Spurious warning (UNKNOWN_HTML_TAG_IN_TEMPLATE) for MathML elements

[nolanlawson]

Currently we only keep a list of known HTML and SVG elements:

lwc/packages/@lwc/template-compiler/src/parser/constants.ts

Line 120 in 7701069

export const KNOWN_HTML_AND_SVG_ELEMENTS = new Set([...HTML_ELEMENTS, ...SVG_ELEMENTS]);

This leads to the template compiler throwing a spurious warning for MathML, e.g.:

<math>
    <mi>π<!-- p --></mi>
    <mo>⁢<!-- &InvisibleTimes; --></mo>
    <msup>
      <mi>r</mi>
      <mn>2</mn>
    </msup>
</math>

The warning thrown is:

lwc/packages/@lwc/errors/src/compiler/error-info/template-transform.ts

Lines 439 to 445 in 7701069

	UNKNOWN_HTML_TAG_IN_TEMPLATE: {
	code: 1123,
	message:
	"Unknown html tag '<{0}>'. For more information refer to https://developer.mozilla.org/en-US/docs/Web/HTML/Element and https://developer.mozilla.org/en-US/docs/Web/SVG/Element",
	level: DiagnosticLevel.Warning,
	url: '',
	},