Fix crash involving unreachable binary ops (#11680)

Fixes #11679

mypy/checker.py

@@ -4375,7 +4375,8 @@ def find_isinstance_check(self, node: Expression
         If either of the values in the tuple is None, then that particular
         branch can never occur.
 
-        Guaranteed to not return None, None. (But may return {}, {})
+        May return {}, {}.
+        Can return None, None in situations involving NoReturn.
         """
         if_map, else_map = self.find_isinstance_check_helper(node)
         new_if_map = self.propagate_up_typemap_info(self.type_map, if_map)

mypy/checkexpr.py

@@ -2862,13 +2862,16 @@ def check_boolean_op(self, e: OpExpr, context: Context) -> Type:
         with (self.msg.disable_errors() if right_map is None else nullcontext()):
             right_type = self.analyze_cond_branch(right_map, e.right, expanded_left_type)
 
+        if left_map is None and right_map is None:
+            return UninhabitedType()
+
         if right_map is None:
             # The boolean expression is statically known to be the left value
-            assert left_map is not None  # find_isinstance_check guarantees this
+            assert left_map is not None
             return left_type
         if left_map is None:
             # The boolean expression is statically known to be the right value
-            assert right_map is not None  # find_isinstance_check guarantees this
+            assert right_map is not None
             return right_type
 
         if e.op == 'and':

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

@@ -1416,3 +1416,15 @@ x = 1  # E: Statement is unreachable
 raise Exception
 x = 1  # E: Statement is unreachable
 [builtins fixtures/exception.pyi]
+
+[case testUnreachableNoReturnBinaryOps]
+# flags: --warn-unreachable
+from typing import NoReturn
+
+a: NoReturn
+a and 1  # E: Right operand of "and" is never evaluated
+a or 1  # E: Right operand of "or" is never evaluated
+a or a  # E: Right operand of "or" is never evaluated
+1 and a and 1  # E: Right operand of "and" is never evaluated
+a and a  # E: Right operand of "and" is never evaluated
+[builtins fixtures/exception.pyi]