Support domains over composite types.

This is the last major omission in our domains feature: you can now
make a domain over anything that's not a pseudotype.

The major complication from an implementation standpoint is that places
that might be creating tuples of a domain type now need to be prepared
to apply domain_check().  It seems better that unprepared code fail
with an error like "<type> is not composite" than that it silently fail
to apply domain constraints.  Therefore, relevant infrastructure like
get_func_result_type() and lookup_rowtype_tupdesc() has been adjusted
to treat domain-over-composite as a distinct case that unprepared code
won't recognize, rather than just transparently treating it the same
as plain composite.  This isn't a 100% solution to the possibility of
overlooked domain checks, but it catches most places.

In passing, improve typcache.c's support for domains (it can now cache
the identity of a domain's base type), and rewrite the argument handling
logic in jsonfuncs.c's populate_record[set]_worker to reduce duplicative
per-call lookups.

I believe this is code-complete so far as the core and contrib code go.
The PLs need varying amounts of work, which will be tackled in followup
patches.

Discussion: https://postgr.es/m/4206.1499798337@sss.pgh.pa.us

1 files changed, 5 insertions, 4 deletions

diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 2f2f2c7fb07..fc0d6bc2f2e 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -1819,18 +1819,19 @@ ParseComplexProjection(ParseState *pstate, char *funcname, Node *first_arg,
 	}
 
 	/*
-	 * Else do it the hard way with get_expr_result_type().
+	 * Else do it the hard way with get_expr_result_tupdesc().
 	 *
 	 * If it's a Var of type RECORD, we have to work even harder: we have to
-	 * find what the Var refers to, and pass that to get_expr_result_type.
+	 * find what the Var refers to, and pass that to get_expr_result_tupdesc.
 	 * That task is handled by expandRecordVariable().
 	 */
 	if (IsA(first_arg, Var) &&
 		((Var *) first_arg)->vartype == RECORDOID)
 		tupdesc = expandRecordVariable(pstate, (Var *) first_arg, 0);
-	else if (get_expr_result_type(first_arg, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+	else
+		tupdesc = get_expr_result_tupdesc(first_arg, true);
+	if (!tupdesc)
 		return NULL;			/* unresolvable RECORD type */
-	Assert(tupdesc);
 
 	for (i = 0; i < tupdesc->natts; i++)
 	{