support keys in HTML fragments (#683)

Author: rmorshea

src/idom/html.py

@@ -160,16 +160,24 @@
 
 from typing import Any, Mapping
 
-from .core.proto import VdomDict
+from .core.proto import Key, VdomDict
 from .core.vdom import coalesce_attributes_and_children, make_vdom_constructor
 
 
-def _(*children: Any) -> VdomDict:
+def _(*children: Any, key: Key | None = None) -> VdomDict:
     """An HTML fragment - this element will not appear in the DOM"""
     attributes, coalesced_children = coalesce_attributes_and_children(children)
     if attributes:
         raise TypeError("Fragments cannot have attributes")
-    return {"tagName": "", "children": coalesced_children}
+    model: VdomDict = {"tagName": ""}
+
+    if coalesced_children:
+        model["children"] = coalesced_children
+
+    if key is not None:
+        model["key"] = key
+
+    return model
 
 
 # Dcument metadata

tests/test_html.py

@@ -145,7 +145,14 @@ def test_child_of_script_must_be_string():
 
 
 def test_simple_fragment():
+    assert html._() == {"tagName": ""}
     assert html._(1, 2, 3) == {"tagName": "", "children": [1, 2, 3]}
+    assert html._(key="something") == {"tagName": "", "key": "something"}
+    assert html._(1, 2, 3, key="something") == {
+        "tagName": "",
+        "key": "something",
+        "children": [1, 2, 3],
+    }
 
 
 def test_fragment_can_have_no_attributes():