More clearly document what wildcards matches (#1873)

axum/src/docs/routing/route.md

@@ -50,6 +50,11 @@ Examples:
 - `/assets/*path`
 - `/:id/:repo/*tree`
 
+Note that `/*key` doesn't match empty segments. Thus:
+
+- `/*key` doesn't match `/` but does match `/a`, `/a/`, etc.
+- `/x/*key` doesn't match `/x` or `/x/` but does match `/x/a`, `/x/a/`, etc.
+
 Wildcard captures can also be extracted using [`Path`](crate::extract::Path).
 Note that the leading slash is not included, i.e. for the route `/foo/*rest` and
 the path `/foo/bar/baz` the value of `rest` will be `bar/baz`.

axum/src/routing/tests/mod.rs

@@ -380,6 +380,34 @@ async fn wildcard_doesnt_match_just_trailing_slash() {
     assert_eq!(res.text().await, "foo/bar");
 }
 
+#[crate::test]
+async fn what_matches_wildcard() {
+    let app = Router::new()
+        .route("/*key", get(|| async { "root" }))
+        .route("/x/*key", get(|| async { "x" }))
+        .fallback(|| async { "fallback" });
+
+    let client = TestClient::new(app);
+
+    let get = |path| {
+        let f = client.get(path).send();
+        async move { f.await.text().await }
+    };
+
+    assert_eq!(get("/").await, "fallback");
+    assert_eq!(get("/a").await, "root");
+    assert_eq!(get("/a/").await, "root");
+    assert_eq!(get("/a/b").await, "root");
+    assert_eq!(get("/a/b/").await, "root");
+
+    assert_eq!(get("/x").await, "root");
+    assert_eq!(get("/x/").await, "root");
+    assert_eq!(get("/x/a").await, "x");
+    assert_eq!(get("/x/a/").await, "x");
+    assert_eq!(get("/x/a/b").await, "x");
+    assert_eq!(get("/x/a/b/").await, "x");
+}
+
 #[crate::test]
 async fn static_and_dynamic_paths() {
     let app = Router::new()