Fix narrowing information not propagated in assignment and boolean ex…

…pressions (#11207)

Fixes #8925.

Consider the following narrowing (more realistically with TypedDicts),
and the current outcome:

```py
class A:
    tag: Literal["A"]

class B:
    tag: Literal["B"]

abo: A | B | None
if abo is not None and abo.tag == "A":
    reveal_type(abo.tag)  # Type is Literal["A"]
    reveal_type(abo)  # Type is A | B
```

The RHS of the comparison correctly takes into account the LHS, and the
`abo.tag` expression is correctly narrowed based on it, but this does
not propagate upward to then narrow `abo` to `A`.

The problem is that `and`/`or/`not`/assignment expressions recurse using
the `find_isinstance_check_helper` function, which omits the
`propagate_up_typemap_info` calls that its parent function
`find_isinstance_check` performs.

Fix this by replacing these recursive `find_isinstance_check_helper`
calls with `find_isinstance_check`. This might not always be necessary,
but I do not think that always propagating upwards should do any harm,
anyways.

mypy/checker.py

@@ -4473,14 +4473,14 @@ def has_no_custom_eq_checks(t: Type) -> bool:
             if_map = {}
             else_map = {}
 
-            if_assignment_map, else_assignment_map = self.find_isinstance_check_helper(node.target)
+            if_assignment_map, else_assignment_map = self.find_isinstance_check(node.target)
 
             if if_assignment_map is not None:
                 if_map.update(if_assignment_map)
             if else_assignment_map is not None:
                 else_map.update(else_assignment_map)
 
-            if_condition_map, else_condition_map = self.find_isinstance_check_helper(node.value)
+            if_condition_map, else_condition_map = self.find_isinstance_check(node.value)
 
             if if_condition_map is not None:
                 if_map.update(if_condition_map)
@@ -4492,23 +4492,23 @@ def has_no_custom_eq_checks(t: Type) -> bool:
                 (None if else_assignment_map is None or else_condition_map is None else else_map),
             )
         elif isinstance(node, OpExpr) and node.op == 'and':
-            left_if_vars, left_else_vars = self.find_isinstance_check_helper(node.left)
-            right_if_vars, right_else_vars = self.find_isinstance_check_helper(node.right)
+            left_if_vars, left_else_vars = self.find_isinstance_check(node.left)
+            right_if_vars, right_else_vars = self.find_isinstance_check(node.right)
 
             # (e1 and e2) is true if both e1 and e2 are true,
             # and false if at least one of e1 and e2 is false.
             return (and_conditional_maps(left_if_vars, right_if_vars),
                     or_conditional_maps(left_else_vars, right_else_vars))
         elif isinstance(node, OpExpr) and node.op == 'or':
-            left_if_vars, left_else_vars = self.find_isinstance_check_helper(node.left)
-            right_if_vars, right_else_vars = self.find_isinstance_check_helper(node.right)
+            left_if_vars, left_else_vars = self.find_isinstance_check(node.left)
+            right_if_vars, right_else_vars = self.find_isinstance_check(node.right)
 
             # (e1 or e2) is true if at least one of e1 or e2 is true,
             # and false if both e1 and e2 are false.
             return (or_conditional_maps(left_if_vars, right_if_vars),
                     and_conditional_maps(left_else_vars, right_else_vars))
         elif isinstance(node, UnaryExpr) and node.op == 'not':
-            left, right = self.find_isinstance_check_helper(node.expr)
+            left, right = self.find_isinstance_check(node.expr)
             return right, left
 
         # Restrict the type of the variable to True-ish/False-ish in the if and else branches

test-data/unit/check-narrowing.test

@@ -655,6 +655,27 @@ else:
     reveal_type(y["model"])     # N: Revealed type is "Union[TypedDict('__main__.Model1', {'key': Literal['A']}), TypedDict('__main__.Model2', {'key': Literal['B']})]"
 [builtins fixtures/primitives.pyi]
 
+[case testNarrowingExprPropagation]
+from typing import Union
+from typing_extensions import Literal
+
+class A:
+    tag: Literal['A']
+
+class B:
+    tag: Literal['B']
+
+abo: Union[A, B, None]
+
+if abo is not None and abo.tag == "A":
+    reveal_type(abo.tag) # N: Revealed type is "Literal['A']"
+    reveal_type(abo) # N: Revealed type is "__main__.A"
+
+if not (abo is None or abo.tag != "B"):
+    reveal_type(abo.tag) # N: Revealed type is "Literal['B']"
+    reveal_type(abo) # N: Revealed type is "__main__.B"
+[builtins fixtures/primitives.pyi]
+
 [case testNarrowingEqualityFlipFlop]
 # flags: --warn-unreachable --strict-equality
 from typing_extensions import Literal, Final