router - fix setting a route key to itself doesn't drop the key anymore

src/hyperfiddle/router.cljc

@@ -559,8 +559,11 @@
   The corresponding value is preserved."
   ;; Useful for HFQL and `demo-colors`
   [m k f]
-  (-> (assoc m (f k) (get m k))
-    (dissoc k)))
+  (let [k' (f k)
+        m' (assoc m k' (get m k))]
+    (if (= k' k)
+      m'
+      (dissoc m' k))))
 
 (defn set-key "Replaces `old-key` in map `m` by `new-key` without altering the corresponding value.
   Similar to `clojure.set/rename-keys`, but faster and for a single key."
@@ -571,6 +574,7 @@
 (tests
   (set-key nil :a :b)          := {:b nil}
   (set-key {} :a :b)           := {:b nil}
+  (set-key nil :a :a)          := {:a nil}
   (set-key {:a 1} :a :b)       := {:b 1}
   (set-key {:a 1, :b 2} :a :c) := {:c 1, :b 2}
   )