Javascript function type inference breaks across a property accessor but not a function call

Type: Bug

I am writing a typescript declaration file declarations.d.ts that describes some interfaces and a global object. The declarations will be use to assist JavaScript developers that are writing script for an embedded v8 engine that offers global objects like the one being described.

There is a global variable Global of interface type SomeGlobal, which in turn has a property someType of interface type SomeType, and finally SomeType has a callback property of type function like (other:OtherType) => void. Here is the entire file: declarations.d.ts

interface OtherType
{
    stringProperty: string;
}
interface SomeType
{
    callback: (other:OtherType) => void;
}
interface SomeGlobal
{
    someType: SomeType;
    getSomeType(): SomeType;
}

declare var Global: SomeGlobal;

// This is not part of the declarations, it's here to show you that the type of `o` is properly inferred through the property accessor `someType`
Global.someType.callback = (o) => {o.stringProperty}

and the jsconfig.json being used to ensure that code in main.js can see these types:

{
    "compilerOptions": {
        "target": "es6",
        "lib": ["es6"],
        "strict": true
    },
    "include": [
        "*.js",
        "declarations.d.ts"
    ]
}

From here on, working a in main.js that looks like this:

Global.someType.callback = (other) => {};

Global.getSomeType().callback = (other) => {};

In VSCode when you attempt to assign the callback property of SomeType and open the parentheses to start building the arrow function like so:

Global.someType.callback = (

I would expect to see autocomplete help like callback(other: OtherType): void, prompting me to complete the statement like:

Global.someType.callback = (other) => {/* do something*/};

But this is not what happens. If I hover over callback VS will display the appropriate signature for the property (property) SomeType.callback: (other: OtherType) => void, but inside the arrow function param list or function body, the other param just shows up as type any.

What's interesting is that if I go through a function call instead of a property:

Global.getSomeType().callback = (

Then there is correct function type inference for callback and I get the intellisense autocomplete you'd expect.

Am I just missing something silly here, or have I found a bug?

I have attached the 3 demo files for you to inspect. Any help would be most appreciated!

VS Code version: Code 1.95.3 (f1a4fb101478ce6ec82fe9627c43efbf9e98c813, 2024-11-13T14:50:04.152Z)
OS version: Windows_NT x64 10.0.22635
Modes:

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tssandbox.zip

Commencez par reproduire le comportement de declarations.d.ts, jsconfig.json et main.js, ou examinez l’archive tssandbox.zip jointe. Comparez les paramètres déduits pour Global.someType.callback et Global.getSomeType().callback, puis vérifiez que le cas d’accès à une propriété fournit l’inférence OtherType attendue sans modifier le comportement de l’appel de fonction.