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commit    876fa84a275eea578b4a89bb910e184f98d991c2
Author:   Jeff Davis <jdavis@postgresql.org>
Date:     Thu Mar 19 21:59:07 2026 +0000
First released in: 14.23, 15.18, 16.14, 17.10, 18.4

    Fix dependency on FDW handler.
    
    ALTER FOREIGN DATA WRAPPER could drop the dependency on the handler
    function if it wasn't explicitly specified.
    
    Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
    Discussion: https://postgr.es/m/35c44a4b7fb76d35418c4d66b775a88f4ce60c86.camel@j-davis.com
    Backpatch-through: 14


 src/backend/commands/foreigncmds.c         | 5 +++++
 src/test/regress/expected/foreign_data.out | 7 +++++++
 src/test/regress/sql/foreign_data.sql      | 5 +++++
 3 files changed, 17 insertions(+)

diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index 17f40599d26..99d1859ed9e 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -740,6 +740,11 @@ 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;
+	}
 
 	if (validator_given)
 	{
diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index 741572c36ba..08b12be7788 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -106,6 +106,13 @@ ERROR:  conflicting or redundant options
 LINE 1: ...GN DATA WRAPPER test_fdw HANDLER test_fdw_handler HANDLER in...
                                                              ^
 CREATE FOREIGN DATA WRAPPER test_fdw HANDLER test_fdw_handler;
+-- should preserve dependency on test_fdw_handler
+ALTER FOREIGN DATA WRAPPER test_fdw VALIDATOR postgresql_fdw_validator;
+WARNING:  changing the foreign-data wrapper validator can cause the options for dependent objects to become invalid
+DROP FUNCTION test_fdw_handler(); -- ERROR
+ERROR:  cannot drop function test_fdw_handler() because other objects depend on it
+DETAIL:  foreign-data wrapper test_fdw depends on function test_fdw_handler()
+HINT:  Use DROP ... CASCADE to drop the dependent objects too.
 DROP FOREIGN DATA WRAPPER test_fdw;
 -- ALTER FOREIGN DATA WRAPPER
 ALTER FOREIGN DATA WRAPPER foo OPTIONS (nonexistent 'fdw');         -- ERROR
diff --git a/src/test/regress/sql/foreign_data.sql b/src/test/regress/sql/foreign_data.sql
index 084d5559e09..0080bfb8856 100644
--- a/src/test/regress/sql/foreign_data.sql
+++ b/src/test/regress/sql/foreign_data.sql
@@ -67,6 +67,11 @@ CREATE FUNCTION invalid_fdw_handler() RETURNS int LANGUAGE SQL AS 'SELECT 1;';
 CREATE FOREIGN DATA WRAPPER test_fdw HANDLER invalid_fdw_handler;  -- ERROR
 CREATE FOREIGN DATA WRAPPER test_fdw HANDLER test_fdw_handler HANDLER invalid_fdw_handler;  -- ERROR
 CREATE FOREIGN DATA WRAPPER test_fdw HANDLER test_fdw_handler;
+
+-- should preserve dependency on test_fdw_handler
+ALTER FOREIGN DATA WRAPPER test_fdw VALIDATOR postgresql_fdw_validator;
+DROP FUNCTION test_fdw_handler(); -- ERROR
+
 DROP FOREIGN DATA WRAPPER test_fdw;
 
 -- ALTER FOREIGN DATA WRAPPER


[parent: 8ee536c89517]