[dataclasses plugin] Support kw_only=True

Author: tgallant

mypy/plugins/dataclasses.py

@@ -39,6 +39,7 @@ def __init__(
             column: int,
             type: Optional[Type],
             info: TypeInfo,
+            kw_only: bool,
     ) -> None:
         self.name = name
         self.is_in_init = is_in_init
@@ -48,6 +49,7 @@ def __init__(
         self.column = column
         self.type = type
         self.info = info
+        self.kw_only = kw_only
 
     def to_argument(self) -> Argument:
         return Argument(
@@ -77,6 +79,8 @@ def deserialize(
         cls, info: TypeInfo, data: JsonDict, api: SemanticAnalyzerPluginInterface
     ) -> 'DataclassAttribute':
         data = data.copy()
+        if data.get('kw_only') is None:
+            data['kw_only'] = False
         typ = deserialize_and_fixup_type(data.pop('type'), api)
         return cls(type=typ, info=info, **data)
 
@@ -215,6 +219,7 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
         cls = self._ctx.cls
         attrs: List[DataclassAttribute] = []
         known_attrs: Set[str] = set()
+        kw_only = _get_decorator_bool_argument(ctx, 'kw_only', False)
         for stmt in cls.defs.body:
             # Any assignment that doesn't use the new type declaration
             # syntax can be ignored out of hand.
@@ -251,6 +256,10 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
                 is_init_var = True
                 node.type = node_type.args[0]
 
+            if (isinstance(node_type, Instance) and
+                    node_type.type.fullname == 'dataclasses._KW_ONLY_TYPE'):
+                kw_only = True
+
             has_field_call, field_args = _collect_field_args(stmt.rvalue)
 
             is_in_init_param = field_args.get('init')
@@ -274,6 +283,13 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
                 # on self in the generated __init__(), not in the class body.
                 sym.implicit = True
 
+            is_kw_only = kw_only
+            # Use the kw_only field arg if it is provided. Otherwise use the
+            # kw_only value from the decorator parameter.
+            field_kw_only_param = field_args.get('kw_only')
+            if field_kw_only_param is not None:
+                is_kw_only = bool(ctx.api.parse_bool(field_kw_only_param))
+
             known_attrs.add(lhs.name)
             attrs.append(DataclassAttribute(
                 name=lhs.name,
@@ -284,6 +300,7 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
                 column=stmt.column,
                 type=sym.type,
                 info=cls.info,
+                kw_only=is_kw_only,
             ))
 
         # Next, collect attributes belonging to any class in the MRO
@@ -323,10 +340,10 @@ def collect_attributes(self) -> Optional[List[DataclassAttribute]]:
         # arguments that have a default.
         found_default = False
         for attr in all_attrs:
-            # If we find any attribute that is_in_init but that
+            # If we find any attribute that is_in_init, not kw_only, and that
             # doesn't have a default after one that does have one,
             # then that's an error.
-            if found_default and attr.is_in_init and not attr.has_default:
+            if found_default and attr.is_in_init and not attr.has_default and not attr.kw_only:
                 # If the issue comes from merging different classes, report it
                 # at the class definition point.
                 context = (Context(line=attr.line, column=attr.column) if attr in attrs

test-data/unit/check-dataclasses.test

@@ -225,7 +225,7 @@ class Person:
     name: str
     age: int = field(init=None)  # E: No overload variant of "field" matches argument type "None" \
                                  # N: Possible overload variant: \
-                                 # N:     def field(*, init: bool = ..., repr: bool = ..., hash: Optional[bool] = ..., compare: bool = ..., metadata: Optional[Mapping[str, Any]] = ...) -> Any \
+                                 # N:     def field(*, init: bool = ..., repr: bool = ..., hash: Optional[bool] = ..., compare: bool = ..., metadata: Optional[Mapping[str, Any]] = ..., kw_only: bool = ...) -> Any \
                                  # N:     <2 more non-matching overloads not shown>
 
 [builtins fixtures/list.pyi]
@@ -311,6 +311,63 @@ class Application:
 
 [builtins fixtures/list.pyi]
 
+[case testDataclassesOrderingKwOnly]
+# flags: --python-version 3.10
+from dataclasses import dataclass
+
+@dataclass(kw_only=True)
+class Application:
+    name: str = 'Unnamed'
+    rating: int
+
+[builtins fixtures/list.pyi]
+
+[case testDataclassesOrderingKwOnlyOnField]
+# flags: --python-version 3.10
+from dataclasses import dataclass, field
+
+@dataclass
+class Application:
+    name: str = 'Unnamed'
+    rating: int = field(kw_only=True)
+
+[builtins fixtures/list.pyi]
+
+[case testDataclassesOrderingKwOnlyOnFieldFalse]
+# flags: --python-version 3.10
+from dataclasses import dataclass, field
+
+@dataclass
+class Application:
+    name: str = 'Unnamed'
+    rating: int = field(kw_only=False)  # E: Attributes without a default cannot follow attributes with one 
+
+[builtins fixtures/list.pyi]
+
+[case testDataclassesOrderingKwOnlyWithSentinel]
+# flags: --python-version 3.10
+from dataclasses import dataclass, KW_ONLY
+
+@dataclass
+class Application:
+    _: KW_ONLY
+    name: str = 'Unnamed'
+    rating: int
+
+[builtins fixtures/list.pyi]
+
+[case testDataclassesOrderingKwOnlyWithSentinelAndFieldOverride]
+# flags: --python-version 3.10
+from dataclasses import dataclass, field, KW_ONLY
+
+@dataclass
+class Application:
+    _: KW_ONLY
+    name: str = 'Unnamed'
+    rating: int = field(kw_only=False)  # E: Attributes without a default cannot follow attributes with one 
+
+[builtins fixtures/list.pyi]
+
 [case testDataclassesClassmethods]
 # flags: --python-version 3.7
 from dataclasses import dataclass

test-data/unit/lib-stub/dataclasses.pyi

@@ -5,26 +5,56 @@ _T = TypeVar('_T')
 class InitVar(Generic[_T]):
     ...
 
+class _KW_ONLY_TYPE: ...
+KW_ONLY = _KW_ONLY_TYPE
 
 @overload
-def dataclass(_cls: Type[_T]) -> Type[_T]: ...
-
+def dataclass(__cls: Type[_T]) -> Type[_T]: ...
 @overload
-def dataclass(*, init: bool = ..., repr: bool = ..., eq: bool = ..., order: bool = ...,
-    unsafe_hash: bool = ..., frozen: bool = ...) -> Callable[[Type[_T]], Type[_T]]: ...
-
-
+def dataclass(__cls: None) -> Callable[[Type[_T]], Type[_T]]: ...
 @overload
-def field(*, default: _T,
-    init: bool = ..., repr: bool = ..., hash: Optional[bool] = ..., compare: bool = ...,
-    metadata: Optional[Mapping[str, Any]] = ...) -> _T: ...
-
+def dataclass(
+    *,
+    init: bool = ...,
+    repr: bool = ...,
+    eq: bool = ...,
+    order: bool = ...,
+    unsafe_hash: bool = ...,
+    frozen: bool = ...,
+    match_args: bool = ...,
+    kw_only: bool = ...,
+    slots: bool = ...,
+) -> Callable[[Type[_T]], Type[_T]]: ...
+
+@overload  # `default` and `default_factory` are optional and mutually exclusive.
+def field(
+    *,
+    default: _T,
+    init: bool = ...,
+    repr: bool = ...,
+    hash: Optional[bool] = ...,
+    compare: bool = ...,
+    metadata: Optional[Mapping[str, Any]] = ...,
+    kw_only: bool = ...,
+) -> _T: ...
 @overload
-def field(*, default_factory: Callable[[], _T],
-    init: bool = ..., repr: bool = ..., hash: Optional[bool] = ..., compare: bool = ...,
-    metadata: Optional[Mapping[str, Any]] = ...) -> _T: ...
-
+def field(
+    *,
+    default_factory: Callable[[], _T],
+    init: bool = ...,
+    repr: bool = ...,
+    hash: Optional[bool] = ...,
+    compare: bool = ...,
+    metadata: Optional[Mapping[str, Any]] = ...,
+    kw_only: bool = ...,
+) -> _T: ...
 @overload
-def field(*,
-    init: bool = ..., repr: bool = ..., hash: Optional[bool] = ..., compare: bool = ...,
-    metadata: Optional[Mapping[str, Any]] = ...) -> Any: ...
+def field(
+    *,
+    init: bool = ...,
+    repr: bool = ...,
+    hash: Optional[bool] = ...,
+    compare: bool = ...,
+    metadata: Optional[Mapping[str, Any]] = ...,
+    kw_only: bool = ...,
+) -> Any: ...