Version

3.0.7

Reproduction link

https://jsfiddle.net/cafpskt5/22/

Steps to reproduce

1. Define a required boolean prop in component (e.g. bool: { type: Boolean, required: true } in props)
2. Use this component, but don't pass any prop to it.

What is expected?

Gives a warning [Vue warn]: Missing required prop: \"bool\""

What is actually happening?

No warning message output.

1. But if you give :bool= a string or number, it indeed can be validated and gives a warning message ([Vue warn]: Invalid prop: type check failed for prop \"bool\". Expected Boolean, got String with value \"1\".).
2. Other types (Number, String, Object) work well and have no similar bugs like this.

bool is set to false by default. is this about #3337 ?

Yeah, by default if the boolean props are absent then they will be cast to false, but we still need to raise a warning if it is required.