Fixing Duplicate Model IDs In MPS Projects: A CI Guide

Aug 8, 2025 by Sebastian Müller 55 views

Troubleshooting Duplicate Model IDs in MPS: Project Relative Paths and Generated Files

Hey everyone! Ever run into the frustrating issue of having models in your JetBrains MPS project with the same IDs? It's a real head-scratcher, especially when those IDs are tied to project-relative paths, and you're trying to manage things in a CI environment. Plus, dealing with generated files adding to the noise? Ugh! This article dives deep into this problem, offering insights and solutions to keep your MPS projects running smoothly. We'll explore why this happens, how it impacts your workflow, and most importantly, how to fix it. So, if you're battling duplicate model IDs and project-relative path woes, you're in the right place. Let's get started and untangle this MPS mystery together!

Understanding the Problem: Duplicate Model IDs and Project Relative Paths

So, what's the deal with these duplicate model IDs? The core of the issue lies in how MPS identifies models within a project. Each model gets a unique ID, crucial for MPS to keep track of all the moving parts in your language definitions, editors, and generators. However, when these IDs are generated based on project relative paths, things can get tricky. Imagine you have a model defined in a specific directory within your project. MPS might assign an ID based on that directory's path relative to the project root. This works great locally, but the trouble begins when you move to a Continuous Integration (CI) environment. In a CI system, the absolute path of your project can change with each build. This means the project root might be in a different location every time, leading to new IDs being generated for the same models. This is where the headache starts – MPS sees these as different models because the IDs don't match, even though the content is the same. Whitelisting, a common approach to manage these situations, becomes a nightmare because the paths are constantly changing. You're essentially chasing a moving target! This inconsistency can break your builds, mess up your deployments, and generally make your life as a language engineer much harder.

Furthermore, the issue is compounded when generated files get thrown into the mix. Files like aspectcps-beforebaselang.mps, often generated by dataflow aspects, can also contribute to this ID chaos. These files, while essential for certain MPS functionalities, can muddy the waters if they're not handled correctly. Just like with regular models, if these generated files are included in the ID generation process, they can lead to even more duplicate IDs and inconsistencies. To truly solve this problem, we need a strategy that considers both the dynamic nature of CI environments and the presence of generated files. We need to ensure that model IDs remain consistent regardless of the project's absolute path and that generated files don't interfere with this process. This might involve excluding certain files from ID generation or finding a more robust way to identify models across different environments. In the next sections, we'll explore specific solutions and best practices to tackle these challenges head-on.

Why Project Relative Paths Cause Headaches

Let's drill down on why project relative paths specifically cause such headaches. When MPS uses the project's relative path to generate model IDs, it seems convenient at first. It's a way to tie the ID to the model's location within the project structure. However, this approach is fundamentally flawed when you consider the diverse environments in which MPS projects operate. Think about it: your project might live in various places – your local machine, a colleague's computer, a CI server, or even a cloud-based build environment. Each of these locations has its own file system structure and, consequently, different absolute paths. This is the crux of the problem: the absolute path is not a reliable identifier across different systems. When MPS generates an ID based on a project-relative path, it's essentially baking in a dependency on the project's location. This is fine if the project never moves, but in the real world, projects are constantly being moved, copied, and deployed. In a CI environment, for example, each build might create a fresh workspace in a new directory. This means the project's absolute path changes every single time, leading to a cascade of new model IDs. It's like giving each of your friends a different name every time you meet them in a new place – chaos ensues! This inconsistency has several downstream effects. For one, it makes whitelisting model IDs for specific purposes virtually impossible. If the IDs are constantly changing, how can you reliably whitelist them? It also complicates any process that relies on stable model identifiers, such as comparing models across different builds or tracking changes over time. The solution here is to decouple model IDs from project-relative paths. We need a way to identify models that is independent of their location on the file system. This might involve using a hash of the model's content or relying on a more stable identifier that is not tied to the project's path. In the following sections, we'll explore some strategies for achieving this.

The Impact on CI/CD and Whitelisting

Now, let's zoom in on the specific impact this issue has on your Continuous Integration and Continuous Delivery (CI/CD) pipelines, as well as the practice of whitelisting. CI/CD is all about automation and consistency. You want your builds to be reliable and your deployments to be predictable. But when model IDs are changing with every build due to project-relative paths, your CI/CD process can quickly turn into a nightmare. Imagine your build process relies on certain model IDs to perform specific tasks, such as code generation or model validation. If these IDs are constantly changing, your build scripts will break, your tests will fail, and your deployments will be a gamble. You'll find yourself spending more time debugging ID mismatches than actually delivering value. It's like trying to build a house on shifting sand – frustrating and ultimately unproductive. Whitelisting, a common technique for controlling which models are processed or included in a build, becomes equally problematic. Whitelisting involves creating a list of allowed IDs and ensuring that only those IDs are considered. This is a great way to enforce standards and prevent unintended models from making their way into your final product. However, if your model IDs are in constant flux, maintaining an accurate whitelist becomes an exercise in futility. You'll be constantly updating the whitelist to reflect the new IDs, which is both time-consuming and error-prone. It's like trying to herd cats – you'll never quite get them all in the same place at the same time. To effectively use CI/CD and whitelisting, you need stable model IDs. This means IDs that don't change unless the model's content actually changes. By decoupling IDs from project-relative paths, you can create a much more robust and predictable build process. This will not only save you time and frustration but also improve the overall quality of your software. In the following sections, we'll discuss how to achieve this stability and make your CI/CD pipeline a smooth and reliable operation.

Excluding Generated Files: A Necessary Step

Okay, let's talk about generated files – those little helpers that can sometimes cause big headaches. In the context of MPS, generated files like aspectcps-beforebaselang.mps are often created as part of the language engineering process. They're usually the output of some transformation or generation step, and they play a crucial role in the overall functionality of your language. However, these files can also contribute to the duplicate model ID problem if they're not handled correctly. The issue is that, like other models, generated files can be assigned IDs. If these IDs are based on project-relative paths, they're subject to the same instability we've discussed earlier. But there's an added wrinkle: generated files are, well, generated. This means their content can change between builds, even if the underlying source models haven't changed. This can lead to a situation where the same generated file gets a different ID in each build, further exacerbating the ID chaos. To avoid this, a crucial step is to exclude generated files from the ID generation process. This is a common practice in MPS projects, and it's analogous to excluding descriptor models from other aspects. The idea is that generated files are implementation details; they shouldn't be treated as first-class models with stable IDs. By excluding them, you reduce the number of models that can potentially cause ID conflicts and make your overall ID management much simpler. The specific mechanism for excluding generated files might vary depending on your project setup and the tools you're using. However, the principle remains the same: identify the files that are generated and configure your system to ignore them when generating model IDs. This is a simple but effective way to reduce the noise and focus on the models that truly matter. In the next sections, we'll explore some specific techniques for excluding generated files and ensuring that they don't interfere with your model ID management.

Solutions and Best Practices for Managing Model IDs

Alright, let's get down to brass tacks and talk about solutions and best practices for managing model IDs in your MPS projects. We've identified the problem – duplicate IDs caused by project-relative paths and generated files – and we've explored the impact on CI/CD and whitelisting. Now, it's time to figure out how to fix it. The overarching goal is to create a system where model IDs are stable and predictable, regardless of the project's location or the presence of generated files. This requires a multi-pronged approach, addressing both the ID generation mechanism and the handling of generated files. Here are some key strategies:

Decouple IDs from Project-Relative Paths: The most fundamental solution is to stop using project-relative paths as the basis for model IDs. Instead, consider using a more stable identifier, such as a hash of the model's content or a Universally Unique Identifier (UUID). A content-based hash ensures that the ID only changes when the model's content changes, which is exactly what we want. A UUID provides a globally unique ID that is independent of the project's location. The specific implementation will depend on your project's needs and the capabilities of your MPS setup. You might need to customize your model loading or generation process to use these alternative identifiers.
Exclude Generated Files: As we discussed earlier, excluding generated files from the ID generation process is crucial. This prevents these files from contributing to ID conflicts and simplifies your overall ID management. Identify the generated files in your project and configure your system to ignore them when generating IDs. This might involve modifying your build scripts or using specific MPS settings to exclude certain files or directories.
Centralized ID Management: Consider implementing a centralized ID management system for your project. This could involve a dedicated service or component that is responsible for generating and assigning IDs. This allows you to enforce consistent ID generation policies and track the IDs that have been assigned. A centralized system can also make it easier to migrate to a new ID generation scheme in the future.
Consistent Build Environment: While decoupling IDs from project-relative paths is essential, it's also helpful to maintain a consistent build environment as much as possible. This means ensuring that your CI/CD system uses the same versions of MPS and other dependencies across builds. A consistent environment reduces the likelihood of unexpected changes in generated files or other factors that could affect model IDs.
Thorough Testing: Finally, it's crucial to thoroughly test your ID management system to ensure that it's working as expected. This includes testing in different environments, with different project configurations, and with both regular models and generated files. Automated tests can be particularly helpful for detecting ID conflicts and ensuring that IDs remain stable over time.

By implementing these solutions and best practices, you can significantly reduce the risk of duplicate model IDs and create a more robust and predictable MPS project. This will not only make your development process smoother but also improve the overall quality of your software.

Conclusion: Taming the Model ID Beast

So, we've journeyed through the wild world of MPS model IDs, battling duplicate IDs, project-relative paths, and generated file gremlins. It's been quite the adventure, but we've emerged with a solid understanding of the problem and a toolkit of solutions. The key takeaway? Stable model IDs are crucial for a smooth MPS development experience, especially in CI/CD environments. By decoupling IDs from project-relative paths, excluding generated files, and implementing best practices for ID management, you can tame the model ID beast and create a more reliable and predictable system. Remember, the effort you put into managing model IDs upfront will pay off in the long run. You'll spend less time debugging ID conflicts and more time building awesome language solutions. So, go forth and conquer those duplicate IDs! And if you ever find yourself battling the beast again, remember this guide and the strategies we've discussed. You've got this! Happy language engineering, everyone!