syntax_data: {"ast_node_type":"function","tokens":[{"end":95,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn all_field_tys(self, interner: I) -> ty::EarlyBinder<I, impl IntoIterator<Item = I::Ty>>;
context_before:     // FIXME: perhaps use `all_fields` and expose `FieldDef`.