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, 2.0.10 is not same as 2.1.x in my code.

[AlexanderEkdahl]

You can be explicit and use then<T> which let's you specify the result of your then block.

[MaximBalaganskiy]

There is a difference between can and must. This is clearly a serious regression

…

On 28 Dec 2016 3:12 AM, "Alexander Ekdahl" ***@***.***> wrote: You can be explicit and use then which let's you specify the result of your then block. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#10977 (comment)>, or mute the thread <https:/notifications/unsubscribe-auth/ADimvNfzi4-xpLjxtJYeH8C8SvvbqN26ks5rMTj2gaJpZM4KAGp9> .

[raijinsetsu]

This is huge. Could we get an official statement? This is preventing us from upgrading to 2.1 because all of our Promise chains fail to compile.

[rbuckton]

The changes made to the definition of Promise were added to address issues with assignability (#10524) and strict null checks. Just changing the order of the overloads does not solve the problem, as some ordering works better with strict null checks turned on, but makes things worse with strict null checks turned off.

I am currently investigating a solution that seems to be giving the right answer in all of these cases, but it needs further testing and discussion before I can put up a PR.

[FriOne]

@mhegazy this isn't fixed for me. I use https:/shlomiassaf/angular2-modal and this module have types problem from above 2.0.10.

let modal = this.modal.open(AddFolderDialogComponent, {context: new AddFolderContext(parentFolder)});
    modal
      .then(dialog => dialog.result)
      .then((folder: Folder) => this.store.dispatch(new AddFolderAction(folder)))

open() returns Promise<DialogRef<any>>, DialogRef.result contains Promise<any>, I get an error:

TS2345: Argument of type '(folder: Folder) => void' is not assignable to parameter of type '(value: DialogRef) => void | PromiseLike'.
Types of parameters 'folder' and 'value' are incompatible.
Type 'DialogRef' is not assignable to type 'Folder'.
Property 'id' is missing in type 'DialogRef'.

If I'm wrong, please, show me a way to fix it.

[Offirmo]

I confirm, this issue isn't fixed in latest typescript 2.2.1 This is a huge blocker !

[MaximBalaganskiy]

It's got 2.3 tag. Fixed in there

…

On 27 Feb 2017 5:56 PM, "offirmo" ***@***.***> wrote: I confirm, this issue isn't fixed in typescript 2.2. This is a huge blocker ! — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#10977 (comment)>, or mute the thread <https:/notifications/unsubscribe-auth/ADimvMxz24xWszvhLYTwIqSmtkCJdHs8ks5rgnOMgaJpZM4KAGp9> .

[FriOne]

@MaximBalaganskiy Hm, this is a huge blocker as @Offirmo sad. I can't update typescript and angular because it depends on 2.1 now. Also 2.1 has object spreading :( @mhegazy Why it was moved to 2.3?

[Offirmo]

@MaximBalaganskiy 2.3 isn't available in npm yet. Can't wait...

[MaximBalaganskiy]

npm install typescript@next -g should install the latest

[FriOne]

@MaximBalaganskiy Sorry I understood you incorrectly. I thougth 2.3 is unavailable yet.