[stubgen] Preserve dataclass_transform decorator (#18418)

Ref: #18081

mypy/stubgen.py

@@ -113,6 +113,7 @@
     Var,
 )
 from mypy.options import Options as MypyOptions
+from mypy.semanal_shared import find_dataclass_transform_spec
 from mypy.sharedparse import MAGIC_METHODS_POS_ARGS_ONLY
 from mypy.stubdoc import ArgSig, FunctionSig
 from mypy.stubgenc import InspectionStubGenerator, generate_stub_for_c_module
@@ -139,6 +140,7 @@
     has_yield_from_expression,
 )
 from mypy.types import (
+    DATACLASS_TRANSFORM_NAMES,
     OVERLOAD_NAMES,
     TPDICT_NAMES,
     TYPED_NAMEDTUPLE_NAMES,
@@ -701,10 +703,13 @@ def process_decorator(self, o: Decorator) -> None:
         """
         o.func.is_overload = False
         for decorator in o.original_decorators:
-            if not isinstance(decorator, (NameExpr, MemberExpr)):
+            d = decorator
+            if isinstance(d, CallExpr):
+                d = d.callee
+            if not isinstance(d, (NameExpr, MemberExpr)):
                 continue
-            qualname = get_qualified_name(decorator)
-            fullname = self.get_fullname(decorator)
+            qualname = get_qualified_name(d)
+            fullname = self.get_fullname(d)
             if fullname in (
                 "builtins.property",
                 "builtins.staticmethod",
@@ -739,6 +744,9 @@ def process_decorator(self, o: Decorator) -> None:
                 o.func.is_overload = True
             elif qualname.endswith((".setter", ".deleter")):
                 self.add_decorator(qualname, require_name=False)
+            elif fullname in DATACLASS_TRANSFORM_NAMES:
+                p = AliasPrinter(self)
+                self._decorators.append(f"@{decorator.accept(p)}")
 
     def get_fullname(self, expr: Expression) -> str:
         """Return the expression's full name."""
@@ -785,6 +793,8 @@ def visit_class_def(self, o: ClassDef) -> None:
             self.add(f"{self._indent}{docstring}\n")
         n = len(self._output)
         self._vars.append([])
+        if self.analyzed and find_dataclass_transform_spec(o):
+            self.processing_dataclass = True
         super().visit_class_def(o)
         self.dedent()
         self._vars.pop()
@@ -854,13 +864,26 @@ def get_class_decorators(self, cdef: ClassDef) -> list[str]:
                 decorators.append(d.accept(p))
                 self.import_tracker.require_name(get_qualified_name(d))
                 self.processing_dataclass = True
+            if self.is_dataclass_transform(d):
+                decorators.append(d.accept(p))
+                self.import_tracker.require_name(get_qualified_name(d))
         return decorators
 
     def is_dataclass(self, expr: Expression) -> bool:
         if isinstance(expr, CallExpr):
             expr = expr.callee
         return self.get_fullname(expr) == "dataclasses.dataclass"
 
+    def is_dataclass_transform(self, expr: Expression) -> bool:
+        if isinstance(expr, CallExpr):
+            expr = expr.callee
+        if self.get_fullname(expr) in DATACLASS_TRANSFORM_NAMES:
+            return True
+        if find_dataclass_transform_spec(expr) is not None:
+            self.processing_dataclass = True
+            return True
+        return False
+
     def visit_block(self, o: Block) -> None:
         # Unreachable statements may be partially uninitialized and that may
         # cause trouble.

test-data/unit/stubgen.test

@@ -3104,15 +3104,12 @@ class C:
     x = attrs.field()
 
 [out]
-from _typeshed import Incomplete
+import attrs
 
+@attrs.define
 class C:
-    x: Incomplete
+    x = ...
     def __init__(self, x) -> None: ...
-    def __lt__(self, other): ...
-    def __le__(self, other): ...
-    def __gt__(self, other): ...
-    def __ge__(self, other): ...
 
 [case testNamedTupleInClass]
 from collections import namedtuple
@@ -4249,6 +4246,122 @@ class Y(missing.Base):
     generated_kwargs_: float
     def __init__(self, *generated_args__, generated_args, generated_args_, generated_kwargs, generated_kwargs_, **generated_kwargs__) -> None: ...
 
+[case testDataclassTransform]
+# dataclass_transform detection only works with sementic analysis.
+# Test stubgen doesn't break too badly without it.
+from typing_extensions import dataclass_transform
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+def create_model(cls):
+    return cls
+
+@create_model
+class X:
+    a: int
+    b: str = "hello"
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+class ModelBase: ...
+
+class Y(ModelBase):
+    a: int
+    b: str = "hello"
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+class DCMeta(type): ...
+
+class Z(metaclass=DCMeta):
+    a: int
+    b: str = "hello"
+
+[out]
+@typing_extensions.dataclass_transform(kw_only_default=True)
+def create_model(cls): ...
+
+class X:
+    a: int
+    b: str
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+class ModelBase: ...
+
+class Y(ModelBase):
+    a: int
+    b: str
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+class DCMeta(type): ...
+
+class Z(metaclass=DCMeta):
+    a: int
+    b: str
+
+[case testDataclassTransformDecorator_semanal]
+import typing_extensions
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+def create_model(cls):
+    return cls
+
+@create_model
+class X:
+    a: int
+    b: str = "hello"
+
+[out]
+import typing_extensions
+
+@typing_extensions.dataclass_transform(kw_only_default=True)
+def create_model(cls): ...
+
+@create_model
+class X:
+    a: int
+    b: str = ...
+    def __init__(self, *, a, b=...) -> None: ...
+
+[case testDataclassTransformClass_semanal]
+from typing_extensions import dataclass_transform
+
+@dataclass_transform(kw_only_default=True)
+class ModelBase: ...
+
+class X(ModelBase):
+    a: int
+    b: str = "hello"
+
+[out]
+from typing_extensions import dataclass_transform
+
+@dataclass_transform(kw_only_default=True)
+class ModelBase: ...
+
+class X(ModelBase):
+    a: int
+    b: str = ...
+    def __init__(self, *, a, b=...) -> None: ...
+
+[case testDataclassTransformMetaclass_semanal]
+from typing_extensions import dataclass_transform
+
+@dataclass_transform(kw_only_default=True)
+class DCMeta(type): ...
+
+class X(metaclass=DCMeta):
+    a: int
+    b: str = "hello"
+
+[out]
+from typing_extensions import dataclass_transform
+
+@dataclass_transform(kw_only_default=True)
+class DCMeta(type): ...
+
+class X(metaclass=DCMeta):
+    a: int
+    b: str = ...
+    def __init__(self, *, a, b=...) -> None: ...
+
 [case testAlwaysUsePEP604Union]
 import typing
 import typing as t
@@ -4536,16 +4649,17 @@ def f5[T5 = int]() -> None: ...
 # flags: --include-private --python-version=3.13
 from typing_extensions import dataclass_transform
 
-# TODO: preserve dataclass_transform decorator
 @dataclass_transform()
 class DCMeta(type): ...
 class DC(metaclass=DCMeta):
     x: str
 
 [out]
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
 class DCMeta(type): ...
 
 class DC(metaclass=DCMeta):
     x: str
     def __init__(self, x) -> None: ...
-    def __replace__(self, *, x) -> None: ...