Don't show object property name completions when the originating type is a class with private or protected members

[TheMrZZ]

Bug Report

TypeScript currently autocompletes class properties in function arguments. This is an inherently wrong behavior, which leads to confusion and potential errors.

Let's take this code as an example:

class Dish {
  name: string
  protected allergens: string[]

  constructor (name: string, allergens: string[] = []) {
    this.name = name
    this.allergens = allergens
  }
}

function serve(dish: Dish) {
  console.log('Who wants some', dish.name, '?')
}

The serve function should only take a Dish as an argument. Nothing else should be allowed. Yet, TypeScript tries to autocomplete the class properties, if you type an object:

dish.mp4

Of course, you end up with an error, since the object cannot be interpreted as a Dish: Property 'allergens' is protected but type '{ name: string; allergens: string[]; }' is not a class derived from 'Dish'. (2345).
If you remove the allergens property, you'll have another error: Property 'allergens' is missing in type '{ name: string; }' but required in type 'Dish'. (2345).

This is very problematic, especially when your arguments don't just take a class instance, but also an object (like Dish | { somethingElse: string }). You then get an even more confusing autocompletion list.

🔎 Search Terms

TypeScript autocompletes class properties in function arguments.
TypeScript autocompletes class properties in function parameters.
TypeScript incorrectly autocompletes class instances properties, even with protected or private members.
TypeScript hints class properties in autocompletion when argument is either an object or a class instance.

🕗 Version & Regression Information

This is the behavior in every version I tried, including the latest 4.4 builds, and I reviewed the FAQ for all entries.

⏯ Playground Link

Playground link with relevant code

💻 Code

class Dish {
  name: string
  protected allergens: string[]

  constructor (name: string, allergens: string[] = []) {
    this.name = name
    this.allergens = allergens
  }
}

function serve(dish: Dish) {
  console.log('Who wants some', dish.name, '?')
}

// Property 'allergens' is protected but type '{ name: string; allergens: string[]; }' is not a class derived from 'Dish'. (2345)
serve({
  name: 'cake',
  allergens: ['chocolate'],
})

//   Property 'allergens' is missing in type '{ name: string; }' but required in type 'Dish'. (2345)
serve({
  name: 'cake',
})

// Correct sample
const cake = new Dish('cake', ['chocolate'])
serve(cake)

🙁 Actual behavior

Dish properties name and allergens are proposed to autocompletion. However, they shouldn't be, because even if you specify them all, the input will still be incorrect.

🙂 Expected behavior

No Dish property should be autocompleted. In my example, the autocompletion list should be empty when opening an object.