Private field support in babel-template

Current Behavior An error is thrown when templates containing private fields are parsed.

Input Code

module.exports = function ({ template }) {
  const set_private = template`this.#IDENT = VALUE`;
};

Expected behavior/code I would expect to be able to correctly parse and use templates containing private fields.

Environment (fairly certain none of this matters except Babel version)

• Babel version: 7.4.4
• Node/npm version: Node 12
• OS: Ubuntu 19.04
• Monorepo: no
• How you are using Babel: CLI

[nicolo-ribaudo]

Currently it can be replaced with the following code:

const refs = t.privateName(t.identifier('refs'));

return template.ast`
	if (${expr}) {
		this.${refs}[${ref_number}].setAttribute('${attr}', '');
	} else {
		this.${refs}[${ref_number}].removeAttribute('${attr}');
	}
`;

[jhpratt]

Just for reference, here’s something that could trivially be replaced with a template if/when private fields (and other context-dependent nodes) are allowed within templates.

return t.ifStatement(
    expr,
    t.blockStatement([
        t.expressionStatement(
            t.callExpression(
                t.memberExpression(
                    t.memberExpression(
                        t.memberExpression(
                            t.thisExpression(),
                            t.privateName(t.identifier('refs')),
                        ),
                        t.numericLiteral(ref_number),
                        true,
                    ),
                    t.identifier('setAttribute'),
                ),
                [t.stringLiteral(attr), t.stringLiteral('')],
            ),
        ),
    ]),
    t.blockStatement([
        t.expressionStatement(
            t.callExpression(
                t.memberExpression(
                    t.memberExpression(
                        t.memberExpression(
                            t.thisExpression(),
                            t.privateName(t.identifier('refs')),
                        ),
                        t.numericLiteral(ref_number),
                        true,
                    ),
                    t.identifier('removeAttribute'),
                ),
                [t.stringLiteral(attr)],
            ),
        ),
    ]),
);

That could be trivially replaced with the following.

return template.ast`
	if (${expr}) {
		this.#refs[${ref_number}].setAttribute('${attr}', '');
	} else {
		this.#refs[${ref_number}].removeAttribute('${attr}');
	}
`;

Needless to say the latter is far more readable and maintainable. It’s also trivial to write (I did it off the top of my head), where explicitly writing out the AST is tedious and error-prone.