fix: default profile report containers to empty

tests/test_dataclass_defaults.py

@@ -0,0 +1,46 @@
+"""A dataclass field typed as a container defaults to an empty one.
+
+ProfileReport declared `entries: list[EntryReport] = None`: the annotation
+promised a list, the public constructor gave None, and format_report raised
+TypeError on the first loop.
+"""
+
+from __future__ import annotations
+
+import ast
+import unittest
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+
+
+def _is_dataclass(node: ast.ClassDef) -> bool:
+    for deco in node.decorator_list:
+        target = deco.func if isinstance(deco, ast.Call) else deco
+        name = target.attr if isinstance(target, ast.Attribute) else getattr(target, "id", "")
+        if name == "dataclass":
+            return True
+    return False
+
+
+class ContainerFieldsAreNotNone(unittest.TestCase):
+    def test_no_container_annotation_defaults_to_none(self):
+        for path in sorted([*(REPO_ROOT / "scripts").rglob("*.py"), REPO_ROOT / "install.py"]):
+            tree = ast.parse(path.read_text(encoding="utf-8"))
+            for node in ast.walk(tree):
+                if not (isinstance(node, ast.ClassDef) and _is_dataclass(node)):
+                    continue
+                for stmt in node.body:
+                    if not isinstance(stmt, ast.AnnAssign) or stmt.value is None:
+                        continue
+                    annotation = ast.unparse(stmt.annotation)
+                    is_none = isinstance(stmt.value, ast.Constant) and stmt.value.value is None
+                    if is_none and annotation.split("[")[0] in ("list", "dict", "set") \
+                            and "None" not in annotation:
+                        with self.subTest(module=path.name, cls=node.name,
+                                          field=ast.unparse(stmt.target)):
+                            self.fail(f"{annotation} defaults to None")
+
+
+if __name__ == "__main__":
+    unittest.main()