docs: document SupportsInt conversion behavior for query params

CHANGES/1458.doc.rst

@@ -0,0 +1,4 @@
+Documented that objects implementing :class:`~typing.SupportsInt` (such as
+:class:`uuid.UUID`) are converted to :class:`int` when used as query parameter
+values, and that explicit conversion to :class:`str` is needed if the string
+representation is desired -- by :user:`edvatar`.

docs/api.rst

@@ -696,6 +696,25 @@ section generates a new :class:`URL` instance.
       Please see :ref:`yarl-bools-support` for the reason why :class:`bool` is not
       supported out-of-the-box.
 
+   .. warning::
+
+      Any object implementing :class:`~typing.SupportsInt` (i.e. having an
+      :external+python:meth:`~object.__int__` method) will be converted to :class:`int` before being used
+      as a query parameter value. This includes types such as :class:`uuid.UUID`,
+      which will be converted to their integer representation rather than their
+      string representation. To avoid unexpected results, explicitly convert such
+      values to :class:`str` before passing them as query parameters:
+
+      .. code-block:: python
+
+         import uuid
+
+         my_uuid = uuid.UUID("3199712f-1b78-4420-852b-a73ee09e6a8f")
+         # Wrong: will use int(my_uuid) -> a large integer
+         url = URL("http://example.com/").with_query({"id": my_uuid})
+         # Correct: explicitly convert to string
+         url = URL("http://example.com/").with_query({"id": str(my_uuid)})
+
    .. doctest::
 
       >>> URL('http://example.com/path?a=b').with_query('c=d')

yarl/_query.py

@@ -16,7 +16,12 @@
 
 
 def query_var(v: SimpleQuery) -> str:
-    """Convert a query variable to a string."""
+    """Convert a query variable to a string.
+
+    Note: Objects implementing ``SupportsInt`` (e.g. ``uuid.UUID``) will be
+    converted via ``int()`` first. Callers should convert such values to ``str``
+    explicitly if the string representation is desired.
+    """
     cls = type(v)
     if cls is int:  # Fast path for non-subclassed int
         return str(v)