CallHierarchyProvider#prepare should allow to return multiple symbols

[jrieken]

This is TS feedback. When you invoke call hierarchy on a symbol that has multiple definitions that the prepare call should allow to return all definitions

/cc @rbuckton

[jrieken]

Proposal is to overload this signature with an array return type:

prepareCallHierarchy(...): ProviderResult<CallHierarchyItem | CallHierarchyItem[]>;

[jrieken]

@rbuckton this is a follow up from microsoft/TypeScript#31863 (comment). When drilling into a call hierarchy, e.g when calling provideCallHierarchy[Incoming|Outgoing]Calls, then the provider can return multiple items for multiple definitions but call hierarchy cannot start like that. Tho, I am unsure if that's actually an issue, e.g does the case in TS (or other languages) exist that there multiple call'ables with the same name?

[mjbvz]

Hey @rbuckton, can you please provide some example TS where there may be multiple definitions? We tried coming up with one but couldn't. If there are multiple definitions, shouldn't TS server always be able to resolve which definition is being invoked?

[rbuckton]

This issue is something like this:

// a.d.ts
declare function foo(x?: number): void;

// b.d.ts
declare function foo(x?: string): void;

// main.ts
foo(); // <-- Inspect call hierarchy here

For a Call Hierarchy item we normally would choose the actual definition of foo if we can find one, however in this case all declarations of foo are ambient and are split across multiple files. Which one do we pick? If we don't have a way to indicate multiple locations for a call hierarchy item, then we will likely have to resort to overload resolution to pick a declaration, yet both declarations will end up having the same incoming/outgoing calls (since we don't limit a call-hierarchy to a specific overload).

[jrieken]

Alright - thanks for the clarification. I'll update the API as outlined above