JSDoc overload tag

[apendua]

Fixes https://github.com/microsoft/TypeScript/issues/25590

This PR replaces an earlier attempt: https://github.com/microsoft/TypeScript/pull/50789

Since there was no final consensus, I ended up using a new @overload tag to ensure backwards compatibility, e.g.

/**
 * @overload
 * @param {number} x
 * @returns {'number'}
 */
/**
 * @overload
 * @param {string} x
 * @returns {'string'}
 */
/**
 * @overload
 * @param {boolean} x
 * @returns {'boolean'}
 */
/**
 * @param {unknown} x
 * @returns {string}
 */
function typeName(x) {
  return typeof x;
}

I would be happy to modify the implementation if someone suggests a better approach.

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[apendua]

@microsoft-github-policy-service agree

[sandersn]

I did a quick grep of JS code (all the JS that gets installed when installing the dependencies of every package on Definitely Typed). This found one existing use of @overload, in the AWS SDK. The use is similar to this PR, except that it's used on functions with a single signature, and also on classes. Can you add some tests that reflect that use? They don't have to behave the way that the authors meant, they just need to not crash. =)

Here are the interesting cases I've found so far:

callable constructor function

  /**
   * @overload Endpoint(endpoint)
   *   Constructs a new endpoint given an endpoint URL. If the
   *   URL omits a protocol (http or https), the default protocol
   *   set in the global {AWS.config} will be used.
   *   @param endpoint [String] the URL to construct an endpoint from
   */
  constructor: function Endpoint(endpoint, config) {

callable constructor function with overloads

Note that the second overload has zero param tags, just @option and @example.

  /**
   * A credentials object can be created using positional arguments or an options
   * hash.
   *
   * @overload AWS.Credentials(accessKeyId, secretAccessKey, sessionToken=null)
   *   Creates a Credentials object with a given set of credential information
   *   as positional arguments.
   *   @param accessKeyId [String] the AWS access key ID
   *   @param secretAccessKey [String] the AWS secret access key
   *   @param sessionToken [String] the optional AWS session token
   *   @example Create a credentials object with AWS credentials
   *     var creds = new AWS.Credentials('akid', 'secret', 'session');
   * @overload AWS.Credentials(options)
   *   Creates a Credentials object with a given set of credential information
   *   as an options hash.
   *   @option options accessKeyId [String] the AWS access key ID
   *   @option options secretAccessKey [String] the AWS secret access key
   *   @option options sessionToken [String] the optional AWS session token
   *   @example Create a credentials object with AWS credentials
   *     var creds = new AWS.Credentials({
   *       accessKeyId: 'akid', secretAccessKey: 'secret', sessionToken: 'session'
   *     });
   */
  constructor: function Credentials() {

The associated hand-written overload set:

    constructor(options: CredentialsOptions);
    constructor(accessKeyId: string, secretAccessKey: string, sessionToken?: string);

single signature with split return types

There's a lot going on here that would be good to test:

• function in object literal property assignment
• double return tags; I think this is the 'overload' part
• @callback inline type definition impllicitly covering the third parameter

Again, this doesn't need to have the correct semantics, it just needs to not crash.

    /**
     * @overload getSynthesizeSpeechUrl(params = {}, [expires = 3600], [callback])
     *   Generate a presigned url for {AWS.Polly.synthesizeSpeech}.
     *   @note You must ensure that you have static or previously resolved
     *     credentials if you call this method synchronously (with no callback),
     *     otherwise it may not properly sign the request. If you cannot guarantee
     *     this (you are using an asynchronous credential provider, i.e., EC2
     *     IAM roles), you should always call this method with an asynchronous
     *     callback.
     *   @param params [map] parameters to pass to the operation. See the {AWS.Polly.synthesizeSpeech}
     *     operation for the expected operation parameters.
     *   @param expires [Integer] (3600) the number of seconds to expire the pre-signed URL operation in.
     *     Defaults to 1 hour.
     *   @return [string] if called synchronously (with no callback), returns the signed URL.
     *   @return [null] nothing is returned if a callback is provided.
     *   @callback callback function (err, url)
     *     If a callback is supplied, it is called when a signed URL has been generated.
     *     @param err [Error] the error object returned from the presigner.
     *     @param url [String] the signed URL.
     *   @see AWS.Polly.synthesizeSpeech
     */
    getSynthesizeSpeechUrl: function getSynthesizeSpeechUrl(params, expires, callback) {

Here's the hand-created .d.ts overload set for comparison:

  getSynthesizeSpeechUrl(params: Polly.Types.SynthesizeSpeechInput, error: number, callback: (err: AWSError, url: string) => void): void;
  getSynthesizeSpeechUrl(params: Polly.Types.SynthesizeSpeechInput, callback: (err: AWSError, url: string) => void): void;
  getSynthesizeSpeechUrl(params: Polly.Types.SynthesizeSpeechInput, expires?: number): string;

[apendua]

@sandersn

I did a quick grep of JS code (all the JS that gets installed when installing the dependencies of every package on Definitely Typed).

Thank you for taking the effort to find these examples!

They don't have to behave the way that the authors meant, they just need to not crash. =)

Sure, I will try to add the tests for the use cases that you listed.

[apendua]

@sandersn I pushed some additional tests and also used this opportunity to resolve some conflicts. It would be great if you could have a second look 😄

[apendua]

@sandersn Thank you for the review and for the positive feedback!