Skip whitespace and asterisk in JSDoc param

[tschaub]

Skip the newline, whitespace, asterisk combo while parsing param tags.

Fixes #26027

[sandersn]

Which tests break without the first clause? I'd like to avoid lookahead whenever possible, but I don't know how essential it is here.

(You can run the tests with jake runtests-parallel and then diff the results in $ts/tests/baselines/local vs $ts/tests/baselines/reference.)

[tschaub]

With the change in 4599356, here are the changes to the baselines...

Update - I pushed a new commit that passes all current tests.

[tschaub]

@sandersn without a lookahead, this sort of thing would be allowed:

/** 
 * @param {string} * x
 * @param {number} y
 */
function f(x,y) {
}

Update - The most recent commit avoids a lookahead, but treats the above syntax as invalid. More below.

[tschaub]

My take right now is that when parsing JSDoc comments, you generally want to skip whitespace or newline, whitespace, asterisk together. As things are now, after calling skipWhitespace, if the current token is * it is not possible to distinguish between the decoration at the beginning of a line and a potentially significant * somewhere mid-comment.

The scanner.hasPrecedingLineBreak() check is nice. This would allow to distinguish between a * that comes after skipping whitespace except that the token flags aren't consistently maintained during scanJSDocToken.

The changes here parse this type of syntax:

/** 
 * @param
 * {string} x
 * @param {string}
 * y
 */
function f(x,y) {
}

And these are invalid:

/** 
 * @param {string} * x
 * @param * {string} y
 */
function f(x,y) {
}

If this looks like a good direction to go, I'll add tests.

The sometimes-reliable preceding linebreak check also feels fragile - it is not correct after a call to skipWhitespace - and I'm wondering if it makes sense to always skip whitespace or asterisk (when preceded by linebreak and whitespace).

[tschaub]

I added a conformance test.

Since skipping newline + asterisk would be nice elsewhere, I'm wondering if alternative approaches have been considered - like grouping it into a single trivia token during scanning. Perhaps nobody has asked for it yet, but it would be nice to be able to have linebreaks in typedefs for example:

/**
 * @typedef {{
 *    x: number,
 *    y: number,
 *    z: number
 * }} XYZ
 */

I think this would be more straightforward if the newline + asterisk were treated just like a single newline token while parsing the type expression.

Update: I see the linebreak in types issue is already ticked as #23667.

[sandersn]

The typedef problem is unfortunately much harder because it uses the normal Typescript parser, so you'd have to make type parsing skip arbitrary asterisks. I don't think asterisk is a common character in types, so it might work.
Another approach would be to preprocess the jsdoc comment and rescan it for type (and other) parsing. But I think that would be quite expensive.

[sandersn]

Thanks for the fix @tschaub!