Saturday, March 14, 2009

On-the-fly Syntax Checker and Code Outline View for Bespin

I continued to work on bespin and submitted my first complex patch for review. The patch builds on my work about moving JS objects into web workers and implements syntax checking as well as a simple code outline view for JavaScript. All these features are automatically disabled when you do not have access to web workers because syntax checking is too complex to be performed inside the UI thread.

The outline view is activated by typing the outline command:

The functions names are clickable and move the cursor to the line where the function is defined.

Syntax errors are displayed as short info on the bottom of the screen:

It might be possible to underline the relevant code, but I need to dive deeper into bespin to do this (plus get more info out of the JS parser).

While working on the code I made some discoveries about Gears and Web Workers:
  • Apparently you are not allowed to define a constant called Block inside a Gears worker
  • Safari 4 currently does not support any way to load source code into a worker (both importScripts and XMLHttpRequest are not implemented). For now I pasted all source into a bootstrap-script. Another possible solution would be to send a message to the main page asking it to make the http request and send back the result.
  • I removed the ugly hack to send source to the worker inside the hash part of the url and instead send the source to the worker via postMessage immediately after loading.
I tested the system in Safari 4, FF 3.1 beta and FF 3.0.x with Google Gears. The current patch only supports syntax checking for JavaScript. Other languages could be added in a similar fashion to language-dependend syntax highlighters, though.
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