Chained promises produce incorrect types

[MaximBalaganskiy]

TypeScript Version: nightly (2.1.0-dev.20160918)

Code

class A {
 json(): Promise<any> {
 return Promise.resolve({});
 };
}

function test() {
 let p = Promise.resolve(new A());
 p.then(x => x.json()).then(x => x.b);
}

Expected behavior:
Compiled without errors

Actual behavior:
Compiled with an error

error TS2339: Property 'b' does not exist on type 'A'.

[yortus]

I can repro this. This made it a bit clearer:

function test() {
 let p1 = Promise.resolve(new A()); // p1 is Promise<A>
 let p2 = p1.then(x => x.json()); // p2 is Promise<A>, but should be promise<any>
 let p3 = p2.then(x => x.b); // x is A, but should be any
}

The incorrect inference ocurrs on the let p2... line and is a result of choosing the first then overload from the Promise<T> definition in lib.d.ts.

It looks like a result of the changes to the then overloads made recently in #10448.

[wizzard0]

Also, Promise.all is still inferred incorrectly sometimes.

[blakeembrey]

Just updated from 2.1.0-dev.20160911 to 2.1.0-dev.20160928 and run into this. Something simple like Promise.resolve({}).then(() => 'test') now keeps the return type of Promise<{}> instead of Promise<string>.

[doxiaodong]

same with 2.1.1,

[jwbay]

Another problem I hit and a non-obvious workaround (shortened from RWC) --

function test2() {
 return new Promise<number>(resolve => {
 fetch('').then(response => {
 //without the cast, value below is Response and resolve() errors
 //in TS 2.0 value is any since json() returns Promise<any>
 return response.json() as Promise<number>; 
 }).then(value => {
 resolve(value);
 });
 });
}

[Offirmo]

This is a major bug !

[Iezious]

same with 2.1.4, moved to async calls since this bug

[Alexander-Taran]

2.0.10 got the same behavior, Had to switch back to 2.0.7

[doxiaodong]

Alexander Taran (@Alexander-Taran), 2.0.10 is not same as 2.1.x in my code.