Autocomplete/Intellisense Does Not Show All Options For Object Value

[mjbvz]

From @JonnyBoy333 on July 12, 2017 15:31

• VSCode Version: 1.14.0
• OS Version: macOS 10.12.5

Autocomplete/intellisense is not showing all the options for an object that goes into a function parameter even though it is defined in a typescript interface.

Example:

interface Fruit {
    /** Returns a fruit color. */
    getFruitColor(options: { fruit: 'apple' | 'orange' }): string;
    getFruitColor(options: { fruit: 'banana' }): boolean;
}

function testFunction (fruit: Fruit) {
    let color = fruit.getFruitColor({ fruit: '' }); // <-- Autocomplete only shows apple and orange as options and not banana
}

It appears that only the first method's options object is getting indexed by VS autocomplete but not the second one.

Reproduces without extensions: Yes

Copied from original issue: microsoft/vscode#30526

[mjbvz]

Here's the tsserver completions response:

[Trace  - 10:28:51 AM] Response received: completions (53). Request took 1 ms. Success: true 
Result: [
    {
        "name": "apple",
        "kind": "var",
        "kindModifiers": "",
        "sortText": "0"
    },
    {
        "name": "orange",
        "kind": "var",
        "kindModifiers": "",
        "sortText": "0"
    }
]

[JonnyBoy333]

@mjbvz Got it. Thanks for confirming this is Typescript related.

Unfortunately, this would be hard to fix in general.

When we get completions for a string literal directly inside a call expression, we have specialized code to iterate over every possible overload and get all string literals.

But when we get completions inside a string literal at an arbitrary location, we just call getContextualType and look for string literal types in there.

getContextualType will climb up to the signature and ask for its parameter types. Overload resolution will fail since { fruit: "" } is assignable to neither { fruit: "apple" | "orange" } nor { fruit: "banana" }, so we arbitrarily pick the first signature to get the contextual type.

To fix this in general would seem to require writing a getContextualTypes function that handled all overloads, returning all contextual types.