Represent bottom type as Never in messages (#15996)

Fixes #15950

Author: hauntsaninja

mypy/checker.py

@@ -3934,7 +3934,7 @@ def is_valid_defaultdict_partial_value_type(self, t: ProperType) -> bool:
         Examples:
 
           * t is 'int' --> True
-          * t is 'list[<nothing>]' --> True
+          * t is 'list[Never]' --> True
           * t is 'dict[...]' --> False (only generic types with a single type
             argument supported)
         """
@@ -3980,7 +3980,7 @@ def set_inference_error_fallback_type(self, var: Var, lvalue: Lvalue, type: Type
           x = []  # type: ignore
           x.append(1)   # Should be ok!
 
-        We implement this here by giving x a valid type (replacing inferred <nothing> with Any).
+        We implement this here by giving x a valid type (replacing inferred Never with Any).
         """
         fallback = self.inference_error_fallback_type(type)
         self.set_inferred_type(var, lvalue, fallback)
@@ -7403,7 +7403,7 @@ def is_valid_inferred_type(typ: Type, is_lvalue_final: bool = False) -> bool:
 class InvalidInferredTypes(BoolTypeQuery):
     """Find type components that are not valid for an inferred type.
 
-    These include <Erased> type, and any <nothing> types resulting from failed
+    These include <Erased> type, and any uninhabited types resulting from failed
     (ambiguous) type inference.
     """
 
@@ -7424,15 +7424,15 @@ def visit_type_var(self, t: TypeVarType) -> bool:
 
 
 class SetNothingToAny(TypeTranslator):
-    """Replace all ambiguous <nothing> types with Any (to avoid spurious extra errors)."""
+    """Replace all ambiguous Uninhabited types with Any (to avoid spurious extra errors)."""
 
     def visit_uninhabited_type(self, t: UninhabitedType) -> Type:
         if t.ambiguous:
             return AnyType(TypeOfAny.from_error)
         return t
 
     def visit_type_alias_type(self, t: TypeAliasType) -> Type:
-        # Target of the alias cannot be an ambiguous <nothing>, so we just
+        # Target of the alias cannot be an ambiguous UninhabitedType, so we just
         # replace the arguments.
         return t.copy_modified(args=[a.accept(self) for a in t.args])
 
@@ -7774,7 +7774,7 @@ def is_subtype_no_promote(left: Type, right: Type) -> bool:
 
 
 def is_overlapping_types_no_promote_no_uninhabited_no_none(left: Type, right: Type) -> bool:
-    # For the purpose of unsafe overload checks we consider list[<nothing>] and list[int]
+    # For the purpose of unsafe overload checks we consider list[Never] and list[int]
     # non-overlapping. This is consistent with how we treat list[int] and list[str] as
     # non-overlapping, despite [] belongs to both. Also this will prevent false positives
     # for failed type inference during unification.

mypy/checkexpr.py

@@ -2080,7 +2080,7 @@ def infer_function_type_arguments(
                 ):
                     freeze_all_type_vars(applied)
                     return applied
-                # If it didn't work, erase free variables as <nothing>, to avoid confusing errors.
+                # If it didn't work, erase free variables as uninhabited, to avoid confusing errors.
                 unknown = UninhabitedType()
                 unknown.ambiguous = True
                 inferred_args = [
@@ -2444,7 +2444,7 @@ def check_argument_types(
                         callee_arg_types = [orig_callee_arg_type]
                         callee_arg_kinds = [ARG_STAR]
                     else:
-                        # TODO: Any and <nothing> can appear in Unpack (as a result of user error),
+                        # TODO: Any and Never can appear in Unpack (as a result of user error),
                         # fail gracefully here and elsewhere (and/or normalize them away).
                         assert isinstance(unpacked_type, Instance)
                         assert unpacked_type.type.fullname == "builtins.tuple"

mypy/expandtype.py

@@ -285,7 +285,7 @@ def expand_unpack(self, t: UnpackType) -> list[Type]:
         ):
             return [UnpackType(typ=repl)]
         elif isinstance(repl, (AnyType, UninhabitedType)):
-            # Replace *Ts = Any with *Ts = *tuple[Any, ...] and some for <nothing>.
+            # Replace *Ts = Any with *Ts = *tuple[Any, ...] and some for Never.
             # These types may appear here as a result of user error or failed inference.
             return [UnpackType(t.type.tuple_fallback.copy_modified(args=[repl]))]
         else:

mypy/meet.py

@@ -968,11 +968,11 @@ def typed_dict_mapping_overlap(
 
     As usual empty, dictionaries lie in a gray area. In general, List[str] and List[str]
     are considered non-overlapping despite empty list belongs to both. However, List[int]
-    and List[<nothing>] are considered overlapping.
+    and List[Never] are considered overlapping.
 
     So here we follow the same logic: a TypedDict with no required keys is considered
     non-overlapping with Mapping[str, <some type>], but is considered overlapping with
-    Mapping[<nothing>, <nothing>]. This way we avoid false positives for overloads, and also
+    Mapping[Never, Never]. This way we avoid false positives for overloads, and also
     avoid false positives for comparisons like SomeTypedDict == {} under --strict-equality.
     """
     left, right = get_proper_types((left, right))

mypy/messages.py

@@ -2068,7 +2068,7 @@ def report_protocol_problems(
         if supertype.type.fullname in exclusions.get(type(subtype), []):
             return
         if any(isinstance(tp, UninhabitedType) for tp in get_proper_types(supertype.args)):
-            # We don't want to add notes for failed inference (e.g. Iterable[<nothing>]).
+            # We don't want to add notes for failed inference (e.g. Iterable[Never]).
             # This will be only confusing a user even more.
             return
 
@@ -2395,7 +2395,7 @@ def quote_type_string(type_string: str) -> str:
     """Quotes a type representation for use in messages."""
     no_quote_regex = r"^<(tuple|union): \d+ items>$"
     if (
-        type_string in ["Module", "overloaded function", "<nothing>", "<deleted>"]
+        type_string in ["Module", "overloaded function", "Never", "<deleted>"]
         or type_string.startswith("Module ")
         or re.match(no_quote_regex, type_string) is not None
         or type_string.endswith("?")
@@ -2597,7 +2597,7 @@ def format_literal_value(typ: LiteralType) -> str:
         if typ.is_noreturn:
             return "NoReturn"
         else:
-            return "<nothing>"
+            return "Never"
     elif isinstance(typ, TypeType):
         type_name = "type" if options.use_lowercase_names() else "Type"
         return f"{type_name}[{format(typ.item)}]"

mypy/solve.py

@@ -300,8 +300,8 @@ def test(x: U) -> U: ...
     common_upper_bound_p = get_proper_type(common_upper_bound)
     # We include None for when strict-optional is disabled.
     if isinstance(common_upper_bound_p, (UninhabitedType, NoneType)):
-        # This will cause to infer <nothing>, which is better than a free TypeVar
-        # that has an upper bound <nothing>.
+        # This will cause to infer Never, which is better than a free TypeVar
+        # that has an upper bound Never.
         return None
 
     values: list[Type] = []

mypy/typeops.py

@@ -330,7 +330,7 @@ class B(A): pass
             )
 
         # Update the method signature with the solutions found.
-        # Technically, some constraints might be unsolvable, make them <nothing>.
+        # Technically, some constraints might be unsolvable, make them Never.
         to_apply = [t if t is not None else UninhabitedType() for t in typeargs]
         func = expand_type(func, {tv.id: arg for tv, arg in zip(self_vars, to_apply)})
         variables = [v for v in func.variables if v not in self_vars]

mypy/types.py

@@ -3103,7 +3103,7 @@ def visit_none_type(self, t: NoneType) -> str:
         return "None"
 
     def visit_uninhabited_type(self, t: UninhabitedType) -> str:
-        return "<nothing>"
+        return "Never"
 
     def visit_erased_type(self, t: ErasedType) -> str:
         return "<Erased>"

test-data/unit/check-classes.test

@@ -7718,13 +7718,13 @@ class D:
     def __init__(self) -> NoReturn: ...
 
 if object():
-    reveal_type(A())  # N: Revealed type is "<nothing>"
+    reveal_type(A())  # N: Revealed type is "Never"
 if object():
-    reveal_type(B())  # N: Revealed type is "<nothing>"
+    reveal_type(B())  # N: Revealed type is "Never"
 if object():
-    reveal_type(C())  # N: Revealed type is "<nothing>"
+    reveal_type(C())  # N: Revealed type is "Never"
 if object():
-    reveal_type(D())  # N: Revealed type is "<nothing>"
+    reveal_type(D())  # N: Revealed type is "Never"
 
 [case testOverloadedNewAndInitNoReturn]
 from typing import NoReturn, overload
@@ -7764,19 +7764,19 @@ class D:
     def __init__(self, a: int = ...) -> None: ...
 
 if object():
-    reveal_type(A())  # N: Revealed type is "<nothing>"
+    reveal_type(A())  # N: Revealed type is "Never"
 reveal_type(A(1))  # N: Revealed type is "__main__.A"
 
 if object():
-    reveal_type(B())  # N: Revealed type is "<nothing>"
+    reveal_type(B())  # N: Revealed type is "Never"
 reveal_type(B(1))  # N: Revealed type is "__main__.B"
 
 if object():
-    reveal_type(C())  # N: Revealed type is "<nothing>"
+    reveal_type(C())  # N: Revealed type is "Never"
 reveal_type(C(1))  # N: Revealed type is "__main__.C"
 
 if object():
-    reveal_type(D())  # N: Revealed type is "<nothing>"
+    reveal_type(D())  # N: Revealed type is "Never"
 reveal_type(D(1))  # N: Revealed type is "__main__.D"
 
 [case testClassScopeImportWithWrapperAndError]

test-data/unit/check-dataclass-transform.test

@@ -506,7 +506,7 @@ class FunctionModel:
         integer_: tuple
 
 FunctionModel(string_="abc", integer_=1)
-FunctionModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "FunctionModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+FunctionModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "FunctionModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]
@@ -529,7 +529,7 @@ class FunctionModel:
         integer_: int
 
 FunctionModel(string_="abc", integer_=1)
-FunctionModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "FunctionModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+FunctionModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "FunctionModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]
@@ -552,7 +552,7 @@ class BaseClassModel(ModelBase):
         integer_: tuple
 
 BaseClassModel(string_="abc", integer_=1)
-BaseClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "BaseClassModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+BaseClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "BaseClassModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]
@@ -574,7 +574,7 @@ class BaseClassModel(ModelBase):
         integer_: int
 
 BaseClassModel(string_="abc", integer_=1)
-BaseClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "BaseClassModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+BaseClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "BaseClassModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]
@@ -599,7 +599,7 @@ class MetaClassModel(ModelBaseWithMeta):
         integer_: tuple
 
 MetaClassModel(string_="abc", integer_=1)
-MetaClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "MetaClassModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+MetaClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "MetaClassModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]
@@ -624,7 +624,7 @@ class MetaClassModel(ModelBaseWithMeta):
         integer_: int
 
 MetaClassModel(string_="abc", integer_=1)
-MetaClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "MetaClassModel" has incompatible type "Tuple[<nothing>, ...]"; expected "int"
+MetaClassModel(string_="abc", integer_=tuple())  # E: Argument "integer_" to "MetaClassModel" has incompatible type "Tuple[Never, ...]"; expected "int"
 
 [typing fixtures/typing-full.pyi]
 [builtins fixtures/dataclasses.pyi]

test-data/unit/check-dataclasses.test

@@ -2134,8 +2134,8 @@ T = TypeVar('T')
 class A(Generic[T]):
     x: T  # exercises meet(T=int, int) = int
     y: bool  # exercises meet(bool, int) = bool
-    z: str  # exercises meet(str, bytes) = <nothing>
-    w: dict  # exercises meet(dict, <nothing>) = <nothing>
+    z: str  # exercises meet(str, bytes) = Never
+    w: dict  # exercises meet(dict, Never) = Never
     init_var: InitVar[int]  # exercises (non-optional, optional) = non-optional
 
 @dataclass
@@ -2149,8 +2149,8 @@ class B:
 a_or_b: Union[A[int], B]
 _ = replace(a_or_b, x=42, y=True, init_var=42)
 _ = replace(a_or_b, x=42, y=True)  # E: Missing named argument "init_var" for "replace" of "Union[A[int], B]"
-_ = replace(a_or_b, x=42, y=True, z='42', init_var=42)  # E: Argument "z" to "replace" of "Union[A[int], B]" has incompatible type "str"; expected <nothing>
-_ = replace(a_or_b, x=42, y=True, w={}, init_var=42)  # E: Argument "w" to "replace" of "Union[A[int], B]" has incompatible type "Dict[<nothing>, <nothing>]"; expected <nothing>
+_ = replace(a_or_b, x=42, y=True, z='42', init_var=42)  # E: Argument "z" to "replace" of "Union[A[int], B]" has incompatible type "str"; expected Never
+_ = replace(a_or_b, x=42, y=True, w={}, init_var=42)  # E: Argument "w" to "replace" of "Union[A[int], B]" has incompatible type "Dict[Never, Never]"; expected Never
 _ = replace(a_or_b, y=42, init_var=42)  # E: Argument "y" to "replace" of "Union[A[int], B]" has incompatible type "int"; expected "bool"
 
 [builtins fixtures/tuple.pyi]

test-data/unit/check-generic-subtyping.test

@@ -434,7 +434,7 @@ B(1)
 C(1)
 C('a')  # E: Argument 1 to "C" has incompatible type "str"; expected "int"
 D(A(1))
-D(1)  # E: Argument 1 to "D" has incompatible type "int"; expected "A[<nothing>]"
+D(1)  # E: Argument 1 to "D" has incompatible type "int"; expected "A[Never]"
 
 
 [case testInheritedConstructor2]

test-data/unit/check-generics.test

@@ -573,7 +573,7 @@ def func(x: IntNode[T]) -> IntNode[T]:
     return x
 reveal_type(func) # N: Revealed type is "def [T] (x: __main__.Node[builtins.int, T`-1]) -> __main__.Node[builtins.int, T`-1]"
 
-func(1) # E: Argument 1 to "func" has incompatible type "int"; expected "Node[int, <nothing>]"
+func(1) # E: Argument 1 to "func" has incompatible type "int"; expected "Node[int, Never]"
 func(Node('x', 1)) # E: Argument 1 to "Node" has incompatible type "str"; expected "int"
 reveal_type(func(Node(1, 'x'))) # N: Revealed type is "__main__.Node[builtins.int, builtins.str]"
 
@@ -834,7 +834,7 @@ reveal_type(x) # N: Revealed type is "builtins.int"
 def f2(x: IntTP[T]) -> IntTP[T]:
     return x
 
-f2((1, 2, 3)) # E: Argument 1 to "f2" has incompatible type "Tuple[int, int, int]"; expected "Tuple[int, <nothing>]"
+f2((1, 2, 3)) # E: Argument 1 to "f2" has incompatible type "Tuple[int, int, int]"; expected "Tuple[int, Never]"
 reveal_type(f2((1, 'x'))) # N: Revealed type is "Tuple[builtins.int, builtins.str]"
 
 [builtins fixtures/for.pyi]
@@ -904,7 +904,7 @@ n.y = 'x' # E: Incompatible types in assignment (expression has type "str", vari
 def f(x: Node[T, T]) -> TupledNode[T]:
     return Node(x.x, (x.x, x.x))
 
-f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "Node[<nothing>, <nothing>]"
+f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "Node[Never, Never]"
 f(Node(1, 'x')) # E: Cannot infer type argument 1 of "f"
 reveal_type(Node('x', 'x')) # N: Revealed type is "a.Node[builtins.str, builtins.str]"
 
@@ -2279,7 +2279,7 @@ class Box(Generic[T]):
 
 class IteratorBox(Box[Iterator[T]]): ...
 
-@IteratorBox.wrap  # E: Argument 1 to "wrap" of "Box" has incompatible type "Callable[[], int]"; expected "Callable[[], Iterator[<nothing>]]"
+@IteratorBox.wrap  # E: Argument 1 to "wrap" of "Box" has incompatible type "Callable[[], int]"; expected "Callable[[], Iterator[Never]]"
 def g() -> int:
     ...
 [builtins fixtures/classmethod.pyi]
@@ -3034,8 +3034,8 @@ def id2(x: V) -> V:
 reveal_type(dec1(id1))  # N: Revealed type is "def [S <: __main__.B] (S`1) -> builtins.list[S`1]"
 reveal_type(dec1(id2))  # N: Revealed type is "def [S in (builtins.int, builtins.str)] (S`3) -> builtins.list[S`3]"
 reveal_type(dec2(id1))  # N: Revealed type is "def [UC <: __main__.C] (UC`5) -> builtins.list[UC`5]"
-reveal_type(dec2(id2))  # N: Revealed type is "def (<nothing>) -> builtins.list[<nothing>]" \
-                        # E: Argument 1 to "dec2" has incompatible type "Callable[[V], V]"; expected "Callable[[<nothing>], <nothing>]"
+reveal_type(dec2(id2))  # N: Revealed type is "def (Never) -> builtins.list[Never]" \
+                        # E: Argument 1 to "dec2" has incompatible type "Callable[[V], V]"; expected "Callable[[Never], Never]"
 
 [case testInferenceAgainstGenericLambdas]
 # flags: --new-type-inference

test-data/unit/check-inference-context.test

@@ -22,7 +22,7 @@ if int():
 if int():
     ab = f()
 if int():
-    b = f() # E: Incompatible types in assignment (expression has type "A[<nothing>]", variable has type "B")
+    b = f() # E: Incompatible types in assignment (expression has type "A[Never]", variable has type "B")
 [case testBasicContextInferenceForConstructor]
 from typing import TypeVar, Generic
 T = TypeVar('T')
@@ -37,7 +37,7 @@ if int():
 if int():
     ab = A()
 if int():
-    b = A() # E: Incompatible types in assignment (expression has type "A[<nothing>]", variable has type "B")
+    b = A() # E: Incompatible types in assignment (expression has type "A[Never]", variable has type "B")
 [case testIncompatibleContextInference]
 from typing import TypeVar, Generic
 T = TypeVar('T')
@@ -372,7 +372,7 @@ ao: List[object]
 a: A
 def f(): a, aa, ao # Prevent redefinition
 
-a = [] # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "A")
+a = [] # E: Incompatible types in assignment (expression has type "List[Never]", variable has type "A")
 
 aa = []
 ao = []
@@ -842,7 +842,7 @@ T = TypeVar('T')
 def f(x: Union[List[T], str]) -> None: pass
 f([1])
 f('')
-f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "Union[List[<nothing>], str]"
+f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "Union[List[Never], str]"
 [builtins fixtures/isinstancelist.pyi]
 
 [case testIgnoringInferenceContext]
@@ -911,7 +911,7 @@ from typing import TypeVar, Callable, Generic
 T = TypeVar('T')
 class A(Generic[T]):
     pass
-reveal_type(A()) # N: Revealed type is "__main__.A[<nothing>]"
+reveal_type(A()) # N: Revealed type is "__main__.A[Never]"
 b = reveal_type(A())  # type: A[int] # N: Revealed type is "__main__.A[builtins.int]"
 
 [case testUnionWithGenericTypeItemContext]
@@ -1311,7 +1311,7 @@ from typing import List, TypeVar
 T = TypeVar('T', bound=int)
 def f(x: List[T]) -> T: ...
 
-# mypy infers List[<nothing>] here, and <nothing> is a subtype of str
+# mypy infers List[Never] here, and Never is a subtype of str
 y: str = f([])
 [builtins fixtures/list.pyi]
 
@@ -1323,7 +1323,7 @@ def f(x: List[T]) -> List[T]: ...
 
 # TODO: improve error message for such cases, see #3283 and #5706
 y: List[str] = f([]) \
- # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "List[str]") \
+ # E: Incompatible types in assignment (expression has type "List[Never]", variable has type "List[str]") \
  # N: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance \
  # N: Consider using "Sequence" instead, which is covariant
 [builtins fixtures/list.pyi]
@@ -1343,7 +1343,7 @@ T = TypeVar('T', bound=int)
 def f(x: Optional[T] = None) -> List[T]: ...
 
 y: List[str] = f()  \
-      # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "List[str]") \
+      # E: Incompatible types in assignment (expression has type "List[Never]", variable has type "List[str]") \
       # N: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance \
       # N: Consider using "Sequence" instead, which is covariant
 [builtins fixtures/list.pyi]