Check for name clashes

Author: tobywf

.pylintrc

@@ -14,9 +14,11 @@ disable=
     bad-continuation,  # clashes with black
     line-too-long,  # clashes with black
     ungrouped-imports, # clashes with isort
-    wrong-import-position, # clashes with isort
+    wrong-import-position,  # clashes with isort
     missing-docstring,
     fixme,
+    too-few-public-methods,  # this seems useless
+
 
 [BASIC]
 

README.md

@@ -76,7 +76,7 @@ Most of these limitations/assumptions are enforced. They may make this project u
 * Text content is a string
 * It isn't possible to pass any parameters to the wrapped `@dataclass` decorator
 * Some properties of dataclass `field`s are not exposed: `default_factory`, `repr`, `hash`, `init`, `compare`. For most, it is because I don't understand the implications fully or how that would be useful for XML. `default_factory` is hard only because of [the overloaded type signatures](https://github.com/python/typeshed/blob/master/stdlib/3.7/dataclasses.pyi), and getting that to work with `mypy`
-* Deserialisation is strict; missing required attributes and child elements will cause an error
+* Deserialisation is strict; missing required attributes and child elements will cause an error. I want this to be the default behaviour, but it should be straightforward to add a parameter to `load` for lenient operation
 * Unions of types aren't yet supported
 * Dataclasses must be written by hand, no tools are provided to generate these from, DTDs, XML schema definitions, or RELAX NG schemas
 

src/xml_dataclasses/structs.py

@@ -219,14 +219,31 @@ def text(
     return _xml_field(xml_type=XmlFieldType.Text, default=default, metadata=metadata)
 
 
-class XmlDataclass:  # pylint: disable=too-few-public-methods
+class XmlDataclass:
     __ns__: Optional[str]
     __attributes__: Collection[AttrInfo[Any]]
     __children__: Collection[ChildInfo[Any]]
     __text_field__: Optional[TextInfo[Any]]
     __nsmap__: Optional[Mapping[Optional[str], str]]
 
 
+class _XmlNameTracker:
+    def __init__(self, field_type: str):
+        self.field_type = field_type
+        self.seen: Dict[str, str] = {}
+
+    def add(self, xml_name: str, field_name: str) -> None:
+        try:
+            previous = self.seen[xml_name]
+        except KeyError:
+            self.seen[xml_name] = field_name
+        else:
+            raise ValueError(
+                f"Duplicate {self.field_type} '{xml_name}' on '{field_name}', "
+                f"previously declared on '{previous}'"
+            )
+
+
 def xml_dataclass(cls: Type[Any]) -> Type[XmlDataclass]:
     new_cls = dataclass()(cls)
     try:
@@ -239,6 +256,8 @@ def xml_dataclass(cls: Type[Any]) -> Type[XmlDataclass]:
     except AttributeError:
         new_cls.__nsmap__ = None
 
+    seen_attrs = _XmlNameTracker("attribute")
+    seen_children = _XmlNameTracker("child")
     attrs: List[AttrInfo[Any]] = []
     children: List[ChildInfo[Any]] = []
     text_field = None
@@ -249,9 +268,13 @@ def xml_dataclass(cls: Type[Any]) -> Type[XmlDataclass]:
             raise ValueError(f"Non-XML field '{f.name}' on XML dataclass") from None
 
         if xml_type == XmlFieldType.Attr:
-            attrs.append(AttrInfo.resolve(f))
+            attr_info = AttrInfo.resolve(f)
+            seen_attrs.add(attr_info.xml_name, f.name)
+            attrs.append(attr_info)
         elif xml_type == XmlFieldType.Child:
-            children.append(ChildInfo.resolve(f))
+            child_info = ChildInfo.resolve(f)
+            seen_children.add(child_info.xml_name, f.name)
+            children.append(child_info)
         elif xml_type == XmlFieldType.Text:
             text_field = TextInfo.resolve(f)
         else:

tests/structs_test.py

@@ -302,3 +302,35 @@ class Foo:
     msg = str(exc_info.value)
     assert "Unknown XML field type" in msg
     assert "'object'" in msg
+
+
+def test_xml_dataclass_child_name_clash():
+    class Foo:
+        __ns__ = None
+        bar: XmlDt2 = child(rename="spam")
+        baz: XmlDt2 = child(rename="spam")
+
+    with pytest.raises(ValueError) as exc_info:
+        xml_dataclass(Foo)
+
+    msg = str(exc_info.value)
+    assert "Duplicate child" in msg
+    assert "'spam'" in msg
+    assert "'bar'" in msg
+    assert "'baz'" in msg
+
+
+def test_xml_dataclass_attr_name_clash():
+    class Foo:
+        __ns__ = None
+        bar: str = attr(rename="spam")
+        baz: str = attr(rename="spam")
+
+    with pytest.raises(ValueError) as exc_info:
+        xml_dataclass(Foo)
+
+    msg = str(exc_info.value)
+    assert "Duplicate attribute" in msg
+    assert "'spam'" in msg
+    assert "'bar'" in msg
+    assert "'baz'" in msg