DevTools/Hacking

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Revision as of 14:55, 8 May 2017 by Sole (talk | contribs) (→‎Building, running, updating and rebuilding: redirect to new document location)
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Want to work on Firefox Developer Tools? You've come to the right place! If you want more information about contributing, check out our guide for getting involved.

Building, running, updating and rebuilding

These instructions have been moved to https://devtools-html.github.io/docs/building.html

Configuring your dev profile

You will want to make a couple of quick changes to the profile you use when running your version of Firefox.

Enable remote debugging and the Browser Toolbox

Open DevTools, and click the "Toolbox Options" gear icon in the top right (the image underneath is outdated). Make sure the following two options are checked:

  • Enable browser chrome and add-on debugging toolboxes
  • Enable remote debugging

These settings allow you to use the browser toolbox to set breakpoints inside of the DevTools code, inspect the DevTools themselves, and let you run the Scratchpad in the Browser environment.

Settings for developer tools - "Enable Chrome Debugging" and "Enable Remote Debugging"

You might also want to change the following preference in about:config to false:

  • devtools.debugger.prompt-connection

This will get rid of the prompt displayed every time you open the browser toolbox.

Enabling DevTools Logging

Depending on what you are working on, you may want to make some changes to your profile to enable more logging. If you type about:config in the URL bar, click through the warning page, and search for devtools you can see some of them.

Add the global "dump" function to all windows which logs strings to stdout. 

 browser.dom.window.dump.enabled = true

Dumps all packets sent over the remote debugging protocol to stdout (requires browser.dom.window.dump.enabled): 

 devtools.debugger.log = true

Log every event notification from the EventEmitter class (devtools/shared/event-emitter.js) (requires browser.dom.window.dump.enabled) 

 devtools.dump.emit = true

Restart the browser to apply configuration changes.

You may also be interested in the remote protocol inspector add-on: https://github.com/firebug/rdp-inspector/wiki

Enabling DevTools Assertions

Highly recommended for DevTools hackers!

Add this to your .mozconfig: 

 ac_add_options --enable-debug-js-modules

Assert your own invariants like this: 

 const { assert } = require("devtools/shared/DevToolsUtils");
 // ...
 assert(1 + 1 === 2, "I really hope this is true...");

When assertions are enabled, assertion failures are fatal, log console warnings, and throw errors.

When assertions are not enabled, the assert function is a no-op.

It also enables the "debug" builds of certain third party libraries, such as React.

Developer Tools Directories Overview

  • devtools/shared: Code shared by both the DevTools client (front-end UI) and server. If we are using any third party libraries, or importing external repositories into our tree, those libraries generally live here (eg, devtools/shared/acorn), assuming they are used by both client and server.
    • devtools/shared/client: Code for the DevTools [Remote Debugging Protocol http://searchfox.org/mozilla-central/source/devtools/docs/backend/protocol.md] client. (You may wonder why this is not in devtools/client below: it's mainly because tests in server also need access to the RDP client.)
    • devtools/shared/locales: Strings used in either the DevTools server only, or shared with both the client and server
  • devtools/server: Code for the DevTools [Remote Debugging Protocol http://searchfox.org/mozilla-central/source/devtools/docs/backend/protocol.md] server and transport layer.
  • devtools/client: Front end user interfaces for our tools. Should be pretty obvious what is what based on the directory names and each panel we have in our toolbox. This directory is only shipped with desktop Firefox, as opposed to other directories above, which are shipped with all Gecko products (Firefox OS, Firefox for Android, etc.)
    • devtools/client/locales: Strings used in the DevTools client (front-end UI)
    • devtools/client/themes: CSS and images used in the DevTools client (front-end UI)

DevTools Automated Tests

The contents of this section have been moved to https://dxr.mozilla.org/mozilla-central/source/devtools/docs/tests/README.md and other files in https://dxr.mozilla.org/mozilla-central/source/devtools/docs/tests/

Debugging Intermittent Test Failures

When a test fails sometimes, but not always, it is called an "intermittent". Handling these is complicated enough that we have a separate page with tips on debugging.

Finding documentation

If you read through the source code about something you do not know about, you may find documentation here:

We recommend adding a smart keyword search for DXR and MDN. If you still have questions, ask us on IRC or leave a comment on the Bugzilla ticket.

Making and Submitting a Patch

Before you make any changes, read the documentation on how to use Mozilla's version control.

Before you submit a patch, you should read our Coding Standards and run ESLint to validate your code changes (to avoid loosing time during code reviews with formatting details for instance). In general, try to be File Consistent. For new files, follow the standards.

Once you have a patch file, add it as an attachment to the Bugzilla ticket you are working on and add the feedback? or review? flag depending on if you just want feedback and confirmation you're doing the right thing or if you think the patch is ready to land respectively. Read more about how to submit a patch and the Bugzilla review cycle here.

You can also take a look at the DevTools/Code Review Checklist as it contains a list of checks that your reviewer is likely to go over when reviewing your code.

Coding Standards

DevTools has some coding standards that your changes should follow:

Potential Pitfalls

Today there are a few techniques and conventions we use that can be confusing, especially when you first start working with the code base. We hope to improve these with time to make things easier for everyone, but for now this etherpad might be a helpful set of notes if you are having trouble. If you find new pitfalls that aren't listed there, feel free to add your own entries, so we know to address them. Also, please come talk to us in #devtools on IRC, as that might be the fastest path to solving the issue.

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