feat(store): improve selector decorator types (#1929)

packages/store/src/decorators/selector/selector.ts

@@ -1,7 +1,6 @@
 import { throwSelectorDecoratorError } from '../../configs/messages.config';
-import { ɵSelectorDef } from '../../selectors';
 import { createSelector } from '../../selectors/create-selector';
-import { SelectorSpec, SelectorType } from './symbols';
+import { SelectorDefTuple, SelectorType } from './symbols';
 
 /**
  * Decorator for creating a state selector for the current state.
@@ -11,14 +10,16 @@ export function Selector(): SelectorType<unknown>;
 /**
  * Decorator for creating a state selector from the provided selectors (and optionally the container State, depending on the applicable Selector Options).
  */
-export function Selector<T extends ɵSelectorDef<any>>(selectors: T[]): SelectorType<T>;
+export function Selector<T extends SelectorDefTuple>(selectors: T): SelectorType<T>;
 
-export function Selector<T extends ɵSelectorDef<any>>(selectors?: T[]): SelectorType<T> {
+export function Selector<T extends SelectorDefTuple = []>(
+  selectors?: T
+): SelectorType<unknown> | SelectorType<T> {
   return <U>(
     target: any,
     key: string | symbol,
-    descriptor: TypedPropertyDescriptor<SelectorSpec<T, U>>
-  ): TypedPropertyDescriptor<SelectorSpec<T, U>> | void => {
+    descriptor?: TypedPropertyDescriptor<(...states: any[]) => U>
+  ): TypedPropertyDescriptor<(...states: any[]) => U> | void => {
     descriptor ||= Object.getOwnPropertyDescriptor(target, key)!;
 
     const originalFn = descriptor?.value;

packages/store/src/decorators/selector/symbols.ts

@@ -1,13 +1,104 @@
-import { StateToken, ɵExtractTokenType } from '@ngxs/store/internals';
-
-export type SelectorSpec<T, U> = [T] extends [never]
-  ? (...states: any[]) => any
-  : T extends StateToken<any>
-    ? (state: ɵExtractTokenType<T>) => U
-    : (...states: any[]) => any;
-
-export type SelectorType<T> = <U>(
-  target: any,
-  key: string | symbol,
-  descriptor: TypedPropertyDescriptor<SelectorSpec<T, U>>
-) => TypedPropertyDescriptor<SelectorSpec<T, U>> | void;
+import { ɵSelectorDef, ɵSelectorReturnType } from '../../selectors';
+
+/**
+ * Defines a tuple of selector functions, state tokens, and state classes that a selector decorated
+ * by `@Selector()` can depend on.
+ */
+export type SelectorDefTuple = ɵSelectorDef<any>[] | [ɵSelectorDef<any>];
+
+type UnknownToAny<T> = unknown extends T ? any : T;
+type EnsureArray<T> = T extends any[] ? T : never;
+
+/**
+ * Given a tuple of selector functions, state tokens, state classes, etc., returns a tuple of what
+ * a dependent selector would expect to receive for that parent as an argument when called.
+ *
+ * For example, if the first element in the tuple `T` is a selector function that returns a
+ * `number`, then the first element of the result tuple will be `number`. If the second element
+ * in the tuple `T` is a state class with model `{ name: string }`, then the second element of
+ * the result tuple will be `{ name: string }`.
+ */
+type SelectorReturnTypeList<T extends SelectorDefTuple> = EnsureArray<{
+  [K in keyof T]: T[K] extends ɵSelectorDef<any>
+    ? UnknownToAny<ɵSelectorReturnType<T[K]>>
+    : never;
+}>;
+
+/**
+ * Defines a selector function matching a given argument list of parent selectors/states/tokens
+ * and a given return type.
+ */
+export type SelectorSpec<T, U> = T extends []
+  ? () => any
+  : T extends SelectorDefTuple
+    ? (...states: SelectorReturnTypeList<T>) => U
+    : () => any;
+
+/**
+ * Defines a selector function matching `SelectorSpec<T, U>` but with the assumption that the
+ * container state has been injected as the first argument.
+ */
+type SelectorSpecWithInjectedState<T, U> = SelectorSpec<
+  T extends SelectorDefTuple ? [any, ...T] : [any],
+  T extends SelectorDefTuple ? U : any
+>;
+
+/**
+ * Defines a property descriptor for the `@Selector` decorator that decorates a function with
+ * parent selectors/states/tokens `T` and return type `U`.
+ */
+type DescriptorWithNoInjectedState<T, U> = TypedPropertyDescriptor<SelectorSpec<T, U>>;
+
+/**
+ * Same as `DescriptorWithNoInjectedState` but with state injected as the first argument.
+ */
+type DescriptorWithInjectedState<T, U> = TypedPropertyDescriptor<
+  SelectorSpecWithInjectedState<T, U>
+>;
+
+type DecoratorArgs<T> = [target: any, key: string | symbol, descriptor?: T];
+
+/**
+ * Defines the return type of a call to `@Selector` when there is no argument given
+ * (e.g. `@Selector()` counts, but `@Selector([])` does not)
+ *
+ * This result is a decorator that can only be used to decorate a function with no arguments or a
+ * single argument that is the container state.
+ */
+type SelectorTypeNoDecoratorArgs = {
+  <U>(
+    ...args: DecoratorArgs<DescriptorWithNoInjectedState<unknown, U>>
+  ): void | DescriptorWithNoInjectedState<unknown, U>;
+  <U>(
+    ...args: DecoratorArgs<DescriptorWithInjectedState<unknown, U>>
+  ): void | DescriptorWithInjectedState<unknown, U>;
+};
+
+/**
+ * Defines the return type of a call to `@Selector` when there is an argument given.
+ * (e.g. `@Selector([])` counts, but `@Selector()` does not)
+ *
+ * This result is a decorator that can only be used to decorate a function with an argument list
+ * matching the results of the tuple of parents `T`.
+ */
+type SelectorTypeWithDecoratorArgs<T> = {
+  <U>(
+    ...args: DecoratorArgs<DescriptorWithNoInjectedState<T, U>>
+  ): void | DescriptorWithNoInjectedState<T, U>;
+  /**
+   * @deprecated
+   * Read the deprecation notice at this link: https://ngxs.io/deprecations/inject-container-state-deprecation.md.
+   */
+  <U>(
+    ...args: DecoratorArgs<DescriptorWithInjectedState<T, U>>
+  ): void | DescriptorWithInjectedState<T, U>;
+};
+
+/**
+ * Defines the return type of a call to `@Selector`. This result is a decorator that can only be
+ * used to decorate a function with an argument list matching the results of the tuple of
+ * parents `T`.
+ */
+export type SelectorType<T> = unknown extends T
+  ? SelectorTypeNoDecoratorArgs
+  : SelectorTypeWithDecoratorArgs<T>;

packages/store/tests/selector.spec.ts

@@ -330,7 +330,7 @@ describe('Selector', () => {
         }
 
         @Selector([MyStateV4])
-        static invalid() {
+        static invalid(_: MyStateModel) {
           throw new Error('This is a forced error');
         }
       }
@@ -423,7 +423,7 @@ describe('Selector', () => {
         }
 
         @Selector([MyStateV4])
-        static invalid() {
+        static invalid(_: MyStateModel) {
           throw new Error('This is a forced error');
         }
       }
@@ -495,7 +495,7 @@ describe('Selector', () => {
 
         @Selector([MyStateV3])
         @SelectorOptions({ suppressErrors: false })
-        static invalid() {
+        static invalid(_: MyStateModel) {
           throw new Error('This is a forced error');
         }
       }

packages/store/types/tests/selection.lint.ts

@@ -26,7 +26,7 @@ describe('[TEST]: Action Types', () => {
   it('should be correct type in selector/select decorator', () => {
     class Any {}
 
-    Selector(); // $ExpectType SelectorType<unknown>
+    Selector(); // $ExpectType SelectorTypeNoDecoratorArgs
     assertType(() => Selector([{ foo: 'bar' }])); // $ExpectError
     assertType(() => Selector({})); // $ExpectError
 
@@ -108,6 +108,10 @@ describe('[TEST]: Action Types', () => {
     @State<object[]>({ name: 'themePark' })
     class ThemePark {}
 
+    const numberSelector = (): number => 3;
+    const stringSelector = (): string => 'a';
+    const nullableStringSelector = (): string | null => null;
+
     class MyPandaState {
       @Selector() static pandas0 = (state: string[]): string[] => state; // $ExpectError
 
@@ -135,6 +139,66 @@ describe('[TEST]: Action Types', () => {
       static pandas5(state: string[]): string[] {
         return state;
       }
+
+      // Injected state - selector with no matching argument
+      @Selector([numberSelector]) // $ExpectError
+      static pandas6(state: string[]): number {
+        return state.length;
+      }
+
+      // Injected state - argument with no matching selector
+      @Selector([numberSelector]) // $ExpectError
+      static pandas7(state: string[], other: number, other2: string): number {
+        return state.length + other + other2.length;
+      }
+
+      // Injected state - type mismatch (swapped string/number)
+      @Selector([numberSelector, stringSelector]) // $ExpectError
+      static pandas8(state: string[], other: string, other2: number): number {
+        return state.length + other.length + other2;
+      }
+
+      // Injected state - unhandled nullability
+      @Selector([numberSelector, nullableStringSelector]) // $ExpectError
+      static pandas9(state: string[], other: number, other2: string): number {
+        return state.length + other + other2.length;
+      }
+
+      // Injected state - correct arguments
+      @Selector([numberSelector, stringSelector]) // $ExpectType (state: string[], other: number, other2: string) => number
+      static pandas10(state: string[], other: number, other2: string): number {
+        return state.length + other + other2.length;
+      }
+
+      // No injected state - selector with no matching argument
+      @Selector([numberSelector]) // $ExpectError
+      static pandas11(): number {
+        return 0;
+      }
+
+      // No injected state - argument with no matching selector
+      @Selector([numberSelector]) // $ExpectError
+      static pandas12(other: number, other2: string): number {
+        return other + other2.length;
+      }
+
+      // No injected state - type mismatch (swapped string/number)
+      @Selector([numberSelector, stringSelector]) // $ExpectError
+      static pandas13(other: string, other2: number): number {
+        return other.length + other2;
+      }
+
+      // No injected state - unhandled nullability
+      @Selector([numberSelector, nullableStringSelector]) // $ExpectError
+      static pandas14(other: number, other2: string): number {
+        return other + other2.length;
+      }
+
+      // No injected state - correct arguments
+      @Selector([numberSelector, stringSelector]) // $ExpectType (other: number, other2: string) => number
+      static pandas15(other: number, other2: string): number {
+        return other + other2.length;
+      }
     }
   });
 

packages/store/types/tests/state-token.lint.ts

@@ -125,7 +125,7 @@ describe('[TEST]: StateToken', () => {
         return state;
       }
 
-      @Selector([TodoListState, TODO_LIST_TOKEN]) // (state: string[], other: number) => number
+      @Selector([TodoListState, TODO_LIST_TOKEN]) // $ExpectError
       static todosV4(state: string[], other: number[]): number {
         return state.length + other.length;
       }