Doesn't complain about an undefined type

[NameFILIP]

type A = A;

const a: A = {
  a: '1'
};

https://flow.org/try/#0C4TwDgpgBAglC8sDcAoFBjA9gOwM7CgEMAuWBKAbxSiNIHIBGOlAXySA

Context:
I extracted a type into a type definition:

type FieldName = $Keys<Fields>

and then did a Replace All for $Keys<Fields> with FieldName. This has changed the definition as well. Luckily it was caught in code review, but I was surprised that flow had not reported an error

[ghost]

type A = A defines a generic with an "unknown" type. In your example, view the AST tab and look for "type": "GenericTypeAnnotation". Here's another example illustrating the behavior in question.

[SamChou19815]

This now errors