Rewrite _postgis_drop_if_needed to avoid expanding DEFAULT values

This prevents the function to fail when geometry canonical output
function is non-functional (maybe due to lack of library on system).

References #5046 in master branch

Includes regression testing, which now avoid keeping geometry_out
functional.

postgis/postgis_before_upgrade.sql

@@ -37,34 +37,29 @@ CREATE OR REPLACE FUNCTION _postgis_drop_function_if_needed(
 	function_name text,
 	function_arguments text) RETURNS void AS $$
 DECLARE
-	frec RECORD;
 	sql_drop text;
+	postgis_namespace OID;
+	matching_function REGPROCEDURE;
 BEGIN
-	FOR frec IN
-		SELECT  p.oid as oid,
-				n.nspname as schema,
-				n.oid as schema_oid,
-				p.proname as name,
-				pg_catalog.pg_get_function_arguments(p.oid) as arguments,
-				pg_catalog.pg_get_function_identity_arguments(p.oid) as identity_arguments
-			FROM pg_catalog.pg_proc p
-			LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace
-			WHERE
-				n.oid = (
-					SELECT n.oid
-					FROM pg_proc p
-					JOIN pg_namespace n ON p.pronamespace = n.oid
-					WHERE proname = 'postgis_full_version'
-					) AND
-				LOWER(p.proname) = LOWER(function_name) AND
-				LOWER(pg_catalog.pg_get_function_arguments(p.oid)) ~ LOWER(function_arguments) AND
-				pg_catalog.pg_function_is_visible(p.oid)
-			ORDER BY 1, 2, 4
-	LOOP
-		sql_drop := 'DROP FUNCTION ' || quote_ident(frec.schema) || '.' || quote_ident(frec.name) || ' ( ' || frec.identity_arguments || ' ) ';
-		RAISE DEBUG 'Name (%): %', frec.oid, frec.name;
-		RAISE DEBUG 'Arguments: %', frec.arguments;
-		RAISE DEBUG 'Identity arguments: %', frec.identity_arguments;
+
+	-- Fetch install namespace for PostGIS
+	SELECT n.oid
+	FROM pg_catalog.pg_proc p
+	JOIN pg_catalog.pg_namespace n ON p.pronamespace = n.oid
+	WHERE proname = 'postgis_full_version'
+	INTO postgis_namespace;
+
+	-- Find a function matching the given signature
+	SELECT oid
+	FROM pg_catalog.pg_proc p
+	WHERE pronamespace = postgis_namespace
+	AND LOWER(p.proname) = LOWER(function_name)
+	AND pg_catalog.pg_function_is_visible(p.oid)
+	AND LOWER(pg_catalog.pg_get_function_identity_arguments(p.oid)) ~ LOWER(function_arguments)
+	INTO matching_function;
+
+	IF matching_function IS NOT NULL THEN
+		sql_drop := 'DROP FUNCTION ' || matching_function;
 		RAISE DEBUG 'SQL query: %', sql_drop;
 		BEGIN
 			EXECUTE sql_drop;
@@ -72,7 +67,8 @@ BEGIN
 			WHEN OTHERS THEN
 				RAISE EXCEPTION 'Could not drop function %. You might need to drop dependant objects. Postgres error: %', function_name, SQLERRM;
 		END;
-	END LOOP;
+	END IF;
+
 END;
 $$ LANGUAGE plpgsql;
 

regress/hooks/hook-before-upgrade.sql

@@ -77,10 +77,5 @@ FROM upgrade_test;
 
 -- Break probin of all postgis functions, as we expect
 -- the upgrade procedure to replace them all
-UPDATE pg_proc SET probin = probin || '-uninstalled' WHERE probin like '%postgis%'
--- Some function have DEFAULT values for GEOMETRY type, which
--- makes pg_get_function_arguments choke. This should be fixed!
--- See https://trac.osgeo.org/postgis/ticket/5046#comment:5
--- When ticket #5046 is fixed we can ALSO break geometry_out
-AND proname NOT IN ( 'geometry_out')
-;
+UPDATE pg_proc SET probin = probin || '-uninstalled'
+WHERE probin like '%postgis%';