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fix(id/web): detectLanguage own-key guards — prototype names are not languages (#2787) #2788

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Merged
dezren39 merged 1 commit into from
Oct 30, 2026
Merged

fix(id/web): detectLanguage own-key guards — prototype names are not languages (#2787) #2788

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13 changes: 13 additions & 0 deletions pkgs/id/web/src/highlight.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -414,6 +414,19 @@ describe("detectLanguage", () => {
expect(detectLanguage("")).toBeUndefined();
});

it("returns undefined for prototype-member extensions (#2787)", () => {
// Plain-object lookups on EXT_TO_LANG matched inherited
// Object.prototype members: these returned a function / object
// instead of a language string.
expect(detectLanguage("notes.constructor")).toBeUndefined();
expect(detectLanguage("notes.__proto__")).toBeUndefined();
});

it("returns undefined for prototype-member filenames (#2787)", () => {
expect(detectLanguage("constructor")).toBeUndefined();
expect(detectLanguage("__proto__")).toBeUndefined();
});

it("is case-insensitive for extensions", () => {
expect(detectLanguage("App.JS")).toBe("javascript");
expect(detectLanguage("style.CSS")).toBe("css");
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14 changes: 10 additions & 4 deletions pkgs/id/web/src/highlight.ts
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Expand Up @@ -145,7 +145,10 @@ export function detectLanguage(filename: string): string | undefined {
// A known extension wins over a special-name stem:
// "makefile.md" is Markdown documentation, not a Makefile.
const ext = basename.includes(".") ? basename.split(".").pop()?.toLowerCase() : undefined;
if (ext && EXT_TO_LANG[ext]) {
// Own-key check (#2787): a plain lookup also matches inherited
// Object.prototype members, so "notes.constructor" / "notes.__proto__"
// returned the Object constructor / prototype object as a "language".
if (ext && Object.hasOwn(EXT_TO_LANG, ext)) {
return EXT_TO_LANG[ext];
}

Expand All @@ -156,11 +159,11 @@ export function detectLanguage(filename: string): string | undefined {
? basenameLower.slice(0, basenameLower.lastIndexOf("."))
: basenameLower;

if (FILENAME_TO_LANG[nameWithoutExt]) {
if (Object.hasOwn(FILENAME_TO_LANG, nameWithoutExt)) {
return FILENAME_TO_LANG[nameWithoutExt];
}
// Full basename (e.g., "Dockerfile" with no ext)
if (FILENAME_TO_LANG[basenameLower]) {
if (Object.hasOwn(FILENAME_TO_LANG, basenameLower)) {
return FILENAME_TO_LANG[basenameLower];
}

Expand Down Expand Up @@ -277,7 +280,10 @@ async function getHighlighter(): Promise<ShikiHighlighter> {
async function ensureLanguage(highlighter: ShikiHighlighter, lang: string): Promise<void> {
if (loadedLangs.has(lang)) return;

const importFn = LANG_IMPORTS[lang];
// Own-key check (#2787): `lang` can be an authored code-block language
// attribute; a plain lookup returns Object.prototype members for
// "constructor"/"__proto__", which were then called as import functions.
const importFn = Object.hasOwn(LANG_IMPORTS, lang) ? LANG_IMPORTS[lang] : undefined;
if (!importFn) {
// Language not in our static registry — mark as loaded to avoid retries
loadedLangs.add(lang);
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