fix(core): font setup skips parsing stylesheets that cannot name a font (#5808)

* fix(core): font setup skips parsing stylesheets that cannot name a font

* fix(core): drop the comment the ratchet rejects

Author: miguel-heygen

packages/core/src/fonts/authoredGoogleFonts.ts

@@ -21,6 +21,7 @@ function googleStylesheetFamilies(urlText: string): string[] {
 }
 
 function importUrls(css: string): string[] {
+  if (!/@import/i.test(css)) return [];
   let root: postcss.Root;
   try {
     root = postcss.parse(css);

packages/core/src/fonts/deterministicFonts.test.ts

@@ -1,5 +1,6 @@
 // @vitest-environment node
-import { beforeEach, describe, expect, it } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import postcss from "postcss";
 import { mkdtempSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
@@ -50,6 +51,17 @@ describe("existing font-face recognition", () => {
     const html = `<html><head><style>${css}</style></head><body>Hello</body></html>`;
     expect(await injectDeterministicFontFaces(html, { allowSystemFontCapture: false })).toBe(html);
   });
+
+  it("never parses a stylesheet that has no font-family or custom property", async () => {
+    const parse = vi.spyOn(postcss, "parse");
+    try {
+      const html = `<html><head><style>${"@font-face{{".repeat(1_000)}</style></head><body>Hello</body></html>`;
+      await injectDeterministicFontFaces(html, { allowSystemFontCapture: false });
+      expect(parse).not.toHaveBeenCalled();
+    } finally {
+      parse.mockRestore();
+    }
+  });
 });
 
 describe("Google Fonts CSS request caching", () => {

packages/core/src/fonts/deterministicFonts.ts

@@ -246,6 +246,7 @@ export type FontFamilyDeclaration = {
 };
 
 function collectCssCustomProperties(css: string, customProperties: Map<string, string>): void {
+  if (!css.includes("--")) return;
   const root = parseCssRoot(css);
   if (!root) return;
   root.walkDecls((decl) => {
@@ -272,6 +273,7 @@ function* iterateCssRootFontFamilyDeclarations(
 }
 
 function* iterateCssFontFamilyDeclarations(css: string): Generator<FontFamilyDeclaration> {
+  if (!/font-family/i.test(css)) return;
   const root = parseCssRoot(css);
   if (!root) return;
   yield* iterateCssRootFontFamilyDeclarations(root);