In a few places we intentionally drop privileges to reduce the potential
security surface area of networked program, with the pattern of:
```
if (setgid(getgid()) || setuid(getuid()) {
return 1;
}
```
We can make this a bit nicer to use by creating a wrapper.
This is a bit strange in the IDL syntax, but e.g., in HTMLSelectElement,
we have (simplified):
undefined add(optional (HTMLElement or long)? before = null)
This could instead become:
undefined add(optional (HTMLElement or long) before)
This change generates code for the former as if it were the latter.
There are a few unimplemented features for this type:
1. The value setter should throw a DOMException if it is invoked on an
SVGLength that was declared readonly in another IDL file.
2. SVG::AttributeParser does not parse unit types when it parses lengths
so all SVGLength will have an "unknown" unit for now.
3. Due to (2), methods which convert between units are unimplemented.
We were passing the wrong length argument to substring() when
stringifying a range where start and end are the same text node.
Also, make sure we visit all the contained text nodes when appending
them to the output.
This was caught by an Acid3 subtest.
We already walk the entire paint tree within each stacking context in
the main hit testing function (StackingContext::hit_test()), so there's
no need for each individual paintable to walk its own children again.
By not doing that, we remove a source of O(n^2) traversal which made hit
testing on deeply nested web pages unbearably slow.
This is a convenience accessor to avoid having to say this everywhere:
result.paintable->layout_node().dom_node()
Instead, you can now do:
result.dom_node()
I came across some websites that change an elements CSS "opacity" in
their :hover selectors. That caused us to relayout on hover, which we'd
like to avoid.
With this patch, we now check if a property only affects the stacking
context tree, and if nothing layout-affecting has changed, we only
invalidate the stacking context tree, causing it to be rebuilt on next
paint or hit test.
This makes :hover { opacity: ... } rules much faster. :^)
There's no actual need to build the stacking context tree before
performing layout. Instead, make it lazy and build the tree when it's
actually needed for something.
This avoids a bunch of work in situations where multiple synchronous
layouts are forced (typically by JavaScript) without painting or hit
testing taking place in between.
It also opens up for style invalidations that only target the stacking
context tree.
