Debugging Pyrefly Panics A Guide To Assertion Failed Removed

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Hey everyone, if you're like me and have recently upgraded to Pyrefly 0.25.0, you might have encountered a rather frustrating panic. This guide is all about diving deep into the "assertion failed: removed" panic in Pyrefly, specifically after upgrading to version 0.25.0. We'll break down the error, explore potential causes, and arm you with debugging strategies to tackle this issue head-on. So, let's get started and figure out how to get Pyrefly back on track!

Understanding the Panic: What Does "assertion failed: removed" Mean?

First off, let's dissect the error message itself. The panic occurs in pyrefly/lib/state/state.rs at line 631, and the core message is "assertion failed: removed." This typically indicates that Pyrefly's internal state management has encountered an inconsistency. An assertion in programming is a check that a certain condition is true, and if it's not, the program halts to prevent further corruption or unexpected behavior. In this case, the assertion failure suggests that Pyrefly is trying to access or operate on something that it believes should no longer exist.

Debugging Assertions and Pyrefly's State Management

When dealing with assertions, especially in a complex system like Pyrefly, the key is to understand what part of the state is being managed and why the assertion is failing. Pyrefly, as a Language Server Protocol (LSP) implementation, juggles a lot of information about your code: files, symbols, diagnostics, and more. It maintains an internal representation of your project's state to provide features like autocompletion, go-to-definition, and error checking. This internal state management is crucial for Pyrefly's functionality, and any inconsistencies here can lead to panics.

Potential Causes and How to Investigate

So, what could be causing this "removed" assertion? Here are a few possibilities:

  1. Race Conditions: Pyrefly might be trying to access a resource that's being modified or deleted by another part of the system. This is a classic concurrency issue, and it can be tricky to debug. To investigate this, you might want to look for areas in your code or Pyrefly's usage where concurrent operations are happening. Are you opening, closing, or modifying files rapidly? Are there any external tools interacting with your project files while Pyrefly is running?

  2. Incorrect State Updates: There could be a bug in Pyrefly's logic that's causing it to remove something from its internal state prematurely or incorrectly. This is a code-level issue within Pyrefly itself. If this is the case, reporting a detailed bug report (which we'll cover later) is crucial.

  3. Resource Cleanup Issues: Sometimes, resources aren't cleaned up properly, leading to dangling references. Pyrefly might be holding onto a reference to something that's been deallocated, and when it tries to use that reference, the assertion fails.

  4. File System Events: As an LSP, Pyrefly watches your file system for changes. If there's a rapid sequence of file system events (files being created, deleted, or modified in quick succession), it could potentially trigger a race condition or expose a bug in Pyrefly's event handling.

To start debugging, consider these steps:

  • Simplify Your Project: Try reproducing the issue in a smaller project. If you can isolate the panic to a specific set of files or operations, it becomes much easier to pinpoint the cause.
  • Check File System Activity: Monitor your file system while Pyrefly is running. Are there any unusual patterns of file changes? Are you using any tools that might be aggressively modifying files?
  • Examine Your Code: Look for areas in your code where you're interacting heavily with the file system or performing operations that might affect Pyrefly's state. Are you using any unusual coding patterns or libraries that could be interfering with Pyrefly?

Decoding the Backtrace: A Roadmap to the Panic's Origin

The backtrace provided in the error message is your roadmap to the panic's origin. It's a stack trace that shows the sequence of function calls that led to the assertion failure. While it might look like a jumbled mess of numbers and symbols, it contains valuable clues.

Understanding the Stack Trace

The backtrace lists function calls in reverse order, meaning the last function call in the list is where the panic originated, and the calls above it are the functions that led to that point. Let's break down the example backtrace:

ERROR Thread panicked, shutting down: panicked at pyrefly/lib/state/state.rs:631:21:
assertion failed: removed
Backtrace:
   0: <unknown>
   1: <unknown>
   2: <unknown>
   ...
  18: start_thread
             at /usr/src/debug/glibc-2.28-251.el8_10.22.x86_64/nptl/pthread_create.c:479:8
  19: __clone
             at /usr/src/debug/glibc-2.28-251.el8_10.22.x86_64/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95:0
  • panicked at pyrefly/lib/state/state.rs:631:21: This is the most important line. It tells you exactly where the panic occurred: in the state.rs file within the pyrefly/lib/state directory, at line 631, character 21. This is ground zero for your investigation.
  • <unknown>: Many of the lines in the backtrace show <unknown>. This means that the debugging information (symbols) for those functions is not available. This is common when dealing with optimized or release builds. However, the presence of the file and line number in the panic message is still incredibly valuable.
  • start_thread and __clone: These functions are part of the operating system's threading library. They indicate that the panic occurred within a thread. This reinforces the possibility of a race condition or concurrency issue.

Using the Backtrace to Investigate

  1. Go to the Source: Open the pyrefly/lib/state/state.rs file in your editor and jump to line 631. Examine the code around that line. What assertion is failing? What data is being accessed or modified?
  2. Understand the Context: Try to understand the purpose of the code around the assertion. What part of Pyrefly's state management is involved? What operations are being performed?
  3. Trace Backwards (Mentally): Start thinking about the functions that might have led to this point. What could have caused the assertion to fail? This is where your understanding of Pyrefly's architecture and your project's behavior comes into play.
  4. Look for Clues in the Code: Examine the variables and data structures involved in the assertion. Are they being modified by multiple threads? Are they being accessed in a way that could lead to inconsistencies?

Reporting the Bug: Giving Pyrefly the Information It Needs

If you've tried debugging and still can't pinpoint the issue, or if you suspect a bug within Pyrefly itself, it's time to report it. A well-written bug report is invaluable to the Pyrefly developers and can help them fix the issue quickly.

Creating an Effective Bug Report

  1. Clear and Concise Description: Start with a clear and concise description of the issue. State that you're encountering an "assertion failed: removed" panic after upgrading to Pyrefly 0.25.0.
  2. Steps to Reproduce (If Possible): The holy grail of bug reports is a clear set of steps to reproduce the issue. If you can consistently trigger the panic, provide detailed instructions. Even if you can't reproduce it reliably, describe the circumstances under which it occurred (e.g., "I was working on a large project with many files open, and the panic occurred after I saved a file.")
  3. Full Error Message and Backtrace: Include the complete error message and backtrace. This is crucial information for the developers.
  4. Pyrefly Version: Specify the exact version of Pyrefly you're using (0.25.0 in this case).
  5. Operating System and Environment: Provide information about your operating system (e.g., Windows 10, macOS 12, Linux) and any relevant environment details (e.g., Python version, LSP client you're using).
  6. Code Snippets (If Applicable): If the panic seems to be related to specific code in your project, include relevant code snippets. Make sure to minimize the code to the smallest possible example that still triggers the issue.
  7. Sandbox Link (If Possible): If you can reproduce the issue in a sandbox environment (like a minimal project on GitHub), provide a link to it. This makes it incredibly easy for developers to investigate.
  8. IDE Information (If Applicable): If you're using Pyrefly as an extension in an IDE, provide details about your IDE (e.g., VS Code, Sublime Text) and any relevant extensions.
  9. Your Investigation Steps: Briefly describe the steps you've already taken to debug the issue. This shows the developers that you've put in effort to understand the problem and helps them avoid duplicating your work.

Example Bug Report Snippet

## Bug Report: Pyrefly 0.25.0 "assertion failed: removed" Panic

**Description:**
After upgrading to Pyrefly 0.25.0, I am encountering an "assertion failed: removed" panic. The panic occurs intermittently, and I haven't been able to reproduce it reliably, but it seems to happen when I'm working on large Python files.

**Steps to Reproduce (Intermittent):**
1.  Open a large Python project with many files (e.g., a Django project).
2.  Open several Python files in the editor.
3.  Work on the files for a while (e.g., making edits, saving, running code analysis).
4.  The panic may occur after saving a file or performing a code analysis operation.

**Error Message and Backtrace:**

ERROR Thread panicked, shutting down: panicked at pyrefly/lib/state/state.rs:631:21: assertion failed: removed Backtrace: 0: 1: ... 18: start_thread at /usr/src/debug/glibc-2.28-251.el8_10.22.x86_64/nptl/pthread_create.c:479:8 19: __clone at /usr/src/debug/glibc-2.28-251.el8_10.22.x86_64/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95:0


**Pyrefly Version:** 0.25.0

**Operating System:** macOS 12.3.1

**Environment:** Python 3.9, VS Code 1.67.0

**Investigation Steps:**
I have tried simplifying my project and disabling other VS Code extensions, but the panic still occurs intermittently. I suspect it might be related to file system events or concurrency issues within Pyrefly.

Submitting the Bug Report

The bug report template you find on the Pyrefly's GitHub repository (typically in the "Issues" section) will guide you. Provide as much detail as possible, including the error message, steps to reproduce (if any), and any relevant context about your setup and workflow.

Community Discussion: Sharing the Knowledge

Don't hesitate to check online forums, such as Facebook groups or other developer communities, to see if others are experiencing the same issue. Sharing your experience and comparing notes can often lead to valuable insights and potential workarounds. Even if you don't find a solution, your contribution can help others who encounter the same problem.

Staying Up-to-Date

Keep an eye on Pyrefly's GitHub repository for updates and discussions related to this issue. The developers might be working on a fix, and you might find valuable information in the issue tracker or pull requests.

Conclusion: Debugging is a Journey

The "assertion failed: removed" panic in Pyrefly can be a frustrating issue, but with a systematic approach to debugging, you can increase your chances of finding the root cause and getting Pyrefly back to its smooth self. Remember, the key is to understand the error message, leverage the backtrace, try to reproduce the issue, and provide a detailed bug report if needed. Happy debugging, folks! And always remember, even the most experienced developers run into bugs – it's part of the process. The important thing is to learn from them and help improve the tools we all use.