Do not replace CInstance types with pyrefly types

Summary: If the base type binder has produced a primitive type, it is more specific than the pyrefly-generated type and should not be replaced.

Reviewed By: DinoV, alexmalyshev

Differential Revision: D96394235

fbshipit-source-id: 43ad6086d3cc90a4817b6e780e9807fabc9b353c

Author: martindemello

cinderx/PythonLib/cinderx/compiler/static/pyrefly_type_binder.py

@@ -14,7 +14,7 @@
 from .module_table import ModuleTable
 from .pyrefly_info import PyreflyTypeInfo
 from .type_binder import TerminalKind, TypeBinder
-from .types import Class
+from .types import CInstance, Class
 
 if TYPE_CHECKING:
     from .compiler import Compiler
@@ -46,6 +46,13 @@ def __init__(
     def visit(self, node: AST, *args: object) -> NarrowingEffect | None:
         ret = super().visit(node, *args)
         if isinstance(node, ast.expr) and self._type_info is not None:
+            # If the parent visitor already promoted a literal to a primitive
+            # type (e.g. `x: int64 = 0` promotes 0 to int64), don't override
+            # it with the pyrefly-inferred type.
+            existing_type = self.get_type(node)
+            if isinstance(existing_type, CInstance):
+                return ret
+
             declared_type = self._type_info.lookup(node, self.modules, self.type_env)
 
             if declared_type is None: