Narrow disjoint narrows to Never

Author: A5rocks

mypy/checker.py

@@ -6704,7 +6704,7 @@ def should_coerce_inner(typ: Type) -> bool:
             if target and not is_same_type(target, expr_type):
                 # We have multiple disjoint target types. So the 'if' branch
                 # must be unreachable.
-                return None, {}
+                return {operands[j]: UninhabitedType() for j in chain_indices}, {}
             target = expr_type
             possible_target_indices.append(i)
 

test-data/unit/check-enum.test

@@ -1325,15 +1325,15 @@ reveal_type(y)      # N: Revealed type is "__main__.Foo"
 # The standard output when we end up inferring two disjoint facts about the same expr
 if x is Foo.A and x is Foo.B:
     reveal_type(x)  # E: Statement is unreachable \
-                    # N: Revealed type is "__main__.Foo"
+                    # N: Revealed type is "Never"
 else:
     reveal_type(x)  # N: Revealed type is "__main__.Foo"
 reveal_type(x)      # N: Revealed type is "__main__.Foo"
 
 # ..and we get the same result if we have two disjoint groups within the same comp expr
 if x is Foo.A < x is Foo.B:
     reveal_type(x)  # E: Statement is unreachable \
-                    # N: Revealed type is "__main__.Foo"
+                    # N: Revealed type is "Never"
 else:
     reveal_type(x)  # N: Revealed type is "__main__.Foo"
 reveal_type(x)      # N: Revealed type is "__main__.Foo"
@@ -1352,7 +1352,7 @@ class Foo(Enum):
 x: Foo
 if x is Foo.A is Foo.B:
    reveal_type(x)   # E: Statement is unreachable \
-                    # N: Revealed type is "__main__.Foo"
+                    # N: Revealed type is "Never"
 else:
    reveal_type(x)   # N: Revealed type is "__main__.Foo"
 reveal_type(x)      # N: Revealed type is "__main__.Foo"
@@ -1361,7 +1361,7 @@ literal_a: Literal[Foo.A]
 literal_b: Literal[Foo.B]
 if x is literal_a is literal_b:
    reveal_type(x)   # E: Statement is unreachable \
-                    # N: Revealed type is "__main__.Foo"
+                    # N: Revealed type is "Never"
 else:
    reveal_type(x)   # N: Revealed type is "__main__.Foo"
 reveal_type(x)      # N: Revealed type is "__main__.Foo"
@@ -1370,7 +1370,7 @@ final_a: Final = Foo.A
 final_b: Final = Foo.B
 if x is final_a is final_b:
    reveal_type(x)   # E: Statement is unreachable \
-                    # N: Revealed type is "__main__.Foo"
+                    # N: Revealed type is "Never"
 else:
    reveal_type(x)   # N: Revealed type is "__main__.Foo"
 reveal_type(x)      # N: Revealed type is "__main__.Foo"

test-data/unit/check-narrowing.test

@@ -728,7 +728,7 @@ def test2(switch: FlipFlopEnum) -> None:
 
     assert switch.state == State.B     # E: Non-overlapping equality check (left operand type: "Literal[State.A]", right operand type: "Literal[State.B]")
     reveal_type(switch.state)          # E: Statement is unreachable \
-                                       # N: Revealed type is "Literal[__main__.State.A]"
+                                       # N: Revealed type is "Never"
 
 def test3(switch: FlipFlopEnum) -> None:
     # Same thing, but using 'is' comparisons. Previously mypy's behaviour differed
@@ -741,7 +741,9 @@ def test3(switch: FlipFlopEnum) -> None:
 
     assert switch.state is State.B     # E: Non-overlapping identity check (left operand type: "Literal[State.A]", right operand type: "Literal[State.B]")
     reveal_type(switch.state)          # E: Statement is unreachable \
-                                       # N: Revealed type is "Literal[__main__.State.A]"
+                                       # N: Revealed type is "Never"
+
+
 [builtins fixtures/primitives.pyi]
 
 [case testNarrowingEqualityRequiresExplicitStrLiteral]

test-data/unit/check-unreachable-code.test

@@ -1365,7 +1365,7 @@ def test_typed_fn(obj) -> None:
 
     assert obj.prop is False
     reveal_type(obj.prop)  # E: Statement is unreachable \
-                           # N: Revealed type is "Literal[True]"
+                           # N: Revealed type is "Never"
 
 [case testUnreachableCheckedUntypedFunction]
 # flags: --warn-unreachable --check-untyped-defs
@@ -1378,7 +1378,7 @@ def test_untyped_fn(obj):
 
     assert obj.prop is False
     reveal_type(obj.prop)  # E: Statement is unreachable \
-                           # N: Revealed type is "Literal[True]"
+                           # N: Revealed type is "Never"
 
 [case testConditionalTypeVarException]
 # every part of this test case was necessary to trigger the crash