Boost `patch-package` Reliability: Switch To `postinstall`

Hey everyone! Let's dive deep into a topic that might seem a bit technical at first, but trust me, it’s super important for how our Node.js projects hum along smoothly, especially when we’re dealing with third-party packages. We're talking about npm scripts, specifically the postinstall and prepare hooks, and how they play a huge role in whether our beloved patch-package utility works its magic across all our dependencies. If you've ever seen a pesky DeprecationWarning pop up from http-proxy-middleware even after you thought you patched it, then you're exactly in the right place. We're going to break down why switching patch-package back to postinstall could be the game-changer we need, making our development lives a whole lot easier and our projects more robust. This isn't just about avoiding a warning; it’s about ensuring our custom fixes are applied consistently wherever they're needed, bringing stability and predictability to our module ecosystem. So, grab a coffee, and let's unravel this npm script mystery together!

Hey Guys, Let's Talk patch-package: The prepare vs. postinstall Rundown

Alright, let’s kick things off by really understanding the difference between two crucial npm lifecycle scripts: prepare and postinstall. These aren't just obscure technical terms; they dictate when certain commands run during your package installation process, and that timing is everything when you're trying to apply patches. So, what’s the deal with each of them?

First up, prepare. This script runs in a few scenarios, and understanding them is key. It's executed before a package is packed and published, before a local npm install without arguments (if the package is directly installed, like npm i my-project), and before npm pack. What does this mean in practical terms? Well, it’s primarily designed for tasks that need to happen before your package is ready for distribution or consumption as a top-level project. Think about things like transpiling TypeScript to JavaScript, or bundling your assets. The prepare script makes sure your package is in a pristine, ready-to-go state. However, and this is the crucial part for our discussion, it generally does not run when your package is installed as a transitive dependency—meaning, when another package lists your package as its dependency. This is a super important distinction, because many of our internal middlewares and tools often end up as transitive dependencies in larger applications. If patch-package relies solely on prepare to apply its magic, and your package is being pulled in indirectly, those patches simply won't get applied. It's like having a superhero power that only activates when you're the main character, not when you're part of the supporting cast. This limitation is at the heart of the problem we're seeing with http-proxy-middleware.

Now, let's talk about postinstall. This script is a bit more straightforward and, frankly, often more reliable for tasks like applying patches. As its name suggests, postinstall runs after a package has been successfully installed. This includes all packages, whether they are direct dependencies listed in your package.json or those tucked away as transitive dependencies within other packages. When you run npm install, after all the packages and their dependencies have been fetched and placed in your node_modules directory, postinstall kicks in for each package that defines it. This makes it an incredibly powerful hook for tasks that need to operate on the installed package structure. For patch-package, which modifies files within the node_modules directory, postinstall feels like a natural fit. It ensures that once http-proxy-middleware is installed, regardless of how it got there (directly or via another middleware), patch-package has the opportunity to run and apply its fixes. This consistent execution across the entire dependency tree is precisely what we need to avoid those frustrating deprecation warnings and ensure our custom solutions are universally applied. The main keyword here, folks, is consistency and universal application. Without it, we're constantly fighting against our own tooling, which is exactly what we're trying to avoid in modern development workflows.

The http-proxy-middleware Headache: Why Our Patches Aren't Sticking

Let’s zoom in on the specific pain point that brought this discussion to the forefront: the http-proxy-middleware and that nagging DeprecationWarning: The util._extend API is deprecated. Please use Object.assign() instead. If you've been working with our open-ux-tools middlewares, like backend-proxy-middleware or ui5-proxy-middleware, you've probably encountered this warning. It’s not just an annoying message; it points to older, less efficient code that we really want to iron out. This is exactly where patch-package comes into play. For those unfamiliar, patch-package is an awesome utility that allows you to make local changes to node_modules packages and then save those changes as patches. When someone else installs your project, patch-package reapplies those patches, ensuring everyone works with the same, fixed version of the dependency. It’s a lifesaver for quickly fixing upstream bugs or tweaking behavior without having to wait for the original maintainers to release an update.

Now, the problem arises because patch-package was moved to the prepare script in http-proxy-middleware (specifically, this change was noted in discussions around #1086). While the intention behind this move might have been to ensure patches are applied during npm publish or when the package is installed directly, it created an unforeseen issue for how our internal middlewares consume http-proxy-middleware. Here’s the rub: our middlewares, like backend-proxy-middleware and ui5-proxy-middleware, depend on http-proxy-middleware. This makes http-proxy-middleware a transitive dependency in many of our projects. When you npm install a project that uses, say, backend-proxy-middleware, npm fetches backend-proxy-middleware and its dependencies, including http-proxy-middleware. Because http-proxy-middleware is being installed as a transitive dependency, its prepare script – which is where patch-package is currently hooked – doesn't run. This means the patch that's supposed to fix the DeprecationWarning for util._extend is simply skipped. The result? That pesky warning pops up again and again, leading to noisy console outputs and potentially misleading us into thinking the issue hasn't been addressed. It's a classic case of a solution that works great in one context (direct installation) but falls short in another (transitive dependencies), leaving a gaping hole in our patch application strategy. The underlying issue is really about the scope of when prepare executes versus the scope of when we need our patches to execute. We need those patches to be applied universally, regardless of how deep in the dependency tree http-proxy-middleware might sit. This situation is frustrating because we have the fix, but the mechanism for applying it isn't robust enough for common real-world scenarios in a complex project structure like ours. The consistent application of fixes is absolutely paramount for a clean and efficient development environment, and right now, prepare just isn't cutting it for patch-package in this crucial scenario.

Why postinstall Is Our Best Bet for Broader patch-package Coverage

Given the challenges we've discussed with prepare, it becomes crystal clear why switching patch-package back to postinstall is not just a good idea, but arguably the best solution for ensuring widespread and consistent application of our patches. This move would directly address the core problem of patches not being applied to transitive dependencies, like when our open-ux-tools middlewares pull in http-proxy-middleware. Let's break down why postinstall is such a superior choice in this context and how it would dramatically improve our developer experience.

First and foremost, the postinstall script is specifically designed to run after a package and all its dependencies have been installed into node_modules. This means that whether http-proxy-middleware is a direct dependency of your main project or a deeply nested transitive dependency of, say, backend-proxy-middleware, the postinstall script will execute. This guarantees that patch-package gets its chance to shine and apply the necessary fixes, such as the one for the util._extend deprecation. Imagine the relief of seeing those DeprecationWarning messages vanish completely, not just when you directly install the proxy, but every single time you set up a project that uses any of our affected middlewares. This consistency is gold in development, guys. It removes uncertainty and ensures that everyone on the team, regardless of their project setup, benefits from the same patched versions. It simplifies troubleshooting and allows us to focus on building new features rather than chasing down phantom warnings.

Now, I know some of you might be thinking about the original concern that might have led to moving patch-package to prepare in the first place, perhaps related to ensuring patches were applied in environments where postinstall might be skipped or for specific npm pack/publish scenarios. One of the main points from the past, as alluded to in the prompt's reference to #1084, was that patch-package might need to become a dependency rather than a devDependency if used in postinstall. This is a valid point, and we'll delve deeper into it shortly, but for now, let's focus on the benefit to patch application. By making patch-package a full-fledged dependency, it ensures it's always available when postinstall runs, regardless of whether the package is being used directly or indirectly. This slight trade-off in dependency type is a small price to pay for the massive gain in reliability and consistent patch application across our entire ecosystem. The benefit of having patches reliably applied everywhere they are needed far outweighs the potential overhead of a slightly altered dependency classification for patch-package. It's about pragmatic solutions that work for the majority of use cases, and for managing transitive dependencies, postinstall is simply superior. This move would directly benefit anyone using SAP's open-ux-tools middlewares, ensuring a smoother, warning-free experience, and really nailing down the reliability of our patch-package solutions. We're talking about a significant upgrade in how we manage and fix our third-party code, making our projects more stable and our console outputs cleaner.

Tackling the Dependency Debate: Making patch-package a dependency

Okay, so we've established that postinstall is the logical choice for ensuring our patch-package magic applies consistently across all dependencies, direct or transitive. But, as mentioned, there's a flip side to this coin: for postinstall to reliably execute patch-package, patch-package itself would likely need to be moved from a devDependency to a regular dependency in the package.json. This is where the