fix: current_database() returns the configured catalog name, not the literal "datafusion"

[muratdursun]

Problem

create_current_database_udf() registers a current_database() UDF that returns the hardcoded literal "datafusion", regardless of the catalog the session was actually set up with:

builder.append_value("datafusion"); // always

But setup_pg_catalog(session_context, catalog_name, ...) already knows the real catalog name — it registers pg_catalog under exactly that name a few lines above. So a client that connects to catalog mydb and runs SELECT current_database() gets "datafusion" instead of "mydb".

In PostgreSQL, current_database() reflects the database the client connected to and is fixed for the life of the connection. Tools that key off it — psql's \conninfo / prompt substitution, some ORMs and schema-migration tools that route by current_database(), pg_table_is_visible()-style visibility helpers — misbehave against the hardcoded value.

Fix

Thread the catalog name that setup_pg_catalog already has in scope into the UDF, and return it verbatim:

pub fn create_current_database_udf(database_name: &str) -> ScalarUDF {
    let database_name = database_name.to_string();
    let func = move |_args: &[ColumnarValue]| {
        let mut builder = StringBuilder::new();
        builder.append_value(&database_name);
        ...
    };
    ...
}

and at the call site:

session_context.register_udf(create_current_database_udf(catalog_name));

No new plumbing — catalog_name is already a parameter of setup_pg_catalog.

Compatibility note

create_current_database_udf is pub, so adding the &str parameter is a breaking signature change for anyone calling it directly (the in-repo call site is the only caller in this workspace, and it's updated here). If you'd prefer to preserve the old zero-arg signature, I'm happy to instead add a second create_current_database_udf_for(name: &str) and keep the old one as a thin wrapper — just let me know which you'd rather carry.

Test

Added a regression test in datafusion-pg-catalog's pg_catalog test module: set up the catalog under "my_database", run SELECT current_database(), and assert it returns "my_database" (not "datafusion").

Context

Found while building a multi-catalog pg-wire frontend on top of datafusion-pg-catalog, where each connection maps to a distinct catalog and current_database() needs to reflect it.

🤖 Generated with Claude Code

[sunng87]

@muratdursun thank you!