adding m/start-with

dev/dev.clj

@@ -14,11 +14,14 @@
             ;; [clojure.core.async :refer [>!! <!! >! <! go-loop alt! timeout]]
             [clojure.tools.namespace.repl :as tn]
             [check.parts-test]
+            [check.start-with-test]
             [mount]
             [app :refer [create-nyse-schema find-orders add-order]]))  ;; <<<< replace this your "app" namespace(s) you want to be available at REPL time
 
 (defn start []
-  (mount/start-without #'check.parts-test/should-not-start)) ;; example on how to start app without certain states
+  (mount/start-without #'check.start-with-test/test-conn
+                       #'check.start-with-test/test-nrepl
+                       #'check.parts-test/should-not-start)) ;; example on how to start app without certain states
 
 (defn stop []
   (mount/stop))

src/mount/mount.clj

@@ -72,20 +72,33 @@
        (map second)
        (filter mount-state?)))
 
-;; TODO: narrow down by {:mount {:include-ns
-;;                                {:starts-with ["app.foo" "bar.baz"]
-;;                                 :nss ["app.nyse" "app.tools.datomic"] }
-;;                               :exclude-ns
-;;                                {:starts-with ["dont.want.this" "app.debug"]
-;;                                 :nss ["dev" "app.stage"]}}}
-;;
-;; would come from boot/lein dev profile
 (defn- bring [states fun order]
   (->> states
        (sort-by (comp :order meta) order)
        (map #(fun % (meta %)))
        doall))
 
+(defn- rollback! [state]
+  (let [{:keys [origin start stop sub?]} (meta state)]
+    (when origin
+      (alter-meta! state assoc :origin nil
+                   :start (or (:start origin) start)
+                   :stop (or (:stop origin) stop)))))
+
+(defn- unsub [state]
+  (when (-> (meta state) :sub?)
+    (alter-meta! state assoc :sub? nil
+                             :started false)))
+
+(defn- substitute! [state with]
+  (let [{:keys [start stop] :as origin} (meta state)
+        m-with (meta with)]
+    (alter-meta! with assoc :sub? true :started? true) ;; pre: called by "start-with"
+    (alter-meta! state assoc :origin {:start start
+                                      :stop stop}
+                             :start (:start m-with)
+                             :stop (:stop m-with))))
+
 (defn start [& states]
   (let [states (or (seq states) (find-all-states))]
     (bring states up <)
@@ -93,7 +106,9 @@
 
 (defn stop [& states]
   (let [states (or states (find-all-states))]
+    (doall (map unsub states))     ;; unmark substitutions marked by "start-with"
     (bring states down >)
+    (doall (map rollback! states)) ;; restore to origin from "start-with"
     :stopped))
 
 (defn start-with-args [xs & states]
@@ -103,12 +118,10 @@
     (start)))
 
 (defn start-with [with]
-  (if (seq with)
-    (let [app (find-all-states)]
-      ;; needs more thinking on merging, since the ns should not change
-      ;; because it could be used in other states, so only start/stop need to be merged
-      (warn "substituting states is not _yet_ implemented")
-      (start))
+  (let [app (find-all-states)]
+    (doall
+      (for [[from to] with]
+        (substitute! from to)))
     (start)))
 
 (defn start-without [& states]

test/check/start_with_test.clj

@@ -0,0 +1,28 @@
+(ns check.start-with-test
+  (:require [mount :refer [defstate] :as m]
+            [app.config :refer [app-config]]
+            [app.nyse :refer [conn]]
+            [app :refer [nrepl]]
+            [clojure.test :refer :all]))
+
+(defstate test-conn :start (long 42)
+                    :stop (constantly 0))
+
+(defstate test-nrepl :start (vector))
+
+(deftest start-with
+
+  (testing "should start with substitutes"
+    (let [_ (m/start-with {#'app.nyse/conn #'check.start-with-test/test-conn
+                           #'app/nrepl #'check.start-with-test/test-nrepl})]
+      (is (map? app-config))
+      (is (vector? nrepl))
+      (is (= conn 42))
+      (mount/stop)))
+  
+  (testing "should start normally after start-with"
+    (let [_ (m/start)]
+      (is (map? app-config))
+      (is (instance? clojure.tools.nrepl.server.Server nrepl))
+      (is (instance? datomic.peer.LocalConnection conn))
+      (mount/stop))))

test/check/start_without_test.clj

@@ -1,4 +1,4 @@
-(ns check.without-test
+(ns check.start-without-test
   (:require [mount :as m]
             [app.config :refer [app-config]]
             [app.nyse :refer [conn]]