Correct and simplify logic of recording assignments (#556)

libcst/metadata/scope_provider.py

@@ -418,23 +418,33 @@ def __init__(self, parent: "Scope") -> None:
         self._assignment_count = 0
 
     def record_assignment(self, name: str, node: cst.CSTNode) -> None:
-        self._add_assignment(
-            Assignment(name=name, scope=self, node=node, index=self._assignment_count)
+        target = self._find_assignment_target(name)
+        target._assignments[name].add(
+            Assignment(
+                name=name, scope=target, node=node, index=target._assignment_count
+            )
         )
 
     def record_import_assignment(
         self, name: str, node: cst.CSTNode, as_name: cst.CSTNode
     ) -> None:
-        self._add_assignment(
+        target = self._find_assignment_target(name)
+        target._assignments[name].add(
             ImportAssignment(
                 name=name,
-                scope=self,
+                scope=target,
                 node=node,
                 as_name=as_name,
-                index=self._assignment_count,
+                index=target._assignment_count,
             )
         )
 
+    def _find_assignment_target(self, name: str) -> "Scope":
+        return self
+
+    def _find_assignment_target_parent(self, name: str) -> "Scope":
+        return self
+
     def record_access(self, name: str, access: Access) -> None:
         self._accesses[name].add(access)
 
@@ -446,14 +456,6 @@ def _contains_in_self_or_parent(self, name: str) -> bool:
         """Overridden by ClassScope to hide it's assignments from child scopes."""
         return name in self
 
-    def _add_assignment(self, assignment: "BaseAssignment") -> None:
-        assignment.scope = self
-        self._assignments[assignment.name].add(assignment)
-
-    def _add_assignment_as_parent(self, assignment: "BaseAssignment") -> None:
-        """Overridden by ClassScope to forward 'nonlocal' assignments from child scopes."""
-        self._add_assignment(assignment)
-
     @abc.abstractmethod
     def __contains__(self, name: str) -> bool:
         """Check if the name str exist in current scope by ``name in scope``."""
@@ -615,7 +617,7 @@ def record_global_overwrite(self, name: str) -> None:
     def record_nonlocal_overwrite(self, name: str) -> None:
         raise NotImplementedError("declarations in builtin scope are not allowed")
 
-    def _add_assignment(self, assignment: "BaseAssignment") -> None:
+    def _find_assignment_target(self, name: str) -> "Scope":
         raise NotImplementedError("assignments in builtin scope are not allowed")
 
 
@@ -668,13 +670,11 @@ def record_global_overwrite(self, name: str) -> None:
     def record_nonlocal_overwrite(self, name: str) -> None:
         self._scope_overwrites[name] = self.parent
 
-    def _add_assignment(self, assignment: "BaseAssignment") -> None:
-        if assignment.name in self._scope_overwrites:
-            self._scope_overwrites[assignment.name]._add_assignment_as_parent(
-                assignment
-            )
+    def _find_assignment_target(self, name: str) -> "Scope":
+        if name in self._scope_overwrites:
+            return self._scope_overwrites[name]._find_assignment_target_parent(name)
         else:
-            super()._add_assignment(assignment)
+            return super()._find_assignment_target(name)
 
     def __contains__(self, name: str) -> bool:
         if name in self._scope_overwrites:
@@ -707,7 +707,7 @@ class ClassScope(LocalScope):
     When a class is defined, it creates a ClassScope.
     """
 
-    def _add_assignment_as_parent(self, assignment: "BaseAssignment") -> None:
+    def _find_assignment_target_parent(self, name: str) -> "Scope":
         """
         Forward the assignment to parent.
 
@@ -722,7 +722,7 @@ def inner_fn():
                                  # hidden from its children.
 
         """
-        self.parent._add_assignment_as_parent(assignment)
+        return self.parent._find_assignment_target_parent(name)
 
     def _getitem_from_self_or_parent(self, name: str) -> Set[BaseAssignment]:
         """