Wednesday, May 20, 2009

Convergence 1

Warning: Extremely Boring, Project-Specific Post

I worked really hard today, and I have lots to report. I started at 6:30am and worked straight through on GSoC until about 7:30pm. I also spent some time investigating alternate tooling, and I'll talk a bit about this in another post.

So, to recap, we have this stack: Demos/GEF/Draw2d/SWT/JRE. The goal of this week is to get Draw2d to compile under GWT. After that, I'll have to try to get it to run, but for now, I'm just concerned with getting it to compile. This, of course, means figuring out what Draw2d's dependencies are in SWT and the JRE, and where they are not satisfied, writing out stub code and small TODO comments. Also, I will atempt, where possible, to reuse the existing, non-functional code from the previous project that used GWT to compile SWT to js.

To summarize my experiences of today: JRE == SUCCESS, SWT == FAIL.

First some background: GWT already provides some JRE emulation, but it is not sufficient to compile the SWT codebase. To get SWT to compile, one must at least implement certain stub interfaces that GWT does not provide. There are additional issues, such as reflection, that may be more serious, and I'll talk about those in a later post. The extension to the GWT emulation classes live in the project org.eclipse.swt.e4.jcl. Left over from the previous project were three GWT modules which I was never able to compile. Additionally, it was unclear to me how these modules were supposed to compile, as they used the GWT module "source" tag, rather than the "super-source" tag, which, according to all of the documentation I have read, is what one is supposed to use when implementing JRE classes.

Today, I successfully compiled the previous project's JCL classes. In order to accomplish this, I applied Technique 1 from my previous post, which is to say, I added a prefix ("e4") to the JCL packages, where before there was no prefix, and I used <super-source path="e4"/> in my GWT modules. I had to futz a bit to discover in which order I should import the modules, but after that, they compiled without complaint, w00t

//TODO: insert complete project structure here

Note that, since yesterday, I have been developing this prototype outside of the Eclipse environment. My toolset has consisted of GNU Screen, Vim, a Vim plugin called VimExplorer, and Ant. This has allowed me to ignore all of the IDE-specific confusion that I have so far encountered. My next post will be about my experiences using some of these tools.

I was feeling very optimistic after succeded in getting JCL to compile, so I set it as my goal to get the necessary SWT libraries to compile as well. Unfortunately, I failed in this task, because, I believe, I took the wrong approach. The approach I took was to attempt to reuse directly the SWT emulation classes left over from the previous project, just as I reused the previous project's JCL classes. Unfortunately, these SWT emulation classes had many missing dependencies. My strategy was to just keep hacking on it (adding in missing classes, stub methods, etc.), until the thing worked. I spent most of the afternoon working on this, probably about 4 hours. Ultimately, I ended up pulling in most of the code in "org.eclipse.swt/Eclipse SWT/common". I didn't get to the end of the dependency chain, but I think I got far enough along to recognize a trend that I wasn't happy with, namely, pulling in dependencies that in turn rely on other dependencies, etc. It should be a major priority to limit dependencies, because the more deps I cut out, the less complex my project will be. Given that this project is still at the prototyping stage, reducing complexity is of critical importance.

Note that I also tried compiling "org.eclipse.swt/Eclipse SWT/common", but this pulled in some native code which GWT was unhappy with. So, I really do need to be selective.

The alternative to today's approach is to start at the top of the stack (work top-down) and discover what the dependencies are for the Draw2d demos; then, find out what the dependencies are for Draw2d; then, very carefully, attempt to pull in those deps from org.eclipse.swt, or stub them out. I intend to use Doxygen to figure out the complete dependency chain. This will be tomorrow's work.

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