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>

doc/src/sgml/information_schema.sgml

@@ -3323,6 +3323,15 @@ ORDER BY c.ordinal_position;
        in future versions.)
       </entry>
      </row>
+
+     <row>
+      <entry><literal>parameter_default</literal></entry>
+      <entry><type>character_data</type></entry>
+      <entry>
+       The default expression of the parameter, or null if none or if the
+       function is not owned by a currently enabled role.
+      </entry>
+     </row>
     </tbody>
    </tgroup>
   </table>

src/backend/catalog/information_schema.sql

@@ -1133,10 +1133,15 @@ CREATE VIEW parameters AS
            CAST(null AS sql_identifier) AS scope_schema,
            CAST(null AS sql_identifier) AS scope_name,
            CAST(null AS cardinal_number) AS maximum_cardinality,
-           CAST((ss.x).n AS sql_identifier) AS dtd_identifier
+           CAST((ss.x).n AS sql_identifier) AS dtd_identifier,
+           CAST(
+             CASE WHEN pg_has_role(proowner, 'USAGE')
+                  THEN pg_get_function_arg_default(p_oid, (ss.x).n)
+                  ELSE NULL END
+             AS character_data) AS parameter_default
 
     FROM pg_type t, pg_namespace nt,
-         (SELECT n.nspname AS n_nspname, p.proname, p.oid AS p_oid,
+         (SELECT n.nspname AS n_nspname, p.proname, p.oid AS p_oid, p.proowner,
                  p.proargnames, p.proargmodes,
                  _pg_expandarray(coalesce(p.proallargtypes, p.proargtypes::oid[])) AS x
           FROM pg_namespace n, pg_proc p

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

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201311211
+#define CATALOG_VERSION_NO	201311261
 
 #endif

src/include/catalog/pg_proc.h

@@ -1973,6 +1973,8 @@ DATA(insert OID = 2232 (  pg_get_function_identity_arguments	   PGNSP PGUID 12 1
 DESCR("identity argument list of a function");
 DATA(insert OID = 2165 (  pg_get_function_result	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 25 "26" _null_ _null_ _null_ _null_ pg_get_function_result _null_ _null_ _null_ ));
 DESCR("result type of a function");
+DATA(insert OID = 3808 (  pg_get_function_arg_default   PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 25 "26 23" _null_ _null_ _null_ _null_ pg_get_function_arg_default _null_ _null_ _null_ ));
+DESCR("function argument default");
 
 DATA(insert OID = 1686 (  pg_get_keywords		PGNSP PGUID 12 10 400 0 0 f f f f t t s 0 0 2249 "" "{25,18,25}" "{o,o,o}" "{word,catcode,catdesc}" _null_ pg_get_keywords _null_ _null_ _null_ ));
 DESCR("list of SQL keywords");

src/include/utils/builtins.h

@@ -665,6 +665,7 @@ extern Datum pg_get_functiondef(PG_FUNCTION_ARGS);
 extern Datum pg_get_function_arguments(PG_FUNCTION_ARGS);
 extern Datum pg_get_function_identity_arguments(PG_FUNCTION_ARGS);
 extern Datum pg_get_function_result(PG_FUNCTION_ARGS);
+extern Datum pg_get_function_arg_default(PG_FUNCTION_ARGS);
 extern char *deparse_expression(Node *expr, List *dpcontext,
 				   bool forceprefix, bool showimplicit);
 extern List *deparse_context_for(const char *aliasname, Oid relid);

src/test/regress/expected/create_function_3.out

@@ -425,9 +425,37 @@ SELECT proname, proisstrict FROM pg_proc
  functext_f_4 | t
 (4 rows)
 
+-- information_schema tests
+CREATE FUNCTION functest_IS_1(a int, b int default 1, c text default 'foo')
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1 + $2';
+CREATE FUNCTION functest_IS_2(out a int, b int default 1)
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1';
+CREATE FUNCTION functest_IS_3(a int default 1, out b int)
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1';
+SELECT routine_name, ordinal_position, parameter_name, parameter_default
+    FROM information_schema.parameters JOIN information_schema.routines USING (specific_schema, specific_name)
+    WHERE routine_schema = 'temp_func_test' AND routine_name ~ '^functest_is_'
+    ORDER BY 1, 2;
+ routine_name  | ordinal_position | parameter_name | parameter_default 
+---------------+------------------+----------------+-------------------
+ functest_is_1 |                1 | a              | 
+ functest_is_1 |                2 | b              | 1
+ functest_is_1 |                3 | c              | 'foo'::text
+ functest_is_2 |                1 | a              | 
+ functest_is_2 |                2 | b              | 1
+ functest_is_3 |                1 | a              | 1
+ functest_is_3 |                2 | b              | 
+(7 rows)
+
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;
-NOTICE:  drop cascades to 16 other objects
+NOTICE:  drop cascades to 19 other objects
 DETAIL:  drop cascades to function functest_a_1(text,date)
 drop cascades to function functest_a_2(text[])
 drop cascades to function functest_a_3()
@@ -444,5 +472,8 @@ drop cascades to function functext_f_1(integer)
 drop cascades to function functext_f_2(integer)
 drop cascades to function functext_f_3(integer)
 drop cascades to function functext_f_4(integer)
+drop cascades to function functest_is_1(integer,integer,text)
+drop cascades to function functest_is_2(integer)
+drop cascades to function functest_is_3(integer)
 DROP USER regtest_unpriv_user;
 RESET search_path;

src/test/regress/sql/create_function_3.sql

@@ -138,6 +138,30 @@ SELECT proname, proisstrict FROM pg_proc
                      'functext_F_3'::regproc,
                      'functext_F_4'::regproc) ORDER BY proname;
 
+
+-- information_schema tests
+
+CREATE FUNCTION functest_IS_1(a int, b int default 1, c text default 'foo')
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1 + $2';
+
+CREATE FUNCTION functest_IS_2(out a int, b int default 1)
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1';
+
+CREATE FUNCTION functest_IS_3(a int default 1, out b int)
+    RETURNS int
+    LANGUAGE SQL
+    AS 'SELECT $1';
+
+SELECT routine_name, ordinal_position, parameter_name, parameter_default
+    FROM information_schema.parameters JOIN information_schema.routines USING (specific_schema, specific_name)
+    WHERE routine_schema = 'temp_func_test' AND routine_name ~ '^functest_is_'
+    ORDER BY 1, 2;
+
+
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;
 DROP USER regtest_unpriv_user;