Duplicated jsdoc should error

[sandersn]

It's possible to document parameters and function expressions 2-3 different places in JSDoc. However, I can't think of a good reason to do so, and I suspect that it's (1) rare (2) by mistake. Here's an example:

/** @param a - the a */
function f(/* an a */ a) {
}

Today gives the jsdoc

 an a
 - the a

But should give an a and an error on @param a: "Duplicate jsdoc".

The problem is even worse in JS, where jsdoc provides types. Here, the innermost type annotation provides the type and the rest are ignored. This should definitely be an error:

/** @param {string} a */
function f(/* @type {number} */ a) {
}

This example should have an error on @param a: "Duplicate jsdoc"

Thanks to @bterlson for this idea.