1622050 - See whether we can get rid of the "XBL destructor" mutation guards

Status: NEW

(Core :: DOM: Core & HTML, task, P3)

Description

[Boris Zbarsky [:bzbarsky]]

In nsINode::ReplaceOrInsertBefore we have:

    // Removing a child can run script, via XBL destructors.
    nsMutationGuard guard;
...

    if (guard.Mutated(1)) {
      // XBL destructors, yuck.

Is this still a thing we need to worry about? Are there non-XBL-destructor things that can cause extra mutations there?

We also have the bit about:

    // Make sure to remove all the fragment's kids.  We need to do this before
    // we start inserting anything, so we will run out XBL destructors and
    // binding teardown (GOD, I HATE THESE THINGS) before we insert anything
    // into the DOM.

right below that, and more mutation guards in the document fragment case. Need to figure out whether this is all still needed and document why, if it is.

Comment 1

[Worcester12345]

File under "less is more". Is there any reason for keeping these? Does removing them speed up any aspect of the program? How much of a patch would it be to remove?

Comment 2

[Emilio Cobos Álvarez (:emilio)]

(In reply to Worcester12345 from comment #1)

File under "less is more". Is there any reason for keeping these? Does removing them speed up any aspect of the program? How much of a patch would it be to remove?

Unclear, ideally they can be removed, figuring that out is what this bug is about. The speedup / slowdown is probably meaningless, but keeping them if they're not needed is problematic because they make the code confusing (may make you think something may run script when it can't).