expose selectSlice, name and reducerPath in context

Author: EskiMojo14

packages/toolkit/src/createSlice.ts

@@ -190,7 +190,11 @@ interface InternalReducerHandlingContext<State> {
   actionCreators: Record<string, any>
 }
 
-export interface ReducerHandlingContext<State> {
+export interface ReducerHandlingContext<
+  State,
+  Name extends string,
+  ReducerPath extends string,
+> {
   /**
    * Adds a case reducer to handle a single action type.
    * @param actionCreator - Either a plain action type string, or an action creator generated by [`createAction`](./createAction) that can be used to determine the action type.
@@ -199,7 +203,7 @@ export interface ReducerHandlingContext<State> {
   addCase<ActionCreator extends TypedActionCreator<string>>(
     actionCreator: ActionCreator,
     reducer: CaseReducer<State, ReturnType<ActionCreator>>,
-  ): ReducerHandlingContext<State>
+  ): ReducerHandlingContext<State, Name, ReducerPath>
   /**
    * Adds a case reducer to handle a single action type.
    * @param actionCreator - Either a plain action type string, or an action creator generated by [`createAction`](./createAction) that can be used to determine the action type.
@@ -208,7 +212,7 @@ export interface ReducerHandlingContext<State> {
   addCase<Type extends string, A extends Action<Type>>(
     type: Type,
     reducer: CaseReducer<State, A>,
-  ): ReducerHandlingContext<State>
+  ): ReducerHandlingContext<State, Name, ReducerPath>
 
   /**
    * Allows you to match incoming actions against your own filter function instead of only the `action.type` property.
@@ -224,7 +228,7 @@ export interface ReducerHandlingContext<State> {
   addMatcher<A>(
     matcher: TypeGuard<A>,
     reducer: CaseReducer<State, A extends Action ? A : A & Action>,
-  ): ReducerHandlingContext<State>
+  ): ReducerHandlingContext<State, Name, ReducerPath>
   /**
    * Add an action to be exposed under the final `slice.actions[reducerName]` key.
    *
@@ -238,7 +242,10 @@ export interface ReducerHandlingContext<State> {
    *
    * dispatch(addPost(post))
    */
-  exposeAction(actionCreator: unknown): ReducerHandlingContext<State>
+  exposeAction(
+    actionCreator: unknown,
+  ): ReducerHandlingContext<State, Name, ReducerPath>
+
   /**
    * Add a case reducer to be exposed under the final `slice.caseReducers[reducerName]` key.
    *
@@ -252,12 +259,34 @@ export interface ReducerHandlingContext<State> {
    *
    * slice.caseReducers.addPost([], addPost(post))
    */
-  exposeCaseReducer(reducer: unknown): ReducerHandlingContext<State>
+  exposeCaseReducer(
+    reducer: unknown,
+  ): ReducerHandlingContext<State, Name, ReducerPath>
+
   /**
    * Provides access to the initial state value given to the slice.
    * If a lazy state initializer was provided, it will be called and a fresh value returned.
    */
   getInitialState(): State
+
+  /**
+   * The `name` option provided for the slice.
+   */
+  name: Name
+
+  /**
+   * The `reducerPath` option provided for the slice.
+   * Defaults to `name` if not provided.
+   */
+  reducerPath: ReducerPath
+
+  /**
+   * Tries to select the slice's state from a possible root state shape, using `reducerPath`.
+   * Throws an error if slice's state is not found.
+   *
+   * *Note that only the original `reducerPath` option is used - if a different `reducerPath` is used when injecting, this will not be reflected.*
+   */
+  selectSlice(state: Record<ReducerPath, State>): State
 }
 
 export interface ReducerDetails {
@@ -314,10 +343,10 @@ export type ReducerCreator<Type extends RegisteredReducerType> = {
 } & (ReducerDefinitionsForType<Type> extends never
   ? {}
   : {
-      handle<State>(
+      handle<State, Name extends string, ReducerPath extends string>(
         details: ReducerDetails,
         definition: ReducerDefinitionsForType<Type>,
-        context: ReducerHandlingContext<State>,
+        context: ReducerHandlingContext<State, Name, ReducerPath>,
       ): void
     })
 
@@ -388,7 +417,7 @@ export interface Slice<
    * Equivalent to `slice.getSelectors((state: RootState) => state[slice.reducerPath])`.
    */
   get selectors(): Id<
-    SliceDefinedSelectors<State, Selectors, { [K in ReducerPath]: State }>
+    SliceDefinedSelectors<State, Selectors, Record<ReducerPath, State>>
   >
 
   /**
@@ -410,7 +439,7 @@ export interface Slice<
    *
    * Will throw an error if slice is not found.
    */
-  selectSlice(state: { [K in ReducerPath]: State }): State
+  selectSlice(state: Record<ReducerPath, State>): State
 }
 
 /**
@@ -898,7 +927,7 @@ export function buildCreateSlice<
     }
 
     function getContext({ reducerName }: ReducerDetails) {
-      const context: ReducerHandlingContext<State> = {
+      const context: ReducerHandlingContext<State, Name, ReducerPath> = {
         addCase(
           typeOrActionCreator: string | TypedActionCreator<any>,
           reducer: CaseReducer<State>,
@@ -946,6 +975,17 @@ export function buildCreateSlice<
           return context
         },
         getInitialState,
+        name,
+        reducerPath,
+        selectSlice(state) {
+          const sliceState = state[reducerPath]
+          if (typeof sliceState === 'undefined') {
+            throw new Error(
+              `Could not find "${name}" slice in state. In order for slice creators to use \`context.selectSlice\`, the slice must be nested in the state under its reducerPath: "${reducerPath}"`,
+            )
+          }
+          return sliceState
+        },
       }
       return context
     }