minor bug in sort_inner_and_outer()

Hi,

While looking at sort_inner_and_outer() I was rather confused what is
stored in all_pathkeys, because the code does this:

List *all_pathkeys;

...

all_pathkeys = select_outer_pathkeys_for_merge(root,
extra->mergeclause_list,
joinrel);

foreach(l, all_pathkeys)
{
List *front_pathkey = (List *) lfirst(l);
...

/* Make a pathkey list with this guy first */
if (l != list_head(all_pathkeys))
outerkeys = lcons(front_pathkey,
...);
else
...

which seems to suggest all_pathkeys is a list of lists, because why else
would front_pathkey be a (List *). But that doesn't seem to be the case,
front_pathkey is actually a PathKey, not a List, as demonstrated by gdb:

(gdb) p *front_pathkey
$2 = {type = T_PathKey, length = 0, ...}

Maybe it's some clever list-fu that I can't comprehend, but I guess it's
a bug present since ~2004. It's benign because we only ever pass the
front_pathkey to lcons() which does not really care.

regards

--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
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