Non-ambiguous Never is fine as inference result

Author: A5rocks

mypy/checker.py

@@ -8500,7 +8500,7 @@ def is_valid_inferred_type(typ: Type, is_lvalue_final: bool = False) -> bool:
         # the context. This resolution happens in leave_partial_types when
         # we pop a partial types scope.
         return is_lvalue_final
-    elif isinstance(proper_type, UninhabitedType):
+    elif isinstance(proper_type, UninhabitedType) and proper_type.ambiguous:
         return False
     return not typ.accept(InvalidInferredTypes())
 

test-data/unit/check-incremental.test

@@ -5415,8 +5415,6 @@ reveal_type(z)
 [out]
 tmp/c.py:2: note: Revealed type is "a.<subclass of "a.A" and "a.B">"
 [out2]
-tmp/a.py:7: error: Need type annotation for "y"
-tmp/b.py:2: error: Need type annotation for "z"
 tmp/c.py:2: note: Revealed type is "Never"
 
 [case testIsInstanceAdHocIntersectionIncrementalUnreachableToIntersection]
@@ -5448,8 +5446,6 @@ from b import z
 reveal_type(z)
 [builtins fixtures/isinstance.pyi]
 [out]
-tmp/a.py:7: error: Need type annotation for "y"
-tmp/b.py:2: error: Need type annotation for "z"
 tmp/c.py:2: note: Revealed type is "Never"
 [out2]
 tmp/c.py:2: note: Revealed type is "a.<subclass of "a.A" and "a.B">"

test-data/unit/check-python38.test

@@ -697,7 +697,7 @@ def f1() -> None:
         x = 1
 
     if (x := d[x]) is None:  # E: Name "x" may be undefined
-        y = x  # E: Need type annotation for "y"
+        y = x
     z = x
 [builtins fixtures/dict.pyi]
 

test-data/unit/check-tuples.test

@@ -940,7 +940,7 @@ for x in t:
 [case testForLoopOverEmptyTuple]
 import typing
 t = ()
-for x in t: pass  # E: Need type annotation for "x"
+for x in t: pass
 [builtins fixtures/for.pyi]
 
 [case testForLoopOverNoneValuedTuple]
@@ -1604,7 +1604,6 @@ t5: Tuple[int, int] = (1, 2, "s", 4)  # E: Incompatible types in assignment (exp
 
 # long initializer assignment with mismatched pairs
 t6: Tuple[int, int, int, int, int, int, int, int, int, int, int, int] = (1, 2, 3, 4, 5, 6, 7, 8, "str", "str", "str", "str", 1, 1, 1, 1, 1) # E: Incompatible types in assignment (expression has type Tuple[int, int, ... <15 more items>], variable has type Tuple[int, int, ... <10 more items>])
-
 [builtins fixtures/tuple.pyi]
 
 [case testTupleWithStarExpr]

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

@@ -1550,12 +1550,7 @@ x = 0  # not unreachable
 [case testUnpackNever]
 x: str
 if isinstance(x, int):
-    # mypy wants a type annotation for y because it's `Never`.
-    # This doesn't make much sense in this case, but it's a
-    # requirement for composable behavior.
-    # (and `ys` should also get flagged.)
-
-    y, *ys = x  # E: Need type annotation for "y"
+    y, *ys = x
     reveal_type(y)  # N: Revealed type is "Never"
     reveal_type(ys)  # N: Revealed type is "builtins.list[Never]"
 [builtins fixtures/isinstancelist.pyi]

test-data/unit/fine-grained.test

@@ -9693,8 +9693,6 @@ reveal_type(z)
 c.py:2: note: Revealed type is "a.<subclass of "a.A" and "a.B">"
 ==
 c.py:2: note: Revealed type is "Never"
-a.py:7: error: Need type annotation for "y"
-b.py:2: error: Need type annotation for "z"
 
 [case testIsInstanceAdHocIntersectionFineGrainedIncrementalUnreachableToIntersection]
 import c
@@ -9725,8 +9723,6 @@ from b import z
 reveal_type(z)
 [builtins fixtures/isinstance.pyi]
 [out]
-a.py:7: error: Need type annotation for "y"
-b.py:2: error: Need type annotation for "z"
 c.py:2: note: Revealed type is "Never"
 ==
 c.py:2: note: Revealed type is "a.<subclass of "a.A" and "a.B">"