Wrong error "type is not structurally comparable" if some fields of a record definition are unresolvable

[vasily-kirichenko]

[dsyme]

There is a systematic issue in the compiler where we return obj as the type in error recovery. IIRC normally this is an "error" type variable solved to equal obj. By more systematically checking for is-erroneous-type-variable then I think it's possible to remove errors like this.

We could alternatively have an explicit "error" type though that might cause as many problems as it solves (and, with the error flag on a solved type variable, we already effectively have this information, we're just not using it)/

[dsyme]

@isaacabraham Could you please add this to the "improved error reporting" bug tracker? thanks

[vasily-kirichenko]

Duplication of #777