sqlsmith: generate IMPLICIT CAST in function arguments

[kwannoel]

Enable implicit cast conservatively to avoid wrong type inference.

Examples

1. Generated in explicit cast:
   Suppose we generate implicit cast from smallint -> int, where int is the expected type of the expression.
   We can end up with:

    CAST(1::smallint AS BOOLEAN)
   

2. Generated in function / Agg Call:
   We attempt to generate an argument to min of type int, and end up with 1::smallint, since that can be implicit cast to int.
   We end up with:

   min(1::smallint)
   

   The type of the expression is wrong.
3. Generated in SELECT CTE:
   Column type can be wrong.

Background

see this for context: #6939

Solution

Just generate for functions with fixed return type. For instance, CONCAT, CONCAT_WS.

• Generate for all locations with enforce_bool_clause.

Feel free to suggest other alternatives.

[fuyufjh]

Hi, any progress?

[kwannoel]

Hi, any progress?

Nope, but will probably work on it this week. Didn't prioritize it because previously it didn't really catch any bugs.