Neovim Vtsls Bug: High RAM Usage With Specific Filenames

The Mysterious RAM Consumption Bug

Encountering a bug that leads to insane RAM consumption when opening a file with a specific name is a developer's nightmare. The scenario described involves Neovim, the popular text editor, and vtsls, a language server for TypeScript, exhibiting erratic behavior. Specifically, the issue surfaces when attempting to open a file named authorize-interceptor.fn.ts. The problem is not present when the file is named slightly differently, such as authorize-intercept.fn.ts, or when using a very long filename without the .fn part. This suggests a very specific set of conditions triggering the bug. The user reports that opening the problematic file causes Neovim's RAM usage to skyrocket, reaching up to 20GB within about 30 seconds. This makes the editor unusable and forces a hard close. The fact that the same file opens without issue in Visual Studio Code (VSCode) points to the issue being specific to the Neovim/vtsls environment.

The core of the problem seems to be linked to the filename's structure, specifically the length and the inclusion of a specific extension (.fn). The report indicates that filenames longer than 19 characters, with an extra extension before .ts, trigger the issue. This length constraint is a critical piece of information for anyone debugging or attempting to reproduce the bug. Furthermore, the user tried changing the extension, and the issue persisted, indicating that the problem is not isolated to a particular file type or extension, but rather to the combination of the filename length and the .fn extension. The last line of the custom log print before the lsp setup call for vtsls, suggests that the problem might originate from the language server protocol (LSP) configuration or interaction within Neovim. This is valuable as it narrows down the potential areas to investigate within the code. The user's Neovim setup uses the nightly version (12.0), so this might be relevant to the bug. It is important to rule out the basic causes, such as a corrupted Neovim configuration or an outdated version of vtsls. Verifying that the same issue exists with a minimal configuration or the latest versions of the relevant software can help identify whether the problem is specific to the user's environment or a broader issue.

Troubleshooting and Diagnosis

When faced with a bug that consumes insane amounts of RAM, the initial steps involve narrowing down the scope of the problem. This can be achieved by a systematic approach, which includes the identification of the root cause of the error. Given the specifics of the issue, here are the troubleshooting steps that should be considered. Firstly, it's crucial to confirm if the bug is reproducible in a clean, minimal Neovim configuration. This involves temporarily disabling all plugins and custom configurations to see if the issue persists. If the RAM consumption doesn't occur in the minimal setup, then it's highly likely that one of the user's configurations or plugins is the culprit. In this case, re-enabling configurations and plugins one by one, while testing after each activation, will help pinpoint the problematic element. This process is commonly known as the binary search method. Next, ensure that vtsls and its related dependencies are up-to-date. Outdated versions of language servers or their dependencies are known to cause unpredictable behavior. Update vtsls and any relevant packages through the appropriate package manager (e.g., npm or yarn) to ensure compatibility. The user has already noted that the issue occurs regardless of the file extension, which rules out some potential causes. However, it's worth experimenting with different file types to verify that the bug is truly extension-agnostic. The focus should remain on the filename's length and structure. Memory profiling tools can provide deeper insights into the bug. Tools like perf or valgrind can help track memory allocation and identify where the RAM is being consumed. These tools will pinpoint the exact functions or parts of the code responsible for the excessive memory usage. Investigating the Neovim logs is critical. Neovim logs often contain detailed information about the editor's operation, including any errors or warnings. Enable detailed logging in Neovim and examine the logs when the file is opened to see if any clues about the root cause are present.

Potential Causes and Solutions

The behavior described strongly suggests several potential causes for the excessive RAM consumption. The combination of filename length and extension dependency points towards several areas in the LSP or vtsls implementation that might be the source of the problem. One likely cause is a parsing issue. It is possible that vtsls or some component of the LSP used by Neovim has a bug that misinterprets or mishandles long filenames with the .fn extension. This could lead to a memory leak or an infinite loop when parsing the file contents or metadata. Another potential cause is related to the indexing or caching mechanisms within vtsls. Language servers often index files to provide features like autocompletion and code navigation. A bug in the indexing process, particularly when dealing with the specific filename pattern, might cause the server to repeatedly index the file or create excessive data structures in memory. Further investigation of the code related to indexing and caching is required to confirm this hypothesis. Another possibility is a resource exhaustion issue. The file opening process might trigger a recursive operation or consume excessive resources (e.g., file handles or network connections). This can lead to a rapid increase in RAM usage, especially if the operation is not properly managed or has an issue with exception handling. Consider whether the issue is related to how the file is being parsed. For example, the use of regular expressions or complex string manipulation on the filename could contribute to the problem. Optimizing the parsing routines and ensuring proper bounds checking may help to resolve the issue. If the bug is identified as a parsing or indexing issue within the language server, then fixing the parsing logic or optimizing the indexing algorithms should resolve the issue. If the issue is a resource exhaustion, ensuring proper resource management (e.g., closing file handles, limiting the number of threads, and implementing timeouts) is essential. If the issue is related to incorrect handling of the filename within the LSP or Neovim, then it will require changes to the code to handle longer filenames correctly or to implement a more robust filename parsing mechanism.

Steps to Reproduce and Report the Bug

To effectively report this bug, the user needs to provide a clear and concise set of steps to reproduce the issue. This will help developers replicate the problem and identify the underlying cause. The following steps should be taken to reproduce the bug: First, ensure you have Neovim (nightly 12.0) and vtsls installed and configured. Create a file named authorize-interceptor.fn.ts (or any other filename longer than 19 characters with an extension like .fn.ts). Open the file in Neovim using vtsls. Monitor the RAM usage of Neovim. The RAM usage should increase rapidly (e.g., up to 20GB within 30 seconds). If you have other plugins, try disabling them to make sure it's not a plugin conflict. Then, the user must clearly outline the observed behavior. Include the exact RAM consumption, the time it takes to reach that level, and any error messages displayed in Neovim's output or logs. Include the following details to ensure the report is complete. Provide the exact versions of Neovim, vtsls, and any related dependencies. List any relevant plugins or configurations that may impact the issue. Include the operating system and any relevant system information (e.g., CPU, RAM). Attach Neovim's logs, especially those generated when opening the problematic file. If possible, provide a minimal configuration file or a small, reproducible example project to help developers reproduce the bug. Report the bug on the appropriate platform. This typically involves opening an issue on the vtsls or Neovim repository on GitHub. Use the provided information to report the bug in a well-structured and informative way. Make it easy for developers to understand the issue and reproduce it. The bug report should start with a clear summary of the problem, a description of the expected behavior, and an explanation of the actual behavior. Include the steps to reproduce, the system information, and any relevant logs or configuration files. The more detailed the bug report, the easier it will be to find and fix the issue. A detailed report dramatically increases the chances of it being addressed promptly.

Conclusion

This bug, which causes extreme RAM consumption when opening specific files with Neovim and vtsls, requires careful investigation and a systematic approach to resolve. From confirming the problem with a minimal configuration to meticulously profiling memory usage, each step is critical in isolating the root cause. With the user providing detailed information, including clear steps to reproduce the bug and the exact versions of the related software, the development team has a significant chance of identifying the underlying source of the error. Addressing this issue will ultimately improve the performance and reliability of Neovim and its language server capabilities. This requires a collaborative effort between the user and the development community to ensure the best possible experience for all users.

For more information on debugging Neovim and language server issues, consider the following link: Neovim Debugging Guide.