Use TupleDescAttr macro consistently

A few places were directly accessing the attrs[] array. This goes
against the standards set by 2cd708452. Fix that.

Discussion: https://postgr.es/m/CAApHDvrBztXP3yx=NKNmo3xwFAFhEdyPnvrDg3=M0RhDs+4vYw@mail.gmail.com

contrib/pageinspect/gistfuncs.c

@@ -309,7 +309,7 @@ gist_page_items(PG_FUNCTION_ARGS)
 					bool		typisvarlena;
 					Oid			typoid;
 
-					typoid = tupdesc->attrs[i].atttypid;
+					typoid = TupleDescAttr(tupdesc, i)->atttypid;
 					getTypeOutputInfo(typoid, &foutoid, &typisvarlena);
 					value = OidOutputFunctionCall(foutoid, itup_values[i]);
 				}

src/backend/catalog/heap.c

@@ -839,18 +839,19 @@ AddNewAttributeTuples(Oid new_rel_oid,
 	/* add dependencies on their datatypes and collations */
 	for (int i = 0; i < natts; i++)
 	{
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+
 		/* Add dependency info */
 		ObjectAddressSubSet(myself, RelationRelationId, new_rel_oid, i + 1);
-		ObjectAddressSet(referenced, TypeRelationId,
+		ObjectAddressSet(referenced, TypeRelationId, attr->atttypid);
-						 tupdesc->attrs[i].atttypid);
 		recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
 
 		/* The default collation is pinned, so don't bother recording it */
-		if (OidIsValid(tupdesc->attrs[i].attcollation) &&
+		if (OidIsValid(attr->attcollation) &&
-			tupdesc->attrs[i].attcollation != DEFAULT_COLLATION_OID)
+			attr->attcollation != DEFAULT_COLLATION_OID)
 		{
 			ObjectAddressSet(referenced, CollationRelationId,
-							 tupdesc->attrs[i].attcollation);
+							 attr->attcollation);
 			recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
 		}
 	}

src/backend/commands/prepare.c

@@ -717,7 +717,7 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
 
 				result_types = palloc_array(Oid, result_desc->natts);
 				for (int i = 0; i < result_desc->natts; i++)
-					result_types[i] = result_desc->attrs[i].atttypid;
+					result_types[i] = TupleDescAttr(result_desc, i)->atttypid;
 				values[4] = build_regtype_array(result_types, result_desc->natts);
 			}
 			else

src/backend/executor/nodeIndexonlyscan.c

@@ -658,7 +658,7 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 	/* First, count the number of such index keys */
 	for (int attnum = 0; attnum < indnkeyatts; attnum++)
 	{
-		if (indexRelation->rd_att->attrs[attnum].atttypid == CSTRINGOID &&
+		if (TupleDescAttr(indexRelation->rd_att, attnum)->atttypid == CSTRINGOID &&
 			indexRelation->rd_opcintype[attnum] == NAMEOID)
 			namecount++;
 	}
@@ -676,7 +676,7 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 
 		for (int attnum = 0; attnum < indnkeyatts; attnum++)
 		{
-			if (indexRelation->rd_att->attrs[attnum].atttypid == CSTRINGOID &&
+			if (TupleDescAttr(indexRelation->rd_att, attnum)->atttypid == CSTRINGOID &&
 				indexRelation->rd_opcintype[attnum] == NAMEOID)
 				indexstate->ioss_NameCStringAttNums[idx++] = (AttrNumber) attnum;
 		}

src/backend/executor/nodeMemoize.c

@@ -175,10 +175,10 @@ MemoizeHash_hash(struct memoize_hash *tb, const MemoizeKey *key)
 
 			if (!pslot->tts_isnull[i])	/* treat nulls as having hash key 0 */
 			{
-				FormData_pg_attribute *attr;
+				Form_pg_attribute attr;
 				uint32		hkey;
 
-				attr = &pslot->tts_tupleDescriptor->attrs[i];
+				attr = TupleDescAttr(pslot->tts_tupleDescriptor, i);
 
 				hkey = datum_image_hash(pslot->tts_values[i], attr->attbyval, attr->attlen);
 
@@ -242,7 +242,7 @@ MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
 
 		for (int i = 0; i < numkeys; i++)
 		{
-			FormData_pg_attribute *attr;
+			Form_pg_attribute attr;
 
 			if (tslot->tts_isnull[i] != pslot->tts_isnull[i])
 			{
@@ -255,7 +255,7 @@ MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
 				continue;
 
 			/* perform binary comparison on the two datums */
-			attr = &tslot->tts_tupleDescriptor->attrs[i];
+			attr = TupleDescAttr(tslot->tts_tupleDescriptor, i);
 			if (!datum_image_eq(tslot->tts_values[i], pslot->tts_values[i],
 								attr->attbyval, attr->attlen))
 			{

src/backend/optimizer/util/plancat.c

@@ -174,7 +174,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	{
 		for (int i = 0; i < relation->rd_att->natts; i++)
 		{
-			FormData_pg_attribute *attr = &relation->rd_att->attrs[i];
+			Form_pg_attribute attr = TupleDescAttr(relation->rd_att, i);
 
 			if (attr->attnotnull)
 			{