Prevent parser from believing that views have system columns.

Views should not have any pg_attribute entries for system columns.
However, we forgot to remove such entries when converting a table to a
view.  This could lead to crashes later on, if someone attempted to
reference such a column, as reported by Kohei KaiGai.

This problem is corrected properly in HEAD (by removing the pg_attribute
entries during conversion), but in the back branches we need to defend
against existing mis-converted views.  This fix costs us an extra syscache
lookup per system column reference, which is annoying but probably not
really measurable in the big scheme of things.

src/backend/parser/parse_relation.c

@@ -501,10 +501,17 @@ scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte, char *colname,
 		attnum = specialAttNum(colname);
 		if (attnum != InvalidAttrNumber)
 		{
-			/* now check to see if column actually is defined */
+			/*
+			 * Now check to see if column actually is defined.  Because of
+			 * an ancient oversight in DefineQueryRewrite, it's possible that
+			 * pg_attribute contains entries for system columns for a view,
+			 * even though views should not have such --- so we also check
+			 * the relkind.  This kluge will not be needed in 9.3 and later.
+			 */
 			if (SearchSysCacheExists2(ATTNUM,
 									  ObjectIdGetDatum(rte->relid),
-									  Int16GetDatum(attnum)))
+									  Int16GetDatum(attnum)) &&
+				get_rel_relkind(rte->relid) != RELKIND_VIEW)
 			{
 				var = make_var(pstate, rte, attnum, location);
 				/* Require read access to the column */

src/test/regress/expected/rules.out

@@ -1452,6 +1452,28 @@ ERROR:  cannot drop rule _RETURN on view fooview because view fooview requires i
 HINT:  You can drop view fooview instead.
 drop view fooview;
 --
+-- test conversion of table to view (needed to load some pg_dump files)
+--
+create table fooview (x int, y text);
+select xmin, * from fooview;
+ xmin | x | y 
+------+---+---
+(0 rows)
+
+create rule "_RETURN" as on select to fooview do instead
+  select 1 as x, 'aaa'::text as y;
+select * from fooview;
+ x |  y  
+---+-----
+ 1 | aaa
+(1 row)
+
+select xmin, * from fooview;  -- fail, views don't have such a column
+ERROR:  column "xmin" does not exist
+LINE 1: select xmin, * from fooview;
+               ^
+drop view fooview;
+--
 -- check for planner problems with complex inherited UPDATES
 --
 create table id (id serial primary key, name text);

src/test/regress/sql/rules.sql

@@ -859,6 +859,21 @@ create view fooview as select 'foo'::text;
 drop rule "_RETURN" on fooview;
 drop view fooview;
 
+--
+-- test conversion of table to view (needed to load some pg_dump files)
+--
+
+create table fooview (x int, y text);
+select xmin, * from fooview;
+
+create rule "_RETURN" as on select to fooview do instead
+  select 1 as x, 'aaa'::text as y;
+
+select * from fooview;
+select xmin, * from fooview;  -- fail, views don't have such a column
+
+drop view fooview;
+
 --
 -- check for planner problems with complex inherited UPDATES
 --