Don't set a fast default for anything but a plain table

The fast default code added in Release 11 omitted to check that the
table a fast default was being added to was a plain table. Thus one
could be added to a foreign table, which predicably blows up. Here we
perform that check.

In addition, on the back branches, since some of these might have
escaped into the wild, if we encounter a missing value for
an attribute of something other than a plain table we ignore it.

Fixes bug #17056

Backpatch to release 11,

Reviewed by: Andres Freund, Álvaro Herrera and Tom Lane

src/backend/catalog/heap.c

@@ -2161,6 +2161,13 @@ SetAttrMissing(Oid relid, char *attname, char *value)
 	/* lock the table the attribute belongs to */
 	tablerel = table_open(relid, AccessExclusiveLock);
 
+	/* Don't do anything unless it's a plain table */
+	if (tablerel->rd_rel->relkind != RELKIND_RELATION)
+	{
+		table_close(tablerel, AccessExclusiveLock);
+		return;
+	}
+
 	/* Lock the attribute row and get the data */
 	attrrel = table_open(AttributeRelationId, RowExclusiveLock);
 	atttup = SearchSysCacheAttName(relid, attname);
@@ -2287,7 +2294,8 @@ StoreAttrDefault(Relation rel, AttrNumber attnum,
 		valuesAtt[Anum_pg_attribute_atthasdef - 1] = true;
 		replacesAtt[Anum_pg_attribute_atthasdef - 1] = true;
 
-		if (add_column_mode && !attgenerated)
+		if (rel->rd_rel->relkind == RELKIND_RELATION  && add_column_mode &&
+			!attgenerated)
 		{
 			expr2 = expression_planner(expr2);
 			estate = CreateExecutorState();

src/test/regress/expected/fast_default.out

@@ -797,7 +797,26 @@ SELECT * FROM t WHERE a IS NULL;
 (1 row)
 
 ROLLBACK;
+-- verify that a default set on a non-plain table doesn't set a missing
+-- value on the attribute
+CREATE FOREIGN DATA WRAPPER dummy;
+CREATE SERVER s0 FOREIGN DATA WRAPPER dummy;
+CREATE FOREIGN TABLE ft1 (c1 integer NOT NULL) SERVER s0;
+ALTER FOREIGN TABLE ft1 ADD COLUMN c8 integer DEFAULT 0;
+ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE char(10);
+SELECT count(*)
+  FROM pg_attribute
+  WHERE attrelid = 'ft1'::regclass AND
+    (attmissingval IS NOT NULL OR atthasmissing);
+ count 
+-------
+     0
+(1 row)
+
 -- cleanup
+DROP FOREIGN TABLE ft1;
+DROP SERVER s0;
+DROP FOREIGN DATA WRAPPER dummy;
 DROP TABLE vtype;
 DROP TABLE vtype2;
 DROP TABLE follower;

src/test/regress/sql/fast_default.sql

@@ -524,8 +524,22 @@ SET LOCAL enable_seqscan = false;
 SELECT * FROM t WHERE a IS NULL;
 ROLLBACK;
 
+-- verify that a default set on a non-plain table doesn't set a missing
+-- value on the attribute
+CREATE FOREIGN DATA WRAPPER dummy;
+CREATE SERVER s0 FOREIGN DATA WRAPPER dummy;
+CREATE FOREIGN TABLE ft1 (c1 integer NOT NULL) SERVER s0;
+ALTER FOREIGN TABLE ft1 ADD COLUMN c8 integer DEFAULT 0;
+ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE char(10);
+SELECT count(*)
+  FROM pg_attribute
+  WHERE attrelid = 'ft1'::regclass AND
+    (attmissingval IS NOT NULL OR atthasmissing);
 
 -- cleanup
+DROP FOREIGN TABLE ft1;
+DROP SERVER s0;
+DROP FOREIGN DATA WRAPPER dummy;
 DROP TABLE vtype;
 DROP TABLE vtype2;
 DROP TABLE follower;