[readonly] Fix multi-part imports in the type binder

Summary: The root part of the import name ends up visible in python, so track it as such, since readonly doesn't care about anything beyond that.

Test Plan: New test

Reviewers: shiyuwang93, #cinder_cipp_support

Reviewed By: shiyuwang93

Subscribers: amrithar, aniketpanse, #cinder

Differential Revision: https://phabricator.intern.facebook.com/D35090635

Lib/compiler/readonly/type_binder.py

@@ -1056,10 +1056,15 @@ def visitarg(self, node: ast.arg) -> None:
         self.declare(node.arg, node, readonly_value)
 
     def visitalias(self, node: ast.alias) -> None:
+        root_visible_name = node.name
         if node.asname:
-            self.declare(node.asname, node, MUTABLE)
-        else:
-            self.declare(node.name, node, MUTABLE)
+            root_visible_name = node.asname
+
+        # If this is a multi-part import, make the root name
+        # visible in the current scope.
+        if (loc := root_visible_name.find(".")) != -1:
+            root_visible_name = root_visible_name[:loc]
+        self.declare(root_visible_name, node, MUTABLE)
 
     def visitModule(self, node: ast.Module) -> None:
         self.child_scope(ReadonlyModuleBindingScope(node, self))

Lib/test/test_compiler/test_readonly/test_type_binder.py

@@ -742,6 +742,19 @@ def somefunc():
         errors = self.lint(code)
         self.assertEqual(errors.errors, [])
 
+    def test_import_local_multipart(self) -> None:
+        code = """
+        import e
+
+        def somefunc():
+            import d.f
+            le = e
+            ld = d
+            le = d.f
+        """
+        errors = self.lint(code)
+        self.assertEqual(errors.errors, [])
+
     def test_readonly_walrus(self) -> None:
         code = """
         def g(arr):