Blame for src/app/layout.tsx

import type { Metadata, Viewport } from "next";
import { readFileSync } from "node:fs";
import path from "node:path";
import { Bricolage_Grotesque, Spline_Sans_Mono } from "next/font/google";
import "./globals.css";
import { readEngineInfo } from "@/lib/engine-info";

const engine = readEngineInfo();

// Fonts are fetched once at build time and served from this site, so there is no
// request to Google at runtime. Bricolage Grotesque does everything a person
// reads, Spline Sans Mono is only ever code and file names.
const display = Bricolage_Grotesque({
  subsets: ["latin"],
  variable: "--font-display",
  axes: ["opsz", "wdth"],
  display: "swap",
});
const mono = Spline_Sans_Mono({
  subsets: ["latin"],
  variable: "--font-code",
  display: "swap",
});

export const metadata: Metadata = {
  metadataBase: new URL("https://dssl-sable.vercel.app"),
  title: { default: "DSSL: a style language that tells you what you got wrong", template: "%s | DSSL" },
  description: `DSSL is a styling language for the web: design tokens, its own cascade, loud errors and zero specificity wars. The engine is ${engine.gzKb} kB gzipped, with no build step.`,
  keywords: ["DSSL", "CSS alternative", "style language", "design tokens", "web"],
  icons: { icon: "/favicon.svg" },
  openGraph: { type: "website", siteName: "DSSL", title: "DSSL: a style language that tells you what you got wrong" },
};

export const viewport: Viewport = {
  width: "device-width",
  initialScale: 1,
};

// The ONLY non-DSSL styling in this app: a pre-paint shim so the very first
// frame doesn't flash white before the DSSL engine boots (dark-mode respect).
const prePaint = `
  html { background: #f2f0f7; }
  @media (prefers-color-scheme: dark) { html { background: #130f1b; } }
`;

// v0.3.2, performance: the stylesheets ride INSIDE the HTML. The engine's
// auto-boot picks these <style type="text/dssl"> tags up the moment the module
// executes (right after parse, before first paint), so there is no fetch
// waterfall and no wait for React hydration. Server-side read also means a
// browser refresh picks up .dssl edits instantly in dev.
const DSSL_SHEETS = ["tokens", "site", "home", "docs", "playground", "changelog", "bench"] as const;

function dsslInlineStyles(): { name: string; src: string }[] {
  return DSSL_SHEETS.map((name) => {
    let src = "";
    try {
      src = readFileSync(path.join(process.cwd(), "public", "styles", `${name}.dssl`), "utf8");
    } catch {
      // missing sheet: boot simply won't apply it; errors stay loud elsewhere
    }
    // defensive: a "</style" sequence in source would break out of the tag
    src = src.replace(/<\/style/gi, "<\\/style");
    return { name, src };
  });
}

// Dev-only interop shim: the engine styles the SSR DOM BEFORE React hydrates
// (that is the whole point, no FOUC). React 19 then logs one console.error
// about extra style attributes and, helpfully, does not patch them. Next's
// dev overlay ALSO patches console.error (one layer around everything) and
// counts every error it sees into the "Issues" badge, so a plain filter
// installed here would sit INSIDE Next's collector and the badge would still
// show "1". This shim instead installs an assignment trap: the moment Next
// assigns its own wrapper, we capture it and re-publish OUR filter as the
// outermost layer. DSSL's own hydration diff is swallowed + explained; every
// other console.error still reaches Next's collector untouched.
const hydrationShim = `
(function () {
  var HYD = 'A tree hydrated but some attributes';
  var MARK = '--dssl';
  var inner = console.error;   // native, until Next assigns its wrapper
  var trapped = false;
  function outer() {
    var s = '';
    for (var i = 0; i < arguments.length; i++) {
      var a = arguments[i];
      s += (i ? ' ' : '') + (typeof a === 'string' ? a : (a && a.message ? a.message : ''));
    }
    if (s.indexOf(HYD) !== -1 && s.indexOf(MARK) !== -1) {
      console.info('%cDSSL%c styled this page before React hydrated. The "hydrated but some attributes didn\\u2019t match" notice is expected interop: the engine owns those style attributes, and React explicitly leaves them alone.',
        'background:#b3372e;color:#fff;padding:1px 6px;border-radius:3px;font-weight:700', '');
      return;
    }
    return inner.apply(console, arguments);
  }
  try {
    var desc = Object.getOwnPropertyDescriptor(console, 'error');
    if (!desc || !desc.configurable) throw new Error('not configurable');
    Object.defineProperty(console, 'error', {
      configurable: true,
      get: function () { return trapped ? outer : inner; },
      set: function (fn) { inner = fn; trapped = true; }
    });
  } catch (e) {
    // fallback: plain filter, console noise is still explained away,
    // though the dev-overlay badge may still count the notice.
    console.error = outer;
  }
})();
`;

export default function RootLayout({
  children,
}: Readonly<{ children: React.ReactNode }>) {
  return (
    <html lang="en" className={`${display.variable} ${mono.variable}`} suppressHydrationWarning>
      <head>
        <style dangerouslySetInnerHTML={{ __html: prePaint }} />
        {process.env.NODE_ENV !== "production" && (
          <script dangerouslySetInnerHTML={{ __html: hydrationShim }} />
        )}
        {/* the same sheets, compiled to plain CSS by `dssl build` (scripts/build-site-css.mjs): styled on first paint, with
            JavaScript off, and in the server-rendered HTML. The engine then adds what a build cannot keep. The reset is in it. */}
        <link rel="stylesheet" href="/site.css" />
        {dsslInlineStyles().map(({ name, src }) => (
          <style
            key={name}
            type="text/dssl"
            data-dssl-name={`${name}.dssl`}
            dangerouslySetInnerHTML={{ __html: src }}
          />
        ))}
        {/* engine starts downloading with the document, module defer rules
            mean it executes after parse with the full SSR DOM present */}
        {/* eslint-disable-next-line @next/next/no-sync-scripts -- type="module" is deferred by spec; the rule cannot see that */}
        <script type="module" src="/dssl/boot.js" />
      </head>
      <body>{children}</body>
    </html>
  );
}