Constrained generic types infer `never` on a function, even when the argument meets the constraints

Bug Report

🔎 Search Terms

• inference of generic types fails with typed argument
• infer generic never
• constrained generic infers never

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about 4.3.2

⏯ Playground Link

Playground link with relevant code

💻 Code

type ValidKey = string | number | symbol;

/* The class ultimately being built */
class Test<T, I extends ValidKey & keyof T> {
    idProp: I;

    constructor(idProp: I) {
        this.idProp = idProp;
    }
}

interface WithId<T, I extends ValidKey & keyof T> {
    idProp: I;
}

type IDableEntity<I extends ValidKey> = Record<I, ValidKey>;

class TestBuilder<T extends Record<ValidKey, any>> {
    id<I extends ValidKey & keyof T>(idProp: I): this & WithId<T, I> {
        return {
            ...this,
            "idProp": idProp
        };
    }
}

function testBuilder<T>(): TestBuilder<T> {
    return new TestBuilder<T>();
}

function build<
    T extends IDableEntity<I>,
    I extends ValidKey & keyof T>
(builder: TestBuilder<T> & WithId<T, I>): Test<T, I> {
    return new Test<T, I>(builder.idProp);
}

interface IDable {
    id: string;
}

const foo: TestBuilder<IDable> & WithId<IDable, 'id'> = testBuilder<IDable>().id('id');
const bar = build(foo);
/*
Argument of type 'TestBuilder<IDable> & WithId<IDable, "id">' is not assignable to parameter of type 'TestBuilder<IDableEntity<never>> & WithId<IDableEntity<never>, never>'.
  Type 'TestBuilder<IDable> & WithId<IDable, "id">' is not assignable to type 'WithId<IDableEntity<never>, never>'.
    Types of property 'idProp' are incompatible.
      Type 'string' is not assignable to type 'never'.ts(2345)
*/

This also fails if I create a new type CompleteTestBuilder<T extends IDableEntity<I>, I extends ValidKey & keyof T> = TestBuilder<T> & WithId<T, I> that build accepts as an argument, or if I define CompleteTestBuilder as its own interface extends TestBuilder<T> { idProp: I}.

A simpler version that does NOT fail:

function build2<T>(builder: TestBuilder<T>): TestBuilder<T> {
    return builder;
}

const baz: TestBuilder<IDable> = testBuilder<IDable>();
const qux = build2(baz); // qux: TestBuilder<IDable>

This version also does NOT fail:

function build3<T extends Record<ValidKey, any>>(builder: TestBuilder<T>): (t: T) => string {
    return (t: T) => 'boo';
}

const quux = build3(baz); // quux: (t: IDable) => string

🙁 Actual behavior

The build call fails with the error message:

Argument of type 'TestBuilder<IDable> & WithId<IDable, "id">' is not assignable to parameter of type 'TestBuilder<IDableEntity<never>> & WithId<IDableEntity<never>, never>'.
  Type 'TestBuilder<IDable> & WithId<IDable, "id">' is not assignable to type 'WithId<IDableEntity<never>, never>'.
    Types of property 'idProp' are incompatible.
      Type 'string' is not assignable to type 'never'.ts(2345)

🙂 Expected behavior

I would expect the build call to succeed, and types T and I to be inferred as IDable and "id", respectively. The argument type is already known and correct (it is even inferred correctly - the type assignment for foo is just to show that the type is correct). The types on the function should be able to match.

Beginne mit der verknüpften Playground-Reproduktion und dem generischen Inferenzverhalten in der build-Funktion. Verfolge, wie die Einschränkungen für T und I zu never führen, und überprüfe dann, dass der Aufruf build(foo) erfolgreich ist und T als IDable sowie I als "id" inferiert, ohne die einfacheren Beispiele zu beeinträchtigen.