Add Intellisense to JsDoc

[zhengbli]

This PR provides completion list for the following cases:

• List all the JsDoc tag names right after the @ sign or in the tagname, e.g.:

/** @^ */
var foo = ...

and

/** @pa^ */
var foo = ...

• Full intellisense in certain JsDoc tag braces, e.g.:

/** @type { numbe^ } */
var foo = ...

/** @param { numbe^ } bar */
var foo = ...

The initial implementation only applies to js files, as currently the parser stores the JSDocComment nodes in the tree for js files but not ts files. Support for ts files may need some discussion.

[zhengbli]

@billti @CyrusNajmabadi could you take a look

[DanielRosenwasser]

These branches are identical, just let each fall through and use a variable typeTagOrParamTag of type JSDocTypeTag | JSDocParamTag.

[mhegazy]

consider caching the result. these are not going to change between invocations. saves you the allocations.

see keywordCompletions for an example.

[DanielRosenwasser]

Remove the type annotation.

[billti]

Playing around with this, and it returns no completions if I don't have the param name yet, for example, if the cursor is where the | is below, I get no completions. I have to have @param {|} a to get intellisense at the bar. As these are written left-to-right, this is a pain. It means I have to write the rest of the tag, then come back and complete the type. Is this fixable?

/**
 @param {|}
 */
function foo(a){
  // TODO
}

[zhengbli]

The problem is that if there is no param name, in the parser the JsDoc comment won't be parsed as a valid jstag node right now, so the compiler can't tell me if I'm inside the braces.

[billti]

Seems like we'll need to fix that then. Having to skip over the type and then backtrack to it to get intellisense if not very intuitive or usable. It should be easy to still parse the tag as an @param tag with an empty name until it is provided.

Also, @returns {|} doesn't give type intellisense at the |, is this not implemented yet?

[zhengbli]

I thought the reason we stopped parsing param tag without any param names is to be conservative about the type checking process; however, after I talked to Cyrus it turns out to be fine to keep the parsing going. Therefore now the fix for parsing param tag is added, and the @return tag type expression is considered as well.

[mhegazy]

👍