Use Never in more messages, use ambiguous in join

Switches the logic from python#16994
to use ambiguous (since is_noreturn was only meant for error messages)

See also python#15996

Author: hauntsaninja

mypy/copytype.py

@@ -53,7 +53,7 @@ def visit_none_type(self, t: NoneType) -> ProperType:
         return self.copy_common(t, NoneType())
 
     def visit_uninhabited_type(self, t: UninhabitedType) -> ProperType:
-        dup = UninhabitedType(t.is_noreturn)
+        dup = UninhabitedType()
         dup.ambiguous = t.ambiguous
         return self.copy_common(t, dup)
 

mypy/join.py

@@ -108,9 +108,9 @@ def join_instances(self, t: Instance, s: Instance) -> ProperType:
                     # TODO: contravariant case should use meet but pass seen instances as
                     # an argument to keep track of recursive checks.
                     elif type_var.variance in (INVARIANT, CONTRAVARIANT):
-                        if isinstance(ta_proper, UninhabitedType) and not ta_proper.is_noreturn:
+                        if isinstance(ta_proper, UninhabitedType) and ta_proper.ambiguous:
                             new_type = sa
-                        elif isinstance(sa_proper, UninhabitedType) and not sa_proper.is_noreturn:
+                        elif isinstance(sa_proper, UninhabitedType) and sa_proper.ambiguous:
                             new_type = ta
                         elif not is_equivalent(ta, sa):
                             self.seen_instances.pop()

mypy/messages.py

@@ -2629,10 +2629,7 @@ def format_literal_value(typ: LiteralType) -> str:
     elif isinstance(typ, DeletedType):
         return "<deleted>"
     elif isinstance(typ, UninhabitedType):
-        if typ.is_noreturn:
-            return "NoReturn"
-        else:
-            return "Never"
+        return "Never"
     elif isinstance(typ, TypeType):
         type_name = "type" if options.use_lowercase_names() else "Type"
         return f"{type_name}[{format(typ.item)}]"

mypy/typeanal.py

@@ -645,7 +645,7 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                 return AnyType(TypeOfAny.from_error)
             return self.anal_type(t.args[0])
         elif fullname in NEVER_NAMES:
-            return UninhabitedType(is_noreturn=True)
+            return UninhabitedType()
         elif fullname in LITERAL_TYPE_NAMES:
             return self.analyze_literal_type(t)
         elif fullname in ANNOTATED_TYPE_NAMES:

mypy/types.py

@@ -1169,17 +1169,12 @@ class UninhabitedType(ProperType):
         is_subtype(UninhabitedType, T) = True
     """
 
-    __slots__ = ("ambiguous", "is_noreturn")
+    __slots__ = ("ambiguous",)
 
-    is_noreturn: bool  # Does this come from a NoReturn?  Purely for error messages.
-    # It is important to track whether this is an actual NoReturn type, or just a result
-    # of ambiguous type inference, in the latter case we don't want to mark a branch as
-    # unreachable in binder.
     ambiguous: bool  # Is this a result of inference for a variable without constraints?
 
-    def __init__(self, is_noreturn: bool = False, line: int = -1, column: int = -1) -> None:
+    def __init__(self, line: int = -1, column: int = -1) -> None:
         super().__init__(line, column)
-        self.is_noreturn = is_noreturn
         self.ambiguous = False
 
     def can_be_true_default(self) -> bool:
@@ -1198,12 +1193,12 @@ def __eq__(self, other: object) -> bool:
         return isinstance(other, UninhabitedType)
 
     def serialize(self) -> JsonDict:
-        return {".class": "UninhabitedType", "is_noreturn": self.is_noreturn}
+        return {".class": "UninhabitedType"}
 
     @classmethod
     def deserialize(cls, data: JsonDict) -> UninhabitedType:
         assert data[".class"] == "UninhabitedType"
-        return UninhabitedType(is_noreturn=data["is_noreturn"])
+        return UninhabitedType()
 
 
 class NoneType(ProperType):

test-data/unit/check-flags.test

@@ -408,7 +408,7 @@ reveal_type(f() or no_return())  # N: Revealed type is "builtins.int"
 # flags: --warn-no-return
 from mypy_extensions import NoReturn
 
-x = 0  # type: NoReturn  # E: Incompatible types in assignment (expression has type "int", variable has type "NoReturn")
+x = 0  # type: NoReturn  # E: Incompatible types in assignment (expression has type "int", variable has type Never)
 [builtins fixtures/dict.pyi]
 
 [case testNoReturnAsync]
@@ -477,7 +477,7 @@ def no_return() -> NoReturn: pass
 def f() -> NoReturn:
   no_return()
 
-x: NoReturn = 0 # E: Incompatible types in assignment (expression has type "int", variable has type "NoReturn")
+x: NoReturn = 0 # E: Incompatible types in assignment (expression has type "int", variable has type Never)
 [builtins fixtures/dict.pyi]
 
 [case testShowErrorContextFunction]

test-data/unit/check-literal.test

@@ -839,14 +839,13 @@ b: NoReturn
 c: None
 
 fa(lit)
-fb(lit)  # E: Argument 1 to "fb" has incompatible type "Literal[1]"; expected "NoReturn"
+fb(lit)  # E: Argument 1 to "fb" has incompatible type "Literal[1]"; expected Never
 fc(lit)  # E: Argument 1 to "fc" has incompatible type "Literal[1]"; expected "None"
 
 f_lit(a)
 f_lit(b)
 f_lit(c) # E: Argument 1 to "f_lit" has incompatible type "None"; expected "Literal[1]"
 [builtins fixtures/tuple.pyi]
-[out]
 
 [case testLiteralCheckSubtypingNoStrictOptional]
 # flags: --no-strict-optional
@@ -865,14 +864,13 @@ b: NoReturn
 c: None
 
 fa(lit)
-fb(lit)  # E: Argument 1 to "fb" has incompatible type "Literal[1]"; expected "NoReturn"
+fb(lit)  # E: Argument 1 to "fb" has incompatible type "Literal[1]"; expected Never
 fc(lit)  # E: Argument 1 to "fc" has incompatible type "Literal[1]"; expected "None"
 
 f_lit(a)
 f_lit(b)
 f_lit(c)
 [builtins fixtures/tuple.pyi]
-[out]
 
 [case testLiteralCallingOverloadedFunction]
 from typing import overload, Generic, TypeVar, Any

test-data/unit/check-python310.test

@@ -1406,7 +1406,7 @@ def f(value: int) -> int:  # E: Missing return statement
         case 2:
             return 1
         case o:
-            assert_never(o)  # E: Argument 1 to "assert_never" has incompatible type "int"; expected "NoReturn"
+            assert_never(o)  # E: Argument 1 to "assert_never" has incompatible type "int"; expected Never
 
 [case testMatchExhaustiveNoError]
 from typing import NoReturn, Union, Literal

test-data/unit/check-type-aliases.test

@@ -57,7 +57,7 @@ Never = NoReturn
 a: Never  # Used to be an error here
 
 def f(a: Never): ...
-f(5)  # E: Argument 1 to "f" has incompatible type "int"; expected "NoReturn"
+f(5)  # E: Argument 1 to "f" has incompatible type "int"; expected Never
 [case testImportUnionAlias]
 import typing
 from _m import U

test-data/unit/check-typeddict.test

@@ -1648,7 +1648,7 @@ a.setdefault('y', '') # E: Argument 2 to "setdefault" of "TypedDict" has incompa
 x = ''
 a.setdefault(x, 1) # E: Expected TypedDict key to be string literal
 alias = a.setdefault
-alias(x, 1) # E: Argument 1 has incompatible type "str"; expected "NoReturn"
+alias(x, 1) # E: Argument 1 has incompatible type "str"; expected Never
 
 a.update({})
 a.update({'x': 1})
@@ -1680,8 +1680,8 @@ b.pop('x') # E: Key "x" of TypedDict "B" cannot be deleted
 x = ''
 b.pop(x) # E: Expected TypedDict key to be string literal
 pop = b.pop
-pop('x') # E: Argument 1 has incompatible type "str"; expected "NoReturn"
-pop('invalid') # E: Argument 1 has incompatible type "str"; expected "NoReturn"
+pop('x') # E: Argument 1 has incompatible type "str"; expected Never
+pop('invalid') # E: Argument 1 has incompatible type "str"; expected Never
 [builtins fixtures/dict.pyi]
 
 [case testTypedDictDel]