fix(highlight): use the oniguruma engine so Go struct literals cannot freeze the page

web/src/highlight/highlighter.test.ts

@@ -58,3 +58,20 @@ it("colours a window inside a multiline comment like the complete syntax stream"
   expect(tokenize.range!(lines, 100, 110)).toEqual(complete.slice(100, 110));
   expect(tokenize.range!(lines, 178, 184)).toEqual(complete.slice(178, 184));
 });
+
+it("colours an anonymous Go struct literal without locking up the page", async () => {
+  // Shiki's JavaScript regex engine backtracked forever on this shape, and a
+  // regex running on the main thread cannot be interrupted: the review froze
+  // the moment the window holding it scrolled near.
+  await load("go");
+  const tokenize = tokenizerFor("go")!;
+  const lines = [
+    "func handler(w http.ResponseWriter) {",
+    "\trequire.NoError(t, json.NewEncoder(w).Encode(struct {",
+    '\t\tItems []contracts.Fact `json:"items"`',
+    '\t}{Items: []contracts.Fact{{Candidate: contracts.Candidate{Reference: reference, ChatID: "conversation", BusinessObjectID: "appointment", SourceFlow: "reminder"}, Eligible: true, Revision: "rev"}}}))',
+    "}",
+  ];
+
+  expect(tokenize(lines.join("\n"))).toHaveLength(5);
+}, 2_000);

web/src/highlight/highlighter.ts

@@ -3,18 +3,20 @@ import {
   type GrammarState,
   type HighlighterCore,
 } from "shiki/core";
-import { createJavaScriptRegexEngine } from "shiki/engine/javascript";
+import { createOnigurumaEngine } from "shiki/engine/oniguruma";
 import { bundledLanguages } from "shiki/langs";
 import { dark, light } from "./theme";
 import type { Token, Tokenize } from "./tokens";
 
 /** Shiki, loaded a grammar at a time.
  *
- * The regex engine in JavaScript rather than the WebAssembly one: it costs a
- * few exotic grammars and saves half a megabyte that every reader would carry
- * to read one language. Every grammar Shiki ships is reachable, and each is its
- * own file — the page starts with none of them and fetches the one the file in
- * front of you needs. */
+ * The WebAssembly regex engine, not the JavaScript one. The JavaScript engine
+ * saved half a megabyte, but its translation of the Go grammar backtracked
+ * forever on an anonymous struct literal — and a regex on the main thread
+ * cannot be interrupted, so the whole review froze. The WASM is fetched once,
+ * with the first grammar. Every grammar Shiki ships is reachable, and each is
+ * its own file — the page starts with none of them and fetches the one the
+ * file in front of you needs. */
 
 let core: Promise<HighlighterCore> | null = null;
 let built: HighlighterCore | null = null;
@@ -31,7 +33,7 @@ function highlighter(): Promise<HighlighterCore> {
   core ??= createHighlighterCore({
     langs: [],
     themes: [light, dark],
-    engine: createJavaScriptRegexEngine(),
+    engine: createOnigurumaEngine(import("shiki/wasm")),
   }).then((made) => (built = made));
   return core;
 }