test(server): add a compile-fail test to ensure reasonable error message

tests/compile-fail/unmet_data_requirement.rs

@@ -0,0 +1,41 @@
+#[macro_use] extern crate nickel;
+extern crate cookie;
+
+use nickel::{Nickel, HttpRouter, Cookies, QueryString};
+use nickel::cookies;
+use cookie::Cookie;
+
+struct Data {
+    secret_key: cookies::SecretKey
+}
+
+fn main() {
+    let data = Data { secret_key: cookies::SecretKey([0; 32]) };
+    let mut server = Nickel::with_data(data);
+
+    // Try curl -b MyCookie=bar localhost:6767
+    server.get("/", middleware! { |req|
+        let cookie = req.cookies().find("MyCookie");
+        //~^ ERROR: the trait `core::convert::AsRef<nickel::cookies::SecretKey>` is not implemented for the type `Data`
+        format!("MyCookie={:?}", cookie.map(|c| c.value))
+    });
+
+    // Note: Don't use get for login in real applications ;)
+    // Try http://localhost:6767/login?name=foo
+    server.get("/login", middleware! { |req, mut res|
+        let jar = res.cookies_mut()
+        //~^ ERROR: the trait `core::convert::AsRef<nickel::cookies::SecretKey>` is not implemented for the type `Data`
+                     // long life cookies!
+                     .permanent();
+
+        let name = req.query().get("name")
+                              .unwrap_or("default_name");
+        let cookie = Cookie::new("MyCookie".to_owned(),
+                                 name.to_owned());
+        jar.add(cookie);
+
+        "Cookie set!"
+    });
+
+    server.listen("127.0.0.1:6767");
+}