Fix nil return value

src/babashka/pods/impl.clj

@@ -64,12 +64,20 @@
                             (ex-info message data))
                           value)
                   chan (get @chans id)
+                  promise? (instance? clojure.lang.IPending chan)
                   out (some-> (get reply "out")
                               bytes->string)
                   err (some-> (get reply "err")
                               bytes->string)]
-              (when (or value* error?) (async/put! chan value))
+              (when (or value* error?)
-              (when (or done? error?) (async/close! chan))
+                (if promise?
+                  (deliver chan value)
+                  (async/put! chan value)))
+              (when (or done? error?)
+                (if promise?
+                  (deliver chan nil) ;; some ops don't receive a value but are
+                                     ;; still done.
+                  (async/close! chan)))
               (when out
                 (binding [*out* out-stream]
                   (println out)))
@@ -91,14 +99,15 @@
                    :edn pr-str
                    :json cheshire/generate-string)
         id (next-id)
-        chan (async/chan)
+        chan (if async? (async/chan)
+                 (promise))
         _ (swap! chans assoc id chan)
         _ (write stream {"id" id
                          "op" "invoke"
                          "var" (str pod-var)
                          "args" (write-fn args)})]
     (if async? chan ;; TODO: https://blog.jakubholy.net/2019/core-async-error-handling/
-        (let [v (async/<!! chan)]
+        (let [v @chan]
           (if (instance? Throwable v)
             (throw v)
             v)))))

test-pod/pod/test_pod.clj

@@ -56,7 +56,8 @@
                                               {"name" "assoc"}
                                               {"name" "error"}
                                               {"name" "print"}
-                                              {"name" "print-err"}]}]
+                                              {"name" "print-err"}
+                                              {"name" "return-nil"}]}]
                                     "ops" {"shutdown" {}}})
                             (recur))
               :invoke (let [var (-> (get message "var")
@@ -107,7 +108,12 @@
                                 "id" id})
                               (write
                                {"status" ["done"]
-                                "id" id})))
+                                "id" id}))
+                          pod.test-pod/return-nil
+                          (write
+                           {"status" ["done"]
+                            "id" id
+                            "value" "nil"}))
                         (recur))
               :shutdown (System/exit 0))))))))
 

test/babashka/pods/jvm_test.clj

@@ -14,6 +14,7 @@
     (is (= '[{:a 1, :b 2}
              6
              [1 2 3 4 5 6 7 8 9]
-             "Illegal arguments / {:args (1 2 3)}"] ret))
+             "Illegal arguments / {:args (1 2 3)}"
+             nil] ret))
     (is (= "nil\n(\"hello\" \"print\" \"this\" \"debugging\" \"message\")\n" (str out)))
     (is (= "(\"hello\" \"print\" \"this\" \"error\")\n" (str err)))))

test/babashka/pods/sci_test.clj

@@ -20,6 +20,7 @@
     (is (= '[{:a 1, :b 2}
              6
              [1 2 3 4 5 6 7 8 9]
-             "Illegal arguments / {:args (1 2 3)}"] ret))
+             "Illegal arguments / {:args (1 2 3)}"
+             nil] ret))
     (is (= "nil\n(\"hello\" \"print\" \"this\" \"debugging\" \"message\")\n" (str out)))
     (is (= "(\"hello\" \"print\" \"this\" \"error\")\n" (str err)))))

test/babashka/pods/test_common.clj

@@ -21,4 +21,5 @@
 [(pod/assoc {:a 1} :b 2)
  (pod.test-pod/add-sync 1 2 3)
   @stream-results
-  ex-result]")
+  ex-result
+  (pod.test-pod/return-nil)]")