Fix display of SQL-standard function's arguments in INSERT/SELECT.

If a SQL-standard function body contains an INSERT ... SELECT statement,
any function parameters referenced within the SELECT were always printed
in $N style, rather than using the parameter name if any.  While not
strictly incorrect, this wasn't the intention, and it's inconsistent
with the way that such parameters would be printed in any other kind
of statement.

The cause is that the recursion to get_query_def from
get_insert_query_def neglected to pass down the context->namespaces
list, passing constant NIL instead.  This is a very ancient oversight,
but AFAICT it had no visible consequences before commit e717a9a18
added an outermost namespace with function parameters.  We don't allow
INSERT ... SELECT as a sub-query, except in a top-level WITH clause,
where it couldn't contain any outer references that might need to access
upper namespaces.  So although that's arguably a bug, I don't see any
point in changing it before v14.

In passing, harden the code added to get_parameter by e717a9a18 so that
it won't crash if a PARAM_EXTERN Param appears in an unexpected place.

Per report from Erki Eessaar.  Code fix by me, regression test case
by Masahiko Sawada.

Discussion: https://postgr.es/m/AM9PR01MB8268347BED344848555167FAFE949@AM9PR01MB8268.eurprd01.prod.exchangelabs.com

src/backend/utils/adt/ruleutils.c

@@ -6566,7 +6566,7 @@ get_insert_query_def(Query *query, deparse_context *context)
 	if (select_rte)
 	{
 		/* Add the SELECT */
-		get_query_def(select_rte->subquery, buf, NIL, NULL,
+		get_query_def(select_rte->subquery, buf, context->namespaces, NULL,
 					  context->prettyFlags, context->wrapColumn,
 					  context->indentLevel);
 	}
@@ -7919,10 +7919,12 @@ get_parameter(Param *param, deparse_context *context)
 	 * If it's an external parameter, see if the outermost namespace provides
 	 * function argument names.
 	 */
-	if (param->paramkind == PARAM_EXTERN)
+	if (param->paramkind == PARAM_EXTERN && context->namespaces != NIL)
 	{
-		dpns = lfirst(list_tail(context->namespaces));
-		if (dpns->argnames)
+		dpns = llast(context->namespaces);
+		if (dpns->argnames &&
+			param->paramid > 0 &&
+			param->paramid <= dpns->numargs)
 		{
 			char	   *argname = dpns->argnames[param->paramid - 1];
 

src/test/regress/expected/create_function_3.out

@@ -279,6 +279,13 @@ CREATE FUNCTION functest_S_13() RETURNS boolean
         SELECT 1;
         SELECT false;
     END;
+-- check display of function argments in sub-SELECT
+CREATE TABLE functest1 (i int);
+CREATE FUNCTION functest_S_16(a int, b int) RETURNS void
+    LANGUAGE SQL
+    BEGIN ATOMIC
+        INSERT INTO functest1 SELECT a + $2;
+    END;
 -- error: duplicate function body
 CREATE FUNCTION functest_S_xxx(x int) RETURNS int
     LANGUAGE SQL
@@ -417,6 +424,20 @@ SELECT pg_get_functiondef('functest_S_15'::regproc);
  
 (1 row)
 
+SELECT pg_get_functiondef('functest_S_16'::regproc);
+                              pg_get_functiondef                               
+-------------------------------------------------------------------------------
+ CREATE OR REPLACE FUNCTION temp_func_test.functest_s_16(a integer, b integer)+
+  RETURNS void                                                                +
+  LANGUAGE sql                                                                +
+ BEGIN ATOMIC                                                                 +
+  INSERT INTO functest1 (i)  SELECT (functest_s_16.a + functest_s_16.b);      +
+ END                                                                          +
+ 
+(1 row)
+
+DROP TABLE functest1 CASCADE;
+NOTICE:  drop cascades to function functest_s_16(integer,integer)
 -- test with views
 CREATE TABLE functest3 (a int);
 INSERT INTO functest3 VALUES (1), (2);

src/test/regress/sql/create_function_3.sql

@@ -180,6 +180,14 @@ CREATE FUNCTION functest_S_13() RETURNS boolean
         SELECT false;
     END;
 
+-- check display of function argments in sub-SELECT
+CREATE TABLE functest1 (i int);
+CREATE FUNCTION functest_S_16(a int, b int) RETURNS void
+    LANGUAGE SQL
+    BEGIN ATOMIC
+        INSERT INTO functest1 SELECT a + $2;
+    END;
+
 -- error: duplicate function body
 CREATE FUNCTION functest_S_xxx(x int) RETURNS int
     LANGUAGE SQL
@@ -217,6 +225,9 @@ SELECT pg_get_functiondef('functest_S_3a'::regproc);
 SELECT pg_get_functiondef('functest_S_10'::regproc);
 SELECT pg_get_functiondef('functest_S_13'::regproc);
 SELECT pg_get_functiondef('functest_S_15'::regproc);
+SELECT pg_get_functiondef('functest_S_16'::regproc);
+
+DROP TABLE functest1 CASCADE;
 
 -- test with views
 CREATE TABLE functest3 (a int);