I am willing to mentor this, btw.
It already does that. http://mxr.mozilla.org/mozilla-central/source/config/Preprocessor.py#132 And for example, if I look in components/FeedWriter.js in an omni.ja from a try build i did recently, I can see: //@line 652 "e:\builds\moz2_slave\try-w32\build\browser\components\feeds\src\FeedWriter.js"
In that case, the preprocessor is not applied uniformly. Experiment: - add the following line to test_jsctypes.js.in throw new Error("BOOM"); - launch the test. I added this at line 1770 and the stack displayed the error at line 1755.
I confirm that the preprocessor does its job correctly on test_jsctypes.js.in. I will continue the investigation.