Component's props doesn't validate a property with required & default specified correctly

[kuanyui]

Version

3.0.7

Reproduction link

• Vue 2.x reproduce link: https://jsfiddle.net/xbf014gc/10/
• Vue 3.x reproduce link: https://jsfiddle.net/cafpskt5/37/

Steps to reproduce

1. Define a prop in a component, with required: true and default value set.
2. Use this component, but don't pass any prop to this component.

What is expected?

This component can access the pre-defined default value, but get a runtime warning message in console.

What is actually happening?

This component can access the pre-defined default value, and without any warning or log in console.

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The expected behavior is referenced from Vue 2.x.

• Vue 2.x reproduce link: https://jsfiddle.net/xbf014gc/10/ as reference
• Vue 3.x reproduce link: https://jsfiddle.net/cafpskt5/37/

I don't sure whether Vue 3.x has changed its specification on this, but I think the behavior of Vue2.x is indeed more reasonable as a validator for developer.

[HcySunYang]

This can also be fixed in #3363