1272499 - debugger only pauses once on breakpoint inside XBL handler

Status: RESOLVED INVALID

(DevTools :: Debugger, defect, P5)

Description

[Jared Hirsch [:jhirsch] (he/him) (Needinfo please)]

There is a popuphiding handler defined around line 980 of autocomplete.xml:

https://dxr.mozilla.org/mozilla-central/source/toolkit/content/widgets/autocomplete.xml#982

Open the browser toolbox, set a breakpoint at the first line of that handler. The debugger should pause at the breakpoint each time the awesomebar popup closes.

However, it only pauses execution the first time the popup closes. The debugger seems unable to attach more than once, even if other breakpoints are set inside the same file.

If the browser toolbox is closed, then reopened, and a breakpoint is set in the same spot (first line of the popuphiding handler), the debugger will again attach just once.

Comment 1

[Eddy Bruel [:ejpbruel]]

I know very little about XBL handlers, but is it possible that this code causes the source for the handler to be evaluated every time the popup is opened?

If this is the case, we can have multiple versions of the same source, and multiple versions of compiled scripts for each source. If a breakpoint is set on a script for an old version, but not the new one, this would explain the behavior you're seeing (we have code that is supposed to handle it, but I've seen obscure bugs there in the past).

Comment 2

[Jared Hirsch [:jhirsch] (he/him) (Needinfo please)]

Sorry for the delayed response; I've been on PTO for the past few weeks.

> I know very little about XBL handlers, but is it possible that this code causes the source for the
> handler to be evaluated every time the popup is opened?

Ah yeah, I think that could be what's happening (though technically popuphiding is fired just before the popup *closes*).

According to [1], for XBL handlers, "the JavaScript body is compiled just before execution". It seems like there may be an analogy with the behavior of DOM Level 0 inline event handlers in regular HTML documents; has this problem occurred in that case as well?

[1] https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XBL/XBL_1.0_Reference/Event_Handlers

Comment 3

[Eddy Bruel [:ejpbruel]]

(In reply to Jared Hirsch [:_6a68] [NEEDINFO please!] from comment #2)
> Sorry for the delayed response; I've been on PTO for the past few weeks.
> 
> > I know very little about XBL handlers, but is it possible that this code causes the source for the
> > handler to be evaluated every time the popup is opened?
> 
> Ah yeah, I think that could be what's happening (though technically
> popuphiding is fired just before the popup *closes*).
> 
> According to [1], for XBL handlers, "the JavaScript body is compiled just
> before execution". It seems like there may be an analogy with the behavior
> of DOM Level 0 inline event handlers in regular HTML documents; has this
> problem occurred in that case as well?
> 
> [1]
> https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XBL/XBL_1.0_Reference/
> Event_Handlers

I can't tell for sure whether this also happened with inline event handlers in regular HTML documents, but it's definitely possible.

Comment 4

[Logan Smyth [:loganfsmyth]]

Given that XBL isn't common anymore, I don't know if this is still an issue, but going to close since it's unlikely to be prioritized anyway.