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[stubtest] support @type_check_only decorator #16422

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Nov 11, 2023
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7 changes: 7 additions & 0 deletions mypy/nodes.py
Original file line number Diff line number Diff line change
Expand Up @@ -513,6 +513,7 @@ class FuncBase(Node):
"is_static", # Uses "@staticmethod" (explicit or implicit)
"is_final", # Uses "@final"
"is_explicit_override", # Uses "@override"
"is_type_check_only", # Uses "@type_check_only"
"_fullname",
)

Expand All @@ -530,6 +531,7 @@ def __init__(self) -> None:
self.is_static = False
self.is_final = False
self.is_explicit_override = False
self.is_type_check_only = False
# Name with module prefix
self._fullname = ""

Expand Down Expand Up @@ -2866,6 +2868,7 @@ class is generic then it will be a type constructor of higher kind.
"type_var_tuple_suffix",
"self_type",
"dataclass_transform_spec",
"is_type_check_only",
)

_fullname: str # Fully qualified name
Expand Down Expand Up @@ -3016,6 +3019,9 @@ class is generic then it will be a type constructor of higher kind.
# Added if the corresponding class is directly decorated with `typing.dataclass_transform`
dataclass_transform_spec: DataclassTransformSpec | None

# Is set to `True` when class is decorated with `@typing.type_check_only`
is_type_check_only: bool

FLAGS: Final = [
"is_abstract",
"is_enum",
Expand Down Expand Up @@ -3072,6 +3078,7 @@ def __init__(self, names: SymbolTable, defn: ClassDef, module_name: str) -> None
self.metadata = {}
self.self_type = None
self.dataclass_transform_spec = None
self.is_type_check_only = False

def add_type_vars(self) -> None:
self.has_type_var_tuple_type = False
Expand Down
6 changes: 6 additions & 0 deletions mypy/semanal.py
Original file line number Diff line number Diff line change
Expand Up @@ -251,6 +251,7 @@
REVEAL_TYPE_NAMES,
TPDICT_NAMES,
TYPE_ALIAS_NAMES,
TYPE_CHECK_ONLY_NAMES,
TYPED_NAMEDTUPLE_NAMES,
AnyType,
CallableType,
Expand Down Expand Up @@ -1568,6 +1569,9 @@ def visit_decorator(self, dec: Decorator) -> None:
removed.append(i)
else:
self.fail("@final cannot be used with non-method functions", d)
elif refers_to_fullname(d, TYPE_CHECK_ONLY_NAMES):
# TODO: support `@overload` funcs.
dec.func.is_type_check_only = True
elif isinstance(d, CallExpr) and refers_to_fullname(
d.callee, DATACLASS_TRANSFORM_NAMES
):
Expand Down Expand Up @@ -1868,6 +1872,8 @@ def analyze_class_decorator(self, defn: ClassDef, decorator: Expression) -> None
self.fail("@runtime_checkable can only be used with protocol classes", defn)
elif decorator.fullname in FINAL_DECORATOR_NAMES:
defn.info.is_final = True
elif refers_to_fullname(decorator, TYPE_CHECK_ONLY_NAMES):
defn.info.is_type_check_only = True
elif isinstance(decorator, CallExpr) and refers_to_fullname(
decorator.callee, DATACLASS_TRANSFORM_NAMES
):
Expand Down
27 changes: 27 additions & 0 deletions mypy/stubtest.py
Original file line number Diff line number Diff line change
Expand Up @@ -484,6 +484,19 @@ def _verify_metaclass(
def verify_typeinfo(
stub: nodes.TypeInfo, runtime: MaybeMissing[type[Any]], object_path: list[str]
) -> Iterator[Error]:
if stub.is_type_check_only:
# This type only exists in stubs, we only check that the runtime part
# is missing. Other checks are not required.
if not isinstance(runtime, Missing):
yield Error(
object_path,
'is marked as "@type_check_only", but also exists at runtime',
stub,
runtime,
stub_desc=repr(stub),
)
return

if isinstance(runtime, Missing):
yield Error(object_path, "is not present at runtime", stub, runtime, stub_desc=repr(stub))
return
Expand Down Expand Up @@ -1066,6 +1079,7 @@ def verify_var(
def verify_overloadedfuncdef(
stub: nodes.OverloadedFuncDef, runtime: MaybeMissing[Any], object_path: list[str]
) -> Iterator[Error]:
# TODO: support `@type_check_only` decorator
if isinstance(runtime, Missing):
yield Error(object_path, "is not present at runtime", stub, runtime)
return
Expand Down Expand Up @@ -1260,6 +1274,19 @@ def apply_decorator_to_funcitem(
def verify_decorator(
stub: nodes.Decorator, runtime: MaybeMissing[Any], object_path: list[str]
) -> Iterator[Error]:
if stub.func.is_type_check_only:
# This function only exists in stubs, we only check that the runtime part
# is missing. Other checks are not required.
if not isinstance(runtime, Missing):
yield Error(
object_path,
'is marked as "@type_check_only", but also exists at runtime',
stub,
runtime,
stub_desc=repr(stub),
)
return

if isinstance(runtime, Missing):
yield Error(object_path, "is not present at runtime", stub, runtime)
return
Expand Down
45 changes: 45 additions & 0 deletions mypy/test/teststubtest.py
Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,7 @@ class Sequence(Iterable[_T_co]): ...
class Tuple(Sequence[_T_co]): ...
class NamedTuple(tuple[Any, ...]): ...
def overload(func: _T) -> _T: ...
def type_check_only(func: _T) -> _T: ...
def deprecated(__msg: str) -> Callable[[_T], _T]: ...
def final(func: _T) -> _T: ...
"""
Expand Down Expand Up @@ -2046,6 +2047,50 @@ def some(self) -> int: ...
error=None,
)

@collect_cases
def test_type_check_only(self) -> Iterator[Case]:
yield Case(
stub="from typing import type_check_only, overload",
runtime="from typing import overload",
error=None,
)
# You can have public types that are only defined in stubs
# with `@type_check_only`:
yield Case(
stub="""
@type_check_only
class A1: ...
""",
runtime="",
error=None,
)
# Having `@type_check_only` on a type that exists at runtime is an error
yield Case(
stub="""
@type_check_only
class A2: ...
""",
runtime="class A2: ...",
error="A2",
)
# The same is true for functions:
yield Case(
stub="""
@type_check_only
def func1() -> None: ...
""",
runtime="",
error=None,
)
yield Case(
stub="""
@type_check_only
def func2() -> None: ...
""",
runtime="def func2() -> None: ...",
error="func2",
)


def remove_color_code(s: str) -> str:
return re.sub("\\x1b.*?m", "", s) # this works!
Expand Down
3 changes: 3 additions & 0 deletions mypy/types.py
Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,9 @@
# Supported @final decorator names.
FINAL_DECORATOR_NAMES: Final = ("typing.final", "typing_extensions.final")

# Supported @type_check_only names.
TYPE_CHECK_ONLY_NAMES: Final = ("typing.type_check_only", "typing_extensions.type_check_only")

# Supported Literal type names.
LITERAL_TYPE_NAMES: Final = ("typing.Literal", "typing_extensions.Literal")

Expand Down
3 changes: 3 additions & 0 deletions test-data/unit/fixtures/typing-full.pyi
Original file line number Diff line number Diff line change
Expand Up @@ -196,3 +196,6 @@ def override(__arg: T) -> T: ...

# Was added in 3.11
def reveal_type(__obj: T) -> T: ...

# Only exists in type checking time:
def type_check_only(__func_or_class: T) -> T: ...