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fix(web): stop highlighter freezes and worker spin by using the Oniguruma WASM engine #8360

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fix(web): stop highlighter freezes and worker spin by using the Oniguruma WASM engine #8360

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c626afc
fix(web): highlight with the Oniguruma WASM engine, not the JS regex …
LetZico Aug 27, 2026
5e5651c
fix(web): cover the SSR settings preview highlighter site; trim engin…
LetZico Aug 27, 2026
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2 changes: 2 additions & 0 deletions apps/web/src/components/DiffPanel.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ import {
resolveDiffThemeName,
resolveFileDiffPath,
} from "../lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "../lib/syntaxHighlighting";
import { areAllDiffFilesCollapsed, toggleAllDiffFiles } from "../lib/diffCollapse";
import { useTurnDiffSummaries } from "../hooks/useTurnDiffSummaries";
import { useProject, useThread } from "../state/entities";
Expand Down Expand Up @@ -960,6 +961,7 @@ export default function DiffPanel({
lineDiffType: "none",
overflow: wordWrap ? "wrap" : "scroll",
theme: resolveDiffThemeName(resolvedTheme),
preferredHighlighter: PREFERRED_HIGHLIGHTER,
themeType: resolvedTheme as DiffThemeType,
stickyHeaders: true,
...(loadDiffFiles ? { loadDiffFiles } : {}),
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2 changes: 2 additions & 0 deletions apps/web/src/components/DiffWorkerPoolProvider.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import * as Schema from "effect/Schema";
import { useEffect, useMemo, type ReactNode } from "react";
import { useTheme } from "../hooks/useTheme";
import { resolveDiffThemeName, type DiffThemeName } from "../lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "../lib/syntaxHighlighting";

export class DiffWorkerError extends Schema.TaggedErrorClass<DiffWorkerError>()("DiffWorkerError", {
operation: Schema.Literals(["create-worker", "get-render-options", "set-render-options"]),
Expand Down Expand Up @@ -73,6 +74,7 @@ export function DiffWorkerPoolProvider({ children }: { children?: ReactNode }) {
}}
highlighterOptions={{
theme: diffThemeName,
preferredHighlighter: PREFERRED_HIGHLIGHTER,
tokenizeMaxLineLength: 1_000,
useTokenTransformer: true,
}}
Expand Down
2 changes: 2 additions & 0 deletions apps/web/src/components/chat/MessagesTimeline.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@ import {
resolveDiffThemeName,
resolveFileDiffPath,
} from "../../lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "../../lib/syntaxHighlighting";
import ChatMarkdown from "../ChatMarkdown";
import {
BotIcon,
Expand Down Expand Up @@ -2078,6 +2079,7 @@ function UserMessageReviewCommentCard({ comment }: { comment: ReviewCommentConte
collapsed: false,
diffStyle: "unified",
theme: resolveDiffThemeName(ctx.resolvedTheme),
preferredHighlighter: PREFERRED_HIGHLIGHTER,
}}
/>
))}
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3 changes: 3 additions & 0 deletions apps/web/src/components/files/FilePreviewPanel.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ import { useClientSettings } from "~/hooks/useSettings";
import { useTheme } from "~/hooks/useTheme";
import { getLocalStorageItem, setLocalStorageItem, useLocalStorage } from "~/hooks/useLocalStorage";
import { DIFF_SURFACE_THEME_UNSAFE_CSS, resolveDiffThemeName } from "~/lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "~/lib/syntaxHighlighting";
import { cn } from "~/lib/utils";
import { isPreviewSupportedInRuntime } from "~/previewStateStore";
import { resolvePathLinkTarget } from "~/terminal-links";
Expand Down Expand Up @@ -670,6 +671,7 @@ function EditableFileSurface({
onLineSelectionEnd: handleLineSelectionEnd,
overflow: wordWrap ? "wrap" : "scroll",
theme: resolveDiffThemeName(resolvedTheme),
preferredHighlighter: PREFERRED_HIGHLIGHTER,
themeType: resolvedTheme,
unsafeCSS: FILE_LINK_REVEAL_UNSAFE_CSS,
onPostRender: handlePostRender,
Expand Down Expand Up @@ -1039,6 +1041,7 @@ export default function FilePreviewPanel({
disableFileHeader: true,
overflow: wordWrap ? "wrap" : "scroll",
theme: resolveDiffThemeName(resolvedTheme),
preferredHighlighter: PREFERRED_HIGHLIGHTER,
themeType: resolvedTheme,
unsafeCSS: FILE_LINK_REVEAL_UNSAFE_CSS,
onPostRender: onFilePostRender,
Expand Down
2 changes: 2 additions & 0 deletions apps/web/src/components/pullRequest/PullRequestCodeTab.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@ import {
resolveFileDiffPreviousPath,
type RenderablePatch,
} from "~/lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "~/lib/syntaxHighlighting";
import { cn } from "~/lib/utils";
import { createPullRequestDiffFileContentsLoader } from "~/lib/diffFileContents";
import {
Expand Down Expand Up @@ -743,6 +744,7 @@ export function PullRequestCodeTab({
lineDiffType: "none" as const,
overflow: wordWrap ? ("wrap" as const) : ("scroll" as const),
theme: resolveDiffThemeName(resolvedTheme),
preferredHighlighter: PREFERRED_HIGHLIGHTER,
themeType: resolvedTheme,
stickyHeaders: true,
loadDiffFiles,
Expand Down
3 changes: 2 additions & 1 deletion apps/web/src/components/settings/SettingsFontPreviews.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import { terminalThemeFromApp } from "../ThreadTerminalDrawer";
import { useTheme } from "../../hooks/useTheme";
import { DISCONNECTED_COMPOSER_PLACEHOLDER } from "../../composerPlaceholder";
import { resolveDiffThemeName, type DiffThemeName } from "../../lib/diffRendering";
import { PREFERRED_HIGHLIGHTER } from "../../lib/syntaxHighlighting";
import { GhosttyTerminalSurface } from "~/terminal/ghostty/surface";

// The font previews are the real surfaces, not lookalikes: the composer's
Expand Down Expand Up @@ -79,7 +80,7 @@ function loadDiffPreviewHtml(theme: DiffThemeName): Promise<readonly string[]> {
if (promise === undefined) {
promise = preloadPatchFile({
patch: DIFF_PREVIEW_PATCH,
options: { diffStyle: "unified", theme },
options: { diffStyle: "unified", theme, preferredHighlighter: PREFERRED_HIGHLIGHTER },
}).then((results) => results.map((result) => result.prerenderedHTML));
diffPreviewHtmlByTheme.set(theme, promise);
}
Expand Down
11 changes: 10 additions & 1 deletion apps/web/src/lib/syntaxHighlighting.ts
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Original file line number Diff line number Diff line change
@@ -1,11 +1,20 @@
import {
getSharedHighlighter,
type DiffsHighlighter,
type HighlighterTypes,
type SupportedLanguages,
} from "@pierre/diffs";

import { resolveDiffThemeName } from "./diffRendering";

/**
* Always highlight with the Oniguruma WASM engine — the JS regex engine can
* backtrack catastrophically and hang the tokenizing thread. The shared
* highlighter is a first-caller-wins singleton, so every creation site must
* pass this value.
*/
export const PREFERRED_HIGHLIGHTER: HighlighterTypes = "shiki-wasm";
Comment on lines +10 to +16

@macroscopeapp macroscopeapp Bot Aug 27, 2026

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The invariant documented here ("first-caller-wins singleton, so every creation site must pass this value") is not applied everywhere: apps/web/src/components/settings/SettingsFontPreviews.tsx:80-83 still calls preloadPatchFile({ patch: DIFF_PREVIEW_PATCH, options: { diffStyle: "unified", theme } }), and its own comment above states that pipeline "always awaits the shared highlighter". Appearance settings can easily be opened before any diff/file surface mounts, in which case that call wins the race and pins the JS regex engine for the whole session — exactly the hang this PR fixes.

Suggested smallest fix: add preferredHighlighter: PREFERRED_HIGHLIGHTER to the options passed to preloadPatchFile. If the SSR options type does not accept it, please note in this comment that the SSR path builds its own highlighter rather than the shared singleton, so the invariant stated here is accurate.

Posted via Macroscope — UI Consistency

@LetZico LetZico Aug 27, 2026

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Confirmed and fixed in 5e5651c — preloadPatchFile reaches DiffHunksRenderer.initializeHighlighter(), which does create the shared singleton with the shiki-js default, so this was a real missed site. preferredHighlighter: PREFERRED_HIGHLIGHTER is now passed there too (the SSR options type accepts it). Typecheck and the 2,859 apps/web unit tests pass.

@macroscopeapp macroscopeapp Bot Aug 27, 2026

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Sorry, I'm unable to act on this request because you do not have permissions within this repository.


const highlighterPromiseCache = new Map<string, Promise<DiffsHighlighter>>();

export function getSyntaxHighlighterPromise(language: string): Promise<DiffsHighlighter> {
Expand All @@ -15,7 +24,7 @@ export function getSyntaxHighlighterPromise(language: string): Promise<DiffsHigh
const promise = getSharedHighlighter({
themes: [resolveDiffThemeName("dark"), resolveDiffThemeName("light")],
langs: [language as SupportedLanguages],
preferredHighlighter: "shiki-js",
preferredHighlighter: PREFERRED_HIGHLIGHTER,
}).catch((error) => {
if (language === "text") {
highlighterPromiseCache.delete(language);
Expand Down
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