Wrong image scaling for SVG with clipping

[CendioOssman]

If an SVG image has clipped elements in it, rst2pdf will scale that image based on the unclipped elements, not the final result. This results in a smaller and oddly positioned image.

Description of problem
Put the following SVG in a document. It will be scaled down, and be oddly aligned to the left:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!-- Created with Inkscape (http://www.inkscape.org/) -->

<svg
   width="1027"
   height="699"
   viewBox="0 0 271.72709 184.94375"
   version="1.1"
   id="svg5"
   xml:space="preserve"
   xmlns="http://www.w3.org/2000/svg"
   xmlns:svg="http://www.w3.org/2000/svg"><defs
     id="defs2"><clipPath
       clipPathUnits="userSpaceOnUse"
       id="clipPath742"><rect
         style="fill:#00ff00;stroke-width:0.396875;stroke-linecap:round;stroke-linejoin:round"
         id="rect744"
         width="272.52084"
         height="185.20833"
         x="23.010065"
         y="-40.970455"
         rx="1.3229169"
         ry="1.3229169" /></clipPath></defs><g
     id="layer1"
     transform="translate(-23.010065,40.970454)"><path
       fill-rule="nonzero"
       fill="#ffffff"
       fill-opacity="1"
       d="M 23.010065,-40.970454 H 294.64896 V 143.8851 H 23.010065 Z m 0,0"
       id="path387"
       style="stroke-width:0.352778" /><rect
       style="fill:#ff0000;stroke-width:0.396875;stroke-linecap:round;stroke-linejoin:round"
       id="rect632"
       width="2815.1667"
       height="164.04167"
       x="33.593399"
       y="-30.387121"
       rx="1.3229167"
       ry="1.3229167"
       clip-path="url(#clipPath742)" /></g><rect
     style="fill:#00ff00;stroke-width:0.396875;stroke-linecap:round;stroke-linejoin:round"
     id="rect410"
     width="187.37076"
     height="110.43581"
     x="42.14032"
     y="38.162937"
     rx="1.3229169"
     ry="1.3229169" /></svg>

What is the expected output? What do you see instead?
The SVG is rendered just like in other applications, i.e. according to the width and height of the <svg>.

🖥 Versions
Python 3.6.12
rst2pdf 0.98
reportlab 3.6.1
svglib 1.1.0
sphinx 4.2.0

Additional information
I figured this might be a svglib issue, but some quick debugging suggests the issue is elsewhere. svglib returns a ReportLab Drawing with the correct dimensions. Not sure what happens after that that results in the bad scaling. Hence why I'm reporting the issue here.

[lornajane]

Thanks @CendioOssman, I don't think I've seen that before and I appreciate the detailed bug report. I don't use SVGs but I'm happy to test a patch if anyone does have a fix for this.