Speech generation error for empty mtr

[TylerZeroMaster]

Issue Summary

When math input for tex-mml-svg/MathJax.mathml2svgPromise contains at least one empty mtr and speech is enabled, a speech generation error is logged to the console (not thrown), and speechis not generated.

Steps to Reproduce:

1. Follow steps to load tex-mml-svg component in node
2. Call MathJax.mathml2svgPromise with sample math and display: false
3. See error logged in console

Sample math that is affected by this issue:

  <m:math xmlns="http://www.w3.org/1999/xhtml" xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline">
    <m:semantics>
      <m:mrow>
        <m:mrow data-sm="./modules/m82530/index.cnxml:873:42">
          <m:mspace width="4em" data-sm="./modules/m82530/index.cnxml:873:50" />
          <m:mtable data-sm="./modules/m82530/index.cnxml:873:73">
            <!-- Empty mtr -->
            <m:mtr data-sm="./modules/m82530/index.cnxml:873:83" />
            <m:mtr data-sm="./modules/m82530/index.cnxml:873:91">
              <m:mtd columnalign="right" data-sm="./modules/m82530/index.cnxml:873:98">
                <m:msup data-sm="./modules/m82530/index.cnxml:873:125">
                  <m:mi data-sm="./modules/m82530/index.cnxml:873:133">n</m:mi>
                  <m:mn data-sm="./modules/m82530/index.cnxml:873:147">2</m:mn>
                </m:msup>
                <m:mo data-sm="./modules/m82530/index.cnxml:873:170">+</m:mo>
                <m:mi data-sm="./modules/m82530/index.cnxml:873:184">n</m:mi>
              </m:mtd>
              <m:mtd columnalign="left" data-sm="./modules/m82530/index.cnxml:873:206">
                <m:mo data-sm="./modules/m82530/index.cnxml:873:232">=</m:mo>
              </m:mtd>
              <m:mtd columnalign="left" data-sm="./modules/m82530/index.cnxml:873:254">
                <m:mn data-sm="./modules/m82530/index.cnxml:873:280">132</m:mn>
              </m:mtd>
            </m:mtr>
          </m:mtable>
        </m:mrow>
      </m:mrow><m:annotation-xml encoding="MathML-Content">
        <m:mrow data-sm="./modules/m82530/index.cnxml:873:42">
          <m:mspace width="4em" data-sm="./modules/m82530/index.cnxml:873:50" />
          <m:mtable data-sm="./modules/m82530/index.cnxml:873:73">
            <m:mtr data-sm="./modules/m82530/index.cnxml:873:83" />
            <m:mtr data-sm="./modules/m82530/index.cnxml:873:91">
              <m:mtd columnalign="right" data-sm="./modules/m82530/index.cnxml:873:98">
                <m:msup data-sm="./modules/m82530/index.cnxml:873:125">
                  <m:mi data-sm="./modules/m82530/index.cnxml:873:133">n</m:mi>
                  <m:mn data-sm="./modules/m82530/index.cnxml:873:147">2</m:mn>
                </m:msup>
                <m:mo data-sm="./modules/m82530/index.cnxml:873:170">+</m:mo>
                <m:mi data-sm="./modules/m82530/index.cnxml:873:184">n</m:mi>
              </m:mtd>
              <m:mtd columnalign="left" data-sm="./modules/m82530/index.cnxml:873:206">
                <m:mo data-sm="./modules/m82530/index.cnxml:873:232">=</m:mo>
              </m:mtd>
              <m:mtd columnalign="left" data-sm="./modules/m82530/index.cnxml:873:254">
                <m:mn data-sm="./modules/m82530/index.cnxml:873:280">132</m:mn>
              </m:mtd>
            </m:mtr>
          </m:mtable>
        </m:mrow>
      </m:annotation-xml>
    </m:semantics>
  </m:math>

• At first I thought this was more closely related to SRE, however, when I run SRE.toSpeech on the sample math, it works.
• I believe this is a bug because removing the empty mtr element fixes the issue; however, empty mtr is valid MathML.
• I would expect the speech to generate normally, as it does when the mtr elements have been removed, without any errors appearing in the console. ("1 lines Line 1: n squared plus n equals 132")

Technical details:

• MathJax Version: 4.0.0
• Client OS: Mac OS X 14.7.8
• Browser: N/A (liteDOM adaptor)
• Node Version: 22.16.0

I am using the following MathJax configuration:

{
  loader: {
    paths: { mathjax: 'mathjax' },
    load: [ 'adaptors/liteDOM', 'output/svg' ],
    require: [Function: require]
  },
  output: { linebreaks: { inline: true }, font: 'mathjax-stix2' },
  tex: {
    formatError (_, error) {
      throw new Error(error.message)
    }
  },
  startup: {
    ready () {
      // https://github.com/mathjax/MathJax/issues/3185
      const { MmlMath } = MathJax._.core.MmlTree.MmlNodes.math
      const { MmlMstyle } = MathJax._.core.MmlTree.MmlNodes.mstyle
      MmlMath.defaults.scriptsizemultiplier = MmlMstyle.defaults.scriptsizemultiplier = 0.8

      MathJax.startup.defaultReady()
    }
  },
  options: { sre: { locale: 'en', braille: 'nemeth' } },
  svg: { fontCache: 'local', blacker: 0, scale: 1.15 }
}

and loading MathJax via

global.MathJax = this.config // (the above config)
require(this.lib) // (e.g. tex-mml-svg)
await MathJax.startup.promise

Supporting information:

The specific error logged is:

TypeError: Cannot read properties of undefined (reading 'mathmlTree')
    at Rp.applicable (<node_modules>/mathjax/tex-mml-svg.js:1:1687515)
    at Object.run (<node_modules>/mathjax/tex-mml-svg.js:1:1635743)
    at kp.tableToMultiline (<node_modules>/mathjax/tex-mml-svg.js:1:1635908)
    at Ip.table_ (<node_modules>/mathjax/tex-mml-svg.js:1:1672675)
    at Ip.parse (<node_modules>/mathjax/tex-mml-svg.js:1:1671311)
    at Ip.parseList (<node_modules>/mathjax/tex-mml-svg.js:1:1631689)
    at Ip.rows_ (<node_modules>/mathjax/tex-mml-svg.js:1:1671840)
    at Ip.parse (<node_modules>/mathjax/tex-mml-svg.js:1:1671311)
    at Ip.rows_ (<node_modules>/mathjax/tex-mml-svg.js:1:1671688)
    at Ip.parse (<node_modules>/mathjax/tex-mml-svg.js:1:1671311)
Speech generation error: Cannot read properties of null (reading 'indexOf')

Removing the empty mtr resolves the issue (but it does create a slight difference visually).
Right now, to avoid the visual differences, I am using a separate version of the mathml for speech generation in these cases.

// first try normally
// ... MathJax bits ...
// Speech generation error is logged, but no error is thrown
// Try to get speech from node
filterNode(adaptor, node, speech, braille);
// Use lack of speech to detect error condition
if (speech.length === 0 && isMml) {
  const parsed = adaptor.parse(item);
  const toRemove = [];
  let mathNode;
  const filterMath = (node) => {
    const { kind, children } = node;
    if (mathNode === undefined && kind.endsWith('math')) mathNode = node;
    if (Array.isArray(children) && children.length > 0) children.forEach(filterMath);
    else if (kind.endsWith('mtr')) toRemove.push(node);
  };
  filterMath(parsed.body);
  toRemove.forEach(adaptor.remove.bind(adaptor));
  if (mathNode) {
    const speechReadyItem = adaptor.outerHTML(mathNode);
    const speechNode = await MathJax.mathml2svgPromise(speechReadyItem, options);
    filterNode(adaptor, speechNode, speech, braille);
  }
}
// ... and so on

I do not think this problem is in my configuration or usage, but the most relevant part of the script would be here if anyone is looking for more context.

[dpvc]

Thanks for the report. You are correct that it is not your configuration or usage.

@zorkow, here is a minimal example. The empty row must be followed by a row with at least two entries.

<math xmlns="http://www.w3.org/1999/xhtml">
  <mtable>
    <mtr />
    <mtr>
      <mtd></mtd>
      <mtd></mtd>
    </mtr>
  </mtable>
</math>

@TylerZeroMaster, your code includes the comment

// Speech generation error is logged, but no error is thrown

Note that the speech component has a speechError() configuration parameter that you can use to trap any speech errors. See the documentation, though it is incorrectly referred to as enrichError() lower down on that page.

[dpvc]

PS, an easier mechanism for removing the empty mtr nodes would be to incorporate

  MathJax = {
    mml: {
      mmlFilters: [
        function ({data}) {
          Array.from(data.querySelectorAll('mtr:empty')).forEach((mtr) => mtr.remove());
        },
      ],
    }
 };

into your MathJax configuration.

[zorkow]

One of SRE's heuristics did not consider the case that it might come across and empty row.
PR 827 fixes this.