Inference of function arguments is inconsitent when reordering object properties

[hayes]

🔎 Search Terms

inference infer order function arguments

🕗 Version & Regression Information

This affects all tested version of typescript back to 3.3.3 (oldest version available in the playground)

In 5.0 the started to only affect function using the function keyword, arrow functions and object methods are no-longer affected after 5.0

after 5.0 functions using the function keyword are still affected (functions, generators, and async generators)

⏯ Playground Link

https://www.typescriptlang.org/play/?target=11#code/JYOwLgpgTgZghgYwgAgMoFcBGBnBViYQBiwEANgCYDyADmMAPYjYA8AogG4TgB8yA3gChkybFlz5CALmQAKAJTIAvH07cww5FAjYGZLjNkQu4GWvCKVyEOgC2hKIIC+gwRQgIycbchjoQCPRMyO4woBC0QczsJmA8spoMdIzMMhg4eATEpJSRKazmcQA0gvIyHAzAFK4A9DXI0FAMUFJuEGEgEclM2LJCItq6+hCGxuqWfGPgJSJiGZIQCgJaEGDoUCDIAIwATADMyE4lTvK19Y3NraHheT19moN6BnJTYBMNsTOi4pnSvv6BFJLfgrNYbbb7Q7HU6COrWBgNKBNKDIADuAAtuMgaE0aNAwABPZDNdwo4DYUSouA0PEUK7tG7dZj3WY-BbA0HrTa7A5HB46J4jF6xd6vaFneGI5FozGbdDYUAAc2Q3iaqP+ASivmayAABnMJFldfSOl0or1+ishs8jCLlJNPpoDb8hUsrCDtGDuZC+ScgA

💻 Code

interface SubscribeFieldOptions<Event> {
 subscribe: () => Event
 resolve: (event: Event) => number
}

declare function defineOptions<Event>(
 options: SubscribeFieldOptions<Event>,
): void

defineOptions({
// error: Type 'unknown' is not assignable to type 'number'
 resolve: (event) => event,
 subscribe() { return 123 },
})

// error: Type 'unknown' is not assignable to type 'number'
defineOptions({
 resolve: (event) => event,
 subscribe: function() { return 123 },
})

// no error when property order is swapped:
defineOptions({
 subscribe() { return 123 },
 resolve: (event) => event,
})

// no error when using arrow function for `subscribe`:
defineOptions({
 resolve: (event) => event,
 subscribe: () => { return 123 },
})

🙁 Actual behavior

The event argument is inferred as unknown when using a the resolve method is defined before the subscribe method in the defineOptions call, and resolve is a function, async function, function* or async function*

🙂 Expected behavior

The event argument of the resolve function should be correctly inferred regardless of what kind of function definition is used (arrow, method, function, async function, generator, async generator)

Additional information about the issue

No response

[RyanCavanaugh]

See #47599

[hayes]

Thanks, and sorry for the duplicate. Finding the right issue when you don't know all the right terminology is really hard!