Microsoft/TypeScript

Don't suggest converting custom promise-like returning function to async ones

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#40,701 opened on Sep 22, 2020

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 (4 comments) (1 reaction) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
Domain: LS: RefactoringsExperience EnhancementHelp WantedSuggestion

Description

Search Terms

async converted function

Suggestion

Do not suggest that a function is converted to async if its return value is explicitly set to something that is not the global Promise type.

Use Cases

If using a package that provides an extended version of promises (for instance cancellable promises) then the transformation is wrong to occur.

Examples

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

Contributor guide

Tech stack
typescript
Domain
developer experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScript compiler internalsunderstanding of async/await
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate the TypeScript codebase's code action for converting functions to async, likely in src/services/codeActions.ts. The goal is to modify the condition that suggests async conversion to exclude functions returning custom promise like types not assignable to the global Promise type. Check if there's an existing check for Promise and extend it to respect custom promise types.