Add test to make sure that we can't leak info fooling the planner

Makefile

@@ -27,4 +27,6 @@ ifneq ($(MAJORVERSION), 10)
 	REGRESS += 02_partitioning_hash
 endif
 
-REGRESS += 03_inheritance 99_cleanup
+REGRESS += 03_inheritance \
+	   10_security \
+	   99_cleanup

expected/10_security.out

@@ -0,0 +1,34 @@
+--setup
+LOAD 'pg_anonymize';
+CREATE TABLE customer_security(
+    id integer,
+    name text,
+    country text
+);
+INSERT INTO customer_security VALUES (1, 'Secret Name', 'Taiwan');
+SECURITY LABEL ON COLUMN customer_security.name IS $$'XXX'::text$$;
+-- mask our own user
+SELECT current_user \gset
+SECURITY LABEL FOR pg_anonymize ON ROLE :current_user IS 'anonymize';
+SELECT * FROM customer_security;
+ id | name | country 
+----+------+---------
+  1 | XXX  | Taiwan
+(1 row)
+
+-- It shouldn't be possible to access the original fooling the planner
+CREATE FUNCTION leak_info(name text, country text) RETURNS BOOL AS
+$_$
+BEGIN
+    RAISE NOTICE 'saw % - %', name, country;
+
+    RETURN true;
+END;
+$_$ LANGUAGE plpgsql COST 0.0000000000000000000001;
+SELECT * FROM customer_security WHERE leak_info(name, country);
+NOTICE:  saw XXX - Taiwan
+ id | name | country 
+----+------+---------
+  1 | XXX  | Taiwan
+(1 row)
+

test/sql/10_security.sql

@@ -0,0 +1,30 @@
+--setup
+LOAD 'pg_anonymize';
+
+CREATE TABLE customer_security(
+    id integer,
+    name text,
+    country text
+);
+
+INSERT INTO customer_security VALUES (1, 'Secret Name', 'Taiwan');
+
+SECURITY LABEL ON COLUMN customer_security.name IS $$'XXX'::text$$;
+
+-- mask our own user
+SELECT current_user \gset
+SECURITY LABEL FOR pg_anonymize ON ROLE :current_user IS 'anonymize';
+
+SELECT * FROM customer_security;
+
+-- It shouldn't be possible to access the original fooling the planner
+CREATE FUNCTION leak_info(name text, country text) RETURNS BOOL AS
+$_$
+BEGIN
+    RAISE NOTICE 'saw % - %', name, country;
+
+    RETURN true;
+END;
+$_$ LANGUAGE plpgsql COST 0.0000000000000000000001;
+
+SELECT * FROM customer_security WHERE leak_info(name, country);