Bug: pinned shiki ^3.0.0 hangs render on Go struct{} fields

[evillguy]

Prerequisites

• I have searched for duplicate or closed issues
• I have read the contributing guidelines

Describe the issue

Some Go files freeze the browser tab when they render in a diff. I tracked it down to syntax highlighting: shiki runs into catastrophic backtracking on Go anonymous-struct fields (struct{}) when the struct tag has a long unbroken run of non-whitespace characters.

The cause is the pinned shiki version. @pierre/diffs requires shiki ^3.0.0, which installs 3.23.0. Its default shiki-js engine converts the Go grammar's struct_variables_types_fields rule (which uses \S+) into a JS RegExp that backtracks exponentially. shiki tracked the same problem in shikijs/shiki#1026.

The cost climbs fast with the length of that non-whitespace run: roughly 190ms at 20 chars, 4.6s at 25, and it never returns past about 30. A field that isn't struct{} doesn't hit it.

Reproduction

Stackblitz

import { CodeView } from "@pierre/diffs/react";
 import type { CodeViewFileItem } from "@pierre/diffs";

 // Go anonymous-struct field with one long no-space struct tag.
 const contents = "type T struct {\n\tX struct{} `" + "x".repeat(40) + "`\n}\n";

 const exampleItem: CodeViewFileItem = {
   id: "foo",
   type: "file",
   file: { name: "x.go", contents },
 };

 function App() {
   return (
     <CodeView
       items={[exampleItem]}
       style={{ height: 600, overflow: "auto" }}
       // Uncomment to confirm the cause (Oniguruma engine renders instantly):
       // options={{ preferredHighlighter: "shiki-wasm" }}
     />
   );
 }

 export default App;

Expected: highlights in a few ms.
Actual: the tab hangs on load (main-thread catastrophic backtracking). Shrinking the "x".repeat(40) shows the exponential curve: ~20 ≈ 190 ms, ~25 ≈ 4.6 s, ~30+ never returns. Switching to shiki-wasm allows the page to render.

What browser(s) are you seeing the problem on?

Chrome

What version of @pierre/diffs are you using?

1.2.5 (also 1.2.9 / 1.3.0-beta.4)

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AI disclosure: issue written with assistance from Claude Opus 4.8 based on usage in my private codebase.