Add support for recursive Union

mashumaro/core/meta/types/common.py

@@ -60,6 +60,8 @@ def __init__(self, expression: str):
 class FieldContext:
     name: str
     metadata: Mapping
+    packer: Optional[str] = None
+    unpacker: Optional[str] = None
 
     def copy(self, **changes: Any) -> "FieldContext":
         return replace(self, **changes)
@@ -181,8 +183,13 @@ def _get_call_expr(self, spec: ValueSpec, method_name: str) -> str:
     def _before_build(self, spec: ValueSpec) -> None:
         pass
 
+    def _get_existing_method(self, spec: ValueSpec) -> Optional[str]:
+        return None
+
     def build(self, spec: ValueSpec) -> str:
         self._before_build(spec)
+        if method := self._get_existing_method(spec):
+            return method
         lines = CodeLines()
         method_name = self._add_definition(spec, lines)
         with lines.indent():

mashumaro/core/meta/types/pack.py

@@ -289,11 +289,27 @@ def pack_any(spec: ValueSpec) -> Optional[Expression]:
 def pack_union(
     spec: ValueSpec, args: tuple[type, ...], prefix: str = "union"
 ) -> Expression:
+    if spec.type is spec.owner and spec.field_ctx.packer:
+        return spec.field_ctx.packer
     lines = CodeLines()
+
     method_name = (
         f"__pack_{prefix}_{spec.builder.cls.__name__}_{spec.field_ctx.name}__"
         f"{random_hex()}"
     )
+
+    if not spec.field_ctx.packer:
+        method_args = ", ".join(
+            filter(None, ("value", spec.builder.get_pack_method_flags()))
+        )
+        if spec.builder.is_nailed:
+            union_packer = (
+                f"{spec.self_attrs_name}.{method_name}({method_args})"
+            )
+        else:
+            union_packer = f"{method_name}({method_args})"
+        spec.field_ctx.packer = union_packer
+
     method_args = "self, value" if spec.builder.is_nailed else "value"
     default_kwargs = spec.builder.get_pack_method_default_flag_values()
     if default_kwargs:
@@ -304,7 +320,7 @@ def pack_union(
     packer_arg_types: dict[str, list[type]] = {}
     for type_arg in args:
         packer = PackerRegistry.get(
-            spec.copy(type=type_arg, expression="value")
+            spec.copy(type=type_arg, expression="value", owner=spec.type)
         )
         if packer not in packers:
             if packer == "value":
@@ -363,7 +379,9 @@ def pack_union(
     if spec.builder.get_config().debug:
         print(f"{type_name(spec.builder.cls)}:")
         print(lines.as_text())
+
     exec(lines.as_text(), spec.builder.globals, spec.builder.__dict__)
+
     method_args = ", ".join(
         filter(None, (spec.expression, spec.builder.get_pack_method_flags()))
     )

mashumaro/core/meta/types/unpack.py

@@ -162,11 +162,21 @@ def _get_call_expr(self, spec: ValueSpec, method_name: str) -> str:
 class UnionUnpackerBuilder(AbstractUnpackerBuilder):
     def __init__(self, args: tuple[type, ...]):
         self.union_args = args
+        self.method_name: Optional[str] = None
 
     def get_method_prefix(self) -> str:
         return "union"
 
+    def _generate_method_name(self, spec: ValueSpec) -> str:
+        method_name = super()._generate_method_name(spec)
+        self.method_name = method_name
+        return method_name
+
     def _add_body(self, spec: ValueSpec, lines: CodeLines) -> None:
+        if not spec.field_ctx.unpacker and self.method_name:
+            spec.field_ctx.unpacker = self._get_call_expr(
+                spec, self.method_name
+            )
         orig_lines = lines
         lines = CodeLines()
         unpackers = set()
@@ -175,7 +185,7 @@ def _add_body(self, spec: ValueSpec, lines: CodeLines) -> None:
         type_match_statements = 0
         for type_arg in self.union_args:
             unpacker = UnpackerRegistry.get(
-                spec.copy(type=type_arg, expression="value")
+                spec.copy(type=type_arg, expression="value", owner=spec.type)
             )
             type_arg_unpackers.append((type_arg, unpacker))
             if isinstance(unpacker, TypeMatchEligibleExpression):
@@ -230,6 +240,10 @@ def _add_body(self, spec: ValueSpec, lines: CodeLines) -> None:
             orig_lines.append("__value_type = type(value)")
         orig_lines.extend(lines)
 
+    def _get_existing_method(self, spec: ValueSpec) -> Optional[str]:
+        if spec.owner is spec.type:
+            return spec.field_ctx.unpacker
+
 
 class TypeVarUnpackerBuilder(UnionUnpackerBuilder):
     def get_method_prefix(self) -> str:

tests/conftest.py

@@ -6,6 +6,7 @@
     collect_ignore = [
         "test_generics_pep_695.py",
         "test_pep_695.py",
+        "test_recursive_union.py",
     ]
 
 if PY_313_MIN:

tests/test_recursive_union.py

@@ -0,0 +1,72 @@
+from dataclasses import dataclass
+
+from mashumaro import DataClassDictMixin
+from mashumaro.codecs import BasicDecoder, BasicEncoder
+
+type JSON = str | int | float | bool | dict[str, JSON] | list[JSON] | None
+
+
+@dataclass
+class MyClass:
+    x: str
+    y: JSON
+
+
+def test_encoder_with_recursive_union():
+    encoder = BasicEncoder(JSON)
+    assert encoder.encode(
+        {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+    ) == {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+
+
+def test_encoder_with_recursive_union_in_dataclass():
+    encoder = BasicEncoder(MyClass)
+    assert encoder.encode(
+        MyClass(
+            x="x", y={"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+        )
+    ) == {
+        "x": "x",
+        "y": {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]},
+    }
+
+
+def test_decoder_with_recursive_union():
+    decoder = BasicDecoder(JSON)
+    assert decoder.decode(
+        {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+    ) == {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+
+
+def test_decoder_with_recursive_union_in_dataclass():
+    decoder = BasicDecoder(MyClass)
+    assert decoder.decode(
+        {
+            "x": "x",
+            "y": {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]},
+        }
+    ) == MyClass(
+        x="x", y={"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+    )
+
+
+def test_dataclass_dict_mixin_with_recursive_union():
+    @dataclass
+    class MyClassWithMixin(DataClassDictMixin):
+        x: str
+        y: JSON
+
+    assert MyClassWithMixin(
+        x="x", y={"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+    ).to_dict() == {
+        "x": "x",
+        "y": {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]},
+    }
+    assert MyClassWithMixin.from_dict(
+        {
+            "x": "x",
+            "y": {"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]},
+        }
+    ) == MyClassWithMixin(
+        x="x", y={"x": [{"x": {"x": [{"x": ["x", 1, 1.0, True, None]}]}}]}
+    )