"once" builds should have non-zero exit codes on failure

[palfrey]

I've got a build under Docker where I failed to copy in some of the source files prior to running figwheel as lein figwheel :once dev, and got the below error. I can fix it, but I was surprised at the non-zero exit code. I can't seem to find anything to make this error output when exceptions like this are hit.

Compiling build :dev to "resources/public/js/compiled/app.js" from ["src/cljs"]...
Failed to compile build :dev from ["src/cljs"] in 0.333 seconds.
----  Exception    ----

  src/cljs (No such file or directory)

----  Exception Stack Trace  ----

java.io.FileNotFoundException: src/cljs (No such file or directory)
 at java.io.FileInputStream.open0 (FileInputStream.java:-2)
    java.io.FileInputStream.open (FileInputStream.java:195)
    java.io.FileInputStream.<init> (FileInputStream.java:138)