I vote we don't change this. PEP 484 says:

> The string literal should contain a valid Python expression (i.e., compile(lit, '', 'eval') should be a valid code object) and it should evaluate without errors once the module has been fully loaded. 

But compile() fails for leading whitespace.

I also don't see a real use case for this. The dataclasses tests were presumably just added for completeness. If there's evidence this is a common pattern in the wild maybe we can reconsider.