Обсуждение: ALTER FOREIGN DATA WRAPPER can drop dependency on handler

CREATE FUNCTION test_fdw_handler()
    RETURNS fdw_handler
    AS :'regresslib', 'test_fdw_handler'
    LANGUAGE C;

CREATE FOREIGN DATA WRAPPER test_fdw HANDLER test_fdw_handler;

-- correctly raises dependency ERROR
DROP FUNCTION test_fdw_handler;

ALTER FOREIGN DATA WRAPPER test_fdw VALIDATOR postgresql_fdw_validator;

-- fails to raise dependency error ERROR
DROP FUNCTION test_fdw_handler;


Patch attached.

Note: I found this while investigating a related issue for the FDW
connection function, with patch here:

https://www.postgresql.org/message-id/fd49b44dc65da8e71ab20c1cf1ec7e65921c20f5.camel@j-davis.com

I am keeping this patch separate for a clean backport.

Regards,
    Jeff Davis

On Wed, Mar 18, 2026 at 12:09:54PM -0700, Jeff Davis wrote:
> --- a/src/backend/commands/foreigncmds.c
> +++ b/src/backend/commands/foreigncmds.c
> @@ -786,6 +786,11 @@ AlterForeignDataWrapper(ParseState *pstate, AlterFdwStmt *stmt)
>          ereport(WARNING,
>                  (errmsg("changing the foreign-data wrapper handler can change behavior of existing foreign
tables")));
>      }
> +    else
> +    {
> +        /* handler unchanged */
> +        fdwhandler = fdwForm->fdwhandler;
> +    }

This matches what we do for the validator a few lines down, so it makes
sense to me.  Could it be worth adding a test or two?

-- 
nathan

On Wed, 2026-03-18 at 14:29 -0500, Nathan Bossart wrote:
> This matches what we do for the validator a few lines down, so it
> makes
> sense to me.  Could it be worth adding a test or two?

Added a test.

Testing in the other direction (adding HANDLER and leaving VALIDATOR
unspecified, then dropping the validator) is slightly more complex
because I don't want to drop the built-in postgresql_fdw_validator. But
the patch in the other thread can be extended with a new test or two
also, which will cover that case.

Will backport all the way.

Regards,
    Jeff Davis

On Wed, Mar 18, 2026 at 01:40:38PM -0700, Jeff Davis wrote:
> Added a test.

LGTM

-- 
nathan