useTheme returns undefined as value before using the ToggleThemeButton

[christiaanwesterbeek]

What you were expecting:
Getting the theme value with the react-admin hook: useTheme().

What happened instead:
useTheme() hook returns undefined as value.

Steps to reproduce:
Go to this sandbox https://stackblitz.com/edit/github-m4as1b?file=src%2Fposts%2FPostList.tsx and see how in PostList that theme is undefined on first load of the application before using the ToggleThemeButton.

Related code:

import { useTheme } from 'react-admin;
//...
const [theme] = useTheme();
console.log('theme', theme);

Other information:

This was reported before #7805.

And fixed by @djhi on Jul 18, 2022: https://github.com/marmelab/react-admin/pull/7960/files#diff-5b4990e166ffe43cc265179d72851c8246ac299966ca41c97996202c540db43b

The fix got kind of reverted on May 3, 2023 with this commit 566fae4#diff-5b4990e166ffe43cc265179d72851c8246ac299966ca41c97996202c540db43b

Environment

• React-admin version: 4.16.2
• Last version that did not exhibit the issue (if applicable): see dates/versions of earlier fix and fix-revert
• React version:
• Browser: Chrome
• Stack trace (in case of a JS error):

[adguernier]

Hello and thanks for this very detailed report! Reproduced.