(CLJS) A local named `new` breaks go macro in cljs (not in clj)

Question

`
(<! (go

  (let [new 42]
    [new])))

`

yields: #object(link: TypeError TypeError: 42.call is not a function)

new is not properly handled.

Answer 1

Reference: https://clojure.atlassian.net/browse/ASYNC-176 (reported by alex+import)

Answer 2

I don't have an answer to this question. I was facing the same problem and did a bit of digging and thought I can share it here to help whoever is looking at this. I found that this issue is associated with creating cljs.core/PersistentVector. Here are my examples:

(require '[cljs.core.async :refer [go <! chan put!]])

(def c (chan))

(put! c {:hi "here"})

;; This fails
(go
  (let [{:keys [new] :as msg} (<! c)]
    (js/console.log [:msg-received msg])))
;; ioc_helpers.cljs:50 Uncaught TypeError: inst_25288.call is not a function
;; at switch__20329__auto__ (eval at figwheel$repl$eval_javascript_STAR__STAR_ (repl.cljc:364), <anonymous>:86:29)
;; at eval (eval at figwheel$repl$eval_javascript_STAR__STAR_ (repl.cljc:364), <anonymous>:166:51)
;; at mini_reframe$app$state_machine__20330__auto____1 (eval at figwheel$repl$eval_javascript_STAR__STAR_ (repl.cljc:364), <anonymous>:188:4)
;; at mini_reframe$app$state_machine__20330__auto__ (eval at figwheel$repl$eval_javascript_STAR__STAR_ (repl.cljc:364), <anonymous>:204:57)
;; at cljs$core$async$impl$ioc_helpers$run_state_machine (ioc_helpers.cljs:43)
;; at cljs$core$async$impl$ioc_helpers$run_state_machine_wrapped (ioc_helpers.cljs:47)
;; at eval (eval at figwheel$repl$eval_javascript_STAR__STAR_ (repl.cljc:364), <anonymous>:218:67)
;; at cljs$core$async$impl$dispatch$process_messages (dispatch.cljs:27)
;; at MessagePort.channel.port1.onmessage (nexttick.js:218)

(put! c {:hi "here"})

;; All the below cases work
(go
  (let [{:keys [a] :as msg} (<! c)]
    (js/console.log [:msg-received msg])))
;; [:msg-received {:hi "here"}]

(put! c {:hi "here"})

(go
  (let [msg (<! c)]
    (js/console.log [:msg-received msg])))
;; [:msg-received {:hi "here"}]

(put! c {:hi "here"})

(go
  (let [{:keys [new] :as msg} (<! c)]
    (js/console.log msg)))
;; {:hi "here"}

(put! c {:hi "here"})

(defn receive-msg [msg]
  (js/console.log [:msg-received msg]))

(go
  (let [{:keys [new] :as msg} (<! c)]
    (receive-msg msg)))
;; [:msg-received {:hi "here"}]

When I compare at the macroexpand-1 results, I found that in the failure case, the let-binding for new seems to be shadowing the JS new keyword, see the inst_23688 symbol before cljs.core/PersistentVector:

  (macroexpand-1
    '(go
       (let [{:keys [new] :as msg} (<! c)]
         (js/console.log [:msg-received msg]))))
  => ...
      (clojure.core/let
           [inst_23687
            (clojure.core/aget state_23694 2)
            inst_23688
            (cljs.core/get inst_23687 :new)
            inst_23689
            (. cljs.core/PersistentVector -EMPTY-NODE)
            inst_23690
            (js* "[~{},~{}]" :msg-received inst_23687)
            inst_23691
            (inst_23688
             cljs.core/PersistentVector
             nil
             2
             5
             inst_23689
             inst_23690
             nil)
            inst_23692
            (js/console.log inst_23691)
            state_23694
            state_23694]
           (cljs.core.async.impl.ioc-helpers/return-chan
            state_23694
            inst_23692))

Whereas in the successful case, there's the plain new JS keyword before the cljs.core/PersistentVector:

  (macroexpand-1
    '(go
       (let [{:keys [a] :as msg} (<! c)]
         (js/console.log [:msg-received msg]))))
=> ...
(clojure.core/let
           [inst_24256
            (clojure.core/aget state_24263 2)
            inst_24257
            (cljs.core/get inst_24256 :a)
            inst_24258
            (. cljs.core/PersistentVector -EMPTY-NODE)
            inst_24259
            (js* "[~{},~{}]" :msg-received inst_24256)
            inst_24260
            (new cljs.core/PersistentVector nil 2 5 inst_24258 inst_24259 nil)
            inst_24261
            (js/console.log inst_24260)
            state_24263
            (cljs.core.async.impl.ioc-macros/aset-all!
             state_24263
             8
             inst_24257)]
           (cljs.core.async.impl.ioc-helpers/return-chan
            state_24263
            inst_24261))