microsoft / microsoft/TypeScript

JSDoc missing syntax for `new Map<string, string>()`

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Description

TypeScript Version: 3.7.x-dev.201xxxxx

Search Terms: JSDoc Map generics assignment any unsafe

Code

class MyServer {
  constructor () {
    // new Map is Map<any, any>; cannot call Map constructor with new Map<string, string[]>
    /** @type {Map<string, string[]>} */
    this.functions = new Map()
  }
}

const myServer = new MyServer()
myServer.functions.get('foo')

Expected behavior:

Expected to be able to say what the Map contains when creating a new map. In typescript you can do new Map<string, string[]>() but theres no explicit generic parameter function invocation syntax for JSDoc

Actual behavior:

The type Map<any, any> exists. This fails the eslint rule of no-unsafe-assignment and this fails the no-any rule of tslint etc.

Note that doing something similar for arrays works because there's a special case inference for [] and it also works for Set because the constructor is defined differently and it has generic inference in the initialization statement.

Playground Link: https://www.typescriptlang.org/play?useJavaScript=true#code/MYGwhgzhAECyCeBlApgJwG5ugbwFDWmAHsA7CAF1QFdhyjVoAKASh3wOgHoAqb6AAXLwADshywwwgDwVUASxIBzADTRZCxQG0AugD4AvtG6d2BcgAs5EAHQAzKiVpzSMALzQSyAO5xJLdvq4gbjEZOTQALZIaJgM7p4+CCgYaP5RybF2Dk4u1orI5IwA5LZEREXMuCHgUHDRKQx4BKGyNHQMLGwcXLwCQqI4AIKoqGDwMpQaBkYm3RZWWY7kzmTQ7joBQVUt4ekxWPHedRmplXsNizlkeQXFpeXMQA

Related Issues: Yes, in eslint https://github.com/typescript-eslint/typescript-eslint/issues/2109

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the JavaScript example in the linked TypeScript Playground and compare the current Map<any, any> result with the expected typed assignment. Review how JSDoc types represent generic constructor calls, using the related typescript-eslint issue for context. Done means a supported syntax is defined and the example no longer infers an unsafe any type.

Written by the indexing model from the issue text.

Assessment

Tech stack
javascript, typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
30/100

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