fix subdomain_matching=False behavior

src/flask/app.py

@@ -425,32 +425,40 @@ class Flask(App):
         is created at a point where the request context is not yet set
         up so the request is passed explicitly.
 
-        .. versionadded:: 0.6
-
-        .. versionchanged:: 0.9
-           This can now also be called without a request object when the
-           URL adapter is created for the application context.
+        .. versionchanged:: 3.1
+            If :data:`SERVER_NAME` is set, it does not restrict requests to
+            only that domain, for both ``subdomain_matching`` and
+            ``host_matching``.
 
         .. versionchanged:: 1.0
             :data:`SERVER_NAME` no longer implicitly enables subdomain
             matching. Use :attr:`subdomain_matching` instead.
+
+        .. versionchanged:: 0.9
+           This can be called outside a request when the URL adapter is created
+           for an application context.
+
+        .. versionadded:: 0.6
         """
         if request is not None:
-            # If subdomain matching is disabled (the default), use the
-            # default subdomain in all cases. This should be the default
-            # in Werkzeug but it currently does not have that feature.
-            if not self.subdomain_matching:
-                subdomain = self.url_map.default_subdomain or None
-            else:
-                subdomain = None
+            subdomain = None
+            server_name = self.config["SERVER_NAME"]
+
+            if self.url_map.host_matching:
+                # Don't pass SERVER_NAME, otherwise it's used and the actual
+                # host is ignored, which breaks host matching.
+                server_name = None
+            elif not self.subdomain_matching:
+                # Werkzeug doesn't implement subdomain matching yet. Until then,
+                # disable it by forcing the current subdomain to the default, or
+                # the empty string.
+                subdomain = self.url_map.default_subdomain or ""
 
             return self.url_map.bind_to_environ(
-                request.environ,
-                server_name=self.config["SERVER_NAME"],
-                subdomain=subdomain,
+                request.environ, server_name=server_name, subdomain=subdomain
             )
-        # We need at the very least the server name to be set for this
-        # to work.
+
+        # Need at least SERVER_NAME to match/build outside a request.
         if self.config["SERVER_NAME"] is not None:
             return self.url_map.bind(
                 self.config["SERVER_NAME"],