DevTools/Features/Debugger

Feature	Status	ETA	Owner
DevTools/Features/Debugger	initial remote protocol work+stack trace display)	2011-05-27	Kevin Dangoor

Summary

Initial take on an integrated JavaScript debugger for Firefox.

Team

Have some thoughts on what you want out of a debugger? Inspiration on how to do it? Join us on #devtools on irc.mozilla.org

• Jim Blandy (irc: jimb): Remote debugging protocol, jsd2.
• Dave Camp (irc: dcamp): Firefox integration/UI, Remote debugging protocol.
• Jason Orendorff (irc: jorendorff): jsd2.

Repositories

• http://hg.mozilla.org/users/jblandy_mozilla.com/jsdbg2/ (JSD2)
• http://hg.mozilla.org/users/dcamp_campd.org/remote-debug/ (Remote Debugging Protocol/Firefox UI)
  • toolkit/components/debugger has most of the protocol implementation
  • browser/components/debugger has browser-specific protocol integration, and will have the debugging UI.

Related Bugs & Dependencies

See the status page for the bug list and current status.

Designs

• JSInspector
• Remote_Debugging_Protocol
• DevTools/Features/Debugger/Notes has further implementation notes.

Planning

What follows is some plan-related sketching, please update appropriately. List of milestones/sprints is roughly in order.

Bootstrapping/Stack Traces

• Working remote protocol, exposing stack frames with JSD2.
• Relying on debugger statement, no breakpoints.
• Only "continue" after stopping in debugger.
• UI shell in firefox
• UI for stack traces (without arguments)
• No iframe support just yet.

Description	Area	Bug	Owner	Best	Likely	Worst	Status
Debugging global/Root actor registration/Socket Listener	Remote Proto		dcamp	2d	3d	5d	In remote-debug.
Browser root actor/tab actors (not as thread-like actors)	Browser Proto		dcamp	2d	2d	4d
Protocol handler thread (socket transport)	Remote Proto		dcamp	?	?	?
Debug Object creation and debuggerHook	JSD2		jorendorff	1d	1d	2d	Partly done. Still to do: Debug.prototype.{add,remove,has}Debuggee, Debug.prototype.getDebuggees.
Debug Object loader	JSD2ish		dcamp				In remote-debug
Debug Object support for frame inspection	JSD2		jorendorff				type, this, older, live, callee, generator, arguments complete.
Debug Object support for the toplevel globals in tab actor - debuggerHook spawning a nested event loop.	Browser Proto		dcamp	2d	2d	4d	In progress.
New execution model specification in the remote protocol	Remote Proto		jimb
debuggerHook and "continue" exposed over remote protocol as specified.	Remote Proto		dcamp	3d	3d	5d	Need to see what new spec looks like...
Client JS API (socket transport)	UI Shell		dcamp	1d	2d	3d
HTML UI shell per tab, in its own window	UI Shell		dcamp	2d	2d	5d
UI responding to pauses (from debugger keyword)	Execution Handling		dcamp	2d	2d	4d
HTML Stack frame viewer (no locals/environment yet, just	Execution Handling		dcamp	2d	3d	5d

Source Viewer

• Enough to visualize current line/stack frames/etc.
  • Debug.Script.prototype.{url,startLine,length,getAllOffsets,getLineOffsets,getOffsetLine} - jorendorff
  • Debug.Frame.prototype.{callee,script,offset} - jorendorff
• No source list yet, will only reflect sources handed to it in pause states.
• Can use normal view source/firebug method (loading from necko preferring the cache) for getting static script sources (in-document <script> etc).
• Needs the engine to provide sources for exotic script sources (eval/appendNode/etc.)
• Very simple source viewer, improving the source viewer can happen outside the critical path.

Execution

• throw hook (Debug.hooks.throw) - jorendorff - Done.
• error hook (Debug.hooks.error) - jorendorff
• resume (resumption values) - jorendorff - Done.
• work out low-level stepping support with the JM team - jorendorff/jimb
• implement Debug object stepping support (Debug.hooks.interrupt, Debug.Script.prototype.singleStepMode, etc.) - jorendorff
• step into/step out/finish - dcamp

In this timeframe, we also want to be able to:

• Show native calls on the stack - jorendorff, luke
• Show debugger frames on the stack - jorendorff

Frame Tree Support

• Debug.prototype.{add,remove}Debuggee() - jorendorff
• Frame tree support in the tab actors.

Environment/Property Viewer

• JSD2 support:
  • Debug.Object.prototype.{prototype,class,isFunction,name, getOwnPropertyDescriptor,getOwnPropertyNames,decompile} - jorendorff
  • Debug.Frame.prototype.environment - jorendorff
  • Debug.Environment.prototype.{type,outerEnvironment,object, boundIdentifiers,getVariableDescriptor,findBinding} - jorendorff
• Protocol Support (actors for environments and objects)
  • Pause-lifetime grips.
  • Thread-lifetime grip promotion? Maybe can wait?
• UI panel - simple tree view for objects?

By the time this milestone is complete, we'll have a somewhat competent debugger if you're willing to use debugger; statements instead of breakpoints.

Source Selector

• JSD2 support
  • newScript hook
  • enumerate scripts? Maybe not - since we need currently need to reload anyway to recompile scripts for debugging, might be ok to always just watch the newScript hook.
• Protocol support
  • new script notification.

• UI support: dropdown of available scripts, triggering loads in the source viewer.

Breakpoints

• JSD2 support.
• Protocol-side breakpoints will set physical breakpoints at each script (including newly-added scripts)
• Need to work out breakpoint persistence across reloads (needs to be done early enough to catch scripts run during the load).
• Set breakpoints in the source gutter
• Set breakpoints from a command line (?)
• Disable/Enable/Delete breakpoints

More Milestones

In no particular order...

• Web Worker debugging (might not be needed for an initial release, but would be really nice)
• Chrome debugging (probably not be needed for an initial release)

Floating Tasks

Here are a few tasks that I haven't slotted into any specific milestone, and could be tackled separately alongside the other milestones. At least some of these would block a final release of a capable debugger.

Description	Area	Bug	Owner	Best	Likely	Worst	Status
E10S content process support	Remote Proto		dcamp?	1w	3w	2w
Improved script origin information	JSD2	bug 637572	jimb
Waive slow script dialog (jorendorff was seeing them after resuming)	JSD2
Improve source viewer (after basic source viewer is added)	Firefox UI		No Owner