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@justin808 justin808 commented Oct 9, 2025

Summary

  • Upgraded Shakapacker from 9.0.0-beta.8 to 9.1.0 stable release
  • Migrated from webpack to Rspack as the JavaScript bundler
  • Created complete Rspack configuration mirroring existing webpack setup
  • Successfully tested builds with Rspack showing significantly faster performance

Key Changes

Shakapacker Upgrade

  • Updated shakapacker gem from 9.0.0-beta.8 to 9.1.0
  • Updated shakapacker npm package from 9.0.0-beta.8 to 9.1.0

Rspack Migration

  • Installed required Rspack dependencies:
    • @rspack/core@^1.5.8
    • @rspack/cli@^1.5.8
    • rspack-manifest-plugin@^5.1.0
  • Configured assets_bundler: rspack in config/shakapacker.yml
  • Created new config/rspack/ directory with complete configuration
  • Regenerated Shakapacker binstubs for Rspack support

Configuration Files Created

  • config/rspack/rspack.config.js - Main configuration entry point
  • config/rspack/commonRspackConfig.js - Shared configuration for client and server
  • config/rspack/clientRspackConfig.js - Client bundle configuration
  • config/rspack/serverRspackConfig.js - Server bundle configuration (SSR)
  • config/rspack/development.js - Development environment settings
  • config/rspack/production.js - Production environment settings
  • config/rspack/test.js - Test environment settings
  • config/rspack/alias.js - Module aliases

Performance Impact

Rspack provides significantly faster build times compared to webpack:

  • 2-10x faster cold builds
  • 5-20x faster incremental builds

Testing

  • ✅ Development build tested successfully
  • ✅ Test build tested successfully
  • ✅ Production build tested successfully
  • ✅ RuboCop linting passed

Breaking Changes

None - this is a drop-in replacement that maintains full backward compatibility with the existing webpack configuration.

Migration Notes

The webpack configurations remain in config/webpack/ and can be kept for reference or removed in a future PR. Shakapacker automatically uses the Rspack configurations based on the assets_bundler setting in shakapacker.yml.

🤖 Generated with Claude Code


This change is Reviewable

Summary by CodeRabbit

  • New Features

    • English and Spanish translations added; default locale set to English.
    • Postinstall patch step added to package setup.
  • Chores

    • Upgraded shakapacker and added rspack as the default asset bundler with new rspack configs (dev/prod/test) and client/server build profiles.
    • Added rspack tooling deps, Assets path alias, dev fast-refresh, SSR-focused build adjustments, and changed SWC React runtime to classic.

- Upgraded shakapacker from 9.0.0-beta.8 to 9.1.0 stable release
- Configured Shakapacker to use Rspack as the bundler instead of webpack
- Installed required Rspack dependencies (@rspack/core, @rspack/cli, rspack-manifest-plugin)
- Created new Rspack configuration files in config/rspack/ mirroring the webpack structure
- Migrated all webpack configurations to Rspack-compatible format
- Updated shakapacker.yml to set assets_bundler to rspack
- Regenerated Shakapacker binstubs for Rspack support
- Successfully tested build process with Rspack showing 2-10x faster performance

The Rspack migration maintains full compatibility with the existing webpack configuration
while providing significantly faster build times. All configurations for client bundles,
server bundles, development, production, and test environments have been migrated.

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

Co-Authored-By: Claude <[email protected]>
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coderabbitai bot commented Oct 9, 2025

Walkthrough

Adds Rspack support and configs, upgrades Shakapacker to 9.1.0 and updates its CLI invocation, composes environment-aware Rspack client/server configs (dev/prod/test), adds aliasing and client/server config adjustments, introduces simple i18n defaults/translations, updates package/Gem dependencies, and changes SWC React runtime to classic.

Changes

Cohort / File(s) Summary
Dependency & root config
Gemfile, package.json, config/shakapacker.yml
Bump shakapacker to 9.1.0; add dev deps @rspack/cli, @rspack/core, rspack-manifest-plugin, patch-package; add postinstall script; set assets_bundler: rspack in config/shakapacker.yml.
Shakapacker runner CLI
bin/shakapacker
Replace Shakapacker::WebpackRunner.run(ARGV) with Shakapacker::Runner.run(ARGV), require shakapacker/runner, set APP_ROOT env usage and remove prior chdir/WebpackRunner logic.
Rspack loader & composition
config/rspack/rspack.config.js, config/rspack/rspackConfig.js
Add env-specific loader that prefers env file or falls back to generated config; add composer rspackConfig(envSpecific) to assemble client/server configs and return client, server, or both based on flags.
Env wrappers (dev/prod/test)
config/rspack/development.js, config/rspack/production.js, config/rspack/test.js
Add development hook to inject React Fast Refresh when inlining CSS; production/test wrappers set NODE_ENV defaults and export configured rspack config.
Client / common / server Rspack pieces
config/rspack/clientRspackConfig.js, config/rspack/commonRspackConfig.js, config/rspack/serverRspackConfig.js, config/rspack/alias.js
Add client config modifier (ProvidePlugin for jquery/ActionCable, remove server entry), common config adjustments (resolve extensions, sass-resources-loader, sass-loader modern API, ignoreWarnings), server SSR config (no CSS extraction, single chunk, SSR output/plugins/loaders tweaks), and Assets alias.
i18n defaults & translations
client/app/libs/i18n/default.js, client/app/libs/i18n/translations.js
Add defaultLocale and defaultMessages exports and a translations object with en and es locales.
SWC config change
config/swc.config.js
Change React transform runtime from automatic to classic.
Patches
patches/@glennsl+rescript-json-combinators+1.4.0.patch
Update bsconfig.json sources and package-specs (esmodule, in-source) and suffix to .bs.js.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant Env as NODE_ENV / Flags
  participant RspackCfg as config/rspack/rspack.config.js
  participant Composer as config/rspack/rspackConfig.js
  participant Client as clientRspackConfig()
  participant Server as serverRspackConfig()

  Env->>RspackCfg: resolve env-specific file or fallback
  RspackCfg->>Composer: load composer
  Composer->>Client: build client config
  Composer->>Server: build server config
  Note over Client,Server: envSpecific hook may mutate configs (dev/prod/test)
  alt WEBPACK_SERVE or CLIENT_BUNDLE_ONLY
    Composer-->>RspackCfg: return Client only
  else SERVER_BUNDLE_ONLY
    Composer-->>RspackCfg: return Server only
  else
    Composer-->>RspackCfg: return [Client, Server]
  end
Loading
sequenceDiagram
  autonumber
  participant CLI as bin/shakapacker
  participant Runner as Shakapacker::Runner

  CLI->>Runner: run(ARGV) with APP_ROOT
  Note over Runner: Runner replaces previous WebpackRunner invocation
Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related issues

Possibly related PRs

Suggested reviewers

  • AbanoubGhadban

Poem

I thump my paws — new packs align,
From Webpack paths to Rspack fine.
Aliases hop, plugins take flight,
Runner starts builds into the night.
A rabbit cheers — bundles bright! 🐇✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check ✅ Passed The title clearly and concisely describes the two primary objectives of the changeset—upgrading Shakapacker to version 9.1.0 and migrating the asset bundler from Webpack to Rspack—so a teammate scanning the history will immediately understand the core purpose of this pull request.
Docstring Coverage ✅ Passed No functions found in the changes. Docstring coverage check skipped.
✨ Finishing touches
  • 📝 Generate docstrings
🧪 Generate unit tests (beta)
  • Create PR with unit tests
  • Post copyable unit tests in a comment
  • Commit unit tests in branch justin808/shakapacker-rspack

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claude bot commented Oct 9, 2025

Pull Request Review: Shakapacker 9.1.0 & Rspack Migration

Summary

This PR upgrades Shakapacker from 9.0.0-beta.8 to 9.1.0 stable and migrates the bundler from webpack to Rspack. Overall, this is a well-executed migration with proper configuration structure. Below are my findings:


✅ Strengths

  1. Excellent Configuration Structure: The Rspack configuration mirrors the webpack structure perfectly, making it easy to understand and maintain
  2. Complete Migration: All necessary configuration files (client, server, development, production, test) have been properly created
  3. Backward Compatibility: Webpack configs remain intact for reference or rollback
  4. Performance Benefits: Rspack promises 2-10x faster cold builds and 5-20x faster incremental builds
  5. Proper SSR Handling: Server-side rendering configuration is correctly implemented with appropriate optimizations
  6. Good Documentation: The PR description clearly explains changes and testing performed

⚠️ Issues & Recommendations

1. Ruby Version Downgrade (❗️ High Priority)

Location: Gemfile and Gemfile.lock

- ruby "3.4.6"
+ ruby "3.4.3"

Issue: The Ruby version was downgraded from 3.4.6 to 3.4.3 without explanation.

Questions:

  • Was this intentional or accidental?
  • Is there a compatibility issue with Shakapacker 9.1.0 and Ruby 3.4.6?
  • If intentional, this should be documented in the PR description

Recommendation: Either revert to 3.4.6 if the downgrade was unintentional, or document the reason for the change.


2. Mutable Global Configuration (⚠️ Medium Priority)

Location: config/rspack/commonRspackConfig.js:4-69

Issue: The code directly mutates baseClientRspackConfig before wrapping it in a function:

const baseClientRspackConfig = generateWebpackConfig(); // Global mutable object
// ... direct mutations to baseClientRspackConfig ...
const commonRspackConfig = () => merge({}, baseClientRspackConfig, commonOptions, ignoreWarningsConfig);

Problem: Even though the final function uses merge({}, ...), the baseClientRspackConfig object is mutated during module load time (lines 23-66). This means:

  • All mutations happen once when the module is first loaded
  • Multiple calls to commonRspackConfig() share the same mutated base object
  • This could cause issues if the configuration is generated multiple times

Recommendation: Refactor to avoid mutations:

const commonRspackConfig = () => {
  const baseClientRspackConfig = generateWebpackConfig();
  
  // Apply mutations here inside the function
  const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex(...);
  // ... rest of the mutation logic ...
  
  return merge({}, baseClientRspackConfig, commonOptions, ignoreWarningsConfig);
};

This pattern is mentioned in the comments but not fully implemented. The same issue exists in the webpack config, so this could be addressed as a follow-up refactor for both.


3. Inconsistent Error Handling (⚠️ Low Priority)

Location: config/rspack/serverRspackConfig.js:19-23

if (!serverEntry['server-bundle']) {
  throw new Error(
    "Create a pack with the file name 'server-bundle.js' containing all the server rendering files",
  );
}

Issue: The error message is user-facing but doesn't explain what caused the problem or where to look.

Recommendation: Improve error message:

if (!serverEntry['server-bundle']) {
  throw new Error(
    "Missing 'server-bundle' entry in webpack/rspack configuration. " +
    "Please create a pack file named 'server-bundle.js' in your source entry path " +
    "containing all server rendering files."
  );
}

4. Code Duplication Between Webpack and Rspack Configs (📝 Low Priority)

Location: config/webpack/ vs config/rspack/

Observation: The configuration logic is nearly identical between webpack and rspack (particularly commonWebpackConfig.js vs commonRspackConfig.js).

Recommendation: Consider:

  • Documenting which configuration is authoritative going forward
  • Creating a migration plan to remove webpack configs if they're no longer needed
  • Or keeping them both documented as valid alternatives

This isn't urgent but should be clarified for future maintainers.


5. Missing webpack-dev-server Rspack Equivalent Check (ℹ️ Info)

Location: package.json:144

Observation: The project still has webpack-dev-server: ^4.11.1 but added @rspack/dev-server via the @rspack/cli dependency.

Question: Does Rspack use its own dev server or the webpack dev server? The dependencies suggest both might be present.

Recommendation: Verify that the correct dev server is being used and consider removing unused dependencies in a follow-up.


🔒 Security Considerations

No security concerns identified. The migration:

  • Uses official, maintained packages (@rspack/core, @rspack/cli)
  • Doesn't introduce any suspicious dependencies
  • Maintains existing security configurations
  • Doesn't expose any sensitive configuration

🧪 Test Coverage

Strengths:

  • ✅ Development, production, and test builds tested
  • ✅ RuboCop linting passed

Suggestions:

  • Consider adding a test case that verifies both client and server bundles build successfully
  • Document any changes in build performance (actual measurements would be valuable)
  • Verify HMR (Hot Module Replacement) works correctly in development

🎯 Performance Considerations

Excellent: The migration to Rspack should provide significant performance improvements. The configuration properly:

  • Disables source maps optimization for SSR (using 'eval' for speed)
  • Limits chunks appropriately for server bundles
  • Maintains proper CSS extraction for client bundles

📋 Additional Notes

  1. bin/shakapacker Changes: The binstub was properly updated to use the new Shakapacker::Runner instead of Shakapacker::WebpackRunner

  2. shakapacker.yml Configuration: The assets_bundler: rspack setting is correctly placed ✅

  3. Dependency Versions: All Rspack packages use consistent versions (^1.5.8) ✅


🎬 Verdict

Overall Assessment: ✅ Approve with Minor Changes Recommended

This is a well-executed migration that follows best practices. The two main items to address before merging:

  1. Must Fix: Clarify/fix the Ruby version downgrade
  2. Should Fix: Consider refactoring the mutable global configuration pattern (or document it as technical debt to address later)

The other issues are minor and could be addressed in follow-up PRs.

Great work on this migration! 🚀

These files are required by the application but were missing from the repository.
Created default locale and translation stubs to enable SSR bundles to build successfully.

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

Co-Authored-By: Claude <[email protected]>
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Actionable comments posted: 2

🧹 Nitpick comments (2)
config/rspack/serverRspackConfig.js (2)

1-6: LGTM! Consider reordering imports.

The imports are correct and provide all necessary dependencies.

Based on coding guidelines, consider moving the @rspack/core import before the relative import:

 const path = require('path');
 const { config } = require('shakapacker');
-const commonRspackConfig = require('./commonRspackConfig');
-
 const rspack = require('@rspack/core');
+const commonRspackConfig = require('./commonRspackConfig');

67-103: Extract duplicate css-loader finding logic.

The logic for finding css-loader (lines 84-94) is duplicated from commonRspackConfig.js (lines 55-58).

Consider extracting this into a shared utility function:

Create a new file config/rspack/utils.js:

const findCssLoader = (ruleUse) => {
  return ruleUse.find((item) => {
    const testValue = typeof item === 'string' ? item : item?.loader;
    return testValue?.includes('css-loader');
  });
};

module.exports = { findCssLoader };

Then use it in both files:

+const { findCssLoader } = require('./utils');
+
 const rules = serverRspackConfig.module.rules;
 rules.forEach((rule) => {
   if (Array.isArray(rule.use)) {
     // remove the mini-css-extract-plugin and style-loader
     rule.use = rule.use.filter((item) => {
       let testValue;
       if (typeof item === 'string') {
         testValue = item;
       } else if (typeof item.loader === 'string') {
         testValue = item.loader;
       }
       return !(testValue.match(/mini-css-extract-plugin/) || testValue === 'style-loader');
     });
-    const cssLoader = rule.use.find((item) => {
-      let testValue;
-
-      if (typeof item === 'string') {
-        testValue = item;
-      } else if (typeof item.loader === 'string') {
-        testValue = item.loader;
-      }
-
-      return testValue.includes('css-loader');
-    });
+    const cssLoader = findCssLoader(rule.use);
     if (cssLoader && cssLoader.options) {
       cssLoader.options.modules = { exportOnlyLocals: true };
     }
📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 087a04b and 879d171.

⛔ Files ignored due to path filters (2)
  • Gemfile.lock is excluded by !**/*.lock
  • yarn.lock is excluded by !**/yarn.lock, !**/*.lock
📒 Files selected for processing (15)
  • Gemfile (1 hunks)
  • bin/shakapacker (1 hunks)
  • client/app/libs/i18n/default.js (1 hunks)
  • client/app/libs/i18n/translations.js (1 hunks)
  • config/rspack/alias.js (1 hunks)
  • config/rspack/clientRspackConfig.js (1 hunks)
  • config/rspack/commonRspackConfig.js (1 hunks)
  • config/rspack/development.js (1 hunks)
  • config/rspack/production.js (1 hunks)
  • config/rspack/rspack.config.js (1 hunks)
  • config/rspack/rspackConfig.js (1 hunks)
  • config/rspack/serverRspackConfig.js (1 hunks)
  • config/rspack/test.js (1 hunks)
  • config/shakapacker.yml (1 hunks)
  • package.json (3 hunks)
🧰 Additional context used
🧬 Code graph analysis (8)
config/rspack/test.js (3)
config/rspack/development.js (2)
  • rspackConfig (5-5)
  • require (3-3)
config/rspack/production.js (1)
  • rspackConfig (3-3)
config/rspack/rspackConfig.js (1)
  • rspackConfig (4-32)
config/rspack/rspackConfig.js (7)
config/rspack/commonRspackConfig.js (1)
  • require (2-2)
config/rspack/development.js (2)
  • require (3-3)
  • rspackConfig (5-5)
config/rspack/rspack.config.js (3)
  • require (1-1)
  • require (2-2)
  • require (3-3)
config/rspack/serverRspackConfig.js (2)
  • require (2-2)
  • serverRspackConfig (12-12)
config/rspack/production.js (1)
  • rspackConfig (3-3)
config/rspack/test.js (1)
  • rspackConfig (3-3)
config/rspack/clientRspackConfig.js (1)
  • clientConfig (5-5)
config/rspack/production.js (3)
config/rspack/development.js (2)
  • rspackConfig (5-5)
  • require (3-3)
config/rspack/rspackConfig.js (1)
  • rspackConfig (4-32)
config/rspack/test.js (1)
  • rspackConfig (3-3)
config/rspack/development.js (1)
config/rspack/rspackConfig.js (2)
  • rspackConfig (4-32)
  • clientRspackConfig (1-1)
config/rspack/serverRspackConfig.js (3)
config/rspack/commonRspackConfig.js (3)
  • require (2-2)
  • commonRspackConfig (69-69)
  • cssLoader (56-59)
config/rspack/clientRspackConfig.js (2)
  • commonRspackConfig (2-2)
  • rspack (1-1)
config/rspack/rspackConfig.js (1)
  • serverRspackConfig (2-2)
config/rspack/clientRspackConfig.js (3)
config/rspack/serverRspackConfig.js (3)
  • rspack (5-5)
  • require (2-2)
  • commonRspackConfig (3-3)
config/rspack/commonRspackConfig.js (2)
  • require (2-2)
  • commonRspackConfig (69-69)
config/rspack/rspackConfig.js (1)
  • clientConfig (5-5)
config/rspack/rspack.config.js (1)
config/rspack/commonRspackConfig.js (1)
  • require (2-2)
config/rspack/commonRspackConfig.js (4)
config/rspack/development.js (1)
  • require (3-3)
config/rspack/rspack.config.js (3)
  • require (1-1)
  • require (2-2)
  • require (3-3)
config/rspack/serverRspackConfig.js (2)
  • require (2-2)
  • commonRspackConfig (3-3)
config/rspack/clientRspackConfig.js (1)
  • commonRspackConfig (2-2)
🪛 ESLint
config/rspack/serverRspackConfig.js

[error] 5-5: @rspack/core import should occur before import of ./commonRspackConfig

(import/order)


[error] 32-32: Assignment to property of function parameter 'loader'.

(no-param-reassign)


[error] 71-71: Use object destructuring.

(prefer-destructuring)


[error] 75-75: Assignment to property of function parameter 'rule'.

(no-param-reassign)


[error] 101-101: Assignment to property of function parameter 'rule'.

(no-param-reassign)

config/rspack/rspack.config.js

[error] 9-9: Calls to require() should use string literals

(import/no-dynamic-require)


[error] 9-9: Unexpected require().

(global-require)

config/rspack/commonRspackConfig.js

[error] 23-24: Replace (config)·=>⏎· with ⏎··(config)·=>

(prettier/prettier)


[error] 45-45: Insert ,

(prettier/prettier)


[error] 46-46: Insert ,

(prettier/prettier)

🔇 Additional comments (16)
config/rspack/alias.js (1)

1-9: LGTM!

The alias configuration correctly maps Assets to the client assets directory using path.resolve for cross-platform compatibility.

client/app/libs/i18n/default.js (1)

1-9: LGTM!

The default locale and messages are clearly defined. This provides a solid foundation for the i18n setup.

package.json (1)

94-94: LGTM!

The dependency updates correctly reflect the migration to Rspack and the Shakapacker upgrade to 9.1.0 stable. The Rspack packages are appropriately placed in devDependencies, and version ranges are consistent with the latest releases.

Also applies to: 111-112, 142-142

Gemfile (2)

6-6: Verify the Ruby version downgrade is intentional.

The Ruby version was changed from 3.4.6 to 3.4.3, which is a downgrade. Typically, Ruby versions are upgraded to get the latest patches and security fixes. Please confirm this change is intentional (e.g., to match a production or CI environment constraint) and not a mistake.


9-9: LGTM!

The Shakapacker gem upgrade to 9.1.0 stable aligns with the PR objectives and the corresponding npm package update.

config/rspack/test.js (1)

1-5: LGTM!

The test configuration correctly sets NODE_ENV to 'test' and exports the result of rspackConfig(). This is consistent with the pattern used in the development and production configurations.

config/shakapacker.yml (1)

12-12: LGTM!

The assets_bundler: rspack configuration correctly instructs Shakapacker to use Rspack instead of webpack. This is the key setting that enables the bundler migration described in the PR objectives.

config/rspack/rspack.config.js (2)

5-13: Dynamic require pattern is appropriate here.

The dynamic require() on Line 9 enables environment-specific configuration overrides, which is a common and practical pattern for build tooling. ESLint flags this as a potential issue, but the code includes an existsSync check to ensure safety.

If you'd like to silence the ESLint warnings, you can add an inline comment:

 const envSpecificConfig = () => {
   const path = resolve(__dirname, `${env.nodeEnv}.js`);
   if (existsSync(path)) {
     console.log(`Loading ENV specific rspack configuration file ${path}`);
+    // eslint-disable-next-line import/no-dynamic-require, global-require
     return require(path);
   }

1-15: LGTM!

The configuration entry point correctly loads environment-specific configs when available and falls back to generateWebpackConfig() otherwise. This provides flexibility while maintaining a sensible default.

config/rspack/serverRspackConfig.js (7)

7-12: LGTM!

The comment clearly explains the mutability concern and why creating a fresh config object is necessary. This approach correctly prevents unintended modifications to the shared common config.


14-23: LGTM!

The server entry validation is correct with a clear error message that guides developers on what's needed.


25-42: LGTM!

The server bundle configuration correctly:

  • Assigns the single server entry
  • Removes mini-css-extract-plugin from loaders (server doesn't emit CSS)
  • Disables code splitting with LimitChunkCountPlugin
  • Sets minimize: false for optimization

44-56: LGTM!

The output configuration is appropriate for SSR:

  • Single bundle file server-bundle.js in ssr-generated/ directory
  • Sets globalObject: 'this' for correct server-side execution
  • Includes helpful comment about React on Rails Pro's libraryTarget: 'commonjs2' option

58-65: LGTM! Plugin filtering is appropriate.

The filtering correctly removes plugins unnecessary for server bundles:

  • WebpackAssetsManifest (manifest handled by client build)
  • MiniCssExtractPlugin (CSS handled by client build)
  • ForkTsCheckerWebpackPlugin (type checking not needed for server bundle)

105-113: LGTM!

The devtool setting and target comment are appropriate:

  • eval provides fast builds and good line numbers for SSR debugging
  • Helpful comment explains when to uncomment target: 'node' for React on Rails Pro

115-118: LGTM!

The module export is correct and follows the expected pattern for Shakapacker config functions.

Comment on lines +2 to +8
export const translations = {
en: {
'app.name': 'React Webpack Rails Tutorial',
'comment.form.name_label': 'Name',
'comment.form.text_label': 'Text',
'comment.form.submit': 'Submit',
},
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🛠️ Refactor suggestion | 🟠 Major

Eliminate code duplication with defaultMessages.

The English translations here duplicate defaultMessages from client/app/libs/i18n/default.js. This violates the DRY principle and creates a maintenance burden—updating English text requires changes in two places.

Apply this refactor to import and reuse defaultMessages:

+import { defaultMessages } from './default';
+
 // Translation messages for different locales
 export const translations = {
-  en: {
-    'app.name': 'React Webpack Rails Tutorial',
-    'comment.form.name_label': 'Name',
-    'comment.form.text_label': 'Text',
-    'comment.form.submit': 'Submit',
-  },
+  en: defaultMessages,
   es: {
     'app.name': 'Tutorial de React Webpack Rails',
     'comment.form.name_label': 'Nombre',
     'comment.form.text_label': 'Texto',
     'comment.form.submit': 'Enviar',
   },
 };
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
export const translations = {
en: {
'app.name': 'React Webpack Rails Tutorial',
'comment.form.name_label': 'Name',
'comment.form.text_label': 'Text',
'comment.form.submit': 'Submit',
},
import { defaultMessages } from './default';
// Translation messages for different locales
export const translations = {
en: defaultMessages,
es: {
'app.name': 'Tutorial de React Webpack Rails',
'comment.form.name_label': 'Nombre',
'comment.form.text_label': 'Texto',
'comment.form.submit': 'Enviar',
},
};
🤖 Prompt for AI Agents
In client/app/libs/i18n/translations.js around lines 2 to 8, the English
translations duplicate strings from client/app/libs/i18n/default.js; import
defaultMessages from that file and reuse it rather than hardcoding the same keys
here (e.g., replace the inline en object with a spread/merge of defaultMessages
into translations.en), ensuring any additional or overridden keys remain after
the spread so updates live in one place.

Comment on lines 23 to 66
const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
'.scss'.match(config.test) && config.use,
);

if (scssConfigIndex === -1) {
console.warn('No SCSS rule with use array found in rspack config');
} else {
// Configure sass-loader to use the modern API
const scssRule = baseClientRspackConfig.module.rules[scssConfigIndex];
const sassLoaderIndex = scssRule.use.findIndex((loader) => {
if (typeof loader === 'string') {
return loader.includes('sass-loader');
}
return loader.loader && loader.loader.includes('sass-loader');
});

if (sassLoaderIndex !== -1) {
const sassLoader = scssRule.use[sassLoaderIndex];
if (typeof sassLoader === 'string') {
scssRule.use[sassLoaderIndex] = {
loader: sassLoader,
options: {
api: 'modern'
}
};
} else {
sassLoader.options = sassLoader.options || {};
sassLoader.options.api = 'modern';
}
}

// Fix css-loader configuration for CSS modules if namedExport is enabled
// When namedExport is true, exportLocalsConvention must be camelCaseOnly or dashesOnly
const cssLoader = scssRule.use.find((loader) => {
const loaderName = typeof loader === 'string' ? loader : loader?.loader;
return loaderName?.includes('css-loader');
});

if (cssLoader?.options?.modules?.namedExport) {
cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
}

baseClientRspackConfig.module.rules[scssConfigIndex].use.push(sassLoaderConfig);
}
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⚠️ Potential issue | 🟠 Major

Fix Prettier violations to unblock lint.

eslint --fix fails here:

  • Lines 23-24 need the multiline arrow formatting Prettier expects.
  • Lines 45-46 are missing trailing commas.
    These are hard errors, so bundles won’t build until the style issues are resolved.
🧰 Tools
🪛 ESLint

[error] 23-24: Replace (config)·=>⏎· with ⏎··(config)·=>

(prettier/prettier)


[error] 45-45: Insert ,

(prettier/prettier)


[error] 46-46: Insert ,

(prettier/prettier)

🤖 Prompt for AI Agents
config/rspack/commonRspackConfig.js lines 23-66: Prettier is failing — change
the single-line arrow callback passed to findIndex into an explicit multiline
arrow function with braces and a return (so the function is formatted across
lines), and add missing trailing commas to the object literals you create when
replacing the sass-loader (ensure options: { api: 'modern', }, and the outer
object has a trailing comma as well) so the created objects conform to
Prettier's trailing-comma rules.

Copy link

claude bot commented Oct 10, 2025

Pull Request Review: Update to Shakapacker 9.1.0 and migrate to Rspack

Overall Assessment

This is a well-executed migration from webpack to Rspack with Shakapacker 9.1.0. The PR is comprehensive and maintains backward compatibility. The code quality is generally good, but there are a few areas that could be improved.

✅ Strengths

  1. Thorough Documentation: The PR description is excellent with clear summary, testing details, and performance expectations
  2. Complete Configuration Migration: All necessary Rspack configuration files have been created mirroring the webpack setup
  3. Backward Compatibility: The webpack configurations are retained, providing a safe rollback path
  4. Testing Coverage: Build testing across all environments (development, test, production) has been performed

🔍 Code Quality Issues

Critical Issues

1. Ruby Version Downgrade (Gemfile:6)

-ruby "3.4.6"
+ruby "3.4.3"

This is a concerning change. Why was the Ruby version downgraded from 3.4.6 to 3.4.3? This appears unrelated to the Rspack migration and could:

  • Introduce security vulnerabilities if 3.4.6 contains important fixes
  • Cause issues in production if different environments use different Ruby versions
  • Break compatibility with dependencies that require 3.4.6+

Recommendation: Revert this change or provide explicit justification in the PR description.

High Priority Issues

2. Missing Error Handling in Configuration Files

config/rspack/commonRspackConfig.js:23-66

  • The SCSS configuration logic has complex nested conditionals but no error recovery
  • If cssLoader.options.modules is unexpectedly undefined, line 62 will throw
  • The sass-loader modification assumes the loader exists but doesn't validate

Recommendation: Add defensive checks:

if (cssLoader?.options?.modules?.namedExport) {
  if (!cssLoader.options.modules.exportLocalsConvention) {
    cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
  }
}

3. Potentially Unsafe CSS Loader Configuration

config/rspack/serverRspackConfig.js:95-96

if (cssLoader && cssLoader.options) {
  cssLoader.options.modules = { exportOnlyLocals: true };
}

This overwrites the entire modules configuration instead of merging. This could lose existing module configuration like namedExport, localIdentName, etc.

Recommendation:

if (cssLoader && cssLoader.options) {
  cssLoader.options.modules = {
    ...cssLoader.options.modules,
    exportOnlyLocals: true
  };
}

4. Incomplete Type Safety for Loader Checks

config/rspack/serverRspackConfig.js:100-102

  • Checks for url-loader and file-loader but doesn't verify rule.use.options exists before setting emitFile
  • Could throw if options is undefined

Recommendation:

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options = rule.use.options || {};
  rule.use.options.emitFile = false;
}

Medium Priority Issues

5. New i18n Files Appear Unused or Untested

client/app/libs/i18n/default.js and client/app/libs/i18n/translations.js

  • These files appear to already exist based on the grep results showing existing imports
  • The PR description doesn't mention i18n changes
  • If these are new files, there's no evidence they're being tested or used

Recommendation:

  • If these files already exist, they shouldn't show as "new" in the diff
  • If they're replacing existing files, add migration notes
  • Add tests for the i18n functionality

6. Hardcoded Path in sass-resources-loader

config/rspack/commonRspackConfig.js:15

resources: './client/app/assets/styles/app-variables.scss',
  • Uses a relative path that could break depending on execution context
  • Should use path.resolve(__dirname, ...) for consistency with other paths in the config

Recommendation:

const path = require('path');
// ...
resources: path.resolve(__dirname, '../../client/app/assets/styles/app-variables.scss'),

7. Missing Package Version Constraints

package.json:111-113

"@rspack/cli": "^1.5.8",
"@rspack/core": "^1.5.8",
  • Using caret ranges for critical bundler dependencies
  • If Rspack 1.6.0 introduces breaking changes, builds could fail unexpectedly

Recommendation: Consider using exact versions or tilde ranges for more predictable builds, especially for a bundler migration.

🔒 Security Considerations

No Critical Security Issues Found

  • Dependencies are from official npm registry
  • No obvious code injection vulnerabilities
  • Configuration files don't expose secrets

Minor Concern: The ignoreWarnings configuration in commonRspackConfig.js:20 suppresses a React DOM client warning. Ensure this warning is genuinely expected and not masking a real issue.

⚡ Performance Considerations

Positive:

  • Rspack's performance benefits are well-documented (2-10x faster builds)
  • Configuration appears optimized (modern sass API, proper CSS modules setup)
  • Server bundle optimization disables minimization appropriately for SSR

Suggestions:

  1. Consider adding build time benchmarks to the PR description
  2. Monitor production bundle sizes to ensure no unexpected increases

🧪 Test Coverage

Missing Tests:

  • No automated tests for the new Rspack configuration files
  • No integration tests verifying SSR still works with Rspack
  • No tests for the new i18n files (if they're actually new)

Recommendation: Add smoke tests that verify:

  • Client bundle builds successfully
  • Server bundle builds successfully
  • SSR rendering still functions
  • HMR works in development

📝 Documentation

Good:

  • Comprehensive PR description
  • Inline comments explaining configuration choices
  • References to Rspack documentation

Missing:

  • No update to project README about the bundler change
  • No migration guide for other developers
  • No documentation about when/why to use webpack vs rspack

🎯 Best Practices

Well Done:

  • Consistent code style
  • Logical file organization
  • Proper use of environment-specific configs
  • Good separation of concerns (client/server/common configs)

Could Improve:

  • Add JSDoc comments to exported functions
  • Consider extracting magic strings to constants
  • Add validation for required configuration options

📊 Summary

Approve with Changes Requested

This PR represents solid engineering work on a complex migration. However, the Ruby version downgrade is a blocker that needs explanation, and the CSS loader configuration issues could cause runtime problems.

Required Changes:

  1. ✅ Explain or revert Ruby version downgrade (3.4.6 → 3.4.3)
  2. ✅ Fix CSS modules object spreading in serverRspackConfig.js
  3. ✅ Add defensive checks in commonRspackConfig.js

Recommended Changes:

  1. Use absolute paths for file resources
  2. Add tests for critical build configurations
  3. Document the bundler change in README
  4. Verify i18n files are intentional additions

Nice to Have:

  1. Add JSDoc comments
  2. Include build time benchmarks
  3. Consider stricter dependency versioning

Great work on this migration! Once the critical issues are addressed, this will be a valuable improvement to the project.


Review generated with Claude Code

CI is configured to use Ruby 3.4.6, but Gemfile was accidentally set to 3.4.3 during local development. This was causing bundle install to fail in CI with exit code 18.

Updated:
- Gemfile: ruby 3.4.3 → 3.4.6
- Gemfile.lock: ruby 3.4.3p32 → 3.4.6p32

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

Co-Authored-By: Claude <[email protected]>
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claude bot commented Oct 10, 2025

Pull Request Review: Shakapacker 9.1.0 & Rspack Migration

Summary

This PR successfully upgrades Shakapacker from beta to stable (9.1.0) and migrates from webpack to Rspack. The migration is well-structured and comprehensive. Overall, this is a solid PR with good attention to detail. Below are my findings across different review categories.


✅ Strengths

1. Excellent Configuration Structure

  • Well-organized Rspack configuration with proper separation of concerns (client, server, common, environment-specific)
  • Thoughtful comments explaining complex decisions (e.g., mutable globals, SSR configurations)
  • Proper handling of CSS modules with exportOnlyLocals: true for SSR

2. Backward Compatibility

  • Non-breaking change that maintains full compatibility
  • Old webpack configs preserved for reference
  • Proper migration path documented

3. Modern Best Practices

  • Modern sass-loader API configuration (api: 'modern')
  • Proper devtool settings (eval for SSR for faster debugging)
  • Correct handling of CSS in SSR (no style extraction on server bundle)

⚠️ Issues & Recommendations

High Priority

1. ESLint Configuration Needs Update

Location: .eslintrc:46-47

The ESLint webpack resolver is still pointing to the old webpack config:

webpack:
  config: 'config/webpack/development.js'

Recommendation: Update to point to Rspack config or remove if not needed:

webpack:
  config: 'config/rspack/development.js'

2. Unused i18n Files Without Integration

Locations:

  • client/app/libs/i18n/default.js
  • client/app/libs/i18n/translations.js

These new files define translations but:

  • The translations export is never imported or used anywhere in the codebase
  • defaultMessages is exported but never imported
  • Only defaultLocale is actually used (in selectLanguage.jsx)
  • The existing i18n system uses a different pattern (doesn't reference these files)

Recommendation:

  • Option A: Remove these files if they were added by mistake
  • Option B: If intentional, integrate them into the existing i18n system and document the migration plan
  • Option C: Add a TODO comment explaining future integration plans

3. Potential Code Duplication in serverRspackConfig.js

Location: config/rspack/serverRspackConfig.js:27-36 and 67-83

The code filters out mini-css-extract-plugin from loaders in two places:

  • Lines 27-36: First pass through loaders
  • Lines 67-83: Second pass through rules

Recommendation: Consider consolidating into a single pass or add a comment explaining why two passes are necessary.


Medium Priority

4. Regex Matching Logic Could Be More Robust

Location: config/rspack/commonRspackConfig.js:23-24

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
  '.scss'.match(config.test) && config.use,
);

Issue: This assumes config.test is always a RegExp. If it's a string or function, this could fail silently.

Recommendation:

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
  config.test && config.test.test('.scss') && config.use,
);

5. Missing Error Handling

Location: config/rspack/commonRspackConfig.js:39-52

If sassLoaderIndex is found but the loader has unexpected structure, the code could fail.

Recommendation: Add defensive checks or wrap in try-catch with meaningful error messages.

6. Inconsistent Optional Chaining

Location: config/rspack/serverRspackConfig.js:95

The code uses optional chaining inconsistently. Line 95 uses cssLoader.options without optional chaining after checking cssLoader exists.

Recommendation: Use consistent patterns:

if (cssLoader?.options) {
  cssLoader.options.modules = { exportOnlyLocals: true };
}

Low Priority

7. Version Mismatch in Gemfile.lock

Location: Gemfile.lock

Ruby version changed from 3.4.6p54 to 3.4.6p32 - this appears to be a patch version downgrade.

Question: Is this intentional? Typically, patch versions should move forward, not backward.

8. Missing Type Safety

The Rspack configuration files are JavaScript without JSDoc comments. Consider adding JSDoc for better IDE support:

/**
 * @returns {import('@rspack/core').Configuration}
 */
const configureServer = () => {
  // ...
};

9. Console.warn vs Console.log

Location: config/rspack/commonRspackConfig.js:28

Uses console.warn for a non-warning message. Consider console.error or throw an error since missing SCSS config is likely a serious issue.


🔒 Security Considerations

No security concerns identified. The changes are configuration-only and don't introduce new security vulnerabilities.


🚀 Performance Considerations

Excellent performance improvements expected:

  • Rspack provides 2-10x faster cold builds
  • 5-20x faster incremental builds
  • Proper code splitting maintained
  • SSR optimization with eval devtool is a good choice

🧪 Test Coverage

⚠️ Concerns:

  1. No visible test additions/updates for the new configuration
  2. The i18n files added have no tests
  3. Consider adding:
    • Integration tests verifying Rspack builds succeed
    • Tests confirming SSR still works correctly
    • Tests for the new i18n files (if they're meant to be used)

Note: The PR description mentions builds tested successfully, which is good. Consider adding automated tests to prevent regressions.


📋 Code Quality

Overall: Good (8/10)

Positives:

  • Clean, readable code
  • Good use of comments
  • Follows existing patterns
  • Proper error messages

Areas for improvement:

  • More defensive programming
  • Consistency in optional chaining
  • Type annotations (JSDoc)

🎯 Action Items

Before merging:

  1. ✅ Update or remove ESLint webpack resolver config
  2. ✅ Address the unused i18n files (remove or integrate)
  3. ✅ Clarify Ruby version change in Gemfile.lock

Nice to have:
4. Add JSDoc type annotations
5. Consolidate duplicate filtering logic
6. Add integration tests for Rspack builds
7. More robust regex matching for loader detection


💡 Final Recommendation

Conditional Approval - This is excellent work on a complex migration! The core changes are solid and well-thought-out. Please address the high-priority items (ESLint config and unused i18n files) before merging. The medium and low priority items can be addressed in follow-up PRs if preferred.

Great job on this migration! 🎉


🤖 Generated with Claude Code

justin808 and others added 2 commits October 10, 2025 13:42
The automatic React runtime was causing issues with React on Rails server-side rendering.
Switching to classic runtime ensures compatibility with React on Rails SSR function detection.

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

Co-Authored-By: Claude <[email protected]>
Preserve namedExport and exportLocalsConvention settings when adding
exportOnlyLocals for SSR. This prevents CSS module imports from being
undefined in the server-rendered bundle.

The previous code was replacing the entire modules object, which broke
the namedExport configuration required by Shakapacker 9.

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

Co-Authored-By: Claude <[email protected]>
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Actionable comments posted: 2

🧹 Nitpick comments (3)
config/rspack/serverRspackConfig.js (2)

5-5: Consider reordering import for consistency.

The @rspack/core import should come before local module imports per the import/order convention. As per static analysis hints.

Apply this diff:

 const path = require('path');
 const { config } = require('shakapacker');
-const commonRspackConfig = require('./commonRspackConfig');
-
 const rspack = require('@rspack/core');
+const commonRspackConfig = require('./commonRspackConfig');

8-12: Clarify the merge comment.

The comment mentions using "merge," but this function doesn't call merge directly. The merge happens inside commonRspackConfig() (as seen in the relevant code snippet from line 68 of commonRspackConfig.js). Consider updating the comment to reflect this or removing it to avoid confusion.

config/swc.config.js (1)

13-14: Revise the JSX runtime comment for accuracy. React on Rails supports both the automatic and classic JSX transforms for SSR—as long as your server bundle can resolve react/jsx-runtime—so calling out “better SSR compatibility” is misleading. Either:

  • Keep runtime: 'classic' but update the comment to explain you’re choosing classic to ensure React is in scope without bundling react/jsx-runtime, or
  • Revert to automatic and configure your SSR build to include the new JSX runtime helpers.

config/swc.config.js: lines 13–14

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 087ec70 and 3fe61f0.

📒 Files selected for processing (2)
  • config/rspack/serverRspackConfig.js (1 hunks)
  • config/swc.config.js (1 hunks)
🧰 Additional context used
🧬 Code graph analysis (1)
config/rspack/serverRspackConfig.js (1)
config/rspack/commonRspackConfig.js (3)
  • require (2-2)
  • commonRspackConfig (69-69)
  • cssLoader (56-59)
🪛 ESLint
config/rspack/serverRspackConfig.js

[error] 5-5: @rspack/core import should occur before import of ./commonRspackConfig

(import/order)


[error] 32-32: Assignment to property of function parameter 'loader'.

(no-param-reassign)


[error] 71-71: Use object destructuring.

(prefer-destructuring)


[error] 75-75: Assignment to property of function parameter 'rule'.

(no-param-reassign)


[error] 105-105: Assignment to property of function parameter 'rule'.

(no-param-reassign)

🔇 Additional comments (5)
config/rspack/serverRspackConfig.js (5)

14-23: LGTM!

The validation for the required server-bundle entry is clear and provides a helpful error message if the entry is missing.


38-42: LGTM!

Disabling code splitting and minimization for the server bundle is appropriate for SSR builds.


44-56: LGTM!

The server output configuration correctly sets up the SSR bundle path and options. The commented libraryTarget hint is helpful for React on Rails Pro users.


58-65: LGTM!

Filtering out client-specific plugins (asset manifest, CSS extraction, TypeScript checking) is appropriate for the server bundle.


109-117: LGTM!

The eval devtool setting is a good choice for fast SSR builds with readable stack traces. The commented guidance about setting target: 'node' for React on Rails Pro is helpful.

Comment on lines +27 to +36
// Remove the mini-css-extract-plugin from the style loaders because
// the client build will handle exporting CSS.
// replace file-loader with null-loader
serverRspackConfig.module.rules.forEach((loader) => {
if (loader.use && loader.use.filter) {
loader.use = loader.use.filter(
(item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)),
);
}
});
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🛠️ Refactor suggestion | 🟠 Major

Remove duplicate mini-css-extract-plugin filtering.

This filtering logic is duplicated at lines 67-107, where it's handled more comprehensively along with other SSR-specific loader adjustments. The duplicate code reduces maintainability without adding value.

Apply this diff:

   serverRspackConfig.entry = serverEntry;
 
-  // Remove the mini-css-extract-plugin from the style loaders because
-  // the client build will handle exporting CSS.
-  // replace file-loader with null-loader
-  serverRspackConfig.module.rules.forEach((loader) => {
-    if (loader.use && loader.use.filter) {
-      loader.use = loader.use.filter(
-        (item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)),
-      );
-    }
-  });
-
   // No splitting of chunks for a server bundle
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
// Remove the mini-css-extract-plugin from the style loaders because
// the client build will handle exporting CSS.
// replace file-loader with null-loader
serverRspackConfig.module.rules.forEach((loader) => {
if (loader.use && loader.use.filter) {
loader.use = loader.use.filter(
(item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)),
);
}
});
serverRspackConfig.entry = serverEntry;
// No splitting of chunks for a server bundle
🧰 Tools
🪛 ESLint

[error] 32-32: Assignment to property of function parameter 'loader'.

(no-param-reassign)

🤖 Prompt for AI Agents
In config/rspack/serverRspackConfig.js around lines 27 to 36, remove the
duplicate block that filters out mini-css-extract-plugin from loader.use — this
logic is already implemented comprehensively later (lines 67–107). Delete the
entire forEach that checks loader.use.filter and reassigns loader.use to the
filtered array so only the later SSR-specific loader adjustments remain,
ensuring no functional changes beyond removing the redundant duplicate.

Comment on lines +104 to +106
} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
rule.use.options.emitFile = false;
}
Copy link

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⚠️ Potential issue | 🟠 Major

Add null safety check for rule.use.options.

When rule.use is an object (not an array), accessing rule.use.options.emitFile without verifying that options exists could cause a runtime error if a loader doesn't define options.

Apply this diff:

     // Skip writing image files during SSR by setting emitFile to false
   } else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
-    rule.use.options.emitFile = false;
+    if (rule.use.options) {
+      rule.use.options.emitFile = false;
+    }
   }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
rule.use.options.emitFile = false;
}
// Skip writing image files during SSR by setting emitFile to false
} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
if (rule.use.options) {
rule.use.options.emitFile = false;
}
}
🧰 Tools
🪛 ESLint

[error] 105-105: Assignment to property of function parameter 'rule'.

(no-param-reassign)

🤖 Prompt for AI Agents
In config/rspack/serverRspackConfig.js around lines 104 to 106, the code sets
rule.use.options.emitFile without ensuring rule.use.options exists; update the
branch handling object-style rule.use to first ensure rule.use.options is
defined (e.g. if (!rule.use.options) rule.use.options = {}), then set
rule.use.options.emitFile = false so you avoid runtime errors when options is
undefined.

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claude bot commented Oct 11, 2025

Pull Request Review: Shakapacker 9.1.0 & Rspack Migration

I've completed a comprehensive review of PR #680. Overall, this is a well-executed migration from webpack to Rspack with Shakapacker 9.1.0. Here's my detailed feedback:


✅ Strengths

  1. Excellent Documentation

    • The PR description is thorough and well-structured
    • Clear explanation of changes, performance benefits, and testing
    • Good use of commit messages to track incremental fixes
  2. Comprehensive Configuration Migration

    • Complete Rspack configuration mirroring the webpack setup
    • Proper separation of client/server bundles
    • Environment-specific configurations (dev/prod/test)
  3. SSR Compatibility

    • Thoughtful handling of server-side rendering requirements
    • Correct CSS modules configuration with exportOnlyLocals: true for SSR (config/rspack/serverRspackConfig.js:95-96)
    • Appropriate changes to React runtime (classic instead of automatic) for better SSR compatibility (config/swc.config.js:14)
  4. Performance Focus

    • The switch to Rspack aligns with modern build tool trends
    • Expected 2-10x faster cold builds and 5-20x faster incremental builds

🔍 Issues & Concerns

Critical: Potential Bug in CSS Modules Configuration

Location: config/rspack/serverRspackConfig.js:95-96

if (cssLoader && cssLoader.options) {
  cssLoader.options.modules = { exportOnlyLocals: true };
}

Issue: This code overwrites the entire modules configuration object, potentially losing existing settings like namedExport, exportLocalsConvention, etc. that were configured in commonRspackConfig.js:61-62.

Impact: This could break CSS modules that rely on named exports or specific naming conventions.

Recommendation:

if (cssLoader && cssLoader.options && cssLoader.options.modules) {
  cssLoader.options.modules = {
    ...cssLoader.options.modules,
    exportOnlyLocals: true,
  };
}

Medium: Inconsistent CSS Loader Handling

Location: config/rspack/commonRspackConfig.js:61-62

The code checks for namedExport before setting exportLocalsConvention, but doesn't validate if modules itself is enabled:

if (cssLoader?.options?.modules?.namedExport) {
  cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
}

Recommendation: Add a check to ensure modules is enabled:

if (cssLoader?.options?.modules) {
  if (cssLoader.options.modules.namedExport) {
    cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
  }
}

Low: Code Duplication in serverRspackConfig.js

Location: Lines 30-36 and 72-82

The code filters out mini-css-extract-plugin twice in the same file. The second block (lines 72-82) appears more comprehensive as it also removes style-loader.

Recommendation: Consider consolidating this logic or adding a comment explaining why it's done in two places.


📝 Code Quality Suggestions

  1. Error Handling Enhancement

    Location: config/rspack/serverRspackConfig.js:19-23

    The error message is good, but could benefit from more context:

    if (!serverEntry['server-bundle']) {
      throw new Error(
        "Missing 'server-bundle' entry point. Create a pack with the file name 'server-bundle.js' containing all the server rendering files. Check your entry points configuration."
      );
    }
  2. Magic String in rspackConfig.js

    Location: Line 13 has a typo: the the

    // For HMR, need to separate the the client and server rspack configurations

    Should be:

    // For HMR, need to separate the client and server rspack configurations
  3. Sass Loader Options Safety

    Location: config/rspack/commonRspackConfig.js:39-51

    Good defensive programming, but consider extracting the sass-loader configuration logic into a separate function for better testability.


🔒 Security Assessment

No security concerns identified

  • Dependencies are from trusted sources (@rspack/*, rspack-manifest-plugin)
  • No credentials, API keys, or sensitive data in configuration files
  • Proper use of environment-specific configurations

🧪 Test Coverage

Observations:

  • PR description mentions successful testing of dev/test/prod builds ✅
  • RuboCop linting passed ✅
  • Missing: No automated tests for the new Rspack configurations themselves
  • Missing: No tests verifying CSS modules work correctly in SSR context

Recommendations:

  1. Add integration tests to verify bundle generation
  2. Add tests to ensure CSS modules export correctly for both client and server bundles
  3. Consider adding a test that validates the i18n files are properly bundled

⚡ Performance Considerations

Positive:

  • Rspack is a significant performance upgrade
  • Configuration properly disables optimization for server bundle (serverRspackConfig.js:39-41)
  • eval devtool for server bundle is the right choice for fast SSR debugging (serverRspackConfig.js:108)

Consider:

  • Monitor bundle sizes post-migration to ensure no regression
  • Verify that HMR (Hot Module Replacement) works as expected in development
  • The ignoreWarnings configuration (commonRspackConfig.js:19-21) suppresses React 18+ warnings - ensure this doesn't hide real issues

🎯 Additional Observations

  1. i18n Files Addition

    • The addition of client/app/libs/i18n/default.js and translations.js appears intentional (separate commit)
    • These files are properly imported and used throughout the codebase ✅
    • Good addition for internationalization support
  2. Ruby Version Change

    • Gemfile.lock shows Ruby version changed from 3.4.6p54 to 3.4.6p32
    • This might be environment-specific; ensure CI/CD environments are aligned
  3. Webpack Configuration Retention

    • The PR mentions webpack configs can be kept for reference or removed later
    • Recommendation: Add a follow-up issue/PR to remove old webpack configs to avoid confusion

📋 Summary

Approval Status:Approve with minor fixes recommended

This is a solid migration with good attention to detail. The main concern is the CSS modules configuration bug in serverRspackConfig.js that could break existing functionality. I recommend:

  1. Before merge: Fix the CSS modules configuration overwrite issue
  2. Before merge: Fix the typo ("the the")
  3. After merge: Add automated tests for bundle generation
  4. After merge: Clean up old webpack configurations

The performance benefits of Rspack and the thorough configuration work make this a valuable upgrade. Great work on maintaining backward compatibility!


Review completed by: Claude Code
Reviewed on: $(date +%Y-%m-%d)

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claude bot commented Oct 11, 2025

Code Review: Update to Shakapacker 9.1.0 and Migrate to Rspack

Summary

This PR successfully migrates from webpack to Rspack as the JavaScript bundler and upgrades Shakapacker from beta to stable. The migration is well-executed with comprehensive configuration files that mirror the webpack setup while taking advantage of Rspack-specific optimizations.

✅ Strengths

1. Comprehensive Configuration Migration

  • All webpack configurations have been properly translated to Rspack equivalents
  • Separate client/server bundle configurations maintain SSR functionality
  • Environment-specific configs (development, production, test) are properly structured

2. Well-Documented Changes

  • Clear commit messages explaining each change
  • Inline comments explaining configuration decisions
  • Good explanation of the performance benefits (2-10x faster builds)

3. SSR Compatibility Fixes

  • Multiple commits addressing SSR issues show thorough testing
  • CSS modules configuration properly preserves namedExport settings (commit 3fe61f0)
  • React runtime switched to 'classic' for better SSR compatibility (commit 5d85f15)

4. Proper Dependency Management

  • All required Rspack dependencies added
  • Version constraints are appropriate
  • Ruby version mismatch fixed for CI compatibility

🔍 Issues & Recommendations

High Priority

1. Missing File Path Validation (config/rspack/commonRspackConfig.js:15)

The SCSS resources path is hardcoded without validation:

resources: './client/app/assets/styles/app-variables.scss',

Recommendation: Add path validation or use path.resolve() with existence check to fail fast if the file is missing.

const path = require('path');
const fs = require('fs');
const appVariablesPath = path.resolve(__dirname, '../../client/app/assets/styles/app-variables.scss');
if (!fs.existsSync(appVariablesPath)) {
  throw new Error(`SCSS variables file not found: ${appVariablesPath}`);
}

2. Mutable Global Object Mutation (config/rspack/commonRspackConfig.js:65, 69)

The code mutates baseClientRspackConfig directly:

baseClientRspackConfig.module.rules[scssConfigIndex].use.push(sassLoaderConfig);
// ...
const commonRspackConfig = () => merge({}, baseClientRspackConfig, commonOptions, ignoreWarningsConfig);

Issue: The comment on line 69 says "Copy the object using merge b/c the baseClientRspackConfig and commonOptions are mutable globals", but the config is already mutated on line 65 before the merge.

Recommendation: Either:

  • Move the mutation inside the function returned by commonRspackConfig, or
  • Deep clone before mutation

3. Potential Null Reference (config/rspack/serverRspackConfig.js:104-106)

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options.emitFile = false;
}

Issue: No check for rule.use.options existence before assignment.

Fix:

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options = rule.use.options || {};
  rule.use.options.emitFile = false;
}

Medium Priority

4. Inconsistent Loader Finding Logic (config/rspack/commonRspackConfig.js:32-37 vs 56-59)

The code uses two different patterns for finding loaders in the same file:

  • Lines 32-37: More defensive with type checking
  • Lines 56-59: More concise with optional chaining

Recommendation: Standardize on one approach for consistency and maintainability.

5. Duplicate Code in serverRspackConfig.js

Lines 27-36 and lines 67-83 both filter out mini-css-extract-plugin and style-loader.

Recommendation: Extract to a helper function:

const removeStyleLoaders = (rules) => {
  rules.forEach((loader) => {
    if (loader.use && loader.use.filter) {
      loader.use = loader.use.filter(
        (item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)) && item !== 'style-loader'
      );
    }
  });
};

6. Hard-coded Plugin Names (config/rspack/serverRspackConfig.js:60-65)

plugin.constructor.name !== 'WebpackAssetsManifest' &&
plugin.constructor.name !== 'MiniCssExtractPlugin' &&
plugin.constructor.name !== 'ForkTsCheckerWebpackPlugin'

Issue: Constructor names can be minified in production builds, causing this filter to fail.

Recommendation: Use instanceof checks or plugin-specific properties instead.

Low Priority

7. I18n Translation Files (client/app/libs/i18n/)

The new translation files appear to be stub/placeholder data:

  • default.js and translations.js have minimal, hardcoded strings
  • No clear integration with the rest of the application

Recommendation:

  • Add comments explaining how these integrate with the app
  • Consider if these should be in a config/locale directory instead
  • Add tests for i18n functionality

8. Missing Error Handling (config/rspack/serverRspackConfig.js:19-23)

if (!serverEntry['server-bundle']) {
  throw new Error(
    "Create a pack with the file name 'server-bundle.js' containing all the server rendering files",
  );
}

Enhancement: This error message could be more helpful by suggesting where to create the file:

throw new Error(
  "Server bundle entry 'server-bundle' not found. Create a pack at client/app/packs/server-bundle.js containing all server rendering files",
);

9. Ruby Version Patch Mismatch (Gemfile.lock)

ruby 3.4.6p32

The patch level changed from p54 to p32, which seems like a downgrade. This might be intentional but should be verified.

🔒 Security Considerations

No security issues identified

  • No secrets or credentials in the code
  • Dependencies are from trusted sources
  • No arbitrary code execution vulnerabilities
  • Proper file path handling (though could be improved as noted above)

⚡ Performance Considerations

Performance improvements are excellent

  • Rspack provides 2-10x faster cold builds
  • 5-20x faster incremental builds
  • Proper optimization settings for production
  • Server bundle minimization is appropriately disabled

Minor optimization: Consider adding build caching configuration in production.js for even better performance.

🧪 Test Coverage

Concerns:

  • No new tests added for the Rspack configuration
  • No tests for the i18n translation files
  • The PR mentions tests were run successfully, but no test changes are included

Recommendation: Consider adding integration tests that verify:

  • Both client and server bundles build successfully
  • CSS modules work correctly in both bundles
  • HMR functionality works in development
  • Production builds are optimized correctly

📝 Code Quality

Overall: Good quality with room for improvement

Positives:

  • Clear separation of concerns
  • Good use of comments
  • Consistent naming conventions
  • Proper error messages

Areas for improvement:

  • Reduce code duplication
  • Add more defensive programming
  • Standardize patterns across files
  • Add JSDoc comments for exported functions

🎯 Recommendation

APPROVE with minor revisions

This is a solid migration that maintains backward compatibility while providing significant performance benefits. The high-priority issues should be addressed to prevent potential runtime errors, but they don't block the merge given that the builds are passing.

Before Merging:

  1. Fix the null reference issue in serverRspackConfig.js:104-106
  2. Address the mutable global object concern in commonRspackConfig.js
  3. Consider adding the file path validation for robustness

Post-Merge:

  1. Add integration tests for the Rspack configuration
  2. Refactor duplicate code in serverRspackConfig.js
  3. Document the i18n integration
  4. Consider removing old webpack configs if no longer needed

Great work on this migration! The performance improvements will be very valuable for the development experience.

🤖 Generated with Claude Code

Rspack needs explicit configuration to resolve ReScript compiled .bs.js files
from node_modules dependencies. Without this, ReScript library imports like
@glennsl/rescript-json-combinators fail to resolve.

This is critical for React on Rails apps using ReScript components.

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

Co-Authored-By: Claude <[email protected]>
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claude bot commented Oct 11, 2025

Pull Request Review: Shakapacker 9.1.0 & Rspack Migration

Great work on this major infrastructure upgrade! This is a well-executed migration that brings significant performance improvements. Below is my detailed review:


Strengths

  1. Excellent Migration Strategy

    • Clean separation of Rspack configs mirroring the webpack structure
    • Maintains backward compatibility - webpack configs remain intact
    • Comprehensive testing across all environments (dev/test/prod)
  2. Well-Structured Configuration

    • Good use of functional composition in rspackConfig.js for environment-specific modifications
    • Proper handling of SSR vs client bundles with separate configs
    • Smart handling of mutable global configs via merge() in commonRspackConfig.js:69
  3. SSR Configuration (serverRspackConfig.js)

    • Correctly preserves CSS module settings while adding exportOnlyLocals: true (lines 95-100)
    • Appropriate devtool choice (eval) for faster SSR builds
    • Proper chunk limitation for server bundles
  4. Good Developer Experience

    • Added ReScript .bs.js extension support for proper module resolution
    • Fixed React runtime to 'classic' for SSR compatibility
    • Proper HMR configuration with React Refresh

⚠️ Issues & Recommendations

1. Critical: Potential Runtime Error in serverRspackConfig.js

Location: config/rspack/serverRspackConfig.js:104-106

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options.emitFile = false;
}

Issue: This will throw an error if rule.use.options is undefined.

Fix:

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options = rule.use.options || {};
  rule.use.options.emitFile = false;
}

2. Code Quality: Typo in rspackConfig.js

Location: config/rspack/rspackConfig.js:13

// For HMR, need to separate the the client and server rspack configurations

Fix: Remove duplicate "the"

// For HMR, need to separate the client and server rspack configurations

3. Inconsistent Module Mutation Pattern

Location: config/rspack/commonRspackConfig.js:61-63

While you correctly use merge() to avoid mutating globals when creating the config, you're still mutating cssLoader.options.modules directly:

if (cssLoader?.options?.modules?.namedExport) {
  cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
}

Recommendation: For consistency, consider creating a new object:

if (cssLoader?.options?.modules?.namedExport) {
  cssLoader.options.modules = {
    ...cssLoader.options.modules,
    exportLocalsConvention: 'camelCaseOnly'
  };
}

4. Missing Error Handling

Location: config/rspack/commonRspackConfig.js:39-51

If sassLoader is found but has an unexpected structure, the code could fail silently or throw.

Recommendation: Add validation:

if (sassLoaderIndex !== -1) {
  const sassLoader = scssRule.use[sassLoaderIndex];
  if (typeof sassLoader === 'string') {
    scssRule.use[sassLoaderIndex] = {
      loader: sassLoader,
      options: { api: 'modern' }
    };
  } else if (sassLoader && typeof sassLoader === 'object') {
    sassLoader.options = sassLoader.options || {};
    sassLoader.options.api = 'modern';
  } else {
    console.warn('Unexpected sass-loader structure:', sassLoader);
  }
}

5. i18n Translation Files - Missing Usage

Location: client/app/libs/i18n/default.js & translations.js

The new i18n files export defaultMessages and translations, but I see existing code imports from libs/i18n/default. Good! However:

  • translations.js exports a translations object but it's not imported/used anywhere
  • Consider if both files are needed or if they should be consolidated

Recommendation: Either:

  1. Export both from a single file, or
  2. Remove translations.js if only defaultMessages is used

6. Security Consideration: New Dependencies

The PR adds significant new dependencies:

  • @rspack/core, @rspack/cli - Core bundler (expected)
  • rspack-manifest-plugin - For manifest generation
  • Various @rspack/binding-* - Platform-specific bindings

Recommendation: Consider:

  • Running npm audit to check for vulnerabilities
  • Documenting minimum platform requirements (some bindings are platform-specific)
  • Verifying license compatibility for production use

7. Performance Testing

Location: PR description mentions "2-10x faster builds"

Recommendation: Consider adding:

  • Build time benchmarks to CI/CD (could track regression)
  • Memory usage comparison (Rspack should be more efficient)
  • Bundle size comparison to ensure no bloat

8. Documentation Gap

Missing:

  • Migration guide for other contributors
  • Rollback instructions if issues arise
  • Updated webpack → rspack in relevant docs

Recommendation: Add a docs/rspack-migration.md with:

  • What changed and why
  • How to troubleshoot common issues
  • How to revert if needed (switching assets_bundler back to webpack)

🔍 Testing Recommendations

  1. SSR Testing: Verify server-side rendering works correctly with:

    • CSS modules (both named exports and locals)
    • React components
    • i18n integration
  2. HMR Testing: Confirm Hot Module Replacement works in development:

    • JS changes hot reload
    • CSS/SCSS changes hot reload
    • No full page refresh needed
  3. Production Build: Verify production bundle:

    • Correct minification
    • Source maps generation
    • No dev-only code leaked
  4. ReScript Integration: Test that ReScript compiled .bs.js files resolve correctly from node_modules


📊 Overall Assessment

Code Quality: ⭐⭐⭐⭐☆ (4/5)

  • Well-structured, follows good patterns
  • Minor issues with error handling

Security: ⭐⭐⭐⭐☆ (4/5)

  • New dependencies need audit verification
  • No obvious security issues in code

Performance: ⭐⭐⭐⭐⭐ (5/5)

  • Excellent performance improvements expected
  • Smart configuration choices (eval for SSR, etc.)

Test Coverage: ⭐⭐⭐☆☆ (3/5)

  • Manual testing done, but could benefit from automated tests

🎯 Verdict

This PR is very close to merge-ready once the critical issue in serverRspackConfig.js:104-106 is fixed. The other recommendations are nice-to-haves that can be addressed in follow-up PRs.

Required before merge:

  • Fix rule.use.options undefined error in serverRspackConfig.js

Recommended before merge:

  • Run security audit on new dependencies
  • Add basic rollback documentation

Can be follow-up PRs:

  • Consolidate i18n files
  • Add build performance metrics
  • Comprehensive migration documentation

Great work on this migration! The performance benefits will be substantial. 🚀


Review generated with analysis of 18 changed files across ~900 additions

The @glennsl/rescript-json-combinators package ships without compiled
.bs.js files and its bsconfig.json lacks package-specs configuration.
This causes module resolution failures when Rspack tries to import
these files.

Add patch-package to apply a fix that:
- Removes reference to non-existent examples directory
- Adds package-specs for ES module output
- Configures .bs.js suffix for compiled files

This ensures yarn res:build compiles the dependency correctly.

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

Co-Authored-By: Claude <[email protected]>
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claude bot commented Oct 11, 2025

PR Review: Update to Shakapacker 9.1.0 and migrate to Rspack

Summary

This PR successfully migrates from Shakapacker 9.0.0-beta.8 to 9.1.0 stable and transitions from webpack to Rspack as the bundler. The migration is well-structured with comprehensive configuration files and good iterative fixes for edge cases.

✅ Strengths

1. Excellent Migration Approach

  • Clean separation of client and server configurations
  • Proper handling of mutable global configs using merge()
  • Good documentation in code comments explaining rationale

2. Thorough Edge Case Handling

  • Fixed ReScript .bs.js resolution (commit fbc5781)
  • Patched third-party dependency issues with patch-package
  • Addressed SSR compatibility with React runtime switching
  • Fixed CSS modules configuration for server bundles

3. Performance Benefits

  • Rspack provides 2-10x faster cold builds and 5-20x faster incremental builds
  • This is a significant improvement for developer experience

⚠️ Issues & Recommendations

1. CSS Modules Configuration Logic (config/rspack/commonRspackConfig.js:54-63)

Severity: Medium

The logic for finding and configuring the CSS loader could fail silently:

const cssLoader = scssRule.use.find((loader) => {
  const loaderName = typeof loader === 'string' ? loader : loader?.loader;
  return loaderName?.includes('css-loader');
});

if (cssLoader?.options?.modules?.namedExport) {
  cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
}

Issues:

  • If cssLoader is a string (not an object), the assignment will fail
  • No validation that cssLoader.options is mutable
  • The condition only applies the fix when namedExport is true, but the setting might be needed regardless

Recommendation:

if (cssLoader && typeof cssLoader === 'object' && cssLoader.options?.modules?.namedExport) {
  cssLoader.options = cssLoader.options || {};
  cssLoader.options.modules = cssLoader.options.modules || {};
  cssLoader.options.modules.exportLocalsConvention = 'camelCaseOnly';
}

2. Sass Loader Configuration (config/rspack/commonRspackConfig.js:39-52)

Severity: Low

Similar pattern with potential type safety issues when sassLoader might be a string vs object.

Current code:

if (typeof sassLoader === 'string') {
  scssRule.use[sassLoaderIndex] = {
    loader: sassLoader,
    options: {
      api: 'modern'
    }
  };
} else {
  sassLoader.options = sassLoader.options || {};
  sassLoader.options.api = 'modern';
}

This is actually well-handled! No changes needed here.

3. Server Bundle CSS Modules Config (config/rspack/serverRspackConfig.js:95-101)

Severity: Medium

The spread operator preserves existing config, but there's a potential issue:

if (cssLoader && cssLoader.options && cssLoader.options.modules) {
  cssLoader.options.modules = {
    ...cssLoader.options.modules,
    exportOnlyLocals: true,
  };
}

Issue: This assumes cssLoader is an object with an options property. If it's a string, this will fail.

Recommendation:

if (cssLoader && typeof cssLoader === 'object' && cssLoader.options?.modules) {
  cssLoader.options.modules = {
    ...cssLoader.options.modules,
    exportOnlyLocals: true,
  };
}

4. I18n Translation Files (client/app/libs/i18n/)

Severity: Low

The newly added translation files are stub/default implementations:

  • default.js and translations.js contain the same English messages
  • This creates duplication and potential maintenance issues

Questions:

  • Are these files actually being imported/used by the application?
  • Should default.js import from translations.js to avoid duplication?

Recommendation:

// default.js
import { translations } from './translations';

export const defaultLocale = 'en';
export const defaultMessages = translations.en;

5. Patch-Package Dependency

Severity: Low - Informational

Using patch-package for @glennsl/rescript-json-combinators is pragmatic but creates maintenance burden:

  • The patch needs to be reapplied on every install
  • Upstream fix would be better long-term

Recommendation:

  • Consider opening an issue/PR with the upstream package
  • Document why this patch is needed in a comment or README
  • Add the patch file to version control (already done ✓)

6. Ruby Version Mismatch

Severity: Critical - Already Fixed ✓

Great catch fixing the Ruby version mismatch (3.4.3 → 3.4.6) in commit 087ec70. This was blocking CI.

7. Warning Suppression

Severity: Low

ignoreWarnings: [/Module not found: Error: Can't resolve 'react-dom\/client'/]

This suppresses a legitimate warning. Consider:

  • Is this a real issue that should be fixed?
  • If not, add a comment explaining why it's safe to ignore

🔒 Security Considerations

No security concerns identified:

  • Dependency updates are from official packages
  • No sensitive data exposure
  • Patch-package modifications are transparent and version-controlled
  • No dynamic code execution or eval usage beyond standard build tools

🧪 Test Coverage

Observation: No new tests added for the Rspack configuration.

While build configuration typically doesn't have unit tests, consider:

  • Integration tests that verify both client and server bundles build successfully
  • Tests that SSR works correctly with the new configuration
  • The PR description mentions manual testing was done ✓

📋 Documentation

Missing:

  • Migration guide for other developers/projects
  • Performance benchmarks (actual numbers for this project)
  • Rollback procedure if issues arise

Suggestion: Add a docs/rspack-migration.md file documenting:

  • Why Rspack was chosen
  • Migration steps taken
  • Known issues and workarounds
  • Performance improvements observed

🎯 Final Verdict

Recommendation: Approve with minor improvements

This is a solid migration PR that demonstrates:

  • ✅ Good understanding of the build system
  • ✅ Iterative problem-solving approach
  • ✅ Comprehensive testing
  • ✅ Clear communication in commit messages

The identified issues are mostly edge cases and code quality improvements that can be addressed in a follow-up PR or before merge.

Priority Fixes Before Merge:

  1. Add type safety checks for loader configuration (Medium priority)
  2. Deduplicate i18n translations (Low priority)
  3. Add comment explaining why react-dom/client warning is ignored

Nice to Have (Follow-up PR):

  • Documentation for the migration
  • Consider upstream PR for rescript-json-combinators
  • Performance benchmarks

Great work on this migration! 🚀

- Remove postinstall-postinstall dependency (causes engine check issues)
- Regenerate patch file using patch-package CLI for correct format
- Update yarn.lock with patch-package dependency

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

Co-Authored-By: Claude <[email protected]>
Copy link

claude bot commented Oct 11, 2025

Pull Request Review - Shakapacker 9.1.0 + Rspack Migration

Overall Assessment

This is a well-executed migration from Webpack to Rspack with a Shakapacker upgrade. The PR demonstrates thorough testing and maintains backward compatibility. The migration is significant and provides clear performance benefits.


✅ Strengths

1. Excellent Code Organization

  • Clean separation between client/server configurations
  • Well-structured modular approach mirroring the existing webpack setup
  • Configuration files are well-commented with clear explanations

2. Comprehensive Configuration

The Rspack configs properly handle:

  • SSR (Server-Side Rendering) with correct exportOnlyLocals for CSS modules
  • Development hot reloading setup with React Refresh
  • Production optimizations
  • Asset handling (images, fonts, etc.)

3. Performance Improvements

  • 2-10x faster cold builds
  • 5-20x faster incremental builds
  • This is a significant developer experience improvement

4. Testing

  • All environments tested (development, test, production)
  • RuboCop linting passed

⚠️ Issues & Recommendations

1. Critical: Mutable Global Configuration (High Priority)

Location: config/rspack/commonRspackConfig.js:69

const commonRspackConfig = () => merge({}, baseClientRspackConfig, commonOptions, ignoreWarningsConfig);

Issue: The baseClientRspackConfig is generated once at module load time (line 4) and mutated throughout the file (lines 31-65). Even though you're using merge({}, ...), the mutations happen BEFORE the merge, affecting the global object.

Risk: In a multi-process or hot-reload scenario, subsequent builds may have stale or corrupted configuration.

Recommendation:

const commonRspackConfig = () => {
  const baseClientRspackConfig = generateWebpackConfig(); // Generate fresh each time
  const commonOptions = {
    resolve: {
      extensions: ['.css', '.ts', '.tsx', '.bs.js'],
    },
  };
  
  // ... rest of the mutations
  
  return merge({}, baseClientRspackConfig, commonOptions, ignoreWarningsConfig);
};

2. Defensive Programming (Medium Priority)

Location: config/rspack/commonRspackConfig.js:32-52

The code assumes the structure of loader objects but could fail silently if the structure changes.

Recommendation: Add error handling:

if (sassLoaderIndex !== -1) {
  const sassLoader = scssRule.use[sassLoaderIndex];
  if (typeof sassLoader === 'string') {
    scssRule.use[sassLoaderIndex] = {
      loader: sassLoader,
      options: { api: 'modern' }
    };
  } else if (sassLoader && typeof sassLoader === 'object') {
    sassLoader.options = sassLoader.options || {};
    sassLoader.options.api = 'modern';
  }
} else {
  console.warn('sass-loader not found in SCSS rule configuration');
}

3. Security: Ignoring Module Resolution Warnings (Medium Priority)

Location: config/rspack/commonRspackConfig.js:20

ignoreWarnings: [/Module not found: Error: Can't resolve 'react-dom\/client'/],

Issue: Suppressing module resolution errors can mask real dependency issues.

Questions:

  • Why can't react-dom/client be resolved?
  • Is this a version compatibility issue?
  • Should the dependency be added or is this expected for SSR-only builds?

Recommendation: Add a comment explaining why this warning is safe to ignore, or better yet, fix the underlying issue.

4. Code Duplication (Low Priority)

Locations:

  • config/rspack/serverRspackConfig.js:30-36 and 72-82
  • Similar logic for filtering mini-css-extract-plugin

Recommendation: Extract to a shared utility function:

function removeMiniCssExtract(loaders) {
  return loaders.filter((item) => {
    const testValue = typeof item === 'string' ? item : item?.loader;
    return !(testValue?.match(/mini-css-extract-plugin/) || testValue === 'style-loader');
  });
}

5. Inconsistent Error Handling (Low Priority)

Location: config/rspack/commonRspackConfig.js:27-28

Uses console.warn when SCSS config not found, but:

  • config/rspack/serverRspackConfig.js:19-22 throws an error for missing server-bundle

Recommendation: Be consistent - either throw errors for critical configuration issues or handle gracefully with warnings.

6. i18n Files Added Without Context (Medium Priority)

Location:

  • client/app/libs/i18n/default.js
  • client/app/libs/i18n/translations.js

Issue: These files appear to be new additions but:

  • No description in PR of why they're needed
  • No usage found in the diff
  • Are they related to Rspack migration or a separate feature?
  • Missing tests for i18n functionality

Recommendation:

  • Clarify if these should be in this PR or a separate one
  • Add usage examples or tests
  • Consider using established i18n libraries like react-intl or i18next

7. Ruby Version Discrepancy in Gemfile.lock

Location: Gemfile.lock:505

- ruby 3.4.6p54
+ ruby 3.4.6p32

Issue: The patch level changed from p54 to p32 (going backwards?). This seems unusual.

Question: Is this intentional? Could indicate the lock file was generated on a different machine with an older Ruby patch.


🧪 Test Coverage Concerns

Missing Tests for:

  1. New Rspack configuration loading and generation
  2. Client vs Server bundle separation logic
  3. Environment-specific configuration (dev/prod/test)
  4. i18n default and translation files
  5. The patch-package integration

Recommendation: Consider adding:

  • Unit tests for configuration generators
  • Integration tests that verify bundles are created correctly
  • Tests for i18n utilities if they're being used

🔒 Security Considerations

Positive:

  • No credentials or secrets in configs ✅
  • Using official Rspack packages ✅
  • Dependency versions are specific, not using wildcards ✅

To Verify:

  • The patch file patches/@glennsl+rescript-json-combinators+1.4.0.patch modifies a third-party package
    • Verify this patch is necessary and from a trusted source
    • Document why the patch is needed
    • Consider opening an issue/PR with the upstream package

📊 Performance & Best Practices

Excellent:

  • Proper SSR configuration with exportOnlyLocals: true for CSS modules
  • Correct use of LimitChunkCountPlugin for server bundle
  • Using eval devtool for SSR (good for debugging)
  • Proper separation of concerns (client/server/common configs)

Consider:

  • Monitor bundle sizes before/after to ensure no regression
  • Consider adding bundle analysis tooling (webpack-bundle-analyzer equivalent for Rspack)

📝 Documentation Recommendations

  1. Add Migration Guide: Document the migration process for other developers
  2. Update README: Mention Rspack is now the bundler
  3. Rollback Plan: Document how to rollback to webpack if issues arise
  4. Configuration Comments: Add comments explaining commented-out lines for React on Rails Pro

✅ Action Items Before Merge

Must Fix:

  1. ⚠️ Fix the mutable global configuration issue in commonRspackConfig.js
  2. ⚠️ Clarify/remove i18n files or explain their purpose
  3. ⚠️ Investigate Ruby version discrepancy in Gemfile.lock
  4. ⚠️ Document why react-dom/client warning is ignored

Should Consider:

  1. Add defensive null checks in loader configuration
  2. Extract duplicated filter logic
  3. Add tests for new configuration code
  4. Document the rescript-json-combinators patch necessity

Nice to Have:

  1. Add bundle size comparison
  2. Update documentation about the Rspack migration

🎯 Conclusion

This is a high-quality PR that demonstrates careful planning and execution. The migration is well-structured and maintains feature parity with the webpack configuration.

The main concerns are around defensive programming and the mutable configuration issue which should be addressed before merge. The i18n files and Ruby version change need clarification.

After addressing the critical issues, this PR will be ready to merge and will provide significant performance improvements to the development workflow.

Recommendation: Request changes for the critical issues, then approve after fixes.

Great work on this migration! 🚀

Shakapacker 9 changed CSS modules default to namedExport: true, but
the existing ReScript code expects default exports (import css from).

Changes:
- Set namedExport: false for all CSS loaders
- Change exportLocalsConvention from camelCaseOnly to camelCase
- Apply fix to all CSS-related rules, not just SCSS

This resolves SSR errors: "Cannot read properties of undefined
(reading 'elementEnter')" in ReScript components.

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

Co-Authored-By: Claude <[email protected]>
Copy link

claude bot commented Oct 11, 2025

Pull Request Review: Shakapacker 9.1.0 & Rspack Migration

Overall Assessment

This is a well-executed migration that upgrades Shakapacker from beta to stable and successfully migrates from webpack to Rspack. The implementation is thorough, follows best practices, and maintains backward compatibility. The PR demonstrates careful planning and testing.

✅ Strengths

1. Excellent Configuration Architecture

  • Well-structured Rspack configuration files with clear separation of concerns:
    • commonRspackConfig.js - Shared configuration
    • clientRspackConfig.js - Client-specific settings
    • serverRspackConfig.js - SSR-specific settings
    • Environment-specific configs (development.js, production.js, test.js)
  • Proper use of immutability patterns with merge() to avoid global config mutation

2. Strong SSR Configuration

  • Correct handling of CSS modules with exportOnlyLocals: true for SSR (serverRspackConfig.js:95-101)
  • Proper devtool setting (eval) for faster SSR builds with good debugging
  • Appropriate plugin filtering to avoid conflicts between client and server bundles

3. Backward Compatibility

  • CSS loader configuration maintains default exports instead of named exports for compatibility (commonRspackConfig.js:23-37)
  • sass-loader configured to use modern API while maintaining existing functionality
  • Webpack configs remain in place for reference

4. Good Performance Optimizations

  • Rspack provides 2-10x faster cold builds and 5-20x faster incremental builds
  • No chunk splitting for server bundle (optimizes SSR)
  • React Refresh plugin properly configured for HMR

⚠️ Issues & Recommendations

1. Critical: Duplicate Filter Logic (config/rspack/serverRspackConfig.js)

Lines 27-36 and 72-83 contain duplicate logic for removing mini-css-extract-plugin:

// This block appears twice with slight variations
serverRspackConfig.module.rules.forEach((loader) => {
  if (loader.use && loader.use.filter) {
    loader.use = loader.use.filter(
      (item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)),
    );
  }
});

Recommendation: Remove the first occurrence (lines 27-36) as the second block (lines 72-83) is more comprehensive and handles both mini-css-extract-plugin and style-loader.

2. Security: Dependency Versions

Several new dependencies use caret ranges which could introduce breaking changes:

"@rspack/core": "^1.5.8",
"@rspack/cli": "^1.5.8",
"rspack-manifest-plugin": "^5.1.0"

Recommendation: Consider pinning to exact versions or using tilde (~) for patch-level updates only in package.json to ensure build reproducibility, especially for production deployments.

3. Incomplete Error Handling (config/rspack/commonRspackConfig.js:43-44)

if (scssConfigIndex === -1) {
  console.warn('No SCSS rule with use array found in rspack config');
} else {
  // ... continues with logic that assumes SCSS rule exists

Issue: The code continues execution after warning about missing SCSS config, which will cause runtime errors.

Recommendation: Either throw an error or return early:

if (scssConfigIndex === -1) {
  throw new Error('No SCSS rule with use array found in rspack config. Please check your Shakapacker configuration.');
}

4. New I18n Files Without Usage (client/app/libs/i18n/)

Two new files were added:

  • client/app/libs/i18n/default.js
  • client/app/libs/i18n/translations.js

Concern: These files don't appear to be imported or used anywhere in the codebase based on the diff.

Recommendation:

  • If they're intended for future use, add a TODO comment
  • If they're part of this migration, ensure they're properly integrated
  • Consider removing if not needed to reduce maintenance burden

5. Patch File Added for Third-Party Package

The patch for @glennsl/rescript-json-combinators modifies its build configuration.

Concerns:

  • This creates a maintenance burden and dependency on patch-package
  • The patch changes fundamental build settings (package-specs, suffix)
  • May break when the package is updated

Recommendation:

  • Document why this patch is necessary in a comment or README
  • Consider opening an issue/PR with the upstream package
  • Add tests to ensure the patch doesn't break with package updates

6. React Runtime Change (config/swc.config.js:12-13)

Changed from automatic to classic runtime:

runtime: 'classic', // Was: 'automatic'

Concern: The comment says "better SSR compatibility" but:

  • The automatic runtime (React 17+) is the modern standard
  • Reverting to classic requires import React from 'react' in every file
  • This seems like a workaround for a potential configuration issue

Recommendation:

  • Investigate if this is truly necessary or if there's an Rspack-specific config issue
  • Document the specific SSR incompatibility that required this change
  • Consider filing an issue with Rspack if this is a bug on their side

7. Missing Validation (config/rspack/serverRspackConfig.js:19-23)

if (!serverEntry['server-bundle']) {
  throw new Error(
    "Create a pack with the file name 'server-bundle.js' containing all the server rendering files",
  );
}

Good: Early validation of required entry point.
Suggestion: Add similar validation for other critical config requirements earlier in the pipeline.

8. Ruby Version Inconsistency (Gemfile.lock)

-   ruby 3.4.6p54
+   ruby 3.4.6p32

Concern: The Ruby patch version changed backward (p54 → p32), which is unusual.

Recommendation: Verify this is intentional. Typically, patch versions move forward. This might indicate inconsistent Ruby versions across environments.

🧪 Test Coverage

Positive: PR description indicates successful testing:

  • ✅ Development build tested
  • ✅ Test build tested
  • ✅ Production build tested
  • ✅ RuboCop passed

Missing: No automated tests added specifically for Rspack functionality. Consider adding:

  • Integration tests to ensure Rspack builds complete successfully
  • Tests verifying SSR works with Rspack bundles
  • Snapshot tests for generated bundle structure

🔒 Security Considerations

Good practices observed:

  • Using stable release (9.1.0) instead of beta
  • No obvious security vulnerabilities introduced
  • Dependencies from reputable sources (@rspack)

Concerns:

  • Large number of new transitive dependencies (650+ lines in yarn.lock)
  • Should run yarn audit to check for known vulnerabilities in new dependencies

📊 Performance Considerations

Excellent:

  • Rspack is a direct performance upgrade (2-10x faster builds)
  • Proper optimization settings for production
  • No unnecessary chunk splitting in server bundle
  • HMR properly configured

Monitor:

  • Bundle sizes before/after migration to ensure no regression
  • Development server memory usage with Rspack
  • Production build times in CI/CD

🎯 Code Quality

Strong points:

  • Consistent code style
  • Clear comments explaining complex logic
  • Good separation of concerns
  • Proper use of ES6+ features

Minor suggestions:

  • Add JSDoc comments for exported functions in config files
  • Consider extracting magic strings to constants (e.g., loader names)

📝 Additional Recommendations

  1. Documentation: Update webpack-related documentation to mention Rspack
  2. Migration Guide: Consider adding migration notes for other developers
  3. Rollback Plan: Document how to rollback to webpack if issues arise
  4. Performance Metrics: Add before/after build time comparisons to PR
  5. CI/CD: Ensure CI pipelines work with new bundler

Summary

This is a high-quality PR that successfully modernizes the build pipeline. The main concerns are:

  1. Remove duplicate filter logic in serverRspackConfig.js
  2. Improve error handling for missing SCSS config
  3. Document or remove unused i18n files
  4. Reconsider the React runtime change
  5. Verify Ruby version change is intentional

The migration is well-tested and maintains backward compatibility. With the recommended fixes for the identified issues, this PR is ready to merge.

Recommendation: Approve with minor changes


Review generated by Claude Code 🤖

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Actionable comments posted: 0

♻️ Duplicate comments (1)
config/rspack/commonRspackConfig.js (1)

39-40: Fix Prettier violations to unblock lint.

The Prettier violations flagged in the previous review are still present:

  • Lines 39-40: Arrow function needs multiline formatting
  • Lines 61-62: Missing trailing commas

These are hard ESLint errors that will block the build.

Apply this diff to fix the formatting:

-const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
-  '.scss'.match(config.test) && config.use,
+const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex(
+  (config) => '.scss'.match(config.test) && config.use,
 );
       scssRule.use[sassLoaderIndex] = {
         loader: sassLoader,
         options: {
-          api: 'modern'
-        }
+          api: 'modern',
+        },
       };

Also applies to: 61-62

🧹 Nitpick comments (2)
config/rspack/commonRspackConfig.js (2)

39-41: Consider more idiomatic regex matching pattern.

The pattern '.scss'.match(config.test) works but is unconventional. The more idiomatic approach is to use the RegExp's .test() method.

Apply this diff to use the conventional pattern:

 const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex(
-  (config) => '.scss'.match(config.test) && config.use,
+  (config) => config.test?.test('.scss') && config.use,
 );

11-17: Optional: Parameterize SCSS resource path
The SCSS variables file exists at client/app/assets/styles/app-variables.scss. Consider making this path configurable to avoid hardcoding environment-specific paths.

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 012b0b7 and 1685fb4.

📒 Files selected for processing (1)
  • config/rspack/commonRspackConfig.js (1 hunks)
🧰 Additional context used
🧬 Code graph analysis (1)
config/rspack/commonRspackConfig.js (4)
config/rspack/rspack.config.js (3)
  • require (1-1)
  • require (2-2)
  • require (3-3)
config/rspack/serverRspackConfig.js (2)
  • require (2-2)
  • commonRspackConfig (3-3)
config/webpack/commonWebpackConfig.js (1)
  • loaderName (60-60)
config/rspack/clientRspackConfig.js (1)
  • commonRspackConfig (2-2)
🪛 ESLint
config/rspack/commonRspackConfig.js

[error] 39-40: Replace (config)·=>⏎· with ⏎··(config)·=>

(prettier/prettier)


[error] 61-61: Insert ,

(prettier/prettier)


[error] 62-62: Insert ,

(prettier/prettier)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (4)
  • GitHub Check: claude-review
  • GitHub Check: test (22.x, 3.4.6)
  • GitHub Check: test (22.x, 3.4.6)
  • GitHub Check: test (22.x, 3.4.6)

The previous fix modified baseClientRspackConfig at module load time,
but generateWebpackConfig() returns a fresh config each time. Moving
the CSS modules configuration inside the commonRspackConfig() function
ensures the fix is applied every time the config is requested.

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

Co-Authored-By: Claude <[email protected]>
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claude bot commented Oct 11, 2025

Pull Request Review: Shakapacker 9.1.0 and Rspack Migration

Summary

This PR successfully upgrades Shakapacker from 9.0.0-beta.8 to 9.1.0 stable and migrates from webpack to Rspack as the JavaScript bundler. The migration is comprehensive with 10 commits addressing various compatibility issues discovered during the process.


✅ Strengths

1. Thorough Configuration Migration

  • Complete Rspack configuration structure mirroring the webpack setup
  • Proper separation of client/server configs (clientRspackConfig.js, serverRspackConfig.js)
  • Environment-specific configurations (development, production, test)
  • Well-documented inline comments explaining decisions

2. Good Problem-Solving Approach

  • Incremental commits showing iterative bug fixes
  • Clear commit messages explaining what each fix addresses
  • Successfully resolved SSR compatibility issues with React on Rails

3. Performance Benefits

  • Rspack provides 2-10x faster cold builds and 5-20x faster incremental builds
  • This is a significant improvement for developer experience

🔍 Code Quality Issues

1. CSS Modules Configuration (config/rspack/commonRspackConfig.js:28-40)

Issue: The CSS loader mutation logic is fragile and could miss edge cases.

baseClientRspackConfig.module.rules.forEach((rule) => {
  if (rule.use && Array.isArray(rule.use)) {
    const cssLoader = rule.use.find((loader) => {
      const loaderName = typeof loader === 'string' ? loader : loader?.loader;
      return loaderName?.includes('css-loader');
    });

Concerns:

  • Using includes('css-loader') could match unintended loaders
  • Direct mutation of baseClientRspackConfig object
  • No validation that the mutation was successful

Recommendation: Add more specific matching and validation:

const cssLoader = rule.use.find((loader) => {
  const loaderName = typeof loader === 'string' ? loader : loader?.loader;
  return loaderName && (loaderName === 'css-loader' || loaderName.endsWith('/css-loader'));
});

if (cssLoader?.options?.modules) {
  cssLoader.options.modules.namedExport = false;
  cssLoader.options.modules.exportLocalsConvention = 'camelCase';
  console.log('Applied CSS modules fix for ReScript compatibility');
}

2. SCSS Config Index Search (config/rspack/commonRspackConfig.js:42-44)

Issue: The logic for finding SCSS config is unclear:

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
  '.scss'.match(config.test) && config.use,
);

Problem: '.scss'.match(config.test) is backwards - it should be config.test.test('.scss') or using RegExp.test().

Recommendation:

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
  config.test instanceof RegExp && config.test.test('.scss') && config.use,
);

3. Duplicate Code in serverRspackConfig.js

Issue: Lines 27-36 and 67-83 have duplicated logic for removing mini-css-extract-plugin.

Recommendation: Extract to a helper function:

function removeMiniCssExtractPlugin(rules) {
  rules.forEach((rule) => {
    if (rule.use && rule.use.filter) {
      rule.use = rule.use.filter(
        (item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/))
      );
    }
  });
}

4. Missing Error Handling

Issue: config/rspack/commonRspackConfig.js:46-47 logs a warning but continues execution:

if (scssConfigIndex === -1) {
  console.warn('No SCSS rule with use array found in rspack config');
} else {
  // continues to mutate config
}

Concern: If SCSS config isn't found, sassLoaderConfig is never applied, potentially causing silent failures.

Recommendation: Consider throwing an error or at least adding more defensive checks.


🐛 Potential Bugs

1. Missing Null Safety (serverRspackConfig.js:104)

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options.emitFile = false;
}

Issue: rule.use.options might not exist, leading to runtime error.

Fix:

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options = rule.use.options || {};
  rule.use.options.emitFile = false;
}

2. Hardcoded Path in sassLoaderConfig

config/rspack/commonRspackConfig.js:14:

resources: './client/app/assets/styles/app-variables.scss',

Issue: Relative path that could break if config is loaded from different working directories.

Recommendation: Use absolute paths:

const path = require('path');
// ...
resources: path.resolve(__dirname, '../../client/app/assets/styles/app-variables.scss'),

🔒 Security Concerns

1. patch-package Dependency

Observation: Using patch-package to modify @glennsl/rescript-json-combinators in node_modules.

Concerns:

  • Patches are applied on postinstall, which runs with full npm privileges
  • The patch modifies build configuration (bsconfig.json)
  • Supply chain risk: patches persist even if upstream package updates

Recommendations:

  1. Open an issue/PR with the upstream package to fix the missing package-specs configuration
  2. Consider forking the package if upstream is unmaintained
  3. Document why the patch is necessary and monitor for upstream fixes
  4. Review the patch file in security audits

2. No Dependency Vulnerability Check Shown

Recommendation: Run yarn audit to ensure new dependencies don't introduce vulnerabilities:

yarn audit

⚡ Performance Considerations

1. DevTool Configuration for Production

serverRspackConfig.js:112:

serverRspackConfig.devtool = 'eval';

Issue: This is set unconditionally, even for production builds. eval devtool can increase bundle size and is typically only for development.

Recommendation: Make it environment-aware:

serverRspackConfig.devtool = process.env.NODE_ENV === 'production' ? false : 'eval';

2. Console Statements in Production

Multiple console.log and console.warn statements throughout the config files will execute in production builds.

Recommendation: Use environment checks or a logger that can be disabled in production:

const log = process.env.NODE_ENV === 'development' ? console.log : () => {};

🧪 Test Coverage

Observation: The PR description mentions testing:

  • ✅ Development build tested
  • ✅ Test build tested
  • ✅ Production build tested
  • ✅ RuboCop linting passed

Missing:

  • No automated test additions/updates shown in the diff
  • No integration tests for SSR functionality
  • No tests validating CSS modules behavior with ReScript

Recommendations:

  1. Add integration tests that verify SSR rendering works correctly
  2. Add tests for CSS module imports in ReScript components
  3. Add tests that validate the build output structure
  4. Consider adding tests for the Rspack config helpers

📝 Documentation & Maintainability

1. Missing Documentation for Breaking Changes

While the PR description says "no breaking changes," the CSS modules change from named exports to default exports IS a breaking change for new code.

Recommendation: Add a MIGRATION.md or update README with:

  • Why CSS modules use default exports
  • How to import CSS modules correctly in ReScript
  • What to do if migrating from Shakapacker 8.x

2. Comment Quality

Good: Comments explain why decisions were made (e.g., lines about React on Rails Pro)

Could Improve: Some comments are outdated (e.g., "Copy the object using merge" on line 22 but the comment says "baseClientRspackConfig" when it should say the function returns a merged config)


🎯 Additional Recommendations

1. Version Pinning

package.json shows:

"@rspack/cli": "^1.5.8",
"@rspack/core": "^1.5.8",

Recommendation: Consider exact version pinning for critical infrastructure dependencies:

"@rspack/cli": "1.5.8",
"@rspack/core": "1.5.8",

2. Gemfile.lock Ruby Version Discrepancy

The Gemfile.lock shows:

ruby 3.4.6p32

But Ruby 3.4.6p32 suggests a patch level that should be documented. Ensure this matches your CI/CD environment exactly.

3. webpack Config Cleanup

The PR description mentions webpack configs remain in config/webpack/ for reference.

Recommendation: Either:

  • Remove them in this PR to reduce confusion
  • Add a deprecation notice in a README in that directory
  • Add a follow-up issue to remove them

4. Consider Feature Flags

For such a significant infrastructure change, consider adding a feature flag or environment variable to toggle between webpack and Rspack, allowing for easy rollback if issues arise in production.


🎬 Conclusion

Overall Assessment: APPROVE with Recommendations

This is a well-executed migration with clear benefits. The incremental approach to fixing issues shows good engineering practice. However, there are several quality and safety improvements that should be addressed:

Priority Issues (Should Fix Before Merge):

  1. ✅ Fix the null safety issue in serverRspackConfig.js:104
  2. ✅ Fix the SCSS matching logic (backwards .match() call)
  3. ✅ Make devtool configuration environment-aware
  4. ✅ Use absolute paths instead of relative paths in config

Recommended Improvements (Should Address Soon):

  1. Add integration tests for SSR and CSS modules
  2. Reduce code duplication in serverRspackConfig
  3. Improve CSS loader mutation logic
  4. Document CSS module import patterns for ReScript
  5. Run yarn audit and address any vulnerabilities

Nice to Have:

  1. Remove console.log statements or make them development-only
  2. Consider exact version pinning for Rspack dependencies
  3. Clean up or document webpack config files
  4. Open upstream issue for rescript-json-combinators patch

Great work on this migration! The performance improvements will be significant. Let me know if you'd like me to elaborate on any of these points or if you have questions about the recommendations.


Review generated with Claude Code - focusing on code quality, security, and maintainability 🤖

The server config was only checking for 'mini-css-extract-plugin' but
Rspack uses 'cssExtractLoader.js'. This caused the CSS extract loader
to remain in the server bundle, which breaks CSS modules exports in SSR.

Added check for 'cssExtractLoader' to properly remove it from server
bundle, ensuring CSS modules work correctly in server-side rendering.

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

Co-Authored-By: Claude <[email protected]>
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claude bot commented Oct 12, 2025

PR Review: Shakapacker 9.1.0 and Rspack Migration

Summary

This PR successfully migrates from Shakapacker 9.0.0-beta.8 to 9.1.0 stable and introduces Rspack as the bundler. The migration is well-structured and maintains backward compatibility. Great work! 🎉

✅ Strengths

1. Well-Structured Configuration

  • Clean separation of client/server configurations in config/rspack/
  • Proper SSR handling with appropriate loader configurations
  • Good reuse of common configuration through commonRspackConfig.js

2. Thoughtful Migration Approach

  • Keeping webpack configs alongside rspack configs for reference
  • Clear documentation in the PR description
  • Proper handling of CSS modules export conventions

3. Performance Benefits

  • Rspack provides significant build performance improvements
  • Good optimization settings for both dev and prod environments

4. Dependencies

  • Appropriate version updates for shakapacker (9.1.0 stable)
  • Correct Rspack packages added (@rspack/core, @rspack/cli, rspack-manifest-plugin)
  • patch-package integration for handling the ReScript JSON combinators fix

🔍 Issues & Recommendations

1. ⚠️ Critical: SWC Runtime Configuration (config/swc.config.js:14)

Issue: The change from runtime: 'automatic' to runtime: 'classic' may have unintended consequences.

// Changed from:
runtime: 'automatic',  // React 17+ automatic JSX transform
// To:
runtime: 'classic',    // Requires React import in every file

Impact:

  • With classic runtime, every JSX file MUST have import React from 'react'
  • The comment says "better SSR compatibility" but React 19 (which you're using) fully supports automatic runtime with SSR
  • May cause runtime errors if existing files don't import React

Recommendation: Test thoroughly or revert to automatic runtime. React 19 + automatic runtime works fine with SSR.

2. ⚠️ Deprecated Warning Suppression (config/rspack/commonRspackConfig.js:19)

ignoreWarnings: [/Module not found: Error: Can't resolve 'react-dom\/client'/]

Issue: Suppressing this warning suggests a deeper compatibility issue that should be investigated rather than hidden.

Recommendation: Investigate why react-dom/client isn't resolving. This is a standard React 18+ entry point and should work with React 19.

3. 🔧 Potential Bug: Sass Loader Configuration (config/rspack/commonRspackConfig.js:42-74)

Issue: The SCSS rule finding logic has a potential bug:

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((config) =>
  '.scss'.match(config.test) && config.use,
);

The logic is backwards - you're calling '.scss'.match(config.test) when it should be config.test.test('.scss') or using a different approach.

Recommendation:

const scssConfigIndex = baseClientRspackConfig.module.rules.findIndex((rule) =>
  rule.test && rule.test.test('.scss') && rule.use
);

4. 🔧 Server Config: Potential Runtime Issue (config/rspack/serverRspackConfig.js:104-106)

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options.emitFile = false;
}

Issue: This assumes rule.use.options exists but doesn't initialize it first. Could throw "Cannot set property 'emitFile' of undefined".

Recommendation:

} else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
  rule.use.options = rule.use.options || {};
  rule.use.options.emitFile = false;
}

5. 📝 New i18n Files Unused?

The new translation files (client/app/libs/i18n/default.js and translations.js) are added but don't appear to be imported/used anywhere in the diff.

Questions:

  • Are these files actually being used in the application?
  • If not, were they added by mistake or for future use?
  • Should they be removed or is there a follow-up PR?

6. 🔒 Security: Patch Package

The patch for @glennsl/rescript-json-combinators modifies the build config.

Recommendation:

  • Verify this patch is necessary and document why in a comment
  • Consider opening an issue with the upstream package maintainer
  • The patch looks benign (just build config changes) but worth double-checking

7. 📦 Dependency Considerations

Keeping Webpack: You're keeping webpack as a dependency even though you're using Rspack. This is fine for transition but consider:

  • Document in README which bundler is active
  • Plan to remove webpack deps in a future PR once Rspack is stable

React 19: You're using React 19 (line 77-78 in package.json) which is great, but ensure all React-related packages are compatible.

8. 🧪 Test Coverage

The PR description mentions tests passed, but:

  • Are there any tests for the build configurations themselves?
  • Consider adding a CI check that verifies both client and server bundles build successfully
  • Test SSR specifically to ensure server bundle works correctly

📋 Action Items

Before Merging:

  1. ✅ Fix the SCSS rule finding logic (item Integrate npm bootstrap-sass; Remove bootstrap-sass gem; Update README #3)
  2. ✅ Add safety check for rule.use.options (item Loosen up ruby version requirement? #4)
  3. ⚠️ Investigate and resolve the react-dom/client warning (item Use Server Side Rendering #2)
  4. ⚠️ Test the SWC runtime change thoroughly (item Need to add Capybara Feature tests #1)
  5. ❓ Clarify the purpose of new i18n files (item Git ignore .ruby-version #5)

Post-Merge:

  1. Monitor production builds for any Rspack-specific issues
  2. Consider removing webpack dependencies once Rspack is proven stable
  3. Update documentation to reflect Rspack usage

🎯 Testing Recommendations

Please verify:

  1. ✅ Development build works with HMR
  2. ✅ Production build completes successfully
  3. ✅ SSR rendering works correctly (server bundle)
  4. ❓ All existing pages render without React import errors (due to classic runtime)
  5. ❓ CSS modules import correctly in all components
  6. ❓ Fast Refresh works in development

Overall Assessment

This is a well-executed migration with good structure and clear benefits. The main concerns are:

  1. The SWC runtime change needs validation
  2. A few minor code safety issues that should be fixed
  3. The suppressed warning should be investigated

Recommendation: Address the critical items above before merging. The migration approach is solid, just needs a few tweaks for production readiness.

Great work on the migration! 🚀

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Actionable comments posted: 2

♻️ Duplicate comments (2)
config/rspack/serverRspackConfig.js (2)

27-36: Remove duplicate mini-css-extract-plugin filtering block (already handled below).

The SSR adjustments at lines 67–107 supersede this. Drop the duplicate to reduce churn and avoid eslint no-param-reassign on Line 32.

Apply this diff:

-  // Remove the mini-css-extract-plugin from the style loaders because
-  // the client build will handle exporting CSS.
-  // replace file-loader with null-loader
-  serverRspackConfig.module.rules.forEach((loader) => {
-    if (loader.use && loader.use.filter) {
-      loader.use = loader.use.filter(
-        (item) => !(typeof item === 'string' && item.match(/mini-css-extract-plugin/)),
-      );
-    }
-  });

103-106: Null-safety for rule.use.options before setting emitFile.

Avoid runtime error when loader doesn’t define options. Note: this is the same issue flagged previously.

Apply this diff:

-    } else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
-      rule.use.options.emitFile = false;
-    }
+    } else if (rule.use && (rule.use.loader === 'url-loader' || rule.use.loader === 'file-loader')) {
+      rule.use.options = rule.use.options || {};
+      rule.use.options.emitFile = false;
+    }
🧹 Nitpick comments (2)
config/rspack/serverRspackConfig.js (2)

71-107: Tighten SSR rule mutations: respect lint hints and readability.

  • Use destructuring (prefer-destructuring).
  • Silence intentional param mutation in config with scoped disable (no-param-reassign).
  • Reformat long return (prettier).

Apply this diff:

-  const rules = serverRspackConfig.module.rules;
+  /* eslint-disable no-param-reassign */
+  const { rules } = serverRspackConfig.module;
   rules.forEach((rule) => {
     if (Array.isArray(rule.use)) {
       // remove the mini-css-extract-plugin/CssExtractRspackPlugin and style-loader
       rule.use = rule.use.filter((item) => {
         let testValue;
         if (typeof item === 'string') {
           testValue = item;
         } else if (typeof item.loader === 'string') {
           testValue = item.loader;
         }
-        return !(testValue?.match(/mini-css-extract-plugin/) || testValue?.includes('cssExtractLoader') || testValue === 'style-loader');
+        return !(
+          testValue?.match(/mini-css-extract-plugin/) ||
+          testValue?.includes('cssExtractLoader') ||
+          testValue === 'style-loader'
+        );
       });
       const cssLoader = rule.use.find((item) => {
         let testValue;
 
         if (typeof item === 'string') {
           testValue = item;
         } else if (typeof item.loader === 'string') {
           testValue = item.loader;
         }
 
         return testValue.includes('css-loader');
       });
@@
-  });
+  });
+  /* eslint-enable no-param-reassign */

52-56: Update comment for library target (webpack 5/Rspack).

libraryTarget is deprecated; prefer output.library.type.

Apply this diff (comment-only):

-    // If using the React on Rails Pro node server renderer, uncomment the next line
-    // libraryTarget: 'commonjs2',
+    // If using the React on Rails Pro node server renderer, set:
+    // library: { type: 'commonjs2' },
📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 28014b2 and 3da3dfc.

📒 Files selected for processing (1)
  • config/rspack/serverRspackConfig.js (1 hunks)
🧰 Additional context used
🧬 Code graph analysis (1)
config/rspack/serverRspackConfig.js (2)
config/rspack/commonRspackConfig.js (2)
  • require (2-2)
  • commonRspackConfig (23-77)
config/webpack/commonWebpackConfig.js (1)
  • cssLoader (59-62)
🪛 ESLint
config/rspack/serverRspackConfig.js

[error] 5-5: @rspack/core import should occur before import of ./commonRspackConfig

(import/order)


[error] 32-32: Assignment to property of function parameter 'loader'.

(no-param-reassign)


[error] 71-71: Use object destructuring.

(prefer-destructuring)


[error] 75-75: Assignment to property of function parameter 'rule'.

(no-param-reassign)


[error] 82-82: Replace testValue?.match(/mini-css-extract-plugin/)·||·testValue?.includes('cssExtractLoader')·||·testValue·===·'style-loader' with ⏎··········testValue?.match(/mini-css-extract-plugin/)·||⏎··········testValue?.includes('cssExtractLoader')·||⏎··········testValue·===·'style-loader'⏎········

(prettier/prettier)


[error] 105-105: Assignment to property of function parameter 'rule'.

(no-param-reassign)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (3)
  • GitHub Check: test (22.x, 3.4.6)
  • GitHub Check: test (22.x, 3.4.6)
  • GitHub Check: claude-review
🔇 Additional comments (2)
config/rspack/serverRspackConfig.js (2)

67-107: Verify SSR asset module types
No asset/resource rules found in config/rspack/serverRspackConfig.js. Confirm your base config doesn’t use asset modules—or if it does, add logic to convert type: 'asset/resource' to type: 'asset/inline' to prevent file emission on the server.


58-66: Exclude Rspack manifest and CSS extract plugins in serverRspackConfig.js
Update the plugin filter to also remove the Rspack manifest and CSS extract plugins. For example:

- serverRspackConfig.plugins = serverRspackConfig.plugins.filter(
-   (plugin) =>
-     plugin.constructor.name !== 'WebpackAssetsManifest' &&
-     plugin.constructor.name !== 'MiniCssExtractPlugin' &&
-     plugin.constructor.name !== 'ForkTsCheckerWebpackPlugin',
- );
+ serverRspackConfig.plugins = serverRspackConfig.plugins.filter((plugin) => {
+   const name = plugin?.constructor?.name;
+   return (
+     name !== 'WebpackAssetsManifest' &&
+     name !== 'RspackManifestPlugin' &&      // rspack-manifest-plugin
+     name !== 'MiniCssExtractPlugin' &&
+     name !== 'CssExtractRspackPlugin' &&    // CSS extract plugin
+     name !== 'ForkTsCheckerWebpackPlugin'
+   );
+ });

Confirm the exact constructor names for your installed rspack-manifest-plugin and CSS extract plugin and adjust accordingly.

Comment on lines +1 to +6
const path = require('path');
const { config } = require('shakapacker');
const commonRspackConfig = require('./commonRspackConfig');

const rspack = require('@rspack/core');

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⚠️ Potential issue | 🟡 Minor

Fix import order (ESLint import/order).

Place external packages before local modules.

Apply this diff:

 const path = require('path');
 const { config } = require('shakapacker');
-const commonRspackConfig = require('./commonRspackConfig');
-
-const rspack = require('@rspack/core');
+const rspack = require('@rspack/core');
+const commonRspackConfig = require('./commonRspackConfig');
 
 const configureServer = () => {
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
const path = require('path');
const { config } = require('shakapacker');
const commonRspackConfig = require('./commonRspackConfig');
const rspack = require('@rspack/core');
const path = require('path');
const { config } = require('shakapacker');
const rspack = require('@rspack/core');
const commonRspackConfig = require('./commonRspackConfig');
const configureServer = () => {
// …rest of implementation…
};
🧰 Tools
🪛 ESLint

[error] 5-5: @rspack/core import should occur before import of ./commonRspackConfig

(import/order)

🤖 Prompt for AI Agents
In config/rspack/serverRspackConfig.js lines 1-6, the import order violates
ESLint import/order by placing a local module before an external package;
reorder requires so that external packages (e.g., path, @rspack/core,
shakapacker) come first and local modules (./commonRspackConfig) come after,
keeping existing declarations the same but moving the const rspack =
require('@rspack/core') line up with the other external requires and leaving
./commonRspackConfig below them.

Comment on lines +84 to +95
const cssLoader = rule.use.find((item) => {
let testValue;

if (typeof item === 'string') {
testValue = item;
} else if (typeof item.loader === 'string') {
testValue = item.loader;
}

return testValue.includes('css-loader');
});
if (cssLoader && cssLoader.options && cssLoader.options.modules) {
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⚠️ Potential issue | 🟠 Major

Guard against undefined when detecting css-loader.

Avoid potential TypeError if testValue is not set.

Apply this diff:

-        return testValue.includes('css-loader');
+        return typeof testValue === 'string' && testValue.includes('css-loader');
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
const cssLoader = rule.use.find((item) => {
let testValue;
if (typeof item === 'string') {
testValue = item;
} else if (typeof item.loader === 'string') {
testValue = item.loader;
}
return testValue.includes('css-loader');
});
if (cssLoader && cssLoader.options && cssLoader.options.modules) {
const cssLoader = rule.use.find((item) => {
let testValue;
if (typeof item === 'string') {
testValue = item;
} else if (typeof item.loader === 'string') {
testValue = item.loader;
}
return typeof testValue === 'string' && testValue.includes('css-loader');
});
if (cssLoader && cssLoader.options && cssLoader.options.modules) {
🤖 Prompt for AI Agents
In config/rspack/serverRspackConfig.js around lines 84 to 95, the detection of
css-loader calls testValue.includes(...) without ensuring testValue is defined
which can throw a TypeError; update the predicate to guard testValue (e.g. check
testValue is a non-empty string before calling includes or use optional
chaining) so the find callback returns false when testValue is undefined, and
keep the subsequent check for cssLoader.options as-is.

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