Generalize handling of nullable pg_attribute columns in DDL

DDL code uses tuple descriptors to pass around pg_attribute values
during table and index creation.  But tuple descriptors don't include
the variable-length/nullable columns of pg_attribute, so they have to
be handled separately.  Right now, the attoptions field is handled in
a one-off way with a separate argument passed to
InsertPgAttributeTuples().  The other affected fields of pg_attribute
are right now not needed at relation creation time.

The goal of this patch is to generalize this to allow handling
additional variable-length/nullable columns of pg_attribute in a
similar manner.  For that, create a new struct
FormExtraData_pg_attribute, which is to be passed around in parallel
to the tuple descriptor and optionally supplies the additional
columns.  Right now, this struct only contains one field for
attoptions, so no functionality is actually changed by this.

Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/4da8d211-d54d-44b9-9847-f2a9f1184c76@eisentraut.org

src/backend/catalog/heap.c

@@ -684,10 +684,11 @@ CheckAttributeType(const char *attname,
  *		Construct and insert a set of tuples in pg_attribute.
  *
  * Caller has already opened and locked pg_attribute.  tupdesc contains the
- * attributes to insert.  attcacheoff is always initialized to -1.  attoptions
- * supplies the values for the attoptions fields and must contain the same
- * number of elements as tupdesc or be NULL.  The other variable-length fields
- * of pg_attribute are always initialized to null values.
+ * attributes to insert.  attcacheoff is always initialized to -1.
+ * tupdesc_extra supplies the values for certain variable-length/nullable
+ * pg_attribute fields and must contain the same number of elements as tupdesc
+ * or be NULL.  The other variable-length fields of pg_attribute are always
+ * initialized to null values.
  *
  * indstate is the index state for CatalogTupleInsertWithInfo.  It can be
  * passed as NULL, in which case we'll fetch the necessary info.  (Don't do
@@ -701,7 +702,7 @@ void
 InsertPgAttributeTuples(Relation pg_attribute_rel,
 						TupleDesc tupdesc,
 						Oid new_rel_oid,
-						const Datum *attoptions,
+						const FormExtraData_pg_attribute tupdesc_extra[],
 						CatalogIndexState indstate)
 {
 	TupleTableSlot **slot;
@@ -723,6 +724,7 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 	while (natts < tupdesc->natts)
 	{
 		Form_pg_attribute attrs = TupleDescAttr(tupdesc, natts);
+		const FormExtraData_pg_attribute *attrs_extra = tupdesc_extra ? &tupdesc_extra[natts] : NULL;
 
 		ExecClearTuple(slot[slotCount]);
 
@@ -754,10 +756,15 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 		slot[slotCount]->tts_values[Anum_pg_attribute_attislocal - 1] = BoolGetDatum(attrs->attislocal);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attinhcount - 1] = Int16GetDatum(attrs->attinhcount);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attcollation - 1] = ObjectIdGetDatum(attrs->attcollation);
-		if (attoptions && attoptions[natts] != (Datum) 0)
-			slot[slotCount]->tts_values[Anum_pg_attribute_attoptions - 1] = attoptions[natts];
+		if (attrs_extra)
+		{
+			slot[slotCount]->tts_values[Anum_pg_attribute_attoptions - 1] = attrs_extra->attoptions.value;
+			slot[slotCount]->tts_isnull[Anum_pg_attribute_attoptions - 1] = attrs_extra->attoptions.isnull;
+		}
 		else
+		{
 			slot[slotCount]->tts_isnull[Anum_pg_attribute_attoptions - 1] = true;
+		}
 
 		/*
 		 * The remaining fields are not set for new columns.

src/backend/catalog/index.c

@@ -512,6 +512,20 @@ AppendAttributeTuples(Relation indexRelation, const Datum *attopts)
 	Relation	pg_attribute;
 	CatalogIndexState indstate;
 	TupleDesc	indexTupDesc;
+	FormExtraData_pg_attribute *attrs_extra = NULL;
+
+	if (attopts)
+	{
+		attrs_extra = palloc0_array(FormExtraData_pg_attribute, indexRelation->rd_att->natts);
+
+		for (int i = 0; i < indexRelation->rd_att->natts; i++)
+		{
+			if (attopts[i])
+				attrs_extra[i].attoptions.value = attopts[i];
+			else
+				attrs_extra[i].attoptions.isnull = true;
+		}
+	}
 
 	/*
 	 * open the attribute relation and its indexes
@@ -525,7 +539,7 @@ AppendAttributeTuples(Relation indexRelation, const Datum *attopts)
 	 */
 	indexTupDesc = RelationGetDescr(indexRelation);
 
-	InsertPgAttributeTuples(pg_attribute, indexTupDesc, InvalidOid, attopts, indstate);
+	InsertPgAttributeTuples(pg_attribute, indexTupDesc, InvalidOid, attrs_extra, indstate);
 
 	CatalogCloseIndexes(indstate);
 

src/include/catalog/heap.h

@@ -98,7 +98,7 @@ extern List *heap_truncate_find_FKs(List *relationIds);
 extern void InsertPgAttributeTuples(Relation pg_attribute_rel,
 									TupleDesc tupdesc,
 									Oid new_rel_oid,
-									const Datum *attoptions,
+									const FormExtraData_pg_attribute tupdesc_extra[],
 									CatalogIndexState indstate);
 
 extern void InsertPgClassTuple(Relation pg_class_desc,

src/include/catalog/pg_attribute.h

@@ -208,6 +208,19 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
  */
 typedef FormData_pg_attribute *Form_pg_attribute;
 
+/*
+ * FormExtraData_pg_attribute contains (some of) the fields that are not in
+ * FormData_pg_attribute because they are excluded by CATALOG_VARLEN.  It is
+ * meant to be used by DDL code so that the combination of
+ * FormData_pg_attribute (often via tuple descriptor) and
+ * FormExtraData_pg_attribute can be used to pass around all the information
+ * about an attribute.  Fields can be included here as needed.
+ */
+typedef struct FormExtraData_pg_attribute
+{
+	NullableDatum attoptions;
+} FormExtraData_pg_attribute;
+
 DECLARE_UNIQUE_INDEX(pg_attribute_relid_attnam_index, 2658, AttributeRelidNameIndexId, pg_attribute, btree(attrelid oid_ops, attname name_ops));
 DECLARE_UNIQUE_INDEX_PKEY(pg_attribute_relid_attnum_index, 2659, AttributeRelidNumIndexId, pg_attribute, btree(attrelid oid_ops, attnum int2_ops));
 

src/tools/pgindent/typedefs.list

@@ -850,6 +850,7 @@ FormData_pg_ts_parser
 FormData_pg_ts_template
 FormData_pg_type
 FormData_pg_user_mapping
+FormExtraData_pg_attribute
 Form_pg_aggregate
 Form_pg_am
 Form_pg_amop