Fix CSS module handling in pack generator

Fixes #1768 - CSS module files (like HeavyMarkdownEditor.module.css)
were being processed as React components, creating invalid JavaScript
variable names with dots that caused build failures.

Changes:
- Add COMPONENT_EXTENSIONS regex to filter valid React component files
- Add filter_component_files method to exclude non-component files
- Update common/client/server component path methods to use filtering
- Add comprehensive tests for CSS module handling
- Ensure only .js, .jsx, .ts, .tsx files are processed as components

This prevents CSS modules and other non-React files from being
treated as components while maintaining backward compatibility.

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

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

Author: justin808

lib/react_on_rails/packs_generator.rb

@@ -6,6 +6,7 @@ module ReactOnRails
   # rubocop:disable Metrics/ClassLength
   class PacksGenerator
     CONTAINS_CLIENT_OR_SERVER_REGEX = /\.(server|client)($|\.)/
+    COMPONENT_EXTENSIONS = /\.(jsx?|tsx?)$/
     MINIMUM_SHAKAPACKER_VERSION = "6.5.1"
 
     def self.instance
@@ -228,14 +229,20 @@ def component_name_to_path(paths)
       paths.to_h { |path| [component_name(path), path] }
     end
 
+    def filter_component_files(paths)
+      paths.grep(COMPONENT_EXTENSIONS)
+    end
+
     def common_component_to_path
       common_components_paths = Dir.glob("#{components_search_path}/*").grep_v(CONTAINS_CLIENT_OR_SERVER_REGEX)
-      component_name_to_path(common_components_paths)
+      filtered_paths = filter_component_files(common_components_paths)
+      component_name_to_path(filtered_paths)
     end
 
     def client_component_to_path
       client_render_components_paths = Dir.glob("#{components_search_path}/*.client.*")
-      client_specific_components = component_name_to_path(client_render_components_paths)
+      filtered_client_paths = filter_component_files(client_render_components_paths)
+      client_specific_components = component_name_to_path(filtered_client_paths)
 
       duplicate_components = common_component_to_path.slice(*client_specific_components.keys)
       duplicate_components.each_key { |component| raise_client_component_overrides_common(component) }
@@ -245,7 +252,8 @@ def client_component_to_path
 
     def server_component_to_path
       server_render_components_paths = Dir.glob("#{components_search_path}/*.server.*")
-      server_specific_components = component_name_to_path(server_render_components_paths)
+      filtered_server_paths = filter_component_files(server_render_components_paths)
+      server_specific_components = component_name_to_path(filtered_server_paths)
 
       duplicate_components = common_component_to_path.slice(*server_specific_components.keys)
       duplicate_components.each_key { |component| raise_server_component_overrides_common(component) }

spec/dummy/spec/fixtures/automated_packs_generation/components/ComponentWithCSSModule/ror_components/ComponentWithCSSModule.jsx

@@ -0,0 +1,12 @@
+import React from 'react';
+import styles from './ComponentWithCSSModule.module.css';
+
+const ComponentWithCSSModule = () => {
+  return (
+    <div className={styles.container}>
+      <h1 className={styles.title}>Hello from CSS Module Component</h1>
+    </div>
+  );
+};
+
+export default ComponentWithCSSModule;

spec/dummy/spec/fixtures/automated_packs_generation/components/ComponentWithCSSModule/ror_components/ComponentWithCSSModule.module.css

@@ -0,0 +1,9 @@
+/* CSS Module for testing */
+.container {
+  padding: 1rem;
+}
+
+.title {
+  font-size: 2rem;
+  font-weight: bold;
+}

spec/dummy/spec/packs_generator_spec.rb

@@ -435,6 +435,38 @@ def create_new_component(name)
       end
     end
 
+    context "when component with CSS module" do
+      let(:component_name) { "ComponentWithCSSModule" }
+      let(:component_pack) { "#{generated_directory}/#{component_name}.js" }
+
+      before do
+        stub_packer_source_path(component_name: component_name,
+                                packer_source_path: packer_source_path)
+        described_class.instance.generate_packs_if_stale
+      end
+
+      it "generates a pack with valid JavaScript variable names" do
+        expect(File.exist?(component_pack)).to be(true)
+        pack_content = File.read(component_pack)
+        
+        # Check that the generated pack content is valid JavaScript
+        expect(pack_content).to include("import ReactOnRails from 'react-on-rails/client';")
+        expect(pack_content).to include("import #{component_name} from")
+        expect(pack_content).to include("ReactOnRails.register({#{component_name}});")
+        
+        # Verify that variable names don't contain dots (invalid in JS)
+        expect(pack_content).not_to match(/ComponentWithCSSModule\.module/)
+        expect(pack_content).not_to match(/import .+\.module/)
+      end
+
+      it "generates valid JavaScript that can be parsed without syntax errors" do
+        pack_content = File.read(component_pack)
+        
+        # This would fail if the generated JavaScript has syntax errors
+        expect { eval(pack_content.gsub(/import.*from.*['"];/, "").gsub(/ReactOnRails\.register.*/, "")) }.not_to raise_error
+      end
+    end
+
     def generated_server_bundle_file_path
       described_class.instance.send(:generated_server_bundle_file_path)
     end
@@ -658,6 +690,44 @@ def stub_packer_source_path(packer_source_path:, component_name:)
       end
     end
 
+    describe "#component_name" do
+      subject { described_class.instance.send(:component_name, file_path) }
+
+      context "with regular component file" do
+        let(:file_path) { "/path/to/MyComponent.jsx" }
+
+        it { is_expected.to eq "MyComponent" }
+      end
+
+      context "with client component file" do
+        let(:file_path) { "/path/to/MyComponent.client.jsx" }
+
+        it { is_expected.to eq "MyComponent" }
+      end
+
+      context "with server component file" do
+        let(:file_path) { "/path/to/MyComponent.server.jsx" }
+
+        it { is_expected.to eq "MyComponent" }
+      end
+
+      context "with CSS module file" do
+        let(:file_path) { "/path/to/HeavyMarkdownEditor.module.css" }
+
+        # CSS modules should still work with component_name method, but they
+        # should not be processed as React components by the generator
+        it "returns name with dot for CSS modules" do
+          expect(subject).to eq "HeavyMarkdownEditor.module"
+        end
+      end
+
+      context "with TypeScript component file" do
+        let(:file_path) { "/path/to/MyComponent.tsx" }
+
+        it { is_expected.to eq "MyComponent" }
+      end
+    end
+
     describe "#client_entrypoint?" do
       subject { described_class.instance.send(:client_entrypoint?, "dummy_path.js") }