The Closure compiler has three compilation levels. CompilationLevel.WHITESPACE_ONLY CompilationLevel.SIMPLE_OPTIMIZATIONS CompilationLevel.ADVANCED_OPTIMIZATIONS
Right now, JSClosureCompilerWrapper specifies the ADVANCED_OPTIMIZATIONS compilation level. This level changes the code the most, but it can also be the most, well, destructive. Unfortunately, the files in js-release have never worked for one of my projects because my projects need to call out to external libraries. The Closure compiler supports passing in externs files to preserve the right API names for external libraries, of course. I don't actually know if FlexJS exposes the ability to pass in externs at this point in the compilation process (I know externc uses externs files, obviously). However, I'd rather not need to do that regardless. It's a pretty demanding requirement, in my opinion. I think it adds a barrier to entry, and if supported, it should be opt-in. I tried creating a build that used SIMPLE_OPTIMIZATIONS instead. It worked a little bit better. It was able to call out to external libraries, but some things weren't clearly broken in the browser. Unfortunately, the browser console did not show any runtime errors, so it's hard to say what broke without some serious debugging. It seems that Closure compiler's optimizations are still somewhat destructive at the SIMPLE_OPTIMIZATIONS level. When I created a build that used WHITESPACE_ONLY, everything worked as expected. I personally think that WHITESPACE_ONLY should be the default in JSClosureCompilerWrapper. This compilation level still minifies the code, which is what we care about the most for a release build. Most JS developers don't do more than basic minimization, as I've come to understand it. The more advanced stuff that the Closure compiler does is more out of the ordinary. Probably due to the potential for breaking things. I remember when I worked at Yahoo, the recommended best practice was to avoid renaming things during minification. Can we change JSClosureCompilerWrapper to use WHITESPACE_ONLY instead? - Josh
