Prevent empty identifier

Ref. #441, #443

rflx/identifier.py

@@ -1,6 +1,5 @@
 from typing import Optional, Sequence, Union
 
-# from rflx.contract import invariant
 from rflx.error import Location
 
 
@@ -21,6 +20,7 @@ def __init__(
         else:
             assert False, f'unexpected identifier type "{type(identifier).__name__}"'
 
+        assert self._parts, "empty identifier"
         assert "" not in self._parts, "empty part in identifier"
         for c in [" ", ".", ":"]:
             assert all(c not in part for part in self._parts), f'"{c}" in identifier parts'
@@ -85,11 +85,11 @@ def parts(self) -> Sequence[str]:
 
     @property
     def name(self) -> "ID":
-        return ID(self.parts[-1])
+        return self.__class__(self._parts[-1])
 
     @property
     def parent(self) -> "ID":
-        return ID(self.parts[:-1])
+        return self.__class__(self._parts[:-1])
 
     @property
     def _separator(self) -> str:

tests/unit/identifier_test.py

@@ -20,6 +20,12 @@ def test_id_invalid_type() -> None:
 
 @pytest.mark.skipif(not __debug__, reason="depends on assertion")
 def test_id_invalid_empty() -> None:
+    with pytest.raises(AssertionError, match=r"^empty identifier$"):
+        ID([])
+
+
+@pytest.mark.skipif(not __debug__, reason="depends on assertion")
+def test_id_invalid_empty_string() -> None:
     with pytest.raises(AssertionError, match=r"^empty part in identifier$"):
         ID("")
 
@@ -90,5 +96,11 @@ def test_id_parent() -> None:
     assert ID("A::B::C").parent == ID("A::B")
 
 
+@pytest.mark.skipif(not __debug__, reason="depends on assertion")
+def test_id_parent_error() -> None:
+    with pytest.raises(AssertionError, match=r"^empty identifier$"):
+        ID("A").parent  # pylint: disable=expression-not-assigned
+
+
 def test_id_sorted() -> None:
     assert sorted([ID("B"), ID("A")]) == [ID("A"), ID("B")]