Return `Querier` interface from `WithTx` when interface is emitted.

[0xstepit]

What do you want to change?

When you specify the flag: emit_interface: true in the sqlc.yaml, the Querier interface is generated. This is a great feature, however, the WithTx method returns a *Queries pointer, making the use of the interface hard:

func (q *Queries) WithTx(tx *sql.Tx) *Queries {
	return &Queries{
		db: tx,
	}
}

It would be great to return the interface when the previously mentioned flag is set to true:

func (q *Queries) WithTx(tx *sql.Tx) Querier {
	return &Queries{
		db: tx,
	}
}

Happy to create a PR for it if you like the idea.

What database engines need to be changed?

No response

What programming language backends need to be changed?

Go

[rusneustroevkz]

I’m really looking forward to this fix because it would significantly simplify writing unit tests. Currently, the WithTx method returns a *Queries pointer, which makes it difficult to use the Querier interface effectively in tests. If WithTx could return the Querier interface instead (when emit_interface: true is set in sqlc.yaml), it would make mocking and testing much more straightforward and aligned with Go’s best practices.

This change would allow us to mock the Querier interface directly in tests without needing to work around the concrete *Queries type. It would also improve the flexibility and maintainability of the codebase, especially when dealing with transactions in unit tests.

I’d be happy to contribute a PR for this change if the idea is approved. Looking forward to seeing this improvement in a future release!