Re: hiding variable-length fields from Form_pg_* structs

On sön, 2011-11-27 at 18:20 -0500, Tom Lane wrote:
> The low-tech way would be
>
> CATALOG(pg_attribute,1249) BKI_BOOTSTRAP ...
> {
> ...
> int4 attinhcount;
> Oid attcollation;
> aclitem attacl[1];
> #ifdef CATALOG_VARLEN_FIELDS
> text attoptions[1];
> text attfdwoptions[1];
> #endif
> } FormData_pg_attribute;

Good enough.

To clarify, I believe the rule is that the first variable-length field
can be accessed as a struct field. Are there any exceptions to this?
This kind of comment is pretty confusing:

CATALOG(pg_rewrite,2618)
{
NameData rulename;
Oid ev_class;
int2 ev_attr;
char ev_type;
char ev_enabled;
bool is_instead;

/* NB: remaining fields must be accessed via heap_getattr */
pg_node_tree ev_qual;
pg_node_tree ev_action;
} FormData_pg_rewrite;

Also, this code in relcache.c accesses indclass, which is after an
int2vector and an oidvector field:

/* Check to see if it is a unique, non-partial btree index on OID */
if (index->indnatts == 1 &&
index->indisunique && index->indimmediate &&
index->indkey.values[0] == ObjectIdAttributeNumber &&
index->indclass.values[0] == OID_BTREE_OPS_OID &&
heap_attisnull(htup, Anum_pg_index_indpred))
oidIndex = index->indexrelid;