[Experiment] feat(17227): Support @abstract JSDoc tag

[a-tarasyuk]

Fixes #17227

[ajafff]

We also need to determine whether legacy class syntax should be recognized:

/**
 * @class
 * @abstract
 */
function Legacy() {
  /**
   * @type {string}
   * @abstract
   */
  this.prop;
}

/** @abstract */
Legacy.prototype.doStuff = function() {}

[sandersn]

Here's what I think is needed to finish this feature:

1. Survey existing code to see whether requiring @abstract methods only to occur in @abstract classes would result in lots of errors.
2. Figure out how serialisation code results in issuing errors, then move the error earlier.
3. Add test cases.
4. Restrict what's allowed in the body of abstract methods.

[sandersn]

Here are a couple of observations based on my survey of existing usage:

1. The majority of existing @abstract on methods will get an error from the code currently in checkJSDocAbstractTag.
2. There's not much usage, though, so it wouldn't inconvenience many people.
3. Because there's so little usage already, I'm not sure this feature is worth it.

To accept this I think we'd need buyin from an existing user who wants this feature and agrees to test that it meets their needs. Looking at usage rates, only webpack or discord.js make sense to me.

[sandersn]

@typescript-bot pack this

[typescript-bot]

Heya @sandersn, I've started to run the tarball bundle task on this PR at aa4e38e. You can monitor the build here.

[sandersn]

@typescript-bot pack this

[typescript-bot]

Heya @sandersn, I've started to run the tarball bundle task on this PR at 15b01fd. You can monitor the build here.

[typescript-bot]

Hey @sandersn, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/98652/artifacts?artifactName=tgz&fileId=606CC13BB0AC03ADD769068E6B431AFC3E8D76BC07CDFE3667DFE540A6500AC002&fileName=/typescript-4.3.0-insiders.20210316.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

[andrewbranch]

@typescript-bot pack this

[typescript-bot]

Heya @andrewbranch, I've started to run the tarball bundle task on this PR at dfeab9e. You can monitor the build here.

[typescript-bot]

Hey @andrewbranch, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/107205/artifacts?artifactName=tgz&fileId=54C7D117B51B8A5AF5DBD35A138D051B9C0C44266E24F9ED844D8B25ED71229C02&fileName=/typescript-4.4.0-insiders.20210721.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

[trusktr]

@a-tarasyuk Can you please restore the content of the PR (it seems to have been cleared with your last force push) so that someone else can give this a shot on top of the work you made?

[trusktr]

Is there some way to clone/pull the deleted commit, dfeab9e? It appears to be visible on GitHub, but there's a note saying it does not exist in the repo. Same with a-tarasyuk@dfeab9e. I suppose I can see the changes, and manually apply them to the files.

[forivall]

@trusktr idk you're still wondering, but it can be fetched by git fetch origin dfeab9e4522e64e17174cae3ef700b410f6e4352 && git branch feat/17227 FETCH_HEAD - this will restore the branch into your local checkout.