Fix using non-strings as anchors

Previously, non-strings passed to _anchor would be converted to strings.
Restore this ability. The logic is the same as in url_quote.

Fixes: c4b39ba2 ("replace werkzeug.urls with urllib.parse")

CHANGES.rst

@@ -7,6 +7,7 @@ Unreleased
 -   Require Werkzeug >= 2.3.6.
 -   Use ``flit_core`` instead of ``setuptools`` as build backend.
 -   Refactor how an app's root and instance paths are determined. :issue:`5160`
+-   Fix passing non-string values to ``url_for``. :issue:`5206`
 
 
 Version 2.3.2

src/flask/app.py

@@ -1697,6 +1697,8 @@ class Flask(Scaffold):
             return self.handle_url_build_error(error, endpoint, values)
 
         if _anchor is not None:
+            if not isinstance(_anchor, (str, bytes, bytearray)):
+                _anchor = str(_anchor)
             _anchor = _url_quote(_anchor, safe="%!#$&'()*+,/:;=?@")
             rv = f"{rv}#{_anchor}"
 

tests/test_helpers.py

@@ -106,6 +106,7 @@ class TestUrlFor:
             return "42"
 
         assert flask.url_for("index", _anchor="x y") == "/#x%20y"
+        assert flask.url_for("index", _anchor=5) == "/#5"
 
     def test_url_for_with_scheme(self, app, req_ctx):
         @app.route("/")