Support inferring module specifier to allow custom import function

[mohsen1]

Search Terms

Modules, import(), Module Specifier, Module Namespace

Suggestion

Support inferring module specifier passed to type import function (import() in type name space) to allow custom import function.

Use Cases

if I have a function that wraps require, it's impossible to declare types for it:

function myRequire(moduleSpecifier) {
  return require(moduleSpecifer);
}

Ideally I would like to declare types for a function like that as following:

declare function myRequire(moduleSpecifier: string): import(moduleSpecifier);

Use Cases

• Custom require functions are very common, specially for testing where they do mocking
• Jest mock functions can take advantage of this

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

[AlCalzone]

It's not entirely impossible, but doesn't look nice either (and you have to duplicate the import specifier):

function load<T>(stuff: string): T {
	return require(stuff) as T;
}

const foo = load<typeof import("./index")>("./index");

[mohsen1]

@AlCalzone That's what we're doing currently but repeating the module specifier and all that extra syntax is why I opened this issue.

/cc @DanielRosenwasser

This issue would be hard to fix the way the compiler is designed currently, since it means we would have to load in new files while type-checking. Currently we can get the full set of imports just by parsing.