Purpose

A repo demonstrating CLJS Issue 2023

This repo provides a minimal harness for testing the efficacy of using js/goog.DEBUG to provoke Dead Code Elimination in production builds.

It compares the efficacy of js/goog.DEBUG and goog.DEBUG. It can be used to show a change of behaviour (bug!) occured sometime between ClojureScript 1.9.293 and 1.9.456.

Test Steps:

1. Choose to download a particular version of ClojureScript.
   Download the cljs.jar for the release you want to test, into the root of this repo.

2. In the root of this repo, at the commandline, trigger a compile by executing:

   • Windows: java -cp "cljs.jar;src" clojure.main build.clj
   • Linux/Mac: java -cp cljs.jar:src clojure.main build.clj

   Look in build.clj for the compile options used. Notice use of :advanced compilation and that goog.DEBUG is set to false.

3. open out/main.js and inspect the compiled code.
   Look at the end of the file for what strings exist.
   If you see "If this string appears in main.js then '^boolean js/goog.DEBUG' is failing to cause DCE" the string is self explanatory.

To appreciate step 3, look at the tiny amount of code in src\core.cljs.

My Experimental Results

By varing Step 1 (above), I found:

• For ClojureScript version 1.9.456 there was a problem (the damning string showed up in main.js)
• For ClojureScript version 1.9.293 there was NO problem (no damning string showed up in main.js)