Change CommandType.StoredProcedure to execute procedures instead of functions

PostgreSQL originally only had functions - procedures were introduced in PG 11 - so specifying CommandType.StoredProcedure makes Npgsql generate function invocation syntax (SELECT * FROM func(...). We can consider changing StoredProcedure to generate procedure invocation syntax instead (CALL ...). The current situation is inconsistent/terminologically confusing - I assume newcomers justifiably expect CommandType.StoredProcedure to invoke PostgreSQL stored procedures.

This would be quite a breaking change - any code using CommandType.StoredProcedure to invoke functions would stop working. Options:

• Make the breaking change, and have an AppContext switch for the old behavior. This is breaking, but anyone upgrading to Npgsql would simply have to turn on the switch and everything would work as before.
• Have an AppContext switch for the new behavior. This would make the behavior opt-in, but this may not have much value: the main value in changing the meaning of CommandType.StoredProcedure is to make things clearer/more consistent for new people etc.
• Not do anything. Users can invoke both functions and procedures with SQL themselves (i.e. not use CommandType.StoredProcedure at all).

/cc @vonzshik @NinoFloris @Brar

[roji]

@Wraith2 I agree, but that’s a bit tricky… since CommandType.StoredProcedure is currently used to invoke functions (SELECT * FROM func(), code upgrading to Npgsql 6.0 would simply start failing, since Npgsql will start producing SQL for invoking procedures (CALL foo())… I actually tried to suggest to PostgreSQL that they allow invoking functions with CALL, so that the transition could be backwards compatible, but they didn’t go this way…

[NinoFloris]

There is also the matter of all the different pg compatible databases failing the backend version check. I’m in favor for doing this at a specific npgsql version.