feat(compiler): Improve type inference for parameters compared to constants only

[orisano]

What do you want to change?

We would like to improve the type inference of parameters compared to constants only.
Currently, it is absolutely inferred that interface{}.

https://play.sqlc.dev/p/9ba65e1196da80daf0543327f12974275bf7d83b6ae5ce32a0c0f75034d2528d

query:

-- name: Many :many
SELECT id FROM foo WHERE @param = 'foo';

generated:

func (q *Queries) Many(ctx context.Context, param interface{}) ([]int64, error) {

What type of param should be inferred, sql.NullString or string?

What database engines need to be changed?

PostgreSQL, MySQL, SQLite

What programming language backends need to be changed?

Go

[kyleconroy]

In this case I think string would be the correct option, but it's not always going to be the right answer. It depends on a query-by-query basis.

[orisano]

What is the case of a constant-only comparison where the parameter type is sql.NullString?
What is the difference between sqlc.narg and sqlc.arg?