From f5f110482636061a4c12b10b5bd529df18444893 Mon Sep 17 00:00:00 2001
From: Tommi Reiman <tommi@iki.fi>
Date: Mon, 21 Aug 2017 09:02:03 +0300
Subject: [PATCH] Router option to handle conflicts

---
 README.md                       | 17 +++++++++--------
 src/reitit/core.cljc            | 29 ++++++++++++++++++++---------
 test/cljc/reitit/core_test.cljc | 21 ++++++++++++++++++---
 3 files changed, 47 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index 7cad9a20..ca5a865f 100644
--- a/README.md
+++ b/README.md
@@ -392,14 +392,15 @@ Authorized access to guarded route:
 
 Routers can be configured via options. Options allow things like [`clojure.spec`](https://clojure.org/about/spec) validation for meta-data and fast, compiled handlers. The following options are available for the `reitit.core/router`:
 
-  | key        | description |
-  | -----------|-------------|
-  | `:path`    | Base-path for routes (default `""`)
-  | `:routes`  | Initial resolved routes (default `[]`)
-  | `:meta`    | Initial expanded route-meta vector (default `[]`)
-  | `:expand`  | Function of `arg opts => meta` to expand route arg to route meta-data (default `reitit.core/expand`)
-  | `:coerce`  | Function of `route opts => route` to coerce resolved route, can throw or return `nil`
-  | `:compile` | Function of `route opts => handler` to compile a route handler
+  | key          | description |
+  | -------------|-------------|
+  | `:path`      | Base-path for routes (default `""`)
+  | `:routes`    | Initial resolved routes (default `[]`)
+  | `:meta`      | Initial expanded route-meta vector (default `[]`)
+  | `:expand`    | Function of `arg opts => meta` to expand route arg to route meta-data (default `reitit.core/expand`)
+  | `:coerce`    | Function of `route opts => route` to coerce resolved route, can throw or return `nil`
+  | `:compile`   | Function of `route opts => handler` to compile a route handler
+  | `:conflicts` | Function of `[route route] => side-effect` to handle conflicting routes (default `reitit.core/throw-on-conflicts!`)"
 
 ## Special thanks
 
diff --git a/src/reitit/core.cljc b/src/reitit/core.cljc
index 3f8db58b..fc8b3342 100644
--- a/src/reitit/core.cljc
+++ b/src/reitit/core.cljc
@@ -66,6 +66,12 @@
       (or (some #(if (impl/conflicting-routes? r %) [r %]) rest)
           (recur rest)))))
 
+(defn throw-on-conflicts! [routes]
+  (throw
+    (ex-info
+      (str "router contains conflicting routes: " routes)
+      {:routes routes})))
+
 (defn name-lookup [[_ {:keys [name]}] opts]
   (if name #{name}))
 
@@ -103,7 +109,8 @@
   {:lookup name-lookup
    :expand expand
    :coerce (fn [route _] route)
-   :compile (fn [[_ {:keys [handler]}] _] handler)})
+   :compile (fn [[_ {:keys [handler]}] _] handler)
+   :conflicts throw-on-conflicts!})
 
 (defn linear-router
   "Creates a [[LinearRouter]] from resolved routes and optional
@@ -191,18 +198,22 @@
   If routes contain wildcards, a [[LinearRouter]] is used, otherwise a
   [[LookupRouter]]. The following options are available:
 
-  | key        | description |
-  | -----------|-------------|
-  | `:path`    | Base-path for routes (default `\"\"`)
-  | `:routes`  | Initial resolved routes (default `[]`)
-  | `:meta`    | Initial expanded route-meta vector (default `[]`)
-  | `:expand`  | Function of `arg opts => meta` to expand route arg to route meta-data (default `reitit.core/expand`)
-  | `:coerce`  | Function of `route opts => route` to coerce resolved route, can throw or return `nil`
-  | `:compile` | Function of `route opts => handler` to compile a route handler"
+  | key          | description |
+  | -------------|-------------|
+  | `:path`      | Base-path for routes (default `\"\"`)
+  | `:routes`    | Initial resolved routes (default `[]`)
+  | `:meta`      | Initial expanded route-meta vector (default `[]`)
+  | `:expand`    | Function of `arg opts => meta` to expand route arg to route meta-data (default `reitit.core/expand`)
+  | `:coerce`    | Function of `route opts => route` to coerce resolved route, can throw or return `nil`
+  | `:compile`   | Function of `route opts => handler` to compile a route handler
+  | `:conflicts` | Function of `[route route] => side-effect` to handle conflicting routes (default `reitit.core/throw-on-conflicts!`)"
   ([data]
    (router data {}))
   ([data opts]
    (let [opts (meta-merge default-router-options opts)
          routes (resolve-routes data opts)]
+     (when-let [conflicts (:conflicts opts)]
+       (when-let [conflicting-routes (first-conflicting-routes routes)]
+         (conflicts conflicting-routes)))
      ((if (some impl/contains-wilds? (map first routes))
         linear-router lookup-router) routes opts))))
diff --git a/test/cljc/reitit/core_test.cljc b/test/cljc/reitit/core_test.cljc
index 854b02ed..b099233d 100644
--- a/test/cljc/reitit/core_test.cljc
+++ b/test/cljc/reitit/core_test.cljc
@@ -1,8 +1,8 @@
 (ns reitit.core-test
   (:require [clojure.test :refer [deftest testing is are]]
-            [reitit.core :as reitit #?@(:cljs [:refer [Match]])])
+            [reitit.core :as reitit #?@(:cljs [:refer [Match Routing]])])
   #?(:clj
-     (:import (reitit.core Match)
+     (:import (reitit.core Match Routing)
               (clojure.lang ExceptionInfo))))
 
 (deftest reitit-test
@@ -171,4 +171,19 @@
            ["/a/*b"]]
 
     true [["/v2/public/messages/dataset/bulk"]
-          ["/v2/public/messages/dataset/:dataset-id"]]))
+          ["/v2/public/messages/dataset/:dataset-id"]])
+
+  (testing "router with conflicting routes"
+    (testing "throws by default"
+      (is (thrown-with-msg?
+            ExceptionInfo
+            #"router contains conflicting routes"
+            (reitit/router
+              [["/a"] ["/a"]]))))
+    (testing "can be configured to ignore"
+      (is (instance?
+            Routing
+            (reitit/router
+              [["/a"] ["/a"]]
+              {:conflicts (constantly nil)}))))))
+