Fixes to LV: in x.y expressions y is no longer tracked, in x[i] LHS x is not seen as written to

src/styx_compiler/control_flow.py

@@ -630,18 +630,22 @@ def _visit_expression(
             expression: cst.Subscript = cst.ensure_type(expression, cst.Subscript)
             prev = self._visit_expression(expression.value, instance, prev, context)
             for element in expression.slice:
-                if m.matches(element, m.Index()):
-                    element: cst.Index = cst.ensure_type(element, cst.Index)  # noqa: PLW2901
+                baseslice: cst.BaseSlice = cst.ensure_type(element, cst.SubscriptElement).slice
+                if m.matches(baseslice, m.Index()):
+                    element: cst.Index = cst.ensure_type(baseslice, cst.Index)  # noqa: PLW2901
                     prev = self._visit_expression(element.value, instance, prev)
                     prev = self._make_cfg_node(element, instance, prev)  # Index
-                elif m.matches(element, m.Slice()):
-                    element: cst.Slice = cst.ensure_type(element, cst.Slice)  # noqa: PLW2901
-                    prev = self._visit_expression(element.lower, instance, prev)
-                    prev = self._visit_expression(element.upper, instance, prev)
-                    prev = self._visit_expression(element.step, instance, prev)
+                elif m.matches(baseslice, m.Slice()):
+                    element: cst.Slice = cst.ensure_type(baseslice, cst.Slice)  # noqa: PLW2901
+                    if element.lower is not None:
+                        prev = self._visit_expression(element.lower, instance, prev)
+                    if element.upper is not None:
+                        prev = self._visit_expression(element.upper, instance, prev)
+                    if element.step is not None:
+                        prev = self._visit_expression(element.step, instance, prev)
                     prev = self._make_cfg_node(element, instance, prev)  # Slice
                 else:
-                    msg = f"Unknown subscript element type {element}"
+                    msg = f"Unknown BaseSlice type {baseslice}"
                     raise RuntimeError(msg)
             prev = self._make_cfg_node(expression, instance, prev)  # Subscript
         else:

src/styx_compiler/live_variables.py

@@ -40,8 +40,9 @@ def _get_lhs_names(self, target: cst.BaseExpression) -> Sequence[QualifiedName]:
             if result is not None:
                 return result
         if m.matches(target, m.Subscript()):
-            target: cst.Subscript = cst.ensure_type(target, cst.Subscript)
-            return self._get_lhs_names(target.value)
+            # target: cst.Subscript = cst.ensure_type(target, cst.Subscript)
+            # Don't return the name of the target.value, since only the subscripted part is written to
+            return []
         if m.matches(target, m.StarredElement() | m.Element()):
             return self._get_lhs_names(target.value)
         if m.matches(target, m.Name()):
@@ -99,12 +100,6 @@ def visit_Name(self, node: cst.Name) -> bool | None:
         if result is not None:
             self._tfs[Node(index, 0)] = lambda lives, names=result: lives.union(names)
 
-    def visit_Attribute(self, node: cst.Attribute) -> bool | None:
-        index = self._provider.get_metadata(IndexProvider, node)
-        result = self.resolve_name(node)
-        if result is not None:
-            self._tfs[Node(index, 0)] = lambda lives, names=result: lives.union(names)
-
 
 class LiveVariablesDataflowPropertyProvider(cst.BatchableMetadataProvider[DataflowProperty]):
     METADATA_DEPENDENCIES = (IndexProvider, QualifiedNameProvider)