Suggestion

In#9211: we are planning to enforce the following invariants in our AST forTSDeclareFunction:

• body must be undefined, so the following is a parsing error:

  declarefunctionfoo(){}

  (I don't think it's possible to havedeclare: false and a body anyway, since that would be a normal function declaration)
• Ifdeclare: true, thenasync andgenerator are bothfalse:

  declareasyncfunctionfoo();declarefunction*foo();

@sosukesuzuki@fisker Do these look safe to you?