From 2a5189ed634622c97f23c9ec1f974bafc0b74c1d Mon Sep 17 00:00:00 2001
From: Wojciech Kordalski <wkordalski@pm.me>
Date: Thu, 27 Feb 2025 22:55:14 +0100
Subject: [PATCH] Add information about the meaning of `Router<S>` to `Router`
 documentation (#3235)

---
 axum/src/routing/mod.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/axum/src/routing/mod.rs b/axum/src/routing/mod.rs
index 2e975d99..9c30288e 100644
--- a/axum/src/routing/mod.rs
+++ b/axum/src/routing/mod.rs
@@ -58,6 +58,12 @@ macro_rules! panic_on_err {
 pub(crate) struct RouteId(u32);
 
 /// The router type for composing handlers and services.
+///
+/// `Router<S>` means a router that is _missing_ a state of type `S` to be able
+/// to handle requests. Thus, only `Router<()>` (i.e. without missing state) can
+/// be passed to [`serve`]. See [`Router::with_state`] for more details.
+///
+/// [`serve`]: crate::serve()
 #[must_use]
 pub struct Router<S = ()> {
     inner: Arc<RouterInner<S>>,