inf-clojure does not return prompt on entering new-line

[slipset]

Expected behavior

When opening a new inf-clojure process and typing RET multiple times, I expect to see
multiple prompts:

Planck 2.8.1
ClojureScript 1.9.946
    Docs: (doc function-name-here)
          (find-doc "part-of-name-here")
  Source: (source function-name-here)
    Exit: Control+D or :cljs/quit or exit or quit
 Results: Stored in vars *1, *2, *3, an exception in *e

cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=> 
cljs.user=>

Actual behavior

Process inf-clojure finished
Planck 2.8.1
ClojureScript 1.9.946
    Docs: (doc function-name-here)
          (find-doc "part-of-name-here")
  Source: (source function-name-here)
    Exit: Control+D or :cljs/quit or exit or quit
 Results: Stored in vars *1, *2, *3, an exception in *e

cljs.user=> 

Steps to reproduce the problem

M-x inf-clojure
Type RET a couple of times.

I can change this behaviour by redefining inf-clojure--send-string so that it does not check for
(> (length string) 0) when sending the command, and stuff works as I expect, eg
with

(defun inf-clojure--send-string (proc string)
  (inf-clojure--set-repl-type proc)
      (comint-simple-send proc string))

things work as I expect.

[arichiardi]

So that change was introduced in order to avoid spurious prompts when the string to send is empty. There were cases when this was happening quite often (especially in lumo), so I put a patch that admittedly is not the best. I should probably remove it and investigate what actually happens now that we can dump the REPL activity.

[bbatsov]

Yeah, we should fix this.