JavaScript:New to SpiderMonkey

This is a page to help new member of the JS team or new contributors to SpiderMonkey to orient themselves. It's maintained by Paul Biggar (pbiggar@mozilla.com), who is currently new to SpiderMonkey. Please help by telling me what you found useful when you were new.

Tutorial: your first patch

The first step to getting involved with SpiderMonkey is to make your first patch. This guides you through it, and at the end you should have learnt a lot of the procedures and formalisms involved in getting things done here.

We'll assume you're on a Unix-y platform, and that you know what you're doing. We'll ignore nearly all details.

Get the code

We work out of the "tracemonkey" branch of the Mozilla Mercurial repository. Download it:

hg clone http://hg.mozilla.org/tracemonkey

Build Firefox

The tracemonkey/ directory contains a full copy of all the firefox source code. Before building it, you need a .mozconfig file. Download one we made earlier:

wget http://TODO/.mozconfig -O ~/.mozconfig

Build it:

cd tracemonkey 
make -f client.mk build 

This builds an "out-of-source" build, where the object files and binaries are in obj-i686-pc-linux-gnu (depending of course on your platform).

This is going to take a long time, maybe an hour on a four core machine. It's a good time to peruse the rest of this guide.

Build the js shell

Most of the time, you'll be working with the Javascript shell, instead of the full Firefox browser. So build the shell:

cd js/src 
mkdir build_DBG.OBJ 
cd build_DBG.OBJ 
../configure --enable-debug --disable-optimize

Fix something

At this point, you're ready to make your first fix.

TODO: something useless. Maybe adding a datemicrosecond function.

Building your changes

Having made the change, build the shell again.

cd build_DBG.OBJ 
make

Testing your changes

It builds. Hurray. Time to run the tests to check you haven't broken anything.

python trace-tests/trace-test.py build_DBG.OBJ/js

The trace tests are pretty quick, and should give you an idea if you've gotten something wrong. Assuming nothing goes wrong, try the ref-tests:

cd build_DBG.OBJ 
python ../tests/jstests.py ./js --args="-j"

Benchmark your changes

Tests all pass. Congrats, you didn't break anything. Now, did you make it faster or slower? We benchmark using the v8 and SunSpider benchmarks. Get the benchmarks:

svn checkout http://svn.webkit.org/repository/webkit/trunk/SunSpider

And now run them:

cd SunSpider 
./sunspider --args="-j" --shell=../build_DBG.OBJ/js --run=30 --suite=sunspider-0.9.1 
cd ..

Optimized build

Whoops, we benchmarked the debug version. Let's make an optimized build to test instead.

mkdir build_OPT.OBJ 
cd build_OPT.OBJ 
../configure --disable-debug --enable-optimize
make 
cd ..

Repeat the sunspider steps above, and take note of the line that looks like:

Results are located at sunspider-0.9.1-results/sunspider-results-2010-08-07-17.56.48.js

You'll need that later.

Baseline version / Mercurial Queues

We need to time our optimized version against the baseline version. This calls for a brief introduction to mercurial queues, which most people think is a pretty good way of managing their SpiderMonkey workflow:

hg qinit
hg qnew my_first_patch -f
hg qrefresh

This puts your current work into a patch, managed by Mercurial, symbolically called my_first_patch. To pop the patch off:

hg qpop

And we're back to our pristine version.

Compare

Build again and rerun SunSpider again. You should now have two files like:

sunspider-0.9.1-results/sunspider-results-2010-08-07-17.56.48.js

Compare them using the compare script:

cd SunSpider 
sunspider-compare-results --shell=build_DBG.OBJ/js FILE1 FILE2

Get a real bug

At this point, you've seen nearly everything you need to do hack on SpiderMonkey. So it's time to get a real bug to work on. Go to the IRC channel, #jsapi on irc.mozilla.org, and say the magic words:

"I'm a beginner who wants to hack on SpiderMonkey. Can anyone give me a starter bug?"

I'm hoping that works, I haven't tried it myself.

Fix the bug, updating the bug report with your progress. When it's done, repeat all the steps above. Then it's time to get your patch into the tree.

Submit a patch

To get the patch from mercurial, use:

hg qdiff # if you're using queues or
hg diff  # if you're not

Add it to the bug as an attachment.

Get a review

Nothing gets into the tree without a review, so you'll need one. The easiest way to get a review is to go to the #jsapi IRC channel on irc.mozilla.org and ask for a volunteer. Point them to the bug. In all likelyhood, they'll give you a review and ask you to change something. Fix what they ask, resubmit the patch to bugzilla, and ask for another review. After you repeat this step a few times, they'll say something like "review=me" meaning it's now good to commit.

Try server

On your first commit, you're likely to be a little wary of breaking things. Mozilla has a "tryserver" where you can send a patch, and it'll be built on tons of machines which will report back to you.

The guide for getting "level 1" access, which you need for the try server, is here. Ask your reviewer to vouch for you, and send in the paperwork ASAP.

TODO: Move this elsewhere. Level 1 access can take ages.

https://wiki.mozilla.org/Build:TryServer

Commit

You can't commit until you have "level 2" access, and you don't have level 2 access (at time of writing, I don't have level 2 access), so you'll need someone to do this for you. The volunteer from IRC may do this, otherwise you'll need a new volunteer.

After committing, a large series of tests will be run to make sure you didn't break anything. You'll need to hang around to make sure you didn't break something. Check http://tests.themasta.com/tinderboxpushlog/?tree=TraceMonkey for red marks.

TODO: we don't want them worrying about false positives either, since there are plenty.

Overview of the JS engine

The JS engine is a swiftly moving target. The most detailed information is available at https://developer.mozilla.org/en/SpiderMonkey. Here are some particularly interesting, mostly up-to-date resources:

High level overviews

http://hacks.mozilla.org/2010/03/a-quick-note-on-javascript-engine-components/

https://developer.mozilla.org/En/SpiderMonkey/Internals

http://users.alliedmods.net/~dvander/jm_presentation.pdf

http://hacks.mozilla.org/2009/07/tracemonkey-overview/

Medium level documentation

Mapping JS idioms to SpiderMonkey code: https://developer.mozilla.org/En/SpiderMonkey/JSAPI_Phrasebook

Detailed documentation

Build: https://developer.mozilla.org/en/SpiderMonkey/Build_Documentation

Testing: https://developer.mozilla.org/en/SpiderMonkey/Running_Automated_JavaScript_Tests

Shell: https://developer.mozilla.org/En/SpiderMonkey/Introduction_to_the_JavaScript_shell

Function reference: https://developer.mozilla.org/en/SpiderMonkey/JSAPI_Reference

Collaboration and teamwork

- Overview
- repository
  - sharing
  - hgrc file
  - useful plugins
  - jaeger + trace + integration
- Tests
- benchmarks
- build a shell
- coding style
  - ignore old doc
  - link to recent doc: JavaScript:SpiderMonkey:C++ Coding Style
  - important compilers and platforms

- bugzilla
  - fixed-in-tracemonkey
- following what other team members are doing
  - status page
  - Get alerted to new bugs: From bugzilla, go to your preferences, then click "Email Preferences" then, near the bottom, follow the user "general@spidermonkey.bugs"
- patch policy
- commit access
  - checkin needed
- reviewers
- mercurial queues
- irc
- mailing list

- who are they, which faces in phonebook
- who's in "charge"
- blogs and twitterers, etc