Implement information_schema.parameters.parameter_default column

Reviewed-by: Ali Dar <ali.munir.dar@gmail.com>
Reviewed-by: Amit Khandekar <amit.khandekar@enterprisedb.com>
Reviewed-by: Rodolfo Campero <rodolfo.campero@anachronics.com>

1 files changed, 84 insertions, 0 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 29a1027a100..348f620f2a4 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2266,6 +2266,90 @@ print_function_arguments(StringInfo buf, HeapTuple proctup,
 	return argsprinted;
 }
 
+static bool
+is_input_argument(int nth, const char *argmodes)
+{
+	return (!argmodes
+			|| argmodes[nth] == PROARGMODE_IN
+			|| argmodes[nth] == PROARGMODE_INOUT
+			|| argmodes[nth] == PROARGMODE_VARIADIC);
+}
+
+/*
+ * Get textual representation of a function argument's default value.  The
+ * second argument of this function is the argument number among all arguments
+ * (i.e. proallargtypes, *not* proargtypes), starting with 1, because that's
+ * how information_schema.sql uses it.
+ */
+Datum
+pg_get_function_arg_default(PG_FUNCTION_ARGS)
+{
+	Oid			funcid = PG_GETARG_OID(0);
+	int32		nth_arg = PG_GETARG_INT32(1);
+	HeapTuple	proctup;
+	Form_pg_proc proc;
+	int			numargs;
+	Oid		   *argtypes;
+	char	  **argnames;
+	char	   *argmodes;
+	int			i;
+	List	   *argdefaults;
+	Node	   *node;
+	char	   *str;
+	int			nth_inputarg;
+	Datum		proargdefaults;
+	bool		isnull;
+	int			nth_default;
+
+	proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
+	if (!HeapTupleIsValid(proctup))
+		elog(ERROR, "cache lookup failed for function %u", funcid);
+
+	numargs = get_func_arg_info(proctup, &argtypes, &argnames, &argmodes);
+	if (nth_arg < 1 || nth_arg > numargs || !is_input_argument(nth_arg - 1, argmodes))
+	{
+		ReleaseSysCache(proctup);
+		PG_RETURN_NULL();
+	}
+
+	nth_inputarg = 0;
+	for (i = 0; i < nth_arg; i++)
+		if (is_input_argument(i, argmodes))
+			nth_inputarg++;
+
+	proargdefaults = SysCacheGetAttr(PROCOID, proctup,
+									 Anum_pg_proc_proargdefaults,
+									 &isnull);
+	if (isnull)
+	{
+		ReleaseSysCache(proctup);
+		PG_RETURN_NULL();
+	}
+
+	str = TextDatumGetCString(proargdefaults);
+	argdefaults = (List *) stringToNode(str);
+	Assert(IsA(argdefaults, List));
+	pfree(str);
+
+	proc = (Form_pg_proc) GETSTRUCT(proctup);
+
+	/* Calculate index into proargdefaults: proargdefaults corresponds to the
+	 * last N input arguments, where N = pronargdefaults. */
+	nth_default = nth_inputarg - 1 - (proc->pronargs - proc->pronargdefaults);
+
+	if (nth_default < 0 || nth_default >= list_length(argdefaults))
+	{
+		ReleaseSysCache(proctup);
+		PG_RETURN_NULL();
+	}
+	node = list_nth(argdefaults, nth_default);
+	str = deparse_expression(node, NIL, false, false);
+
+	ReleaseSysCache(proctup);
+
+	PG_RETURN_TEXT_P(string_to_text(str));
+}
+
 
 /*
  * deparse_expression			- General utility for deparsing expressions