Correctly check updatability of columns targeted by INSERT...DEFAULT.

If a view has some updatable and some non-updatable columns, we failed
to verify updatability of any columns for which an INSERT or UPDATE
on the view explicitly specifies a DEFAULT item (unless the view has
a declared default for that column, which is rare anyway, and one
would almost certainly not write one for a non-updatable column).
This would lead to an unexpected "attribute number N not found in
view targetlist" error rather than the intended error.

Per bug #18546 from Alexander Lakhin.  This bug is old, so back-patch
to all supported branches.

Discussion: https://postgr.es/m/18546-84a292e759a9361d@postgresql.org

src/backend/rewrite/rewriteHandler.c

@@ -2987,7 +2987,7 @@ relation_is_updatable(Oid reloid,
  *
  * This is used with simply-updatable views to map column-permissions sets for
  * the view columns onto the matching columns in the underlying base relation.
- * The targetlist is expected to be a list of plain Vars of the underlying
+ * Relevant entries in the targetlist must be plain Vars of the underlying
  * relation (as per the checks above in view_query_is_auto_updatable).
  */
 static Bitmapset *
@@ -3084,6 +3084,9 @@ rewriteTargetView(Query *parsetree, Relation view)
 	 */
 	viewquery = copyObject(get_view_query(view));
 
+	/* Locate RTE describing the view in the outer query */
+	view_rte = rt_fetch(parsetree->resultRelation, parsetree->rtable);
+
 	/* The view must be updatable, else fail */
 	auto_update_detail =
 		view_query_is_auto_updatable(viewquery,
@@ -3126,17 +3129,26 @@ rewriteTargetView(Query *parsetree, Relation view)
 	}
 
 	/*
-	 * For INSERT/UPDATE the modified columns must all be updatable. Note that
+	 * For INSERT/UPDATE the modified columns must all be updatable.
-	 * we get the modified columns from the query's targetlist, not from the
-	 * result RTE's insertedCols and/or updatedCols set, since
-	 * rewriteTargetListIU may have added additional targetlist entries for
-	 * view defaults, and these must also be updatable.
 	 */
 	if (parsetree->commandType != CMD_DELETE)
 	{
-		Bitmapset  *modified_cols = NULL;
+		Bitmapset  *modified_cols;
 		char	   *non_updatable_col;
 
+		/*
+		 * Compute the set of modified columns as those listed in the result
+		 * RTE's insertedCols and/or updatedCols sets plus those that are
+		 * targets of the query's targetlist(s).  We must consider the query's
+		 * targetlist because rewriteTargetListIU may have added additional
+		 * targetlist entries for view defaults, and these must also be
+		 * updatable.  But rewriteTargetListIU can also remove entries if they
+		 * are DEFAULT markers and the column's default is NULL, so
+		 * considering only the targetlist would also be wrong.
+		 */
+		modified_cols = bms_union(view_rte->insertedCols,
+								  view_rte->updatedCols);
+
 		foreach(lc, parsetree->targetList)
 		{
 			TargetEntry *tle = (TargetEntry *) lfirst(lc);
@@ -3194,9 +3206,6 @@ rewriteTargetView(Query *parsetree, Relation view)
 		}
 	}
 
-	/* Locate RTE describing the view in the outer query */
-	view_rte = rt_fetch(parsetree->resultRelation, parsetree->rtable);
-
 	/*
 	 * If we get here, view_query_is_auto_updatable() has verified that the
 	 * view contains a single base relation.

src/test/regress/expected/updatable_views.out

@@ -1598,6 +1598,9 @@ DETAIL:  View columns that refer to system columns are not updatable.
 INSERT INTO rw_view1 (s, c, a) VALUES (null, null, 1.1); -- should fail
 ERROR:  cannot insert into column "s" of view "rw_view1"
 DETAIL:  View columns that are not columns of their base relation are not updatable.
+INSERT INTO rw_view1 (s, c, a) VALUES (default, default, 1.1); -- should fail
+ERROR:  cannot insert into column "s" of view "rw_view1"
+DETAIL:  View columns that are not columns of their base relation are not updatable.
 INSERT INTO rw_view1 (a) VALUES (1.1) RETURNING a, s, c; -- OK
   a  |         s         |         c         
 -----+-------------------+-------------------

src/test/regress/sql/updatable_views.sql

@@ -845,6 +845,7 @@ CREATE VIEW rw_view1 AS
 
 INSERT INTO rw_view1 VALUES (null, null, 1.1, null); -- should fail
 INSERT INTO rw_view1 (s, c, a) VALUES (null, null, 1.1); -- should fail
+INSERT INTO rw_view1 (s, c, a) VALUES (default, default, 1.1); -- should fail
 INSERT INTO rw_view1 (a) VALUES (1.1) RETURNING a, s, c; -- OK
 UPDATE rw_view1 SET s = s WHERE a = 1.1; -- should fail
 UPDATE rw_view1 SET a = 1.05 WHERE a = 1.1 RETURNING s; -- OK