feat: valid-typeof: always ban undefined

[Zzzen]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[x] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

fixes #15591

What changes did you make? (Give an overview)

check undefined and report

Is there anything you'd like reviewers to focus on?

should we use getStaticValue?

[mdjermanovic]

should we use getStaticValue?

I think we can evaluate that change separately from this PR / original issue. Just handling undefined identifiers looks good for the start, and I'd expect that the majority of cases where getStaticValue can determine a static value that is being compared to typeof expressions will be those with undefined identifiers.

[mdjermanovic]

The suggestion to replace undefined with "undefined" makes sense with requireStringLiterals: true, too.

Maybe we could switch the order of else-ifs:

} else if (sibling.type === "Identifier" && sibling.name === "undefined" && isReferenceToGlobalVariable(sibling)) {
    context.report({
        node: sibling,
        messageId: requireStringLiterals ? "notString" : "invalidValue",
        suggest: [
            {
                messageId: "suggestString",
                data: { type: "undefined" },
                fix(fixer) {
                    return fixer.replaceText(sibling, '"undefined"');
                }
            }
        ]
    });
} else if (requireStringLiterals && !isTypeofExpression(sibling)) {
    context.report({ node: sibling, messageId: "notString" });
}

Test case:

{
    code: "if (typeof bar !== undefined) {}",
    options: [{ requireStringLiterals: true }],
    errors: [
        {
            messageId: "notString",
            type: "Identifier",
            suggestions: [
                {
                    messageId: "suggestString",
                    data: { type: "undefined" },
                    output: 'if (typeof bar !== "undefined") {}'
                }
            ]
        }
    ]
},

[nzakas]

LGTM. Just waiting on @mdjermanovic to confirm his feedback has been addressed.

[mdjermanovic]

LGTM, thanks for contributing!