Flex Compiler SHell (fcsh)

In early summer 2005, the Flex development team was busy working on Flex 2. The new Flex compiler redesign and implementation were finally gaining traction (well, you have no idea how frustrating it was when you had to build a new compiler that integrated with some unstable AS3 compiler pieces and had to run those resulting SWFs in an unstable VM). Anyhow, Dan Smith and I believed that it was the right time to discuss with the Flex Builder team about integrating the Flex compiler into FB2.

FB2 is an Eclipse-based IDE for Flex application development. Similar to other IDEs, FB2 should be able to compile Flex applications incrementally. Back then, the new compiler could barely generate good SWFs and the compiler’s full compile performance was not something we were proud of. But you know, things will get better over time, so I decided to switch focus and work a little bit on the incremental compilation support.

Now that the Flex compiler is open source, you should be able to trace how incremental compilation is done. But it might be difficult to identify the code that is responsible for incremental compilation – there is nothing like incrementalCompile() or something like that. One reason is that the compiler algorithms (API.batch1() and API.batch2()) are actually designed for incremental compilations. They treat full compilations as special cases, i.e. a full compilation is a case where everything needs to be recompiled.

Frankly, it wasn’t that hard to nail the basic incremental compilation support as long as you were dealing one unified algorithm for full vs. incremental. But FB at that point did not have any code in it that would invoke the compiler. Well, for testing, I had to write a tool (not just some test cases) to prove that incremental compilation worked.

To simulate how the compiler works in an IDE, what could be better than doing it in some sort of shell environment (Well, writing an Eclipse plugin as a simulator is straightforward too, but that’s not the point!). Yup, a shell. That’s what I built – Flex Compiler SHell (fcsh). Note that it’s SHell, not Shell. Some official Flex documentation are still using ‘Shell’ – I don’t like that. 😛

It took me a couple of days to get fcsh up and running. There are so many upsides using fcsh than mxmlc and/or compc. One of them is that you eliminate JVM startup time and those 2000+ compiler classes that JVM needs to load for even typical Flex applications. Those overhead could add up to 2 seconds. Another advantage is of course, what it’s built for – incremental compilation. I wasted no time dumping mxmlc and compc and used fcsh exclusively for my daily development work.

Soon after its availability, other folks on the team found good use of it. The QA and doc team dramatically cut their time for building their applications by using fcsh to batch-process their apps.

Due to the nature of my work, i.e. compiler development, I needed to be able to get to data that I couldn’t find in a SWF, e.g. dependency info, bytecode sizes, etc. For this reason, I added a slew of fcsh commands:

• abc – outputs abc bytecodes given a definition name
• dependency – displays a list of dependencies given a file name
• files – lists all the source and SWC files that contribute to the resulting SWF
• sizes – lists the bytecode size of all the definitions in the resulting SWF
• lines – displays the number of ‘debuggable’ lines in the resulting SWF
• memory – displays memory usage (when using JDK 1.5)
• mm.cfg – displays settings in mm.cfg
• trace – turns tracing on/off in mm.cfg
• exportorder – displays the export order of the definitions in the resulting SWF

At first, product management and engineering management weren’t warm to the idea of adding a new tool to the SDK without getting requests from our customers. That’s why you don’t see fcsh in the Flex 2 SDK release.

But the Flex product management reversed their decision and shipped fcsh in Flex 2.0.1. That was great news. But the bad news was that the above-mentioned fcsh commands must be removed.

If you still have Flex SDK 2.0.1 installed, you can check out fcsh.jar. I think it points to flex2.tools.SimpleShell. If you change the manifest to point to flex2.tools.Shell, you will get the full version.

If you only have Flex SDK 3 installed, you’re out of luck because flex2.tools.Shell is no longer distributed. In my opinion, the Flex product/engineering management should consider adding the flex2.tools.Shell class back into the distribution.