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fix(hydration): harden root document hydration path #633

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fix(hydration): harden root document hydration path #633

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19 changes: 18 additions & 1 deletion src/components/theme-provider.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,24 @@ function getThemeScript(storageKey: string, defaultTheme: Theme) {
return `(function(){try{var t=localStorage.getItem(${key});if(t!=='light'&&t!=='dark'&&t!=='system'){t=${fallback}}var d=matchMedia('(prefers-color-scheme: dark)').matches;var r=t==='system'?(d?'dark':'light'):t;var e=document.documentElement;e.classList.add(r);e.style.colorScheme=r}catch(e){}})();`;
}

type ThemeScriptProps = {
defaultTheme?: Theme;
storageKey?: string;
};

/**
* Inline script that resolves and applies the theme to `document.documentElement`
* before paint. It must render in `<head>` so it runs during HTML parsing, ahead
* of body hydration — otherwise its mutation of the root element races React's
* whole-document hydration and can surface as a #418 mismatch.
*/
export function ThemeScript({
defaultTheme = "system",
storageKey = defaultThemeStorageKey,
}: ThemeScriptProps) {
return <ScriptOnce>{getThemeScript(storageKey, defaultTheme)}</ScriptOnce>;
}

function applyResolvedTheme(resolved: ResolvedTheme) {
const root = document.documentElement;
root.classList.remove("light", "dark");
Expand Down Expand Up @@ -90,7 +108,6 @@ export function ThemeProvider({

return (
<ThemeProviderContext value={{ resolvedTheme, theme, setTheme }}>
<ScriptOnce>{getThemeScript(themeStorageKey, defaultTheme)}</ScriptOnce>
{children}
</ThemeProviderContext>
);
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5 changes: 3 additions & 2 deletions src/routes/__root.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ import type { AuthSession } from "#/lib/auth.functions";
import { AppHotkeysProvider } from "#/lib/hotkeys";
import { seo } from "#/lib/seo";
import { getAuthSessionQueryOptions } from "#/lib/session-query";
import { ThemeProvider } from "../components/theme-provider";
import { ThemeProvider, ThemeScript } from "../components/theme-provider";
import PostHogProvider from "../integrations/posthog/provider";
import TanStackQueryDevtools from "../integrations/tanstack-query/devtools";
import appCss from "../styles.css?url";
Expand Down Expand Up @@ -79,9 +79,10 @@ function RootDocument({ children }: { children: React.ReactNode }) {
return (
<html lang="en" suppressHydrationWarning>
<head>
<ThemeScript defaultTheme="system" storageKey="theme" />
<HeadContent />
</head>
<body>
<body suppressHydrationWarning>
<ThemeProvider defaultTheme="system" storageKey="theme">
<AuthSessionRefresher />
<PostHogProvider>
Expand Down
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