add codox task

deps.edn

@@ -22,4 +22,12 @@
   ;; clj -M:outdated
   :outdated {:extra-deps {com.github.liquidz/antq {:mvn/version "2.11.1250"}}
              :main-opts ["-m" "antq.core"]}
+
+  ;; Regenerate docs in docs/
+  ;; clj -X:docs
+  :docs {:extra-deps {codox/codox {:mvn/version "0.10.8"}}
+         :exec-fn codox.main/generate-docs
+         :exec-args {:source-paths ["src/main/clojure"]
+                     :namespaces [clojure.core.async clojure.core.async.flow clojure.core.async.flow.spi]
+                     :output-path "apidocs"}}
   }}

src/main/clojure/clojure/core/async.clj

@@ -277,6 +277,8 @@ to catch and handle."
   "returns derefable [val port] if immediate, nil if enqueued"
   [fret ports opts]
   (assert (pos? (count ports)) "alts must have at least one channel operation")
+  (doseq [port ports :when (vector? port)]
+    (assert (not (nil? (nth port 1))) "alts can't put nil on channel"))
   (let [flag (alt-flag)
         ports (vec ports) ;; ensure vector for indexed nth
         n (count ports)

src/test/clojure/clojure/core/async_test.clj

@@ -465,3 +465,10 @@
              :ok
              (catch AssertionError e
                :ko))))))
+
+(deftest test-alts-put-nil-invalid
+  (is
+    (thrown? AssertionError
+      (let [c1 (a/chan)
+            c2 (a/chan)]
+        (a/alts!! [c1 [c2 nil]])))))