Narrow for type expr comparisons to type exprs (#20639)

I refactored the logic for type(x) narrowing in #20634 , but left this
piece out since it has material semantic impact

Fixes #11952
Fixes #20275

Author: hauntsaninja

mypy/checker.py

@@ -6726,37 +6726,37 @@ def narrow_type_by_identity_equality(
                         else_map = {}  # this is the big difference compared to the above
                         partial_type_maps.append((if_map, else_map))
 
-        exprs_in_type_calls = []
         for i in expr_indices:
-            expr = operands[i]
-            if isinstance(expr, CallExpr) and is_type_call(expr):
-                exprs_in_type_calls.append(expr.args[0])
-
-        if exprs_in_type_calls:
-            for expr_in_type_call in exprs_in_type_calls:
-                for i in expr_indices:
-                    expr = operands[i]
-                    if isinstance(expr, CallExpr) and is_type_call(expr):
-                        continue
-
-                    current_type_range = self.get_isinstance_type(expr)
-                    if_map, else_map = conditional_types_to_typemaps(
-                        expr_in_type_call,
-                        *self.conditional_types_with_intersection(
-                            self.lookup_type(expr_in_type_call),
-                            current_type_range,
-                            expr_in_type_call,
-                        ),
-                    )
+            type_expr = operands[i]
+            if (
+                isinstance(type_expr, CallExpr)
+                and refers_to_fullname(type_expr.callee, "builtins.type")
+                and len(type_expr.args) == 1
+            ):
+                expr_in_type_expr = type_expr.args[0]
+            else:
+                continue
+            for j in expr_indices:
+                if i == j:
+                    continue
+                expr = operands[j]
+
+                current_type_range = self.get_isinstance_type(expr)
+                if_map, else_map = conditional_types_to_typemaps(
+                    expr_in_type_expr,
+                    *self.conditional_types_with_intersection(
+                        self.lookup_type(expr_in_type_expr), current_type_range, expr_in_type_expr
+                    ),
+                )
 
-                    is_final = (
-                        expr.node.is_final
-                        if isinstance(expr, RefExpr) and isinstance(expr.node, TypeInfo)
-                        else False
-                    )
-                    if not is_final:
-                        else_map = {}
-                    partial_type_maps.append((if_map, else_map))
+                is_final = (
+                    expr.node.is_final
+                    if isinstance(expr, RefExpr) and isinstance(expr.node, TypeInfo)
+                    else False
+                )
+                if not is_final:
+                    else_map = {}
+                partial_type_maps.append((if_map, else_map))
 
         # We will not have duplicate entries in our type maps if we only have two operands,
         # so we can skip running meets on the intersections
@@ -8562,11 +8562,6 @@ def has_custom_eq_checks(t: Type) -> bool:
     )
 
 
-def is_type_call(expr: CallExpr) -> bool:
-    """Is expr a call to type with one argument?"""
-    return refers_to_fullname(expr.callee, "builtins.type") and len(expr.args) == 1
-
-
 def convert_to_typetype(type_map: TypeMap) -> TypeMap:
     converted_type_map: dict[Expression, Type] = {}
     if type_map is None:

test-data/unit/check-narrowing.test

@@ -3021,6 +3021,32 @@ if type(x) is not int:
 else:
     reveal_type(x)  # N: Revealed type is "builtins.int"
 
+[case testTypeNarrowingAgainstType]
+# flags: --strict-equality --warn-unreachable
+class A:
+    def foo(self, x: object) -> None:
+        reveal_type(self)  # N: Revealed type is "__main__.A"
+        reveal_type(x)  # N: Revealed type is "builtins.object"
+        if type(self) is type(x):
+            reveal_type(self)  # N: Revealed type is "__main__.A"
+            reveal_type(x)  # N: Revealed type is "__main__.A"
+        else:
+            reveal_type(self)  # N: Revealed type is "__main__.A"
+            reveal_type(x)  # N: Revealed type is "builtins.object"
+        if type(self) == type(x):
+            reveal_type(self)  # N: Revealed type is "__main__.A"
+            reveal_type(x)  # N: Revealed type is "__main__.A"
+        else:
+            reveal_type(self)  # N: Revealed type is "__main__.A"
+            reveal_type(x)  # N: Revealed type is "builtins.object"
+
+class B:
+    y: int
+
+    def __eq__(self, other: object) -> bool:
+        return type(other) is type(self) and other.y == self.y
+[builtins fixtures/primitives.pyi]
+
 [case testNarrowInElseCaseIfFinal]
 # flags: --strict-equality --warn-unreachable
 from typing import final, Union