Not able to inspect state at breakpoint after re-defining function in REPL

debugger-demo.core.cljs

; Consider the following code:

(ns debugger-demo.core)
(defn init []
  (let [a (+ 1 2 3)]
    (js-debugger)))

; Reload the page and let the Dirac REPL connect

; We'll immediately stop at the breakpoint, and by going into the namespace we can inspect the state of the frame at which we have stopped

cljs.user > (require 'debugger-demo.core)
cljs.user > (in-ns 'debugger-demo.core)
debugger-demo.core > a
                   < 6

; But it's easy to break this. First, press play to continue exection.

; And then, let's re-define the init function:

debugger-demo.core > (defn init []
                       (let [a (+ 1 2 5)]
                         (js-debugger)))

; Then call the init function to stop at the breakpoint and try to inspect the state:

debugger-demo.core > (init)
debugger-demo.core > a

; We never get a response in the REPL client, and we see the following error in the REPL server:

SEVERE: Unhandled REPL handler exception processing message {:code a, :dirac short-circuit-presentation, :id 25, :op eval, :scope-info {:frames [{:props [{:name a}], :title Local}]}, :session 48a3efd0-b8f3-4a08-9e64-20d92b89ac27}
java.lang.AssertionError: Assert failed: promise-new-client-response! previous response promise pending
(nil? (clojure.core/deref response-promise-atom)
  at dirac.lib.weasel_server$promise_new_client_response_BANG_.invokeStatic(weasel_server.clj:141)
  at dirac.lib.weasel_server$promise_new_client_response_BANG_.invoke(weasel_server.clj:137)
  at dirac.lib.weasel_server$request_eval.invokeStatic(weasel_server.clj:198)
  at dirac.lib.weasel_server$request_eval.doInvoke(weasel_server.clj:197)
  at clojure.lang.RestFn.invoke(RestFn.java:442)
  at dirac.lib.weasel_server.WeaselREPLEnv._evaluate(weasel_server.clj:50)
  at cljs.repl$evaluate_form.invokeStatic(repl.cljc:518)
  at cljs.repl$evaluate_form.invoke(repl.cljc:452)
  at cljs.repl$repl_STAR_.invokeStatic(repl.cljc:853)
  at cljs.repl$repl_STAR_.invoke(repl.cljc:760)
  at dirac.nrepl.eval$eval_in_cljs_repl_BANG_$start_repl_fn__25076.invoke(eval.clj:245)
  at dirac.nrepl.driver$wrap_with_driver.invokeStatic(driver.clj:142)
  at dirac.nrepl.driver$wrap_with_driver.invoke(driver.clj:126)
  at dirac.nrepl.eval$eval_in_cljs_repl_BANG_.invokeStatic(eval.clj:249)
  at dirac.nrepl.eval$eval_in_cljs_repl_BANG_.doInvoke(eval.clj:212)
  at clojure.lang.RestFn.invoke(RestFn.java:758)
  at dirac.nrepl.utils$evaluate_BANG__STAR_.invokeStatic(utils.clj:134)
  at dirac.nrepl.utils$evaluate_BANG__STAR_.invoke(utils.clj:122)
  at dirac.nrepl.utils$evaluate_BANG_.invokeStatic(utils.clj:148)
  at dirac.nrepl.utils$evaluate_BANG_.invoke(utils.clj:145)
  at dirac.nrepl.piggieback$handle_eval_message_BANG_.invokeStatic(piggieback.clj:63)
  at dirac.nrepl.piggieback$handle_eval_message_BANG_.invoke(piggieback.clj:60)
  at dirac.nrepl.piggieback$handle_nonspecial_nonjoined_message_BANG_.invokeStatic(piggieback.clj:77)
  at dirac.nrepl.piggieback$handle_nonspecial_nonjoined_message_BANG_.invoke(piggieback.clj:70)
  at dirac.nrepl.piggieback$handle_nonspecial_message_BANG_.invokeStatic(piggieback.clj:85)
  at dirac.nrepl.piggieback$handle_nonspecial_message_BANG_.invoke(piggieback.clj:80)
  at dirac.nrepl.piggieback$handle_message_BANG_.invokeStatic(piggieback.clj:92)
  at dirac.nrepl.piggieback$handle_message_BANG_.invoke(piggieback.clj:87)
  at dirac.nrepl.piggieback$handler_job_BANG_.invokeStatic(piggieback.clj:97)
  at dirac.nrepl.piggieback$handler_job_BANG_.invoke(piggieback.clj:94)
  at dirac.nrepl.piggieback$dirac_nrepl_middleware_handler.invokeStatic(piggieback.clj:106)
  at dirac.nrepl.piggieback$dirac_nrepl_middleware_handler.invoke(piggieback.clj:102)
  at clojure.core$partial$fn__5561.invoke(core.clj:2616)
  at clojure.tools.nrepl.middleware$wrap_conj_descriptor$fn__7890.invoke(middleware.clj:22)
  at clojure.tools.nrepl.middleware.pr_values$pr_values$fn__8089.invoke(pr_values.clj:22)
  at clojure.tools.nrepl.middleware$wrap_conj_descriptor$fn__7890.invoke(middleware.clj:22)
  at boot.repl_server$wrap_init_vars$fn__8397$fn__8399.invoke(repl_server.clj:35)
  at clojure.tools.nrepl.middleware.session$session$fn__8241.invoke(session.clj:192)
  at clojure.tools.nrepl.middleware$wrap_conj_descriptor$fn__7890.invoke(middleware.clj:22)
  at clojure.tools.nrepl.server$handle_STAR_.invokeStatic(server.clj:19)
  at clojure.tools.nrepl.server$handle_STAR_.invoke(server.clj:16)
  at clojure.tools.nrepl.server$handle$fn__8314.invoke(server.clj:28)
  at clojure.core$binding_conveyor_fn$fn__5476.invoke(core.clj:2022)
  at clojure.lang.AFn.call(AFn.java:18)
  at java.util.concurrent.FutureTask.run(FutureTask.java:266)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
  at java.lang.Thread.run(Thread.java:745))

A solution is to save the file where the updated init function is defined, triggering a reload/code injection via figwheel/boot-reload/boot-figreload. The next time we call (init), it behaves exactly as the first run.