Known misparses

[fmease]

• fn main() { return x + .. .field }
  • wrong precedence
  • original source: dtolnay
• while || Foo {} {};
  • rustc parses Foo as a unit-struct while we parse it as Foo {}
  • believed cause: we don't forward structpolicy diligently / aggressively enough
  • original source
• our principled approach to parsing ranges using straightforward precedence levels doesn't reflect reality unfortunately since rustc seems to parse ranges in a gnarly(?) "ad hoc" way? still need to figure this out experimentally
• we don't reject raw path segment keywords
• we don't parse for _ in .. {} etc.
  • since { begins an expr, so we try to parse block and expect another block
  • rustc has a hack for this; we also need one (well, I hope looking at structpolicy will suffice which shouldn't be that hacky)
• expr attr precedence