Add support for Optional in clvm_serde types (#16)

* Add support for Optional in clvm_serde types

* Use two byte overhead to handle nil-y values

* Improve coverage

---------

Co-authored-by: Richard Kiss <him@richardkiss.com>

hsms/clvm_serde/__init__.py

@@ -1,5 +1,5 @@
 from dataclasses import is_dataclass, fields, MISSING
-from typing import Any, Callable, Optional, Tuple, Type, get_type_hints
+from typing import Any, Callable, Optional, Tuple, Type, Union, get_type_hints
 
 from chia_base.meta.type_tree import ArgsType, CompoundLookup, OriginArgsType, TypeTree
 from chia_base.meta.typing import GenericAlias
@@ -52,6 +52,21 @@ def serialize_list(items):
     return serialize_list
 
 
+def serialize_for_optional(origin, args, type_tree: TypeTree) -> Program:
+    if len(args) == 2 and type(None) is args[1]:
+        write_item = type_tree(args[0])
+
+        def serialize_optional(item):
+            if item is None:
+                return Program.to((Program.null(), Program.null()))
+            else:
+                return Program.to((1, write_item(item)))
+
+        return serialize_optional
+    else:
+        raise ValueError("No serialization support for Union types (besides Optional)")
+
+
 def serialize_for_tuple(origin, args, type_tree: TypeTree) -> Program:
     write_items = [type_tree(_) for _ in args]
 
@@ -99,6 +114,7 @@ def ser(item):
     list: serialize_for_list,
     tuple: serialize_for_tuple,
     tuple_frugal: ser_for_tuple_frugal,
+    Union: serialize_for_optional,
 }
 
 
@@ -306,11 +322,26 @@ def de(p: Program) -> Tuple[Any, ...]:
 
     return de
 
+def deser_for_optional(origin, args, type_tree: TypeTree):
+    if len(args) == 2 and type(None) is args[1]:
+        read_item = type_tree(args[0])
+
+        def deserialize_optional(p: Program):
+            if p.first() == Program.null():
+                return None
+            else:
+                return read_item(p.rest())
+
+        return deserialize_optional
+    else:
+        raise ValueError("No serialization support for Union types (besides Optional)")
+
 
 DESERIALIZER_COMPOUND_TYPE_LOOKUP: CompoundLookup[FromProgram] = {
     list: deser_for_list,
     tuple: deser_for_tuple,
     tuple_frugal: de_for_tuple_frugal,
+    Union: deser_for_optional,
 }
 
 

tests/test_clvm_serde.py

@@ -1,5 +1,5 @@
 from dataclasses import dataclass, field
-from typing import List, Tuple
+from typing import List, Optional, Union, Tuple
 
 import random
 
@@ -134,6 +134,41 @@ class Foo:
         f1 = fp(p)
         assert f1 == foo
 
+    @dataclass
+    class Foo:
+        a: Optional[int] = field(metadata=dict(key="a"))
+
+    tp = to_program_for_type(Foo)
+    fp = from_program_for_type(Foo)
+    p = Program.to([("a", Program.to((1, 1000)))])
+    foo = fp(p)
+    assert foo.a == 1000
+    p1 = tp(foo)
+    assert p1 == p
+    p = Program.to([("a", Program.to((Program.null(), Program.null())))])
+    foo = fp(p)
+    assert foo.a is None
+    p1 = tp(foo)
+    assert p1 == p
+
+    @dataclass
+    class Foo:
+        a: Optional[List[int]] = field(metadata=dict(key="a"))
+
+    tp = to_program_for_type(Foo)
+    fp = from_program_for_type(Foo)
+    assert fp(tp(Foo([]))) == Foo([])
+
+    @dataclass
+    class Bar:
+        a: Union[int, str]
+
+    with pytest.raises(ValueError):
+        _ = to_program_for_type(Bar)
+
+    with pytest.raises(ValueError):
+        _ = from_program_for_type(Bar)
+
 
 def test_serde_frugal():
     @dataclass