Generate a "pretty" name for an impl from its type and trait. This is designed so that symbols of impl'd methods give some hint of where they came from, (previously they would all just be listed as __extensions__::method_name::hash, with no indication of the type).

Maps a binary operator to its precedence

Returns true if the given pattern consists solely of an identifier and false otherwise.

Returns true if the given struct def is tuple-like; i.e. that its fields are unnamed.