Time format error using H:i format in the editor’s datepicker

[audrasjb]

Describe the bug
See the related ticket: https://core.trac.wordpress.org/ticket/51862

To reproduce
Steps to reproduce the behavior:

1. Open the [Settings]-[General] menu.
2. Select "H:i" in Time Format and save.
3. Edit "Hello world!" In the posted article.
4. Click the date and time in "Publish" of "Status & visibility".
5. Click "Reset" in the displayed calendar.
6. Click "Immediately".
7. Clicking "Date" or "Calendar Help" in the calendar causes an error.

Error:

TypeError: r is not a function
    at http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/components.min.js?ver=7b2eb7033cd3c6d2b4ea663e7d4774a7:7:311452
    at Bh (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:126:456)
    at Dj (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:162:476)
    at unstable_runWithPriority (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react.min.js?ver=16.13.1:25:260)
    at Da (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:60:280)
    at xb (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:162:231)
    at mk.Events.current (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:236:102)
    at Ei (http://localhost:8888/wordpress-develop/wordpress-develop/build/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.13.1:41:59)

Editor version (please complete the following information):

• WordPress version: WP 5.6 RC 1
• Using default block editor, no plugin

Desktop (please complete the following information):

• OS: Mac OSX
• Browser: Chrome

[talldan]

This looks like a regression when I tested. I couldn't reproduce in 5.5.3, but could in the latest 5.6.

[audrasjb]

Thanks for testing and properly milestoning the issue 🙌

[talldan]

Just noting that the same error was reported in #27278, but with different reproduction steps.

[tellthemachines]

Just noting that the same error was reported in #27278, but with different reproduction steps.

That error message seems to appear whenever the editor errors and the "copy error" button is clicked. In my dev environment it appears as Uncaught TypeError: onCopy is not a function, and it occurs in the <ClipboardButton> component.

The actual error caused by the bug this issue reports is TypeError: 'month' must be a valid moment object, in the <CalendarMonth> component. I've traced it back to #24348, but because that was a fairly large refactor I'm still working on identifying the exact cause 😩

[tellthemachines]

Also, I can reproduce this bug with any date/time settings: after clicking "Reset", and reopening the calendar component, unfocusing the month picker causes a crash. It happens because date and time values become invalid when reset for some reason.