1515344 - Computation of BaseURI is bound to the wrong svg element with <svg:use> before being bound to the DOM

Status: NEW

(Core :: CSS Parsing and Computation, enhancement, P3)

Description

[Jonathan Kingston [:jkt] he/him]

Whilst working on https://bugzilla.mozilla.org/show_bug.cgi?id=1494356#c21 we established that the BaseURI is set to the wrong SVG element on the first pass through.


doc.svg
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <defs>
    <marker id="circleMarker" markerWidth="8" markerHeight="8" refX="5" refY="5">
      <circle cx="5" cy="5" r="2" style="stroke: none; fill: red;"/>
    </marker>
  </defs>
  <use xlink:href="embed.svg#path"/>
</svg>

embed.svg
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <defs>
    <marker id="circleMarker" markerWidth="8" markerHeight="8" refX="5" refY="5">
      <circle cx="5" cy="5" r="2" style="stroke: none; fill: lime;"/>
    </marker>
  </defs>
  <path id="path" d="M20,20 L70,20 L120,20" style="stroke: blue; stroke-width: 2px; marker-start: url(#circleMarker);"/>
</svg>

If we remove the bind to tree restyling code https://searchfox.org/mozilla-central/rev/13788edbabb04d004e4a1ceff41d4de68a8320a2/dom/svg/nsSVGElement.cpp#235-254 the svg above in doc.svg has a red marker.

Ultimately the issue then comes through into SVGObserverUtils::GetBaseURLForLocalRef() where the aDocURI ends up being a file://path/doc.svg#circleMarker which seems wrong to me.

Ideally we should defer parsing of the baseURI until the anonymous subtree has been bound. I'm not entirely sure the direction and how to implement this though.