text: Improve markdown code block rendering performance#2400
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madcodelife merged 1 commit intoMay 26, 2026
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Cache code block syntax highlighters per thread and compute styles lazily to avoid repeated highlighter setup for large markdown documents. Add regression tests for code block equality and language cache refresh behavior.
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AzureZee
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) ## Description This changes code block syntax highlighting to compute styles lazily and reuse `SyntaxHighlighter` instances through a thread-local language cache. This avoids repeated highlighter construction during markdown parsing/render setup for large files with many code blocks. It also avoids repeatedly recombining visible input highlight ranges when the ranges are already disjoint. I also tested longbridge#2371 against the same case, but it did not help with the slowdown I was seeing. I first noticed the issue in my side project, then reproduced the same behavior in the example markdown editor. In local testing, Task Manager showed lower CPU usage while editing with this implementation, memory usage stayed about the same. Adds regression coverage for code block equality and cached highlighter refresh behavior when a language is registered after an initial fallback. AI assistance was used to help and prepare this PR. I manually reviewed the resulting code and tested the performance difference before opening the PR. ## Test File I used this AI-generated markdown file to reproduce the issue and test the change: [refactor-opportunities.md](https://github.com/user-attachments/files/28234513/refactor-opportunities.md) ## Videos ### Before <video src="https://github.com/user-attachments/assets/dbcc45ab-f371-40c2-b6b5-1336fee995fe" controls></video> ### After <video src="https://github.com/user-attachments/assets/4e3c0754-55b5-4d54-9eb6-a4261f940ad9" controls></video> ## Tests - `cargo test -p gpui-component code_block_` - `cargo test -p gpui-component input::` - `cargo test -p gpui-component text::` ## Checklist - [x] I have read the [CONTRIBUTING](../CONTRIBUTING.md) document and followed the guidelines. - [x] Reviewed the changes in this PR and confirmed AI-generated code, if any, is accurate. - [x] Passed `cargo run` for story tests related to the changes. - [x] Tested macOS, Windows, and Linux platform performance, if the change is platform-specific.
linyisu
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May 29, 2026
) This changes code block syntax highlighting to compute styles lazily and reuse `SyntaxHighlighter` instances through a thread-local language cache. This avoids repeated highlighter construction during markdown parsing/render setup for large files with many code blocks. It also avoids repeatedly recombining visible input highlight ranges when the ranges are already disjoint. I also tested longbridge#2371 against the same case, but it did not help with the slowdown I was seeing. I first noticed the issue in my side project, then reproduced the same behavior in the example markdown editor. In local testing, Task Manager showed lower CPU usage while editing with this implementation, memory usage stayed about the same. Adds regression coverage for code block equality and cached highlighter refresh behavior when a language is registered after an initial fallback. AI assistance was used to help and prepare this PR. I manually reviewed the resulting code and tested the performance difference before opening the PR. I used this AI-generated markdown file to reproduce the issue and test the change: [refactor-opportunities.md](https://github.com/user-attachments/files/28234513/refactor-opportunities.md) <video src="https://github.com/user-attachments/assets/dbcc45ab-f371-40c2-b6b5-1336fee995fe" controls></video> <video src="https://github.com/user-attachments/assets/4e3c0754-55b5-4d54-9eb6-a4261f940ad9" controls></video> - `cargo test -p gpui-component code_block_` - `cargo test -p gpui-component input::` - `cargo test -p gpui-component text::` - [x] I have read the [CONTRIBUTING](../CONTRIBUTING.md) document and followed the guidelines. - [x] Reviewed the changes in this PR and confirmed AI-generated code, if any, is accurate. - [x] Passed `cargo run` for story tests related to the changes. - [x] Tested macOS, Windows, and Linux platform performance, if the change is platform-specific.
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Description
This changes code block syntax highlighting to compute styles lazily and reuse
SyntaxHighlighterinstances through a thread-local language cache. This avoids repeated highlighter construction during markdown parsing/render setup for large files with many code blocks.It also avoids repeatedly recombining visible input highlight ranges when the ranges are already disjoint.
I also tested #2371 against the same case, but it did not help with the slowdown I was seeing.
I first noticed the issue in my side project, then reproduced the same behavior in the example markdown editor. In local testing, Task Manager showed lower CPU usage while editing with this implementation, memory usage stayed about the same.
Adds regression coverage for code block equality and cached highlighter refresh behavior when a language is registered after an initial fallback.
AI assistance was used to help and prepare this PR. I manually reviewed the resulting code and tested the performance difference before opening the PR.
Test File
I used this AI-generated markdown file to reproduce the issue and test the change:
refactor-opportunities.md
Videos
Before
before.mp4
After
after.mp4
Tests
cargo test -p gpui-component code_block_cargo test -p gpui-component input::cargo test -p gpui-component text::Checklist
cargo runfor story tests related to the changes.