Fix flow typings mobx4 [requires TS3.6, mobx4] (#2161)

* fix for flow typings

* fix async generator typing in flows

package.json

@@ -132,4 +132,4 @@
       "pre-commit": "lint-staged"
     }
   }
-}
+}

src/api/flow.ts

@@ -13,35 +13,9 @@ export function isFlowCancellationError(error: Error) {
 
 export type CancellablePromise<T> = Promise<T> & { cancel(): void }
 
-export interface FlowYield {
-    // fake, only for typing
-    "!!flowYield": undefined
-}
-
-export interface FlowReturn<T> {
-    // fake, only for typing
-    "!!flowReturn": T
-}
-
-// we skip promises that are the result of yielding promises (except if they use flowReturn)
-export type FlowReturnType<R> = IfAllAreFlowYieldThenVoid<
-    R extends FlowReturn<infer FR>
-        ? FR extends Promise<infer FRP>
-            ? FRP
-            : FR
-        : R extends Promise<any>
-        ? FlowYield
-        : R
->
-
-// we extract yielded promises from the return type
-export type IfAllAreFlowYieldThenVoid<R> = Exclude<R, FlowYield> extends never
-    ? void
-    : Exclude<R, FlowYield>
-
 export function flow<R, Args extends any[]>(
-    generator: (...args: Args) => IterableIterator<R>
-): (...args: Args) => CancellablePromise<FlowReturnType<R>> {
+    generator: (...args: Args) => Generator<any, R, any> | AsyncGenerator<any, R, any>
+): (...args: Args) => CancellablePromise<R> {
     if (arguments.length !== 1)
         fail(
             !!process.env.NODE_ENV && `Flow expects one 1 argument and cannot be used as decorator`
@@ -53,7 +27,9 @@ export function flow<R, Args extends any[]>(
         const ctx = this
         const args = arguments
         const runId = ++generatorId
-        const gen = action(`${name} - runid: ${runId} - init`, generator).apply(ctx, args)
+        const gen = action(`${name} - runid: ${runId} - init`, generator as (
+            ...args: Args
+        ) => Generator<any, R, any>).apply(ctx, args)
         let rejector: (error: any) => void
         let pendingPromise: CancellablePromise<any> | undefined = undefined
 
@@ -119,7 +95,7 @@ export function flow<R, Args extends any[]>(
                 rejector(e) // there could be a throwing finally block
             }
         })
-        return (res as CancellablePromise<R>) as any
+        return res as CancellablePromise<R>
     }
 }
 

src/types/observablemap.ts

@@ -270,7 +270,7 @@ export class ObservableMap<K = any, V = any>
         return makeIterable({
             next() {
                 return nextIndex < self._keys.length
-                    ? { value: self.get(self._keys[nextIndex++]), done: false }
+                    ? { value: self.get(self._keys[nextIndex++])!, done: false }
                     : { value: undefined as any, done: true }
             }
         })

test/base/typescript-tests.ts

@@ -1557,9 +1557,9 @@ test("it should support asyncAction as decorator (ts)", async () => {
     class X {
         @observable a = 1
 
-        f = mobx.flow(function* f(initial: number): any {
+        f = mobx.flow(function* f(this: X, initial: number) {
             this.a = initial // this runs in action
-            this.a += yield Promise.resolve(5)
+            this.a += yield Promise.resolve(5) as any
             this.a = this.a * 2
             return this.a
         })
@@ -1590,7 +1590,7 @@ test("flow support async generators", async () => {
             total += number
         }
         return total
-    } as any) // TODO: fix typings
+    })
 
     const p = start()
     const res = await p
@@ -1615,7 +1615,7 @@ test("flow support throwing async generators", async () => {
             total += number
         }
         return total
-    } as any) // TODO: fix typings
+    })
 
     const p = start()
     try {
@@ -1647,3 +1647,14 @@ test("verify #1528", () => {
 
     expect(appState.timer).toBe(0)
 })
+
+test("type of flows that return promises", async () => {
+    mobx.configure({ enforceActions: "observed" })
+
+    const f = mobx.flow(function* f() {
+        return Promise.resolve(5)
+    })
+
+    const n: number = await f()
+    expect(n).toBe(5)
+})

yarn.lock

@@ -7945,9 +7945,9 @@ ts-jest@^24.0.0:
     yargs-parser "10.x"
 
 tslib@^1.8.1, tslib@^1.9.0, tslib@^1.9.3:
-  version "1.9.3"
-  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.9.3.tgz#d7e4dd79245d85428c4d7e4822a79917954ca286"
-  integrity sha512-4krF8scpejhaOgqzBEcGM7yDIEfi0/8+8zDRZhNZZ2kjmHJ4hv3zCbQWxoJGz1iw5U0Jl0nma13xzHXcncMavQ==
+  version "1.10.0"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-1.10.0.tgz#c3c19f95973fb0a62973fb09d90d961ee43e5c8a"
+  integrity sha512-qOebF53frne81cf0S9B41ByenJ3/IuH8yJKngAX35CmiZySA0khhkovshKK+jGCaMnVomla7gVlIcc3EvKPbTQ==
 
 tsutils@^3.7.0:
   version "3.10.0"
@@ -7994,9 +7994,9 @@ typedarray@^0.0.6:
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
 typescript@^3.3.3333:
-  version "3.4.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.4.4.tgz#aac4a08abecab8091a75f10842ffa0631818f785"
-  integrity sha512-xt5RsIRCEaf6+j9AyOBgvVuAec0i92rgCaS3S+UVf5Z/vF2Hvtsw08wtUTJqp4djwznoAgjSxeCcU4r+CcDBJA==
+  version "3.6.4"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.6.4.tgz#b18752bb3792bc1a0281335f7f6ebf1bbfc5b91d"
+  integrity sha512-unoCll1+l+YK4i4F8f22TaNVPRHcD9PA3yCuZ8g5e0qGqlVlJ/8FSateOLLSagn+Yg5+ZwuPkL8LFUc0Jcvksg==
 
 uglify-js@^3.1.4:
   version "3.5.5"