Have QuickInfo use import types to display type aliases that are not in scope

[kpdonn]

Search Terms:
type alias, import, display, quickinfo, intellisense

Code

// @Filename: file1.ts
export type ComplicatedType<T, U> = { [K in Exclude<keyof T, U>]: T[K] } // could be anything here
export declare function getComplicatedType<T, U extends keyof T>(arg: T, exclude: U): ComplicatedType<T, U>

// @Filename: file2.ts
import { getComplicatedType } from "./file1"
interface SomeInterface {
 a: string
 b<T>(arg: T): T,
 c: { c2: string } | { c3: number },
 d?: boolean
}
declare const test: SomeInterface
const result = getComplicatedType(test, "a") // quickinfo on result currently displays something like:
/* const result: {
 b: <T>(arg: T) => T;
 c: {
 c2: string;
 } | {
 c3: number;
 };
 d: boolean | undefined;
} */

Current behavior:
The quick info type shown for result is a fully expanded anonymous type because ComplicatedType is not in scope in file2. Importing ComplicatedType in file2 makes quick info display const result: ComplicatedType<SomeInterface, "a">, but I don't think it's common to import a type alias purely for the quick info benefit if it isn't actually used anywhere in the file.

While the example above isn't that bad, in some cases (#18754, #23458) the fully expanded types can be so large that they actually cause a performance issue for the language service.

Suggested behavior:
Use import types from #22592 to display an accurate qualified reference to ComplicatedType. So in the example above quick info for result could instead display something like:

const result: import("./file1").ComplicatedType<SomeInterface, "a">

Which, although a little verbose, would be much more readable than many fully expanded types.

Related Issues:
#22592 added import types.

#18754, #23458, #6070, #13095 - Various issues related to the display of types.