Support @const JSDoc tag

[emilio-martinez]

TypeScript Version: 2.5.3

Code

/**
 * @const {boolean} This constant is falsy
 */
export const MyFalsyConstant: boolean = false;

Expected behavior:

Type expression and comment should be separate for @const (http://usejsdoc.org/tags-constant.html) tags. See below for further explanation.

Actual behavior:

Parsing the above JSDoc (with help from tsutils which as far as I can see is just using Typescript parsing tools), I get the following node for the @const JSDoc tag.

NodeObject {
  pos: 1299,
  end: 1306,
  flags: 0,
  transformFlags: undefined,
  parent: 
   NodeObject {
     pos: 1292,
     end: 1368,
     flags: 0,
     transformFlags: undefined,
     parent: 
      NodeObject {
        pos: 1290,
        end: 1406,
        flags: 0,
        transformFlags: undefined,
        parent: [Object],
        kind: 208,
        decorators: undefined,
        modifiers: undefined,
        declarationList: [Object],
        jsDoc: [Object],
        _children: [Object] },
     kind: 275,
     tags: [ [Circular], [Object], pos: 1299, end: 1348 ],
     comment: undefined },
  kind: 276,
  atToken: TokenObject { pos: 1299, end: 1300, flags: 0, parent: undefined, kind: 57 },
  tagName: 
   IdentifierObject {
     pos: 1300,
     end: 1305,
     flags: 0,
     parent: undefined,
     escapedText: 'const' },
  comment: '{false} This constant is falsy' }

Destructuring the relevant ts.JSDocTag object (const { typeExpression, comment } = tag), I get the following:

typeExpression: `undefined`
comment: `{false} This constant is falsy`

My expectation would be for the type expression to be separate as outlined in http://usejsdoc.org/tags-constant.html

[mhegazy]

PRs welcomed.

[j-oliveras]

@mhegazy Maybe you want to add help wanted label to this issue (based on your previous comment).

[Kingwl]

I’d like to work on this.

[zachhardesty7]

has any progress been made on this issue? from what I can tell, it looks like #39768 was finished but closed.

[frank-dspeed]

This can be closed Typescript now Supports: since version 4.5+ #39768 implements it

export const CBLErrorDomainByCode = /** @type {const} */ ([, "LITE_CORE","POSIX","SQLITE","FLEECE","NETWORK","WEB_SOCKET"]);

is type

const CBLErrorDomainByCode: readonly [undefined, "LITE_CORE", "POSIX", "SQLITE", "FLEECE", "NETWORK", "WEB_SOCKET"]

works like a charm @RyanCavanaugh

https://www.typescriptlang.org/docs/handbook/jsdoc-supported-types.html#unsupported-tags <- needs a update i do not remember where the issues are for this.

[bjarkler]

I don't think this is fixed - can we reopen, @RyanCavanaugh? #39768 was closed without being merged, and the example in the previous comment uses the @type tag, not the @const tag which this issue is referring to.

[frank-dspeed]

@bjarkler i guess there is no real implementation ongoing with the @const JSDoc tag what now works is the so called typecasting to const so the same as in typescript with as const

i guess thats because it needs to get done and made sure that it is only on assignment.

[GreenAsJade]

Note that the documentation for Typescript points to this issue as being open on this tag.