Feature request: new value for the preserveParens option

[thorn0]

Would be good to have a mode in which ParenthesizedExpression nodes would be created only for parentheses used for JSDoc type assertions.

The syntax of JSDoc type assertions is simple: @type {...} JSDoc comment followed by a parenthesized expression. Anything else is not a type assertion. Reference: Closure Compiler, TypeScript.

[3cp]

This is probably difficult for meriyah, as the content of comment needs to go through some kind of syntax parsing too.

[thorn0]

The syntax is super simple. See the links. No need to parse the type itself. Just the fact that the comment starts with * and contains @type followed by at least something.

[3cp]

I see.

[3cp]

@KFlash can you have a look? I am not sure how to temporarily turn on Context.OptionsPreserveParens if next token is (. Also has to properly reset it after the ParenthesizedExpression. I sensed it might be complicated if need to support recursion .

I am not sure if recursive type casting is possible. @thorn0 ?

/** @type xxx */ ({a: /** @type xxx */ (b) })

Right now, I guess you are turning on preserveParens option globally.

[KFlash]

Can't you just create a new option? Name it thorn. Then you can do the same as you do for the other options

if (options.thorn) context | Context.OptionsThorn | OptionsPreserveParens

@thorn What's the use case for this? And why do you want to turn off ParenthesizedExpression ? It's in the spec and if used in Prettier you can save tons of works for cases like (((((x))))) where your expected output should be '(x)' or no paren at all. Just check if 'type' exist, and avoid printing paren if nested.

[thorn0]

I am not sure if recursive type casting is possible

Yes, possible. Also they can be nested directly (people really use this):

/** @type MyType */ (/** @type any */ (x))

What's the use case for this? And why do you want to turn off ParenthesizedExpression ? It's in the spec

If you mean ESTree, ParenthesizedExpression is not there. It's a non-standard extension. Overall, ESTree's approach is to ignore insignificant parentheses. However, the JSDoc convention that uses such parentheses is widespread and important. So from the point of view of tools like formatters and linters, it makes sense to create these non-standard nodes only for JSDoc. In other cases, they only get in the way. E.g. Prettier doesn't simply print the AST. It also does a lot of checks of the AST structure along the way to choose between different ways to print things. Taking ParenthesizedExpression nodes into account in all those checks would ridiculously complicate them, so actually what happens now in Prettier is an extra step that removes all ParenthesizedExpressions that aren't JSDoc type assertions from the AST before passing it to printing.

Name it thorn

I sincerely believe something like PreserveJsdocParens would be a slightly better name. 😆