Fix issue with repeated-slash requests redirecting

Previously if a request had repeated slashes it could match a single
slash route and hence return a redirect response even if merge_slashes
was False.

Additionally setting the merge_slashes attribute of the map after
initialisation had no affect, compounding this problem.

CHANGES.rst

@@ -5,6 +5,8 @@ Version 3.0.2
 
 Unreleased
 
+-   Ensure setting merge_slashes to False results in NotFound for
+    repeated-slash requests against single slash routes. :issue:`2834`
 -   Fix handling of TypeError in TypeConversionDict.get() to match
     ValueErrors. :issue:`2843`
 -   Fix response_wrapper type check in test client. :issue:`2831`

src/werkzeug/routing/map.py

@@ -109,7 +109,6 @@ def __init__(
 
         self.default_subdomain = default_subdomain
         self.strict_slashes = strict_slashes
-        self.merge_slashes = merge_slashes
         self.redirect_defaults = redirect_defaults
         self.host_matching = host_matching
 
@@ -123,6 +122,14 @@ def __init__(
         for rulefactory in rules or ():
             self.add(rulefactory)
 
+    @property
+    def merge_slashes(self) -> bool:
+        return self._matcher.merge_slashes
+
+    @merge_slashes.setter
+    def merge_slashes(self, value: bool) -> None:
+        self._matcher.merge_slashes = value
+
     def is_endpoint_expecting(self, endpoint: str, *arguments: str) -> bool:
         """Iterate over all rules and check if the endpoint expects
         the arguments provided.  This is for example useful if you have

src/werkzeug/routing/matcher.py

@@ -177,7 +177,7 @@ def _match(
                 rv = _match(self._root, [domain, *path.split("/")], [])
             except SlashRequired:
                 raise RequestPath(f"{path}/") from None
-            if rv is None:
+            if rv is None or rv[0].merge_slashes is False:
                 raise NoMatch(have_match_for, websocket_mismatch)
             else:
                 raise RequestPath(f"{path}")

tests/test_routing.py

@@ -95,6 +95,7 @@ def test_merge_slashes_match():
             r.Rule("/yes/tail/", endpoint="yes_tail"),
             r.Rule("/with/<path:path>", endpoint="with_path"),
             r.Rule("/no//merge", endpoint="no_merge", merge_slashes=False),
+            r.Rule("/no/merging", endpoint="no_merging", merge_slashes=False),
         ]
     )
     adapter = url_map.bind("localhost", "/")
@@ -124,6 +125,9 @@ def test_merge_slashes_match():
 
     assert adapter.match("/no//merge")[0] == "no_merge"
 
+    assert adapter.match("/no/merging")[0] == "no_merging"
+    pytest.raises(NotFound, lambda: adapter.match("/no//merging"))
+
 
 @pytest.mark.parametrize(
     ("path", "expected"),