Fix PostgreSQL function argument default parsing

src/sqlalchemy_declarative_extensions/dialects/postgresql/schema.py

@@ -117,6 +117,7 @@ def char_literals(*literals: str) -> Collection[BindParameter]:
     column("prosecdef"),
     column("prokind"),
     column("provolatile"),
+    column("pronargs"),
     column("proargnames"),
     column("proargmodes"),
     column("proargtypes"),
@@ -318,6 +319,23 @@ def get_types(arg_type_oids):
     )
 
 
+def get_defaults():
+    arg_num = (
+        func.generate_series(1, pg_proc.c.pronargs)
+        .table_valued("arg_num", with_ordinality="ordinality")
+        .alias("arg_num")
+    )
+    return (
+        select(
+            func.array_agg(
+                func.pg_get_function_arg_default(pg_proc.c.oid, arg_num.c.arg_num)
+            )
+        )
+        .select_from(arg_num)
+        .scalar_subquery()
+    )
+
+
 def get_procedures_query(version_info):
     source = get_source_column(version_info)
     return (
@@ -334,9 +352,7 @@ def get_procedures_query(version_info):
             func.coalesce(
                 get_types(pg_proc.c.proallargtypes), get_types(pg_proc.c.proargtypes)
             ).label("arg_types"),
-            func.pg_get_expr(
-                pg_proc.c.proargdefaults, func.cast(literal("pg_proc"), REGCLASS)
-            ).label("arg_defaults"),
+            get_defaults().label("arg_defaults"),
         )
         .select_from(
             pg_proc.join(pg_namespace, pg_proc.c.pronamespace == pg_namespace.c.oid)
@@ -369,9 +385,7 @@ def get_functions_query(version_info):
             func.coalesce(
                 get_types(pg_proc.c.proallargtypes), get_types(pg_proc.c.proargtypes)
             ).label("arg_types"),
-            func.pg_get_expr(
-                pg_proc.c.proargdefaults, func.cast(literal("pg_proc"), REGCLASS)
-            ).label("arg_defaults"),
+            get_defaults().label("arg_defaults"),
         )
         .select_from(
             pg_proc.join(pg_namespace, pg_proc.c.pronamespace == pg_namespace.c.oid)

tests/dialect/postgresql/test_function_defaults.py

@@ -0,0 +1,45 @@
+import pytest
+from pytest_mock_resources import PostgresConfig, create_postgres_fixture
+from sqlalchemy import text
+
+from sqlalchemy_declarative_extensions import Functions
+from sqlalchemy_declarative_extensions.dialects.postgresql import (
+    Function,
+    FunctionParam,
+    FunctionVolatility,
+)
+from sqlalchemy_declarative_extensions.function.compare import compare_functions
+
+pg = create_postgres_fixture(scope="function", engine_kwargs={"echo": True})
+
+
+
+
+@pytest.mark.parametrize(
+    ("default_a", "default_b", "default_c"),
+    [(None, None, "''::text"), (1, 0, "'m'::text"), (None, 2, "'ft'::text")],
+)
+def test_function_argument_defaults(pg, default_a, default_b, default_c):
+    add_label_function = Function(
+        name="add_label",
+        definition="""
+            BEGIN
+                RETURN (((a + b))::text || c);
+            END;
+        """,
+        parameters=[
+            FunctionParam("a", "integer", default=default_a),
+            FunctionParam("b", "integer", default=default_b),
+            FunctionParam("c", "text", default=default_c),
+        ],
+        returns="TEXT",
+        volatility=FunctionVolatility.STABLE,
+        language="plpgsql",
+    ).normalize()
+    create_function = add_label_function.to_sql_create()
+    functions = Functions([add_label_function])
+    with pg.connect() as connection:
+        connection.execute(text("\n".join(create_function)))
+        diff = compare_functions(connection, functions)
+    for op in diff:
+        assert op.from_function == op.function