    rescue StandardError
+      false
+    end
   end
 end

spec/react_on_rails/dev/pack_generator_spec.rb

@@ -5,27 +5,50 @@
 
 RSpec.describe ReactOnRails::Dev::PackGenerator do
   describe ".generate" do
-    it "runs pack generation successfully in verbose mode" do
-      command = "bundle exec rake react_on_rails:generate_packs"
-      allow(described_class).to receive(:system).with(command).and_return(true)
-
-      expect { described_class.generate(verbose: true) }
-        .to output(/📦 Generating React on Rails packs.../).to_stdout_from_any_process
+    before do
+      allow(ReactOnRails::PackerUtils).to receive(:shakapacker_precompile_hook_configured?).and_return(false)
     end
 
-    it "runs pack generation successfully in quiet mode" do
-      command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
-      allow(described_class).to receive(:system).with(command).and_return(true)
+    context "when shakapacker precompile hook is configured" do
+      before do
+        allow(ReactOnRails::PackerUtils).to receive(:shakapacker_precompile_hook_configured?).and_return(true)
+      end
+
+      it "skips pack generation in verbose mode" do
+        expect { described_class.generate(verbose: true) }
+          .to output(/⏭️  Skipping pack generation \(handled by shakapacker precompile hook\)/)
+          .to_stdout_from_any_process
+      end
 
-      expect { described_class.generate(verbose: false) }
-        .to output(/📦 Generating packs\.\.\. ✅/).to_stdout_from_any_process
+      it "skips pack generation in quiet mode" do
+        expect { described_class.generate(verbose: false) }
+          .not_to output.to_stdout_from_any_process
+      end
     end
 
-    it "exits with error when pack generation fails" do
-      command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
-      allow(described_class).to receive(:system).with(command).and_return(false)
+    context "when shakapacker precompile hook is not configured" do
+      it "runs pack generation successfully in verbose mode" do
+        command = "bundle exec rake react_on_rails:generate_packs"
+        allow(described_class).to receive(:system).with(command).and_return(true)
+
+        expect { described_class.generate(verbose: true) }
+          .to output(/📦 Generating React on Rails packs.../).to_stdout_from_any_process
+      end
+
+      it "runs pack generation successfully in quiet mode" do
+        command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
+        allow(described_class).to receive(:system).with(command).and_return(true)
+
+        expect { described_class.generate(verbose: false) }
+          .to output(/📦 Generating packs\.\.\. ✅/).to_stdout_from_any_process
+      end
+
+      it "exits with error when pack generation fails" do
+        command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
+        allow(described_class).to receive(:system).with(command).and_return(false)
 
-      expect { described_class.generate(verbose: false) }.to raise_error(SystemExit)
+        expect { described_class.generate(verbose: false) }.to raise_error(SystemExit)
+      end
     end
   end
 end

spec/react_on_rails/packer_utils_spec.rb

@@ -139,6 +139,72 @@ module ReactOnRails
         expect(described_class.supports_autobundling?).to be(false)
       end
     end
+
+    describe ".shakapacker_precompile_hook_configured?" do
+      let(:mock_config) { instance_double("::Shakapacker::Config") } # rubocop:disable RSpec/VerifiedDoubleReference
+
+      before do
+        allow(::Shakapacker).to receive(:config).and_return(mock_config)
+      end
+
+      context "when shakapacker is not defined" do
+        before do
+          hide_const("::Shakapacker")
+        end
+
+        it "returns false" do
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(false)
+        end
+      end
+
+      context "when precompile hook contains react_on_rails:generate_packs" do
+        it "returns true for single hook" do
+          allow(mock_config).to receive(:send).with(:data).and_return(
+            { "hooks" => { "precompile" => "bundle exec rake react_on_rails:generate_packs" } }
+          )
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(true)
+        end
+
+        it "returns true for hook in array" do
+          allow(mock_config).to receive(:send).with(:data).and_return(
+            { "hooks" => { "precompile" => ["bundle exec rake react_on_rails:generate_packs", "echo done"] } }
+          )
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(true)
+        end
+      end
+
+      context "when precompile hook does not contain react_on_rails:generate_packs" do
+        it "returns false for different hook" do
+          allow(mock_config).to receive(:send).with(:data).and_return(
+            { "hooks" => { "precompile" => "bundle exec rake some_other_task" } }
+          )
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(false)
+        end
+
+        it "returns false when hooks is nil" do
+          allow(mock_config).to receive(:send).with(:data).and_return({})
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(false)
+        end
+
+        it "returns false when precompile hook is nil" do
+          allow(mock_config).to receive(:send).with(:data).and_return({ "hooks" => {} })
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(false)
+        end
+      end
+
+      context "when an error occurs" do
+        it "returns false" do
+          allow(mock_config).to receive(:send).with(:data).and_raise(StandardError.new("test error"))
+
+          expect(described_class.shakapacker_precompile_hook_configured?).to be(false)
+        end
+      end
+    end
   end
 
   describe "version constants validation" do