feat(overmind): improve typing of payload to transition

Author: christianalfoni

packages/node_modules/overmind/src/statemachine.test.ts

@@ -9,18 +9,15 @@ describe('Statemachine', () => {
 
     type States =  {
       state: 'FOO'
-      string: string
     } | {
       state: 'BAR'
-      number: number
     }
 
     const state = statemachine<States>({
       FOO: ['BAR'],
       BAR: ['FOO']
     }, {
       state: 'FOO',
-      string: 'hey'
     })
 
     const config = {

packages/node_modules/overmind/src/statemachine.ts

@@ -7,6 +7,25 @@ type TStates = {
   state: string | number,
 }
 
+export type Exact<Expected, Actual> =
+  keyof Expected extends keyof Actual
+    ? keyof Actual extends keyof Expected
+      ? Expected extends ExactElements<Expected, Actual>
+        ? Expected
+        : never
+      : never
+    : never;
+
+type ExactElements<Expected, Actual> = {
+  [K in keyof Actual]: K extends keyof Expected
+    ? Expected[K] extends Actual[K]
+      ? Actual[K] extends Expected[K]
+        ? Expected[K]
+        : never
+      : never
+    : never
+};
+
 export type StatemachineTransitions<States extends TStates> = {
   [State in States["state"]]: Array<States["state"]>
 }
@@ -19,7 +38,7 @@ export interface MachineMethods<States extends TStates, Base extends IState = {}
     state: T,
     newState: States extends {
       state: T  
-    } ? Omit<States, 'state'> : never,
+    } ? Exact<Omit<States, 'state'>, {}> extends never ?  Omit<States, 'state'> & Partial<Base> : Exact<Partial<Base>, {}> extends never ? Partial<Base> : { [NO_PROP]?: true} : never,
     callback?: ((current: Statemachine<Base, States, States extends {
       state: T
     } ? States : never>) => O)
@@ -32,6 +51,8 @@ const INITIAL_STATE = Symbol('INITIAL_STATE')
 const TRANSITIONS = Symbol('TRANSITIONS')
 const BASE = Symbol('BASE')
 const STATE = Symbol('STATE')
+const CURRENT_KEYS = Symbol('CURRENT_KEYS')
+const NO_PROP = Symbol('NO_PROP')
 
 export class StateMachine<Base extends IState, States extends TStates, State extends TStates = States, >  {
   state: State["state"]
@@ -46,6 +67,7 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
     this[INITIAL_STATE] = state.state
     this[TRANSITIONS] = transitions
     this[BASE] = base || {} 
+    this[CURRENT_KEYS] = Object.keys(state)
     Object.assign(this, state, base)
   }
   matches(...states) {
@@ -70,17 +92,15 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
     if (transitions[this.state].includes(state)) {
       const tree = (this[PROXY_TREE].master.mutationTree || this[PROXY_TREE])
       const base = this[VALUE][BASE]
-      const baseKeys = Object.keys(base || {}).concat('state')
 
       tree.enableMutations()
-      Object.keys(this).forEach((key) => {
-        if (!baseKeys.includes(key)) {
-          delete this[key]
-        }
+      this[VALUE][CURRENT_KEYS].forEach((key) => {
+        delete this[key]
       })
 
       Object.assign(this, newState)
       this.state = state
+      this[VALUE][CURRENT_KEYS] = Object.keys(newState)
 
       let result
       if (callback) {