Add TypeScript Mapped Draft Type

[knpwrs]

These changes enable the following:

importproducefrom'immer';interfaceState{readonlyx: number;}// `x` cannot be modified hereconststate: State={x: 0;};constnewState=produce<State>((draft)=>{// `x` can be modified heredraft.x++;});// `newState.x` cannot be modified here

This helps TypeScript users ensure immutability of their state interfaces. I had to upgrade TypeScript for the index.d.ts file to parse properly. This feature was merged into TypeScript back in February: microsoft/TypeScript#21919

It also appears that the flow/ts.ts file doesn't run and never did. I tested this externally and it works, but I'd like to see a more robust test suite in this repo.

EDIT: I've added some TypeScript tests in Jest.

EDIT:Fixes#97

[coveralls]

Coverage remained the same at 93.137% when pulling 1978d62 on knpwrs:mapped-draft-type into 537aa92 on mweststrate:master.

[knpwrs]

I just pushed a commit to make the Draft type recursive so users can have nested readonly interfaces:

interfaceState{readonlyfoo: number;readonlybaz: {readonlyx: number;readonlyy: number;};}

I'm still trying to figure out how to make arrays work properly.

[knpwrs]

Looks like everything is working now. All of the following compiles and works as expected:

importproducefrom'immer';interfaceState{readonlynum: number;readonlyfoo?: string;bar: string;readonlybaz: {readonlyx: number;readonlyy: number;};readonlyarr: ReadonlyArray<{readonlyvalue: string}>;readonlyarr2: {readonlyvalue: string}[];}conststate: State={num: 0,bar: 'foo',baz: {x: 1,y: 2,},arr: [{value: 'asdf'}],arr2: [{value: 'asdf'}],}constnewState=produce<State>(draft=>{draft.num++;draft.foo='bar';draft.bar='foo';draft.baz.x++;draft.baz.y++;draft.arr[0].value='foo';draft.arr.push({value: 'asf'});draft.arr2[0].value='foo';draft.arr2.push({value: 'asf'});})(state);

[knpwrs]

I only just now noticed the previous discussions in #97 and #109. I believe what I have here is a solution that fixes #97 and addresses the problems in #109.

[ghost]

This would be really useful to us, thank you very much @knpwrs

[knpwrs]

@mweststrate is there any interest from the project owners to add these typings?

[mweststrate]

Yes; but didn't get to reviewing yet 😊 Op za 23 jun. 2018 19:42 schreef Ken Powers <notifications@github.com>:

…

@mweststrate <https://github.com/mweststrate> is there any interest from the project owners to add these typings? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#161 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhFRsW1xcoEuuMj_GEeYBBdiVUNHAks5t_n4igaJpZM4UhG-U> .

[ghost]

Hello @mweststrate
+1 for this PR from my side 😀 👍

[mweststrate]

Reviewed! No comments, looks awesome :). Will release next week