Introspect queries produces an error

Introspecting queries is quite limited at the moment. See discussion

SELECT INTROSPECT
.......   typeof (select shop::Category{id, description} LIMIT 1);
error: cannot introspect transient type variant
  ┌─ query:2:3
  │
2 │   typeof (select shop::Category{id, description} LIMIT 1);
  │   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error

The ability to introspect a query might come in very handy for multiple use cases like generating language specific types for a queries. Typescript for example.

[1st1]

FWIW it’s possible to introspect the exact return type of any query via preparing it at the protocol level. Our JS driver has some private APIs to do that.

[1st1]

We should later discuss if we even want to support INTROSPECT TYPEOF on arbitrary selects.