Remove PrepareContext from DBTX unless emit_prepared_queries: true

[Jille]

sqlc's generated code doesn't use that method (unless emit_prepared_queries is enabled). Let's exclude it from the generated interface so that people providing a custom DBTX don't have to implement a unused function.

This is a minor backwards compatibility break, if someone used the generated DBTX for other code that did actually call PrepareContext.

[kyleconroy]

I agree that this is what we should have done at the start, but now I think it's too late to make this change. The interface is exported in the package, so other code may be depending on the PrepareContext method being on the interface.

[Jille]

This would be a relatively minor breakage for very few people, right? The vast majority of users wouldn't be affected. The only way someone would be affected is if they added more files inside the generated package that would use PrepareContext on Queries.db, without actually using sqlc's prepared queries support.

Previous releases have also broken backwards compatibility (for example #1746) and the many other changes that improve the choice of generated types.

My vote would be to make this change today rather than possibly deciding we want it later when we have 10x the number of users.

[kyleconroy]

The only way someone would be affected is if they added more files inside the generated package that would use PrepareContext on Queries.db, without actually using sqlc's prepared queries support.

The DBTX interface is exported, so any other package could be relying on that method.

[andrewmbenton]

I think this is a good case for forking and modifying the sqlc-gen-go plugin. We consider this to be too big of a breaking change to merge.