Assertion functions don't work with wildcard imports

[dfilatov]

TypeScript Version: 3.7.2

Search Terms:

assert function import export

Code

// Module asserts.ts
function isNonNullable<T>(obj: T): asserts obj is NonNullable<T> {
    if(obj === undefined || obj === null) {
        throw new Error('Must not be a nullable value');
    }
}

export {
    isNonNullable
};

// Module test.ts
import * as asserts from './asserts.ts';

function test(obj: string | null): void {
    asserts.isNonNullable(obj);
    obj.trim();
}

Expected behavior:
Everything works as expected

Actual behavior:
Error: Assertions require every name in the call target to be declared with an explicit type annotation.

If I rewrite test.ts with:

// Module test.ts
import { isNonNullable } from './asserts.ts';

function test(obj: string | null): void {
    isNonNullable(obj);
    obj.trim();
}

then everything compiles without any error

[ilogico]

To reproduce this issue, you have to use namespace imports import * as assert from './assert.js' and export the function through an export list export { check }.
When the function is exported with export function check(..., everything works correctly.

[andrewbranch]

I seem to recall that a lot of cleverness was required to support tracking these assertion signatures through property access without performance regressions, so this isn’t super surprising... But since export function isNonNullable ... does work (thanks @ilogico), I’m hopeful this a simple fix.

[G-Rath]

I believe this issue is preventing shipping assert guards in @types/node, due to @types/adone containing an std object that does:

import assert = require("assert");
...

export {
  assert,
  ...
}

I'm going to look further into this, especially since adone is deprecated, so might be able to hack around it, but if this is fixable that would help too

This is the PR if people want to take a look: DefinitelyTyped/DefinitelyTyped#42786

[dfilatov]

@RyanCavanaugh Is there any plan to fix this?

[RyanCavanaugh]

@dfilatov eventually, yes, or if someone wants to send a PR, that'd be great

[jakebailey]

Here is a similar case which affects the module-ified TS compiler:

// @strict: true

// @filename: src/core/_namespaces/ts.ts
import * as Debug from "../debug";
export { Debug };

// @filename: src/core/debug.ts
export declare function assert(expression: unknown): asserts expression;


// @filename: src/core/foo.ts
import * as ts from "./_namespaces/ts";
import { Debug } from "./_namespaces/ts";

ts.Debug.assert(true);
Debug.assert(true);


// @filename: src/other/_namespaces/ts.ts
export * from "../../core/_namespaces/ts"


// @filename: src/other/bar.ts
import * as ts from "./_namespaces/ts";
import { Debug } from "./_namespaces/ts";

ts.Debug.assert(true);
Debug.assert(true);

ts.Debug.assert doesn't work, but Debug.assert does. That's curious because the latter is still a wildcard import, just not the "top level" one. Using the "top level" one is where it breaks, but going a little more direct works.

[jakebailey]

This turned out to be really simple; will send a PR for it soon.