Nil component

src/darkleaf/di/core.clj

@@ -92,12 +92,21 @@
      :declared-deps  deps
      :remaining-deps (seq deps)}))
 
-(defn- build-obj [built-map head]
+(defn- build-obj* [built-map head]
   (let [factory       (:factory head)
         declared-deps (:declared-deps head)
         built-deps    (select-keys built-map (keys declared-deps))]
     (p/build factory built-deps)))
 
+(defn- build-obj [built-map stack]
+  (try
+    (build-obj* built-map (peek stack))
+    (catch Exception ex
+      (throw (ex-info "An error during component build"
+                      {:type  ::build-error
+                       :stack (map :key stack)}
+                      ex)))))
+
 (defn- build [{:keys [registry *stop-list]} key]
   (loop [stack     (list (stack-frame key :required (registry key)))
          built-map {}]
@@ -126,7 +135,7 @@
                    built-map))
 
           :else
-          (let [obj  (build-obj built-map head)
+          (let [obj  (build-obj built-map stack)
                 stop #(p/demolish factory obj)]
             (vswap! *stop-list conj stop)
             (case [obj dep-type]
@@ -592,12 +601,19 @@
 (defn- stop-fn [variable]
   (-> variable meta (::stop (fn no-op [_]))))
 
+(defn- validate-component-obj! [obj variable]
+  (when (nil? obj)
+    (throw (ex-info "A component fn should not return nil"
+                    {:variable variable}))))
+
 (defn- var->0-component [variable]
   (let [stop (stop-fn variable)]
     (reify p/Factory
       (dependencies [_])
       (build [_ _]
-        (variable))
+        (let [obj (variable)]
+          (validate-component-obj! obj variable)
+          obj))
       (demolish [_ obj]
         (stop obj)))))
 
@@ -608,7 +624,9 @@
       (dependencies [_]
         deps)
       (build [_ deps]
-        (variable deps))
+        (let [obj (variable deps)]
+          (validate-component-obj! obj variable)
+          obj))
       (demolish [_ obj]
         (stop obj)))))
 
@@ -641,7 +659,7 @@
                      [0] (var->0-component variable)
                      [1] (var->1-component variable)
                      (throw (ex-info
-                             "The component must only have 0 or 1 arity"
+                             "A component fn must only have 0 or 1 arity"
                              {:variable variable
                               :arities  arities})))
         #_service  (case arities

test/darkleaf/di/component_test.clj

@@ -0,0 +1,33 @@
+(ns darkleaf.di.component-test
+  (:require
+   [clojure.test :as t]
+   [darkleaf.di.core :as di])
+  (:import
+   (clojure.lang ExceptionInfo)))
+
+(defmacro try-catch [& body]
+  `(try
+     ~@body
+     nil
+     (catch Exception ex#
+       ex#)))
+
+(defn nil-component-0-arity
+  {::di/kind :component}
+  []
+  nil)
+
+(defn nil-component-1-arity
+  {::di/kind :component}
+  [-deps]
+  nil)
+
+(t/deftest nil-component-0-arity-test
+  (let [ex (try-catch (di/start `nil-component-0-arity))]
+    (t/is (= "An error during component build" (-> ex ex-message)))
+    (t/is (= "A component fn can't return nil" (-> ex ex-cause ex-message)))))
+
+(t/deftest nil-component-1-arity-test
+  (let [ex (try-catch (di/start `nil-component-1-arity))]
+    (t/is (= "An error during component build" (-> ex ex-message)))
+    (t/is (= "A component fn can't return nil" (-> ex ex-cause ex-message)))))

test/darkleaf/di/tutorial/y_graceful_stop_test.clj

@@ -32,7 +32,7 @@
                           ::on-stop-dep-ex   on-stop-dep-ex}
         ex               (try
                            (di/start `root registry)
-                           (catch Throwable ex
+                           (catch Exception ex
                              ex))]
-    (t/is (= on-start-root-ex ex))
+    (t/is (= on-start-root-ex (ex-cause ex)))
     (t/is (= [on-stop-dep-ex] (vec (.getSuppressed ex))))))