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

@@ -2986,7 +2986,7 @@ 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 *
@@ -3186,6 +3186,10 @@ rewriteTargetView(Query *parsetree, Relation view)
 	 */
 	viewquery = copyObject(get_view_query(view));
 
+	/* Locate RTE and perminfo describing the view in the outer query */
+	view_rte = rt_fetch(parsetree->resultRelation, parsetree->rtable);
+	view_perminfo = getRTEPermissionInfo(parsetree->rteperminfos, view_rte);
+
 	/*
 	 * Are we doing INSERT/UPDATE, or MERGE containing INSERT/UPDATE?  If so,
 	 * various additional checks on the view columns need to be applied, and
@@ -3225,17 +3229,26 @@ rewriteTargetView(Query *parsetree, Relation view)
 
 	/*
 	 * For INSERT/UPDATE (or MERGE containing INSERT/UPDATE) the modified
-	 * columns must all be updatable. Note that 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.
+	 * columns must all be updatable.
 	 */
 	if (insert_or_update)
 	{
-		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_perminfo->insertedCols,
+								  view_perminfo->updatedCols);
+
 		foreach(lc, parsetree->targetList)
 		{
 			TargetEntry *tle = (TargetEntry *) lfirst(lc);
@@ -3337,9 +3350,6 @@ 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.
@@ -3434,10 +3444,7 @@ rewriteTargetView(Query *parsetree, Relation view)
 	 * Note: the original view's RTEPermissionInfo remains in the query's
 	 * rteperminfos so that the executor still performs appropriate
 	 * permissions checks for the query caller's use of the view.
-	 */
-	view_perminfo = getRTEPermissionInfo(parsetree->rteperminfos, view_rte);
-
-	/*
+	 *
 	 * Disregard the perminfo in viewquery->rteperminfos that the base_rte
 	 * would currently be pointing at, because we'd like it to point now to a
 	 * new one that will be filled below.  Must set perminfoindex to 0 to not

src/test/regress/expected/updatable_views.out

@@ -2101,6 +2101,9 @@ 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

@@ -1111,6 +1111,7 @@ 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