--multipass optimization produces artifacts

[nschloe]

When running

svgo --multipass a.svg  

on the SVG

it will produce extra artifacts:

(See, e.g., the axis labels.)

The problem does not occur without --multipass.

This is with svgo 3.0.2, node 21.0.0, on Arch Linux.

[SethFalco]

Thanks for reporting the bug and sharing an example SVG to reproduce the issue.

The issue was that the original SVG had some instances of <use> that referred to an ID to a node that didn't exist. If the offending node referenced #a… but later the cleanupIds plugin renames another node ID to a, this makes those bad references valid and unintentionally points them to a different node. This causes previously malformed nodes to effectively duplicate an existing node.

See: #1817

MRE

minimal.svg

<svg xmlns="http://www.w3.org/2000/svg">
  <defs>
    <path id="uwu" d="M 2.046875 0 L 10.609375 0 C 12.40625 0 13.734375 -0.5 14.734375 -1.59375 C 15.671875 -2.578125 16.203125 -3.921875 16.203125 -5.40625 C 16.203125 -7.703125 15.15625 -9.078125 12.734375 -10.015625 C 14.484375 -10.8125 15.359375 -12.1875 15.359375 -14.140625 C 15.359375 -15.546875 14.84375 -16.75 13.859375 -17.625 C 12.84375 -18.53125 11.5625 -18.953125 9.75 -18.953125 L 2.046875 -18.953125 Z M 4.46875 -10.796875 L 4.46875 -16.828125 L 9.15625 -16.828125 C 10.5 -16.828125 11.265625 -16.640625 11.90625 -16.140625 C 12.578125 -15.625 12.953125 -14.84375 12.953125 -13.8125 C 12.953125 -12.765625 12.578125 -11.984375 11.90625 -11.46875 C 11.265625 -10.96875 10.5 -10.796875 9.15625 -10.796875 Z M 4.46875 -2.125 L 4.46875 -8.65625 L 10.375 -8.65625 C 12.5 -8.65625 13.78125 -7.4375 13.78125 -5.375 C 13.78125 -3.359375 12.5 -2.125 10.375 -2.125 Z M 4.46875 -2.125"/>
  </defs>
  <use href="#a" x="378" y="464"/>
  <use href="#uwu" x="385" y="464"/>
</svg>

svgo.config.js

module.exports = {
  plugins: [
    "cleanupIds",
  ]
};

Edit: Just realized this is a duplicate of #1195 though, so I'll close this one.