Ignore promotions when simplifying unions (#13781)

Fixes #13760 
Fixes #6060
Fixes #12824

This is a right thing to do, but let's what `mypy_primer` will be. This
also required re-applying #6181 (which is also a right thing to do)
otherwise some tests fail.

Author: ilevkivskyi

mypy/checker.py

@@ -6550,11 +6550,11 @@ def conditional_types(
             return proposed_type, default
         elif not any(
             type_range.is_upper_bound for type_range in proposed_type_ranges
-        ) and is_proper_subtype(current_type, proposed_type):
+        ) and is_proper_subtype(current_type, proposed_type, ignore_promotions=True):
             # Expression is always of one of the types in proposed_type_ranges
             return default, UninhabitedType()
         elif not is_overlapping_types(
-            current_type, proposed_type, prohibit_none_typevar_overlap=True
+            current_type, proposed_type, prohibit_none_typevar_overlap=True, ignore_promotions=True
         ):
             # Expression is never of any type in proposed_type_ranges
             return UninhabitedType(), default

mypy/meet.py

@@ -121,7 +121,11 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
         return original_declared
     if isinstance(declared, UnionType):
         return make_simplified_union(
-            [narrow_declared_type(x, narrowed) for x in declared.relevant_items()]
+            [
+                narrow_declared_type(x, narrowed)
+                for x in declared.relevant_items()
+                if is_overlapping_types(x, narrowed, ignore_promotions=True)
+            ]
         )
     if is_enum_overlapping_union(declared, narrowed):
         return original_narrowed

mypy/subtypes.py

@@ -1677,48 +1677,45 @@ def try_restrict_literal_union(t: UnionType, s: Type) -> list[Type] | None:
     return new_items
 
 
-def restrict_subtype_away(t: Type, s: Type, *, ignore_promotions: bool = False) -> Type:
+def restrict_subtype_away(t: Type, s: Type) -> Type:
     """Return t minus s for runtime type assertions.
 
     If we can't determine a precise result, return a supertype of the
     ideal result (just t is a valid result).
 
     This is used for type inference of runtime type checks such as
-    isinstance(). Currently this just removes elements of a union type.
+    isinstance(). Currently, this just removes elements of a union type.
     """
     p_t = get_proper_type(t)
     if isinstance(p_t, UnionType):
         new_items = try_restrict_literal_union(p_t, s)
         if new_items is None:
             new_items = [
-                restrict_subtype_away(item, s, ignore_promotions=ignore_promotions)
+                restrict_subtype_away(item, s)
                 for item in p_t.relevant_items()
-                if (
-                    isinstance(get_proper_type(item), AnyType)
-                    or not covers_at_runtime(item, s, ignore_promotions)
-                )
+                if (isinstance(get_proper_type(item), AnyType) or not covers_at_runtime(item, s))
             ]
         return UnionType.make_union(new_items)
-    elif covers_at_runtime(t, s, ignore_promotions):
+    elif covers_at_runtime(t, s):
         return UninhabitedType()
     else:
         return t
 
 
-def covers_at_runtime(item: Type, supertype: Type, ignore_promotions: bool) -> bool:
+def covers_at_runtime(item: Type, supertype: Type) -> bool:
     """Will isinstance(item, supertype) always return True at runtime?"""
     item = get_proper_type(item)
     supertype = get_proper_type(supertype)
 
     # Since runtime type checks will ignore type arguments, erase the types.
     supertype = erase_type(supertype)
     if is_proper_subtype(
-        erase_type(item), supertype, ignore_promotions=ignore_promotions, erase_instances=True
+        erase_type(item), supertype, ignore_promotions=True, erase_instances=True
     ):
         return True
     if isinstance(supertype, Instance) and supertype.type.is_protocol:
         # TODO: Implement more robust support for runtime isinstance() checks, see issue #3827.
-        if is_proper_subtype(item, supertype, ignore_promotions=ignore_promotions):
+        if is_proper_subtype(item, supertype, ignore_promotions=True):
             return True
     if isinstance(item, TypedDictType) and isinstance(supertype, Instance):
         # Special case useful for selecting TypedDicts from unions using isinstance(x, dict).

mypy/typeops.py

@@ -531,7 +531,7 @@ def _remove_redundant_union_items(items: list[Type], keep_erased: bool) -> list[
                 continue
             # actual redundancy checks (XXX?)
             if is_redundant_literal_instance(proper_item, proper_tj) and is_proper_subtype(
-                tj, item, keep_erased_types=keep_erased
+                tj, item, keep_erased_types=keep_erased, ignore_promotions=True
             ):
                 # We found a redundant item in the union.
                 removed.add(j)

test-data/unit/check-classes.test

@@ -2394,9 +2394,9 @@ a: Union[int, float]
 b: int
 c: float
 
-reveal_type(a + a)  # N: Revealed type is "builtins.float"
-reveal_type(a + b)  # N: Revealed type is "builtins.float"
-reveal_type(b + a)  # N: Revealed type is "builtins.float"
+reveal_type(a + a)  # N: Revealed type is "Union[builtins.int, builtins.float]"
+reveal_type(a + b)  # N: Revealed type is "Union[builtins.int, builtins.float]"
+reveal_type(b + a)  # N: Revealed type is "Union[builtins.int, builtins.float]"
 reveal_type(a + c)  # N: Revealed type is "builtins.float"
 reveal_type(c + a)  # N: Revealed type is "builtins.float"
 [builtins fixtures/ops.pyi]
@@ -2535,8 +2535,8 @@ def sum(x: Iterable[T]) -> Union[T, int]: ...
 def len(x: Iterable[T]) -> int: ...
 
 x = [1.1, 2.2, 3.3]
-reveal_type(sum(x))  # N: Revealed type is "builtins.float"
-reveal_type(sum(x) / len(x))  # N: Revealed type is "builtins.float"
+reveal_type(sum(x))  # N: Revealed type is "Union[builtins.float, builtins.int]"
+reveal_type(sum(x) / len(x))  # N: Revealed type is "Union[builtins.float, builtins.int]"
 [builtins fixtures/floatdict.pyi]
 
 [case testOperatorWithEmptyListAndSum]

test-data/unit/check-expressions.test

@@ -974,6 +974,18 @@ def f():
 main:6: error: Expression is of type "int", not "Literal[42]"
 [builtins fixtures/tuple.pyi]
 
+[case testAssertTypeNoPromoteUnion]
+from typing import Union, assert_type
+
+Scalar = Union[int, bool, bytes, bytearray]
+
+
+def reduce_it(s: Scalar) -> Scalar:
+    return s
+
+assert_type(reduce_it(True), Scalar)
+[builtins fixtures/tuple.pyi]
+
 -- None return type
 -- ----------------
 

test-data/unit/check-isinstance.test

@@ -1321,8 +1321,7 @@ def f(x: Union[A, B]) -> None:
         f(x)
 [builtins fixtures/isinstance.pyi]
 
-[case testIsinstanceWithOverlappingPromotionTypes-skip]
-# Currently disabled: see https://github.com/python/mypy/issues/6060 for context
+[case testIsinstanceWithOverlappingPromotionTypes]
 from typing import Union
 
 class FloatLike: pass

test-data/unit/check-unions.test

@@ -355,12 +355,12 @@ def foo(a: Union[A, B, C]):
 from typing import TypeVar, Union
 T = TypeVar('T')
 S = TypeVar('S')
-def u(x: T, y: S) -> Union[S, T]: pass
+def u(x: T, y: S) -> Union[T, S]: pass
 
-reveal_type(u(1, 2.3))  # N: Revealed type is "builtins.float"
-reveal_type(u(2.3, 1))  # N: Revealed type is "builtins.float"
-reveal_type(u(False, 2.2)) # N: Revealed type is "builtins.float"
-reveal_type(u(2.2, False)) # N: Revealed type is "builtins.float"
+reveal_type(u(1, 2.3))  # N: Revealed type is "Union[builtins.int, builtins.float]"
+reveal_type(u(2.3, 1))  # N: Revealed type is "Union[builtins.float, builtins.int]"
+reveal_type(u(False, 2.2)) # N: Revealed type is "Union[builtins.bool, builtins.float]"
+reveal_type(u(2.2, False)) # N: Revealed type is "Union[builtins.float, builtins.bool]"
 [builtins fixtures/primitives.pyi]
 
 [case testSimplifyingUnionWithTypeTypes1]
@@ -491,15 +491,15 @@ class E:
 [case testUnionSimplificationWithBoolIntAndFloat]
 from typing import List, Union
 l = reveal_type([]) # type: List[Union[bool, int, float]] \
-    # N: Revealed type is "builtins.list[builtins.float]"
+    # N: Revealed type is "builtins.list[Union[builtins.int, builtins.float]]"
 reveal_type(l) \
     # N: Revealed type is "builtins.list[Union[builtins.bool, builtins.int, builtins.float]]"
 [builtins fixtures/list.pyi]
 
 [case testUnionSimplificationWithBoolIntAndFloat2]
 from typing import List, Union
 l = reveal_type([]) # type: List[Union[bool, int, float, str]] \
-    # N: Revealed type is "builtins.list[Union[builtins.float, builtins.str]]"
+    # N: Revealed type is "builtins.list[Union[builtins.int, builtins.float, builtins.str]]"
 reveal_type(l) \
     # N: Revealed type is "builtins.list[Union[builtins.bool, builtins.int, builtins.float, builtins.str]]"
 [builtins fixtures/list.pyi]
@@ -545,7 +545,7 @@ from typing import Union, Tuple, Any
 
 a: Union[Tuple[int], Tuple[float]]
 (a1,) = a
-reveal_type(a1)  # N: Revealed type is "builtins.float"
+reveal_type(a1)  # N: Revealed type is "Union[builtins.int, builtins.float]"
 
 b: Union[Tuple[int], Tuple[str]]
 (b1,) = b
@@ -558,7 +558,7 @@ from typing import Union, Tuple
 c: Union[Tuple[int, int], Tuple[int, float]]
 (c1, c2) = c
 reveal_type(c1)  # N: Revealed type is "builtins.int"
-reveal_type(c2)  # N: Revealed type is "builtins.float"
+reveal_type(c2)  # N: Revealed type is "Union[builtins.int, builtins.float]"
 [builtins fixtures/tuple.pyi]
 
 [case testUnionMultiassignGeneric]
@@ -625,7 +625,7 @@ b: Union[Tuple[float, int], Tuple[int, int]]
 b1: object
 b2: int
 (b1, b2) = b
-reveal_type(b1) # N: Revealed type is "builtins.float"
+reveal_type(b1) # N: Revealed type is "Union[builtins.float, builtins.int]"
 reveal_type(b2) # N: Revealed type is "builtins.int"
 
 c: Union[Tuple[int, int], Tuple[int, int]]
@@ -639,7 +639,7 @@ d: Union[Tuple[int, int], Tuple[int, float]]
 d1: object
 (d1, d2) = d
 reveal_type(d1)  # N: Revealed type is "builtins.int"
-reveal_type(d2)  # N: Revealed type is "builtins.float"
+reveal_type(d2)  # N: Revealed type is "Union[builtins.int, builtins.float]"
 [builtins fixtures/tuple.pyi]
 
 [case testUnionMultiassignIndexed]

test-data/unit/fixtures/tuple.pyi

@@ -35,6 +35,7 @@ class slice: pass
 class bool(int): pass
 class str: pass # For convenience
 class bytes: pass
+class bytearray: pass
 class unicode: pass
 
 class list(Sequence[T], Generic[T]):