Optimize Scope Analysis memory usage by removing unnecessary Assignment creation

libcst/metadata/scope_provider.py

@@ -36,6 +36,8 @@ from libcst.metadata.expression_context_provider import (
 )
 
 
+@add_slots
+@dataclass(frozen=False)
 class Access:
     """
     An Access records an access of an assignment.
@@ -698,10 +700,19 @@ class ScopeVisitor(cst.CSTVisitor):
                 attr.visit(self)
         return False
 
-    def visit_Arg_keyword(self, node: cst.Arg) -> None:
-        keyword = node.keyword
-        if keyword is not None:
-            self.scope.record_assignment(keyword.value, node)
+    def visit_Arg(self, node: cst.Arg) -> Optional[bool]:
+        # The keyword of Arg is neither an Assignment nor an Access and we explicitly don't visit it.
+        for attr in [
+            node.value,
+            node.equal,
+            node.comma,
+            node.star,
+            node.whitespace_after_star,
+            node.whitespace_after_arg,
+        ]:
+            if isinstance(attr, cst.CSTNode):
+                attr.visit(self)
+        return False
 
     def visit_ClassDef(self, node: cst.ClassDef) -> Optional[bool]:
         self.scope.record_assignment(node.name.value, node)

libcst/metadata/tests/test_scope_provider.py

@@ -987,3 +987,12 @@ class ScopeProviderTest(UnitTest):
             {ensure_type(del_a_b.target, cst.Attribute).value},
         )
         self.assertEqual(scope["b"], ())
+
+    def test_keyword_arg_in_call(self) -> None:
+        m, scopes = get_scope_metadata_provider("call(arg=val)")
+        call = ensure_type(
+            ensure_type(m.body[0], cst.SimpleStatementLine).body[0], cst.Expr
+        ).value
+        scope = scopes[call]
+        self.assertIsInstance(scope, GlobalScope)
+        self.assertEqual(len(scope["arg"]), 0)  # no assignment should exist