Fix: Embroider Vite 1.3.6 Parallel Build Failures

Hey everyone! Let's dive into a tricky issue some of us have been facing: parallel builds failing after upgrading @embroider/vite from version 1.2.1 to 1.3.6. This can be a real headache, especially in monorepo setups where you're trying to build multiple web applications simultaneously to save time. So, if you've encountered this, you're definitely in the right place.

The Problem: ENOTEMPTY Error During Parallel Builds

The core issue manifests as an ENOTEMPTY error during the build process. You'll likely see a stack trace similar to this:

error during build:
[commonjs--resolver] ENOTEMPTY: directory not empty, rename '/private/var/folders/dw/pfvq8t0d1rqbdfqrp8fq68rc0000gn/T/embroider-vite-jump-tmp-wUlvTt' -> '/private/var/folders/dw/pfvq8t0d1rqbdfqrp8fq68rc0000gn/T/embroider-vite-jump-b9840194'
    at renameSync (node:fs:1014:11)
    at maybeCaptureNewOptimizedDep (file:///.../node_modules/.pnpm/@embroider+vite@1.3.6_@embroider+core@4.2.5_@glint+template@1.7.2__@glint+template@1.7._b46bb3134dc0b15be6137748bd4027d3/node_modules/@embroider/vite/dist/src/resolver.js:213:13)
    at resolveId (file:///.../node_modules/.pnpm/@embroider+vite@1.3.6_@embroider+core@4.2.5_@glint+template@1.7.2__@glint+template@1.7._b46bb3134dc0b15be6137748bd4027d3/node_modules/@embroider/vite/dist/src/resolver.js:51:34)
    at async Object.resolveId (file:///.../node_modules/.pnpm/@embroider+vite@1.3.6_@embroider+core@4.2.5_@glint+template@1.7.2__@glint+template@1.7._b46bb3134dc0b15be6137748bd4027d3/node_modules/@embroider/vite/dist/src/resolver.js:123:30)
    ...

This error essentially means that the system is trying to rename a directory, but it can't because the directory isn't empty. This is a classic concurrency issue, where multiple processes are trying to access and modify the same resources simultaneously.

Before the upgrade to version 1.3.6, parallel builds worked just fine. This points to a change in how @embroider/vite handles temporary files or directories in the newer version. The key takeaway here is that the parallel builds, which were a huge time-saver, are now broken, significantly impacting development workflows.

Diving Deeper: Understanding the Root Cause

To really grasp what's going on, let's break down the error message. The ENOTEMPTY error arises from the Node.js fs.renameSync function. This function attempts to synchronously rename a file or directory. When a directory isn't empty, the rename operation fails.

In the context of @embroider/vite, this suggests that multiple build processes are likely trying to use the same temporary directory. Version 1.2.1 probably had some mechanism (or a lack of aggressive cleanup) that avoided this conflict. However, in 1.3.6, the parallel processes are stepping on each other's toes, leading to this ENOTEMPTY error.

The temporary directories mentioned in the error, like /private/var/folders/.../T/embroider-vite-jump-tmp-..., are where @embroider/vite likely stores intermediate build artifacts. When two processes try to rename or manipulate these directories at the same time, the error occurs. Understanding this concurrency issue is crucial for finding a solution.

Why Monorepos Exacerbate the Issue

This problem is particularly noticeable in monorepos because they often involve building multiple applications or packages in parallel. Monorepos are designed to share code and dependencies across multiple projects, which is great for maintainability and code reuse. However, this also means that build processes are more likely to run concurrently.

In a monorepo, you might have several web applications that need to be built for deployment. If you're using a tool like pnpm or yarn with workspaces, you can kick off multiple builds in parallel to speed up the overall process. But if @embroider/vite has a concurrency issue, these parallel builds will likely fail with the ENOTEMPTY error.

Monorepo setups amplify the problem because they inherently encourage parallel processing. This means that the likelihood of encountering the ENOTEMPTY error increases significantly compared to a single-application setup. Identifying that the issue is prominent in a monorepo environment helps narrow down the search for solutions and workarounds.

Potential Solutions and Workarounds

Okay, so we know what the problem is and why it's happening. Now, let's talk about how to fix it. Here are some potential solutions and workarounds you can try:

1. Reverting to Version 1.2.1 (Temporary Fix)

The quickest way to get your builds working again is to revert to version 1.2.1 of @embroider/vite. This is a temporary workaround, not a long-term solution, but it will allow you to continue working while you investigate further.

To do this, you'll need to modify your package.json file and change the version of @embroider/vite back to 1.2.1. Then, run your package manager's install command (e.g., npm install, yarn install, or pnpm install) to install the older version.

Reverting is a practical step to unblock your team, but remember that you'll be missing out on any bug fixes or new features introduced in later versions. Keep an eye on the issue and try other solutions as they become available.

2. Limiting Parallel Builds

Another workaround is to limit the number of parallel builds you're running. This can reduce the chances of multiple processes colliding when trying to access the same temporary directories.

If you're using a build tool like pnpm or yarn, they often have options to control the number of parallel tasks. For example, with pnpm, you can use the --max-parallel flag to limit the number of concurrently executed tasks:

pnpm build --max-parallel 2

This command would limit the build process to a maximum of two parallel tasks. Experiment with different values to find a balance between build speed and stability. Limiting parallelism is a viable strategy to mitigate the issue without fully sacrificing build speed.

3. Investigating Temporary Directory Configuration

It's worth looking into whether @embroider/vite or its underlying dependencies have any configuration options for specifying the temporary directory. If you can configure each build process to use a unique temporary directory, you can avoid the ENOTEMPTY error.

Check the @embroider/vite documentation and any related libraries (like Vite or Rollup) for options related to temporary directories or build caches. Exploring configuration options could reveal a straightforward solution to isolate build processes.

4. Reporting the Issue and Contributing to a Fix

This is a crucial step! If you've encountered this issue, make sure to report it to the @embroider/vite maintainers. You can do this by creating a new issue on the project's GitHub repository. Provide as much detail as possible, including your setup, the steps to reproduce the error, and any workarounds you've tried.

Even better, consider contributing to a fix yourself! If you have the time and expertise, you can dive into the @embroider/vite codebase and try to identify the root cause of the concurrency issue. Submitting a pull request with a proposed solution can help the entire community. Community involvement is key to resolving issues like this quickly and effectively.

Example Scenario: Monorepo with Multiple Apps

Let's illustrate this with a common scenario: a monorepo containing three web applications: app-one, app-two, and app-three. Each application has its own package.json and build script.

Before upgrading to @embroider/vite 1.3.6, you could run the following command (using pnpm) to build all three applications in parallel:

pnpm -r build

This would kick off three build processes simultaneously, significantly reducing the overall build time. However, after upgrading to 1.3.6, this command starts failing intermittently with the ENOTEMPTY error.

To work around this, you might try limiting the parallelism:

pnpm -r --max-parallel 2 build

This command limits the build to a maximum of two parallel processes, which might reduce the frequency of the error. Alternatively, you could revert to version 1.2.1 until a proper fix is available. Understanding this scenario helps in applying the solutions effectively in real-world projects.

Conclusion: Addressing Parallel Build Failures in Embroider Vite

The ENOTEMPTY error during parallel builds after upgrading @embroider/vite is a frustrating issue, especially in monorepo environments. It highlights the challenges of concurrency in build systems and the importance of careful handling of temporary files and directories.

By understanding the root cause of the problem and trying the solutions and workarounds discussed – reverting to a stable version, limiting parallelism, investigating temporary directory configuration, and reporting the issue – you can mitigate the impact on your development workflow.

Remember, community collaboration is vital in resolving these kinds of issues. So, don't hesitate to share your experiences, report bugs, and contribute to the project. Together, we can make @embroider/vite even more robust and reliable for everyone.

If you guys have any thoughts or alternative solutions, feel free to share them in the comments below! Let's get this sorted out together.