Microsoft/TypeScript

Wrong elementwise error location on optional object property that allows arrays too

Open

#57,541 opened on Feb 26, 2024

View on GitHub
 (0 comments) (0 reactions) (0 assignees)TypeScript (6,726 forks)batch import
Domain: Related Error SpansHelp WantedPossible Improvement

Repository metrics

Stars
 (48,455 stars)
PR merge metrics
 (Avg merge 6d 17h) (9 merged PRs in 30d)

Description

🔎 Search Terms

error location elementwise elaboration array optional object

🕗 Version & Regression Information

  • This is a crash
  • This changed between versions ______ and _______
  • This changed in commit or PR _______
  • This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
  • I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.5.0-dev.20240225#code/C4TwDgpgBAyglgOwOYBsIHkBOBBTmCGIAPACoB8UAvFCVAD5SYT4AmA9giiDQNoC6AbgBQQ0JCgAFTGwBucFhBbYAxsDaYqUAN5CoUAM6ZlALgPBMiJML2IwAV2AB+U3YQBrBGwDuCYQF9hUXBoAFl8ZQALRAgAYQ4AMzgkUhU1TH0oCAAPYAgEFgypWXlFVPUKah0bBBk2NwhnWEs0LFwCYhIy9LJ-QIVlFHwmKHjXVTgOAwhgOzAU1XUM7Nz8wuk5BSUFzDIACgBKUyqoZSZ8XLDI6NNd5QSk00uohFj75M7t-TJ9qgpa+V6In001mRC0BiMpgARPFppEAKrAzBQgRQWwOUz6cyWKB+Pb7AB0p2YF3Czwgu2OiFq9SOuj0EJMUBhcIiiIgyIANPTqvZgKYAIwABm5ej83L8+2EQA

💻 Code

type SingleOrArray<T> = T | readonly T[];

type ProvidedActor = {
  src: string;
  input?: unknown;
};

type MachineConfig<TActors extends ProvidedActor> = {
  invoke?: SingleOrArray<TActors>;
};

declare function setup<TActors extends ProvidedActor>(): {
  createMachine: (config: MachineConfig<TActors>) => void;
};

setup<{ src: "fetchUser"; input: string }>().createMachine({
  invoke: {
    src: "fetchUser",
    input: 10,
  },
});

🙁 Actual behavior

invoke property gets highlighted

🙂 Expected behavior

input property should get highlighted as it's the one that it's not correct and it's more specific than invoke

Additional information about the issue

we can observe the error location to change when:

  1. we remove optionality from invoke
  2. we make the provided type argument a union

Contributor guide

Research direction
Investigate the logic for determining error location in TypeScript's checker for optional object properties that also accept arrays. The error should be reported on the mismatched property (`input`) rather than the parent (`invoke`). Look at how TypeScript resolves types for `SingleOrArray<T>` and why the error location is incorrect.
Tech stack
typescript
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65