refactor: add types for mutation errors

apps/demo/src/app/counter-rx-mutation/counter-rx-mutation.ts

@@ -5,7 +5,7 @@ import {
 } from '@angular-architects/ngrx-toolkit';
 import { CommonModule } from '@angular/common';
 import { Component, computed, signal } from '@angular/core';
-import { delay, Observable, of, throwError } from 'rxjs';
+import { catchError, delay, Observable, of, throwError } from 'rxjs';
 
 export type Params = {
   value: number;
@@ -51,6 +51,12 @@ export class CounterRxMutation {
     onSuccess: (response) => {
       console.log('Counter sent to server:', response);
     },
+    // TODO - In the current state, parsing for the error does not narrow unless either
+    // - 3rd error type generic specified
+    // - No generic types specified
+    // This is inline with the existing configuration of this `httpMutation` example before this proposed change
+    // If you uncomment the following, you must still specify the error type or drop the explicit types
+    // parseError: (error) => error as string,
     onError: (error) => {
       console.error('Failed to send counter:', error);
     },
@@ -108,5 +114,11 @@ function calcSum(a: number, b: number): Observable<number> {
       result,
     }));
   }
-  return of(result).pipe(delay(500));
+  return of(result).pipe(
+    delay(500),
+    catchError((error) => {
+      console.error('Error in calcSum:', error);
+      return of(1);
+    }),
+  );
 }

libs/ngrx-toolkit/src/lib/mutation/http-mutation.ts

@@ -41,15 +41,20 @@ export type HttpMutationRequest = {
     | boolean;
 };
 
-export type HttpMutationOptions<Parameter, Result> = Omit<
-  RxMutationOptions<Parameter, NoInfer<Result>>,
+export type HttpMutationOptions<Parameter, Result, Err = unknown> = Omit<
+  RxMutationOptions<Parameter, NoInfer<Result>, NoInfer<Err>>,
   'operation'
 > & {
   request: (param: Parameter) => HttpMutationRequest;
   parse?: (response: unknown) => Result;
+  parseError?: (error: unknown) => Err;
 };
 
-export type HttpMutation<Parameter, Result> = Mutation<Parameter, Result> & {
+export type HttpMutation<Parameter, Result, Err = unknown> = Mutation<
+  Parameter,
+  Result,
+  Err
+> & {
   uploadProgress: Signal<HttpProgressEvent | undefined>;
   downloadProgress: Signal<HttpProgressEvent | undefined>;
   headers: Signal<HttpHeaders | undefined>;
@@ -108,11 +113,11 @@ export type HttpMutation<Parameter, Result> = Mutation<Parameter, Result> & {
  * @param options The options for the HTTP mutation.
  * @returns The HTTP mutation.
  */
-export function httpMutation<Parameter, Result>(
+export function httpMutation<Parameter, Result, Err = unknown>(
   optionsOrRequest:
-    | HttpMutationOptions<Parameter, Result>
+    | HttpMutationOptions<Parameter, Result, Err>
     | ((param: Parameter) => HttpMutationRequest),
-): HttpMutation<Parameter, Result> {
+): HttpMutation<Parameter, Result, Err> {
   const httpClient = inject(HttpClient);
 
   const options =
@@ -121,6 +126,7 @@ export function httpMutation<Parameter, Result>(
       : optionsOrRequest;
 
   const parse = options.parse ?? ((raw: unknown) => raw as Result);
+  const parseError = options.parseError ?? ((raw: unknown) => raw as Err);
 
   const uploadProgress = signal<HttpProgressEvent | undefined>(undefined);
   const downloadProgress = signal<HttpProgressEvent | undefined>(undefined);
@@ -161,7 +167,7 @@ export function httpMutation<Parameter, Result>(
           );
       });
     },
-  }) as HttpMutation<Parameter, Result>;
+  }) as HttpMutation<Parameter, Result, Err>;
 
   mutation.uploadProgress = uploadProgress;
   mutation.downloadProgress = downloadProgress;

libs/ngrx-toolkit/src/lib/mutation/mutation.ts

@@ -1,26 +1,26 @@
 import { Signal } from '@angular/core';
 
-export type MutationResult<Result> =
+export type MutationResult<Result, Err> =
   | {
       status: 'success';
       value: Result;
     }
   | {
       status: 'error';
-      error: unknown;
+      error: Err;
     }
   | {
       status: 'aborted';
     };
 
 export type MutationStatus = 'idle' | 'pending' | 'error' | 'success';
 
-export type Mutation<Parameter, Result> = {
-  (params: Parameter): Promise<MutationResult<Result>>;
+export type Mutation<Parameter, Result, Err> = {
+  (params: Parameter): Promise<MutationResult<Result, Err>>;
   status: Signal<MutationStatus>;
   value: Signal<Result | undefined>;
   isPending: Signal<boolean>;
   isSuccess: Signal<boolean>;
-  error: Signal<unknown>;
-  hasValue(): this is Mutation<Exclude<Parameter, undefined>, Result>;
+  error: Signal<Err | undefined>;
+  hasValue(): this is Mutation<Exclude<Parameter, undefined>, Result, Err>;
 };

libs/ngrx-toolkit/src/lib/mutation/rx-mutation.ts

@@ -13,12 +13,14 @@ import {
 import { concatOp, FlatteningOperator } from '../flattening-operator';
 import { Mutation, MutationResult, MutationStatus } from './mutation';
 
-export type Operation<Parameter, Result> = (param: Parameter) => Result;
+export type Operation<Parameter, Result, Err = unknown> = (
+  param: Parameter,
+) => Result;
 
-export interface RxMutationOptions<Parameter, Result> {
-  operation: Operation<Parameter, Observable<Result>>;
+export interface RxMutationOptions<Parameter, Result, Err = unknown> {
+  operation: Operation<Parameter, Observable<Result>, Observable<Err>>;
   onSuccess?: (result: Result, param: Parameter) => void;
-  onError?: (error: unknown, param: Parameter) => void;
+  onError?: (error: Err, param: Parameter) => void;
   operator?: FlatteningOperator;
   injector?: Injector;
 }
@@ -86,14 +88,14 @@ export interface RxMutationOptions<Parameter, Result> {
  * @param options
  * @returns the actual mutation function along tracking data as properties/methods
  */
-export function rxMutation<Parameter, Result>(
+export function rxMutation<Parameter, Result, Err = unknown>(
   optionsOrOperation:
-    | RxMutationOptions<Parameter, Result>
-    | Operation<Parameter, Observable<Result>>,
-): Mutation<Parameter, Result> {
+    | RxMutationOptions<Parameter, Result, Err>
+    | Operation<Parameter, Observable<Result>, Observable<Err>>,
+): Mutation<Parameter, Result, Err> {
   const inputSubject = new Subject<{
     param: Parameter;
-    resolve: (result: MutationResult<Result>) => void;
+    resolve: (result: MutationResult<Result, Err>) => void;
   }>();
 
   const options =
@@ -106,15 +108,15 @@ export function rxMutation<Parameter, Result>(
   const destroyRef = options.injector?.get(DestroyRef) ?? inject(DestroyRef);
 
   const callCount = signal(0);
-  const errorSignal = signal<unknown>(undefined);
+  const errorSignal = signal<Err | undefined>(undefined);
   const idle = signal(true);
   const isPending = computed(() => callCount() > 0);
   const value = signal<Result | undefined>(undefined);
   const isSuccess = computed(() => !idle() && !isPending() && !errorSignal());
 
   const hasValue = function (
-    this: Mutation<Parameter, Result>,
-  ): this is Mutation<Exclude<Parameter, undefined>, Result> {
+    this: Mutation<Parameter, Result, Err>,
+  ): this is Mutation<Exclude<Parameter, undefined>, Result, Err> {
     return typeof value() !== 'undefined';
   };
 
@@ -147,7 +149,7 @@ export function rxMutation<Parameter, Result>(
               errorSignal.set(undefined);
               value.set(result);
             }),
-            catchError((error: unknown) => {
+            catchError((error: Err) => {
               options.onError?.(error, input.param);
               errorSignal.set(error);
               value.set(undefined);
@@ -165,7 +167,7 @@ export function rxMutation<Parameter, Result>(
               } else if (innerStatus === 'error') {
                 input.resolve({
                   status: 'error',
-                  error: errorSignal(),
+                  error: errorSignal() as Err,
                 });
               } else {
                 input.resolve({
@@ -183,7 +185,7 @@ export function rxMutation<Parameter, Result>(
     .subscribe();
 
   const mutationFn = (param: Parameter) => {
-    return new Promise<MutationResult<Result>>((resolve) => {
+    return new Promise<MutationResult<Result, Err>>((resolve) => {
       if (callCount() > 0 && flatteningOp.exhaustSemantics) {
         resolve({
           status: 'aborted',
@@ -197,7 +199,7 @@ export function rxMutation<Parameter, Result>(
     });
   };
 
-  const mutation = mutationFn as Mutation<Parameter, Result>;
+  const mutation = mutationFn as Mutation<Parameter, Result, Err>;
   mutation.status = status;
   mutation.isPending = isPending;
   mutation.error = errorSignal;

libs/ngrx-toolkit/src/lib/with-mutations.ts

@@ -14,7 +14,7 @@ import { Mutation, MutationStatus } from './mutation/mutation';
 
 // NamedMutationMethods below will infer the actual parameter and return types
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
-type MutationsDictionary = Record<string, Mutation<any, any>>;
+type MutationsDictionary = Record<string, Mutation<any, any, any>>;
 
 // withMethods uses Record<string, Function> internally
 // eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
@@ -31,9 +31,10 @@ type NamedMutationProps<T extends MutationsDictionary> = {
 type NamedMutationMethods<T extends MutationsDictionary> = {
   [Prop in keyof T as `${Prop & string}`]: T[Prop] extends Mutation<
     infer P,
-    infer R
+    infer R,
+    infer E
   >
-    ? Mutation<P, R>
+    ? Mutation<P, R, E>
     : never;
 };