Ensure that pg_get_ruledef()'s output matches pg_get_viewdef()'s.

Various cases involving renaming of view columns are handled by having
make_viewdef pass down the view's current relation tupledesc to
get_query_def, which then takes care to use the column names from the
tupledesc for the output column names of the SELECT.  For some reason
though, we'd missed teaching make_ruledef to do similarly when it is
printing an ON SELECT rule, even though this is exactly the same case.
The results from pg_get_ruledef would then be different and arguably wrong.
In particular, this breaks pre-v10 versions of pg_dump, which in some
situations would define views by means of emitting a CREATE RULE ... ON
SELECT command.  Third-party tools might not be happy either.

In passing, clean up some crufty code in make_viewdef; we'd apparently
modernized the equivalent code in make_ruledef somewhere along the way,
and missed this copy.

Per report from Gilles Darold.  Back-patch to all supported versions.

Discussion: https://postgr.es/m/ec05659a-40ff-4510-fc45-ca9d965d0838@dalibo.com

src/backend/utils/adt/ruleutils.c

@@ -3885,6 +3885,8 @@ make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 	char	   *ev_qual;
 	char	   *ev_action;
 	List	   *actions = NIL;
+	Relation	ev_relation;
+	TupleDesc	viewResultDesc = NULL;
 	int			fno;
 	Datum		dat;
 	bool		isnull;
@@ -3926,6 +3928,8 @@ make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 	if (ev_action != NULL)
 		actions = (List *) stringToNode(ev_action);
 
+	ev_relation = heap_open(ev_class, AccessShareLock);
+
 	/*
 	 * Build the rules definition text
 	 */
@@ -3942,6 +3946,7 @@ make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 	{
 		case '1':
 			appendStringInfo(buf, "SELECT");
+			viewResultDesc = RelationGetDescr(ev_relation);
 			break;
 
 		case '2':
@@ -4034,7 +4039,7 @@ make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 		foreach(action, actions)
 		{
 			query = (Query *) lfirst(action);
-			get_query_def(query, buf, NIL, NULL,
+			get_query_def(query, buf, NIL, viewResultDesc,
 						  prettyFlags, WRAP_COLUMN_DEFAULT, 0);
 			if (prettyFlags)
 				appendStringInfo(buf, ";\n");
@@ -4052,10 +4057,12 @@ make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
 		Query	   *query;
 
 		query = (Query *) linitial(actions);
-		get_query_def(query, buf, NIL, NULL,
+		get_query_def(query, buf, NIL, viewResultDesc,
 					  prettyFlags, WRAP_COLUMN_DEFAULT, 0);
 		appendStringInfo(buf, ";");
 	}
+
+	heap_close(ev_relation, AccessShareLock);
 }
 
 

src/test/regress/expected/create_view.out

@@ -1619,6 +1619,35 @@ select pg_get_viewdef('tt22v', true);
       LEFT JOIN tt6 ON TRUE;
 (1 row)
 
+-- check handling of views with immediately-renamed columns
+create view tt23v (col_a, col_b) as
+select q1 as other_name1, q2 as other_name2 from int8_tbl
+union
+select 42, 43;
+select pg_get_viewdef('tt23v', true);
+        pg_get_viewdef         
+-------------------------------
+  SELECT int8_tbl.q1 AS col_a,+
+     int8_tbl.q2 AS col_b     +
+    FROM int8_tbl             +
+ UNION                        +
+  SELECT 42 AS col_a,         +
+     43 AS col_b;
+(1 row)
+
+select pg_get_ruledef(oid, true) from pg_rewrite
+  where ev_class = 'tt23v'::regclass and ev_type = '1';
+                         pg_get_ruledef                          
+-----------------------------------------------------------------
+ CREATE RULE "_RETURN" AS                                       +
+     ON SELECT TO tt23v DO INSTEAD  SELECT int8_tbl.q1 AS col_a,+
+     int8_tbl.q2 AS col_b                                       +
+    FROM int8_tbl                                               +
+ UNION                                                          +
+  SELECT 42 AS col_a,                                           +
+     43 AS col_b;
+(1 row)
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;

src/test/regress/sql/create_view.sql

@@ -541,6 +541,17 @@ create view tt22v as
 select * from tt5 natural left join tt6;
 select pg_get_viewdef('tt22v', true);
 
+-- check handling of views with immediately-renamed columns
+
+create view tt23v (col_a, col_b) as
+select q1 as other_name1, q2 as other_name2 from int8_tbl
+union
+select 42, 43;
+
+select pg_get_viewdef('tt23v', true);
+select pg_get_ruledef(oid, true) from pg_rewrite
+  where ev_class = 'tt23v'::regclass and ev_type = '1';
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;