fix: expand empty multi-node placeholders without crashing (#365)

src/renaissance/syntax_tree/ast_rewriter.py

@@ -526,11 +526,11 @@ def __get_texts(self, nodes: Sequence[Rewritable], transform: Callable[[str], st
         The text between the nodes is kept. A node with rewrites queued inside it is replaced by its rewritten text,
         and transform, if given, is applied to the text of each node.
         """
+        if not nodes:
+            return ""
         if len(nodes) == 1:
             text = self.__get_text(nodes[0])
             return transform(text) if transform else text
-        # TODO(FrancescoPezzella): an empty `$$x` raises IndexError here, e.g. `f($$args)` -> `g($$args)` on `f()`.
-        #  https://github.com/TNO/Renaissance.Py/issues/329
         start = self.cor_offset(nodes[0].offset)
         end = self.cor_offset(nodes[-1].extended_end_offset)
         rewriter = Rewriter(self.content[start:end])

test/syntax_tree/test_ast_rewriter.py

@@ -1040,10 +1040,11 @@ def test_python_placeholder_replacement(self, source: str, expected: str) -> Non
                 "from a import X  # café\nimport b\n",
             ),
             ("f(1, 2)\n", "f($$args)", "g($$args)", "g(1, 2)\n"),
+            ("f()\n", "f($$args)", "g($$args)", "g()\n"),
         ],
     )
     def test_python_multi_node_placeholder(self, source: str, find: str, replacement: str, expected: str) -> None:
-        """Verify a `$$` placeholder bound to several nodes expands to all of them, keeping their text and layout."""
+        """Verify a `$$` placeholder expands zero or more nodes, preserving text and layout."""
         root = PythonRstNode.load_from_text(source, "test.py")
         pattern = PythonPatternFactory(PythonFactory(PythonRstNode)).create_statements(find)
         rewriter = ASTRewriter(root)