Generic function with function as argument autocomplete broken, unless generic argument of the argument function is it's first argument

[julijan]

🔎 Search Terms

typescript generic function no autocomplete function as argument

🕗 Version & Regression Information

Relevant versions are 5.4.5 and above, tested in all versions from 5.4.5 to 5.8.0 (Nightly) inclusive, I was able to reproduce the bug in all versions.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.2#code/IYZwngdgxgBAZgV2gFwJYHsIwE4FMDmqIyu2ACgDYKEQBCwAJgDwDyADsjLgB4kQMgYAJVxR02ZsWyoI+ADQxgEMAD4VACijAKFAEbAoAawBcMdcDZtTSsAvQcMEEKfbIAlDAC8KmADd0qAx2HM4wAHLoAJIQcKSsHCpupmTY6AC2RLhM-oE+AN4AvgBQRXiExKSU1DL0DOrmlsHIoXkwIOm4yAAWMvimUr0wBR7eMIUKeUUwMAD0MzC6uBToAO6KCMjoYmlsFJ24MEQLqYa4EAq4vmcw3ejUXTddB8hgbAdHbKlv2BRgftqBYAkBhTNodIrDADcJSKc0OEBIeGIvV+CmAGy26V2+xgK3EhkEqDgMAARPY0JgQCTFNh8Ag0mdONtcII4KhsMQFHBxFxuMAdntjEVQJBYIgUI4cAQiIiqjQAOLodDMVy8vgCYSicSSZDSWRo5RqTTaPQGExmcmOUKuNGWazKEY+HJBGDk0IRaKxbDxZCJZKpDIgLLO-LFUrSirkKgKpV1dRu0ytdoM7q9fq6wYFW1WRQOryhiaguGLZZrdGbbbYki4-EgUHJ3AQtyQoA

💻 Code

async function registerPluginBad<Opt extends Record<string, any>>(callback: (app: any, options: Opt) => void, opts: NoInfer<Opt>): Promise<void> {}

registerPluginBad((app, opts: { something: string }) => {}, {
  // below autocomplete is broken, even though the type is properly validated
  some
});


// interestingly, autocomplete works if "options" argument comes first, for example:
async function registerPluginGood<Opt extends Record<string, any>>(callback: (options: Opt, app: any) => void, opts: NoInfer<Opt>): Promise<void> {}

registerPluginGood((opts: { something: string }, app: any) => {}, {
  // below autocomplete works
  some
});

🙁 Actual behavior

This one has to be tested in the playground:
registerPluginBad - second argument does not autocomplete, however type is properly validated
registerPluginGood - exact same function, except the first argument "callback" arguments have changed the order, which for some reason fixes the autocomplete

🙂 Expected behavior

For both functions, autocomplete should work. Argument order should not matter.
Both do not infer from "opts", so any inference should be from "options" argument of the callback.

Additional information about the issue

No response

[Andarist]

The problem here is not that the order of the parameters and arguments is different. Your registerPluginGood call annotates both parameters of the callback. This makes it context-insensitive, and it can, thanks to that, hit different inference paths.

It happens that one of my old PRs addresses this: #56460