# Objective

Closes #4868.

Untitled buffers start as Plain Text and require users to select a
language manually before receiving syntax highlighting. Add lightweight
automatic language detection for code entered or pasted into untitled
buffers.

## Solution

This builds on [Max Stevens's earlier language-detection
work](https://github.com/zed-industries/zed/pull/43057), replacing
Magika with [Betlang](https://github.com/DioxusLabs/betlang).

While researching smaller and faster alternatives to Magika, I came
across Betlang, a recently introduced language detection library
developed by DioxusLabs for dioxus-code. The fact that it comes from
DioxusLabs gave me more confidence in evaluating this relatively new
dependency for Zed. Betlang embeds an approximately 50 KB model, is
MIT-licensed, and depends only on `fearless_simd`, making it well suited
to Zed's cross-platform embedding requirements.

Detection runs on the background executor with bounded input sampling.
It is restricted to untitled buffers, skips content shorter than 20
bytes, and requires at least 50% confidence. These limits have worked
well in local testing. In release builds on Linux with an Intel Core
i5-13600KF, the `betlang::detect` call alone typically completes within
3 ms when processing the maximum sampled input.

## Testing

I added a test for language detection in untitled buffers that covers
both manually entered and pasted content. The test passes successfully.
I also manually tested the feature to verify that the overall experience
works well.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase



https://github.com/user-attachments/assets/96e28ad7-2968-4325-9aff-37fe813a2da7



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Release Notes:

- Added automatic language detection for untitled buffers.

---------

Co-authored-by: Max Stevens <maxstevens2708@gmail.com>