790975 - Support sequences as members of dictionaries in WebIDL

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Olli Pettay [:smaug][[e-mail]]]

I get the error when trying to convert MutationObserver to webidl
http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#mutationobserver
sequence<DOMString> attributeFilter; in the dictionary seems to cause the problem.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Yeah, indeed.  I punted on this when initially doing this stuff.

What the code comments say is:

            # XXXbz we probably _could_ handle this; we just have to be careful
            # with reallocation behavior for arrays.  In particular, if we have
            # a return value that's a sequence of dictionaries of sequences,
            # that will cause us to have an nsTArray containing objects with
            # nsAutoTArray members, which is a recipe for badness as the
            # outermost array is resized.

which is actually more about return values than arguments.  The typeerror there is for arguments.

I need to sit down and think through whether there are any problems with the arguments part of this.  Will try to do it tonight.

Comment 2

[Boris Zbarsky [:bzbarsky]]

OK.  I remember what the issue was now.

Say we have IDL like so:

  dictionary Bar {
    sequence<DOMString> item;
  };

  interface Foo {
    void foo(sequence<Bar> arg);
  };

The binding code will allocate a dom::Sequence<Bar> (which is an auto TArray).  Then it will set the capacity to the desired one.  But Bar has an auto TArray member itself.  So this will end up memmoving Bar and memmoving its members, but auto TArrays are not memmove-safe).

I _think_ we can loosen the restriction here to allow a sequence to be a dictionary member, as long as we're not in the middle of an argument conversion for some other sequence already.  Or something.  Peter, thoughts?

Comment 3

[Boris Zbarsky [:bzbarsky]]

Attachment: Support sequences as dictionary members in WebIDL.

Comment 4

[Boris Zbarsky [:bzbarsky]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/17dcbe563c2b

Comment 5

[Graeme McCutcheon [:graememcc]]

https://hg.mozilla.org/mozilla-central/rev/17dcbe563c2b