Oh My Posh Init Error: Config Size Issue?

by SLV Team 42 views

Hey there, fellow tech enthusiasts! Ever run into a snag where your oh-my-posh prompt refuses to load, even though your config file seems perfectly fine? Well, you're not alone. I've been wrestling with this myself, and it seems like there might be a hidden size limit that's causing oh-my-posh to choke during initialization in PowerShell. Let's dive into what's happening, how to spot it, and what you can do about it.

The Mystery of the Missing Prompt

oh-my-posh, a fantastic tool for customizing your terminal prompt, appears to have a bit of a quirk. It seems there's a limit to how large your configuration file can be before the init process throws a hissy fit. The interesting part? The same config file works flawlessly when you use the print or preview commands. It's like the init process is more sensitive than the other commands.

Let's break down the problem I faced. I was happily tweaking my custom theme, OhMyPosh-Atomic-Custom.json, which is based on the Atomic theme. I added a new segment to display some extra information. After adding it, I reloaded PowerShell, and poof, my customized prompt vanished! Instead, I was staring at the default theme. Not cool!

I then did some troubleshooting and ran the -debug command, which revealed the following message: no config found in session cache, please provide a config using the --config flag. This was a clue that the config file wasn't loading properly. But the real head-scratcher was this: when I ran oh-my-posh print primary --config ./config.json, the prompt displayed perfectly fine.

Reproducing the Issue

Want to see if you can reproduce this on your machine? Here's how you can try:

  1. Start with a Long Config: Begin with an existing oh-my-posh config file, the longer, the better. My config file was around 1300 lines long.
  2. Add a New Segment: Add a new segment to your config file. Make sure it has valid JSON syntax.
  3. Reload PowerShell: Close and reopen your PowerShell window, or use .\[path to your oh-my-posh init script] to reload it.
  4. Observe the Failure: If you're affected by this issue, oh-my-posh will fail to initialize, and you'll likely see the default theme.
  5. Test with Print Command: Run oh-my-posh print primary --config <your config file path>. If it works, you've confirmed the issue.
  6. Remove a Segment: Delete an old or unused segment from your config file, removing a few lines. Then, reload PowerShell. If the issue is related to size, then the config should load.

Expected vs. Actual Behavior

  • Expected Behavior: Your oh-my-posh config should load regardless of its size, or at least provide a clear error message explaining a size limit.
  • Actual Behavior: The PowerShell init process fails silently, and it falls back to the default theme, or sometimes loads an older version of the config. The print commands work fine.

The Size Factor: A Closer Look

Based on my testing, it looks like the magic number for the breaking point is around 36.5-36.7 KiB or about 37,000 characters. My config file was just a tad over that when the problems started. The size difference between the working and failing configurations was quite small, just a few hundred characters, but it was enough to tip the scales.

Here's a breakdown of the size metrics:

  • Size: The failing config was slightly larger (+0.33 KiB) than the working one.
  • Gzipped/Brotli: The compressed sizes also showed a small increase.
  • Lines and Characters: The failing config had a few more lines and characters (+11 lines, +337 characters).

It's important to remember that these are estimates, and the exact threshold might vary depending on your system, or oh-my-posh version.

Character Breakdown: Before and After

To give you a better idea of where the characters are coming from, here's a rough breakdown:

  • Before (Working):
    • Letters: 14136
    • Digits: 555
    • Spaces: 11284
    • Special: 8133
    • Total: 36694
  • After (Failing):
    • Letters: 14249
    • Digits: 564
    • Spaces: 11411
    • Special: 8199
    • Total: 37031

The most important thing to see here is the Total characters between both states which validates our initial assessment.

Possible Causes

So, what's going on here? Here are some hypotheses:

  • Init Script Limit: The script that initializes oh-my-posh might have a hard limit on the config file size or complexity. When the config exceeds this limit, the init process fails without a clear error message.
  • Serialization Issues: The init process might struggle to serialize or load large config files, while the print command handles it just fine.
  • Mismatch Between Commands: There might be a difference between what the print and init commands can handle. The print command is more robust, while the init process is more sensitive.

Troubleshooting Steps and Tips

If you're running into this issue, here are a few things you can try:

  • Keep Your Config Lean: Try to keep your config file as concise as possible. Remove any unnecessary segments or options.
  • Break it Up: Consider splitting your config into multiple files and importing them using the $Env:POSH_THEME variable. This can help keep individual files smaller.
  • Test, Test, Test: After making changes, always reload PowerShell to check if the issue is resolved.
  • Check Your JSON: Make sure your config file is valid JSON using an online validator or a code editor with JSON validation. A small syntax error can also cause problems.
  • Update Your Tools: Make sure you are using the latest version of oh-my-posh and PowerShell. It's possible that the issue has been resolved in a newer version.
  • Use Debugging: If you are comfortable with it, the --debug or --trace command-line flags might provide more detailed information about the init process. This can help pinpoint the exact cause of the failure.

The Environment

Here's the environment I was working with:

  • PowerShell 7.5.4
  • oh-my-posh 27.2.1
  • Windows
  • Config File: OhMyPosh-Atomic-Custom.json (available on my Github, check the original post for the link)

Log Output

The log output can be found in the original post. The key takeaway is the absence of any explicit error message, which makes troubleshooting more difficult.

Conclusion

This config size limit is something to be aware of if you're a heavy oh-my-posh user. By keeping your config files lean, and by following the troubleshooting tips, you can hopefully avoid this issue and enjoy a smooth and customized terminal experience. Hopefully, the oh-my-posh team can address this issue in a future update to provide better error messages and improved handling of large configurations.

Happy prompting, and let me know if you have any questions or further insights!"