Erroneous "Erroneous nesting of equation structures"

[cebola2]

I believe I have found some error in the "Erroneous nesting of equation structures" flagging when using \begin{equation}\end{equation}

Version
MathJax Version:4.0.0-beta.3

I am loading MathJax locally and the configuration is identical to what I had for version 4.0.0-alpha.1, namely

window.MathJax = {
output: {
font: 'mathjax-fira',
linebreaks: {// options for when overflow is linebreak
inline: true, // true for browser-based breaking of inline equations
width: '100%', // a fixed size or a percentage of the container width
lineleading: .2, // the default lineleading in em units
LinebreakVisitor: null // The LinebreakVisitor to use
}
},
loader: {load: ['ui/lazy']},
svg: {
scale: 1,
mtextInheritFont: true,
displayOverflow: "linebreak",
matchFontHeight: false
},
chtml: {
scale: 1,
mtextInheritFont: true,
displayOverflow: "linebreak"
},
options: {
processHtmlClass: "math",
ignoreHtmlClass: "tex2jax_ignore"
},
tex: {
tags: 'ams',
macros: {
sen: "\operatorname{sen}",
tg: "\operatorname{tg}",
arctg: "\operatorname{arctg}",
arcsen: "\operatorname{arcsen}",
arcos: "\operatorname{arcos}",
div: "\operatorname{div}",
rot: "\operatorname{rot}"
},
inlineMath: [['$', '$'], ['\(', '\)']],
displayMath: [['$$', '$$'], ["\[", "\]"]],
processEscapes: true,
autoload: {
color: ['color']
}
}
/* tex: {
packages: {'[+]': ['noerrors', 'action']}
},
loader: {
load: ['[tex]/noerrors', '[tex]/action']
} */
};

Example page:
https://cdi2.palhoto.pt/test

[dpvc]

OK, thanks for the report. I will need to look into it. The logic for handling the nesting of AMS structures has been changed (see the last paragraph of the New TeX Features in the release notes), and obviously something went wrong.

[dpvc]

OK, I found it. There is a bug in

https://github.com/mathjax/MathJax-src/blob/49db078a876cce1f2157c9c58fb98bb145a09068/ts/input/tex/base/BaseMethods.ts#L1709-L1722

where parser.Push(begin) is called twice; the first call should have been removed. This may have been due to a bad merge or bad conflict resolution, as the first one was removed in the commit that modified the nesting checks:

mathjax/MathJax-src@7bb5fbd#diff-8b54d4a07ba56e1e6678245687ace65d468dd87cb4c8770a11b261c94d0231a0

as you can see by the first difference line above.

In any case, the following configuration will fix the error:

MathJax = {
  tex: {
    packages: {'[+]': ['fix-equation']}
  },
  startup: {
    ready() {
      const {Configuration} = MathJax._.input.tex.Configuration;
      const {EnvironmentMap} = MathJax._.input.tex.SymbolMap;
      const {environment} = MathJax._.input.tex.ParseMethods.default;
      const ParseUtil = MathJax._.input.tex.ParseUtil.default;
      new EnvironmentMap('fix-equation', environment, {
        displaymath:   ['Equation', null, false],
        math:          ['Equation', null, false, false],
        equation:      ['Equation', null, true],
        `equation*`:   ['Equation', null, false],
      }, {
        Equation(parser, begin, numbered, display = true) {
          parser.configuration.mathItem.display = display;
          parser.stack.env.display = display;
          ParseUtil.checkEqnEnv(parser);
          parser.Push(begin);
          return parser.itemFactory.create('equation', numbered).
          setProperty('name', begin.getName());
        }
      });
      Configuration.create('fix-equation', {
        handler: {environment: ['fix-equation']}
      });
      MathJax.startup.defaultReady();
    }
  }
};

Merge this into your current configuration (e.g., move the packages option into your existing tex block and add the startup block) and that should take care of it for you.

Thanks for trying out beta.3 and reporting the problem.

[cebola2]

The same test page with the indicated fix:

https://cdi2.palhoto.pt/test_5

Everything works! Thanks for your incredible work with MathJax.

[dpvc]

Glad it is working for you now. Thanks for letting us know.

[egnha]

@dpvc Thank you for the fix. However, while it works for most environments, it doesn't seem to resolve the issue for equation* environments (which worked as expected in v3).

Example:

<html>
<head>
  <script>
    MathJax = {
      tex: {
        packages: {'[+]': ['fix-equation']}
      },
      startup: {
        ready() {
          const {Configuration} = MathJax._.input.tex.Configuration;
          const {EnvironmentMap} = MathJax._.input.tex.SymbolMap;
          const {environment} = MathJax._.input.tex.ParseMethods.default;
          const ParseUtil = MathJax._.input.tex.ParseUtil.default;
          new EnvironmentMap('fix-equation', environment, {
            displaymath:   ['Equation', null, false],
            math:          ['Equation', null, false, false],
            equation:      ['Equation', null, true]
          }, {
            Equation(parser, begin, numbered, display = true) {
              parser.configuration.mathItem.display = display;
              parser.stack.env.display = display;
              ParseUtil.checkEqnEnv(parser);
              parser.Push(begin);
              return parser.itemFactory.create('equation', numbered).
              setProperty('name', begin.getName());
            }
          });
          Configuration.create('fix-equation', {
            handler: {environment: ['fix-equation']}
          });
          MathJax.startup.defaultReady();
        }
      }
    };
  </script>
  <script src="https://cdn.jsdelivr.net/npm/mathjax@4.0.0-beta.3/tex-mml-chtml.js">
  </script>
</head>
<body>
  This works:

  \begin{equation}
  A=B
  \end{equation}

  As does this:

  \[
  A=B
  \]

  But not this:

  \begin{equation*}
  A=B
  \end{equation*}
  
</body>
</html>

This renders as follows (in several major browsers):

(I don't know JS. Have I implemented your fix incorrectly?)

[dpvc]

OK, sorry, I missed equation*, since it is in a different file from the others. Add

            'equation*':      ['Equation', null, false]

after the corresponding definition for equation in your configuration (and add a comma after the equation line) and that should take care of it.

[egnha]

Thanks for your suggestion. However, should `equation*' be 'equation*'? Either way, the error persists. (And equation* as quoted in the first instance also breaks the equation environment.)

[dpvc]

should `equation*' be 'equation*'?

Yes. Sorry about that.

Either way, the error persists.

That suggests you made an error in the configuration and the configuration isn't being processed or is processed in correctly. Here is the full configuration from my example

MathJax = {
  tex: {
    packages: {'[+]': ['fix-equation']}
  },
  startup: {
    ready() {
      const {Configuration} = MathJax._.input.tex.Configuration;
      const {EnvironmentMap} = MathJax._.input.tex.SymbolMap;
      const {environment} = MathJax._.input.tex.ParseMethods.default;
      const ParseUtil = MathJax._.input.tex.ParseUtil.default;
      new EnvironmentMap('fix-equation', environment, {
        displaymath:   ['Equation', null, false],
        math:          ['Equation', null, false, false],
        equation:      ['Equation', null, true],
        'equation*':   ['Equation', null, false]
      }, {
        Equation(parser, begin, numbered, display = true) {
          parser.configuration.mathItem.display = display;
          parser.stack.env.display = display;
          ParseUtil.checkEqnEnv(parser);
          parser.Push(begin);
          return parser.itemFactory.create('equation', numbered).
          setProperty('name', begin.getName());
        }
      });
      Configuration.create('fix-equation', {
        handler: {environment: ['fix-equation']}
      });
      MathJax.startup.defaultReady();
    }
  }
};

This works for me in my test program. I've edited the previous example as well, so others who find this will get the correct behavior from either example.

[egnha]

That works now for me, too. Thank you!