Pick<T, Exclude<keyof T, K>> & Pick<T, Extract<keyof T, K>> should be assignable to T

TypeScript Version: 3.2.1

Search Terms:
3.2.1
extends
intersection generic

Code

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;

type Func<T> = (arg: T) => null

type Context = 'Context';

export function withRouteContextPropConsumer<
    T extends { routeContext: Context }
>(
    funcToWrap: Func<T>,
): Func<Omit<T, "routeContext">> {
    return (args: Omit<T, "routeContext">) => {
        const routeContext: Context = 'Context';
        return funcToWrap({ ...args, routeContext });
    };
}

Expected behavior:
Code compiles without errors

Actual behavior:

Argument of type '{ routeContext: "Context"; }' is not assignable to parameter of type 'T'.

Playground Link: http://www.typescriptlang.org/play/#src=type%20Omit%3CT%2C%20K%20extends%20keyof%20T%3E%20%3D%20Pick%3CT%2C%20Exclude%3Ckeyof%20T%2C%20K%3E%3E%3B%0A%0Atype%20Func%3CT%3E%20%3D%20(arg%3A%20T)%20%3D%3E%20null%0A%0Atype%20Context%20%3D%20'Context'%3B%0A%0Aexport%20function%20withRouteContextPropConsumer%3C%0A%20%20%20%20T%20extends%20%7B%20routeContext%3A%20Context%20%7D%0A%3E(%0A%20%20%20%20funcToWrap%3A%20Func%3CT%3E%2C%0A)%3A%20Func%3COmit%3CT%2C%20%22routeContext%22%3E%3E%20%7B%0A%20%20%20%20return%20(args%3A%20Omit%3CT%2C%20%22routeContext%22%3E)%20%3D%3E%20%7B%0A%20%20%20%20%20%20%20%20const%20routeContext%3A%20Context%20%3D%20'Context'%3B%0A%20%20%20%20%20%20%20%20return%20funcToWrap(%7B%20...args%2C%20routeContext%20%7D)%3B%0A%20%20%20%20%7D%3B%0A%7D
Related Issues: Nothing obvious

After upgrading from 3.0.3 to 3.2.1, it seems that tsc has (at least partially) lost the ability to reason about constrained generics.

In the example above (one of our React context helper functions, modified to remove the React dependency), the function is parameterised over a constrained generic:

T extends { routeContext: Context }

But a few lines later, the compiler complains that the generic T may not have a routeContext attribute. T must have a routeContext attribute however, because of the constraint. Perhaps the Omit helper is confusing things?

Reproduziere den TypeScript-3.2.1-Fehler mit dem bereitgestellten Playground-Beispiel und tsc. Verfolge, wie eingeschränkte Generics, Omit über Pick/Exclude und Object Spread geprüft werden; abgeschlossen ist die Aufgabe, wenn das Beispiel ohne Fehler kompiliert und das Verhalten durch Regressionstests abgedeckt ist.