refactor(core): improve API documentation for input after angular.dev support (#55053)

This commit improves the API documentation for `input` after
we added support for initializer APIs in angular.dev docs generation.

Changes:

- Rename `ReadT` to `T`. This conceptually makes it easy to talk about
  inputs of type `T` if there is no transform involved. The common case.
- Rename `WriteT` to `TransformT`. This makes it clear that this is the
  type that the "transform" needs to handle.
- Improves the "overall" description of the input function so that it
  can be shown as a general overview for the API site.
- Improves usage notes to be a little more helpful, yielding more useful
  content in the API docs usage notes section.
- Add short JSDoc description for each individual overload.

PR Close #55053

goldens/public-api/core/index.md

@@ -937,43 +937,41 @@ export interface InputDecorator {
 
 // @public
 export interface InputFunction {
-    <ReadT>(): InputSignal<ReadT | undefined>;
-    // (undocumented)
-    <ReadT>(initialValue: ReadT, opts?: InputOptionsWithoutTransform<ReadT>): InputSignal<ReadT>;
-    // (undocumented)
-    <ReadT, WriteT>(initialValue: ReadT, opts: InputOptionsWithTransform<ReadT, WriteT>): InputSignalWithTransform<ReadT, WriteT>;
+    <T>(): InputSignal<T | undefined>;
+    <T>(initialValue: T, opts?: InputOptionsWithoutTransform<T>): InputSignal<T>;
+    <T, TransformT>(initialValue: T, opts: InputOptionsWithTransform<T, TransformT>): InputSignalWithTransform<T, TransformT>;
     required: {
-        <ReadT>(opts?: InputOptionsWithoutTransform<ReadT>): InputSignal<ReadT>;
-        <ReadT, WriteT>(opts: InputOptionsWithTransform<ReadT, WriteT>): InputSignalWithTransform<ReadT, WriteT>;
+        <T>(opts?: InputOptionsWithoutTransform<T>): InputSignal<T>;
+        <T, TransformT>(opts: InputOptionsWithTransform<T, TransformT>): InputSignalWithTransform<T, TransformT>;
     };
 }
 
 // @public
-export interface InputOptions<ReadT, WriteT> {
+export interface InputOptions<T, TransformT> {
     alias?: string;
-    transform?: (v: WriteT) => ReadT;
+    transform?: (v: TransformT) => T;
 }
 
 // @public
-export type InputOptionsWithoutTransform<ReadT> = Omit<InputOptions<ReadT, ReadT>, 'transform'> & {
+export type InputOptionsWithoutTransform<T> = Omit<InputOptions<T, T>, 'transform'> & {
     transform?: undefined;
 };
 
 // @public
-export type InputOptionsWithTransform<ReadT, WriteT> = Required<Pick<InputOptions<ReadT, WriteT>, 'transform'>> & InputOptions<ReadT, WriteT>;
+export type InputOptionsWithTransform<T, TransformT> = Required<Pick<InputOptions<T, TransformT>, 'transform'>> & InputOptions<T, TransformT>;
 
 // @public
-export interface InputSignal<ReadT> extends InputSignalWithTransform<ReadT, ReadT> {
+export interface InputSignal<T> extends InputSignalWithTransform<T, T> {
 }
 
 // @public
-export interface InputSignalWithTransform<ReadT, WriteT> extends Signal<ReadT> {
+export interface InputSignalWithTransform<T, TransformT> extends Signal<T> {
     // (undocumented)
-    [ɵINPUT_SIGNAL_BRAND_READ_TYPE]: ReadT;
+    [ɵINPUT_SIGNAL_BRAND_READ_TYPE]: T;
     // (undocumented)
-    [ɵINPUT_SIGNAL_BRAND_WRITE_TYPE]: WriteT;
+    [ɵINPUT_SIGNAL_BRAND_WRITE_TYPE]: TransformT;
     // (undocumented)
-    [SIGNAL]: InputSignalNode<ReadT, WriteT>;
+    [SIGNAL]: InputSignalNode<T, TransformT>;
 }
 
 // @public
@@ -1101,9 +1099,11 @@ export const model: ModelFunction;
 // @public
 export interface ModelFunction {
     <T>(): ModelSignal<T | undefined>;
-    // (undocumented)
     <T>(initialValue: T, opts?: ModelOptions): ModelSignal<T>;
-    required<T>(opts?: ModelOptions): ModelSignal<T>;
+    // (undocumented)
+    required: {
+        <T>(opts?: ModelOptions): ModelSignal<T>;
+    };
 }
 
 // @public

packages/compiler-cli/src/ngtsc/typecheck/src/type_check_block.ts

@@ -722,7 +722,7 @@ class TcbDirectiveInputsOp extends TcbOp {
         // For signal inputs, a `transformType` will never be set as we do not capture
         // the transform in the compiler metadata. Signal inputs incorporate their
         // transform write type into their member type, and we extract it below when
-        // unwrapping the `InputSignal<ReadT, WriteT>`.
+        // setting the `WriteT` of such `InputSignalWithTransform<_, WriteT>`.
 
         if (this.dir.coercedInputFields.has(fieldName)) {
           let type: ts.TypeNode;

packages/core/src/authoring/input/input.ts

@@ -18,7 +18,7 @@ export function inputFunction<ReadT, WriteT>(
   return createInputSignal(initialValue, opts);
 }
 
-export function inputRequiredFunction<ReadT, WriteT>(opts?: InputOptions<ReadT, WriteT>):
+export function inputRequiredFunction<ReadT, WriteT = ReadT>(opts?: InputOptions<ReadT, WriteT>):
     InputSignalWithTransform<ReadT, WriteT> {
   ngDevMode && assertInInjectionContext(input);
   return createInputSignal(REQUIRED_UNSET_VALUE as never, opts);
@@ -31,77 +31,95 @@ export function inputRequiredFunction<ReadT, WriteT>(opts?: InputOptions<ReadT,
  * The function exposes an API for also declaring required inputs via the
  * `input.required` function.
  *
- * @usageNotes
- * Initialize an input in your directive or component by declaring a
- * class field and initializing it with the `input()` or `input.required()`
- * function.
- *
- * ```ts
- * @Directive({..})
- * export class MyDir {
- *   firstName = input<string>();            // string|undefined
- *   lastName = input.required<string>();    // string
- *   age = input(0);                         // number
- * }
- * ```
- *
  * @developerPreview
  */
 export interface InputFunction {
   /**
-   * Initializes an input with an initial value. If no explicit value
-   * is specified, Angular will use `undefined`.
-   *
-   * Consider using `input.required` for inputs that don't need an
-   * initial value.
-   *
-   * @developerPreview
+   * Initializes an input of type `T` with an initial value of `undefined`.
+   * Angular will implicitly use `undefined` as initial value.
    */
-  <ReadT>(): InputSignal<ReadT|undefined>;
-  <ReadT>(initialValue: ReadT, opts?: InputOptionsWithoutTransform<ReadT>): InputSignal<ReadT>;
-  <ReadT, WriteT>(initialValue: ReadT, opts: InputOptionsWithTransform<ReadT, WriteT>):
-      InputSignalWithTransform<ReadT, WriteT>;
+  <T>(): InputSignal<T|undefined>;
+  /** Declares an input of type `T` with an explicit initial value. */
+  <T>(initialValue: T, opts?: InputOptionsWithoutTransform<T>): InputSignal<T>;
+  /**
+   * Declares an input of type `T` with an initial value and a transform
+   * function.
+   *
+   * The input accepts values of type `TransformT` and the given
+   * transform function will transform the value to type `T`.
+   */
+  <T, TransformT>(initialValue: T, opts: InputOptionsWithTransform<T, TransformT>):
+      InputSignalWithTransform<T, TransformT>;
 
   /**
    * Initializes a required input.
    *
-   * Users of your directive/component need to bind to this
+   * Consumers of your directive/component need to bind to this
    * input. If unset, a compile time error will be reported.
    *
    * @developerPreview
    */
   required: {
-    <ReadT>(opts?: InputOptionsWithoutTransform<ReadT>): InputSignal<ReadT>;
-
-    <ReadT, WriteT>(opts: InputOptionsWithTransform<ReadT, WriteT>):
-        InputSignalWithTransform<ReadT, WriteT>;
+    /** Declares a required input of type `T`. */
+    <T>(opts?: InputOptionsWithoutTransform<T>): InputSignal<T>;
+    /**
+     * Declares a required input of type `T` with a transform function.
+     *
+     * The input accepts values of type `TransformT` and the given
+     * transform function will transform the value to type `T`.
+     */
+    <T, TransformT>(opts: InputOptionsWithTransform<T, TransformT>):
+        InputSignalWithTransform<T, TransformT>;
   };
 }
 
 /**
- * The `input` function allows declaration of inputs in directives and
- * components.
+ * The `input` function allows declaration of Angular inputs in directives
+ * and components.
  *
- * Initializes an input with an initial value. If no explicit value
- * is specified, Angular will use `undefined`.
+ * There are two variants of inputs that can be declared:
  *
- * Consider using `input.required` for inputs that don't need an
- * initial value.
+ *   1. **Optional inputs** with an initial value.
+ *   2. **Required inputs** that consumers need to set.
+ *
+ * By default, the `input` function will declare optional inputs that
+ * always have an initial value. Required inputs can be declared
+ * using the `input.required()` function.
+ *
+ * Inputs are signals. The values of an input are exposed as a `Signal`.
+ * The signal always holds the latest value of the input that is bound
+ * from the parent.
  *
  * @usageNotes
- * Initialize an input in your directive or component by declaring a
- * class field and initializing it with the `input()` function.
+ * To use signal-based inputs, import `input` from `@angular/core`.
+ *
+ * ```
+ * import {input} from '@angular/core`;
+ * ```
+ *
+ * Inside your component, introduce a new class member and initialize
+ * it with a call to `input` or `input.required`.
  *
  * ```ts
- * @Directive({..})
- * export class MyDir {
- *   firstName = input<string>();            // string|undefined
- *   lastName = input.required<string>();    // string
- *   age = input(0);                         // number
+ * @Component({
+ *   ...
+ * })
+ * export class UserProfileComponent {
+ *   firstName = input<string>();             // Signal<string|undefined>
+ *   lastName  = input.required<string>();    // Signal<string>
+ *   age       = input(0)                     // Signal<number>
  * }
  * ```
  *
+ * Inside your component template, you can display values of the inputs
+ * by calling the signal.
+ *
+ * ```html
+ * <span>{{firstName()}}</span>
+ * ```
+ *
  * @developerPreview
+ * @initializerApiFunction
  */
 export const input: InputFunction = (() => {
   // Note: This may be considered a side-effect, but nothing will depend on

packages/core/src/authoring/input/input_signal.ts

@@ -18,7 +18,7 @@ import {INPUT_SIGNAL_NODE, InputSignalNode, REQUIRED_UNSET_VALUE} from './input_
  *
  * Options for signal inputs.
  */
-export interface InputOptions<ReadT, WriteT> {
+export interface InputOptions<T, TransformT> {
   /** Optional public name for the input. By default, the class field name is used. */
   alias?: string;
   /**
@@ -31,7 +31,7 @@ export interface InputOptions<ReadT, WriteT> {
    * attribute form to bind to the input via `<my-dir input>`. A transform can then
    * handle such string values and convert them to `boolean`. See: {@link booleanAttribute}.
    */
-  transform?: (v: WriteT) => ReadT;
+  transform?: (v: TransformT) => T;
 }
 
 /**
@@ -39,16 +39,16 @@ export interface InputOptions<ReadT, WriteT> {
  *
  * @developerPreview
  */
-export type InputOptionsWithoutTransform<ReadT> =
+export type InputOptionsWithoutTransform<T> =
     // Note: We still keep a notion of `transform` for auto-completion.
-    Omit<InputOptions<ReadT, ReadT>, 'transform'>&{transform?: undefined};
+    Omit<InputOptions<T, T>, 'transform'>&{transform?: undefined};
 /**
  * Signal input options with the transform option required.
  *
  * @developerPreview
  */
-export type InputOptionsWithTransform<ReadT, WriteT> =
-    Required<Pick<InputOptions<ReadT, WriteT>, 'transform'>>&InputOptions<ReadT, WriteT>;
+export type InputOptionsWithTransform<T, TransformT> =
+    Required<Pick<InputOptions<T, TransformT>, 'transform'>>&InputOptions<T, TransformT>;
 
 export const ɵINPUT_SIGNAL_BRAND_READ_TYPE = /* @__PURE__ */ Symbol();
 export const ɵINPUT_SIGNAL_BRAND_WRITE_TYPE = /* @__PURE__ */ Symbol();
@@ -77,10 +77,10 @@ export const ɵINPUT_SIGNAL_BRAND_WRITE_TYPE = /* @__PURE__ */ Symbol();
  *
  * @developerPreview
  */
-export interface InputSignalWithTransform<ReadT, WriteT> extends Signal<ReadT> {
-  [SIGNAL]: InputSignalNode<ReadT, WriteT>;
-  [ɵINPUT_SIGNAL_BRAND_READ_TYPE]: ReadT;
-  [ɵINPUT_SIGNAL_BRAND_WRITE_TYPE]: WriteT;
+export interface InputSignalWithTransform<T, TransformT> extends Signal<T> {
+  [SIGNAL]: InputSignalNode<T, TransformT>;
+  [ɵINPUT_SIGNAL_BRAND_READ_TYPE]: T;
+  [ɵINPUT_SIGNAL_BRAND_WRITE_TYPE]: TransformT;
 }
 
 /**
@@ -94,7 +94,7 @@ export interface InputSignalWithTransform<ReadT, WriteT> extends Signal<ReadT> {
  *
  * @developerPreview
  */
-export interface InputSignal<ReadT> extends InputSignalWithTransform<ReadT, ReadT> {}
+export interface InputSignal<T> extends InputSignalWithTransform<T, T> {}
 
 /**
  * Creates an input signal.
@@ -103,10 +103,10 @@ export interface InputSignal<ReadT> extends InputSignalWithTransform<ReadT, Read
  *   Can be set to {@link REQUIRED_UNSET_VALUE} for required inputs.
  * @param options Additional options for the input. e.g. a transform, or an alias.
  */
-export function createInputSignal<ReadT, WriteT>(
-    initialValue: ReadT,
-    options?: InputOptions<ReadT, WriteT>): InputSignalWithTransform<ReadT, WriteT> {
-  const node: InputSignalNode<ReadT, WriteT> = Object.create(INPUT_SIGNAL_NODE);
+export function createInputSignal<T, TransformT>(
+    initialValue: T,
+    options?: InputOptions<T, TransformT>): InputSignalWithTransform<T, TransformT> {
+  const node: InputSignalNode<T, TransformT> = Object.create(INPUT_SIGNAL_NODE);
 
   node.value = initialValue;
 
@@ -133,5 +133,5 @@ export function createInputSignal<ReadT, WriteT>(
     inputValueFn.toString = () => `[Input Signal: ${inputValueFn()}]`;
   }
 
-  return inputValueFn as InputSignalWithTransform<ReadT, WriteT>;
+  return inputValueFn as InputSignalWithTransform<T, TransformT>;
 }

packages/core/src/authoring/input/input_signal_node.ts

@@ -14,12 +14,12 @@ export const REQUIRED_UNSET_VALUE = /* @__PURE__ */ Symbol('InputSignalNode#UNSE
  * Reactive node type for an input signal. An input signal extends a signal.
  * There are special properties to enable transforms and required inputs.
  */
-export interface InputSignalNode<ReadT, WriteT> extends SignalNode<ReadT> {
+export interface InputSignalNode<T, TransformT> extends SignalNode<T> {
   /**
    * User-configured transform that will run whenever a new value is applied
    * to the input signal node.
    */
-  transformFn: ((value: WriteT) => ReadT)|undefined;
+  transformFn: ((value: TransformT) => T)|undefined;
 
   /**
    * Applies a new value to the input signal. Expects transforms to be run
@@ -27,9 +27,9 @@ export interface InputSignalNode<ReadT, WriteT> extends SignalNode<ReadT> {
    *
    * This function is called by the framework runtime code whenever a binding
    * changes. The value can in practice be anything at runtime, but for typing
-   * purposes we assume it's a valid `ReadT` value. Type-checking will enforce that.
+   * purposes we assume it's a valid `T` value. Type-checking will enforce that.
    */
-  applyValueToInputSignal<ReadT, WriteT>(node: InputSignalNode<ReadT, WriteT>, value: ReadT): void;
+  applyValueToInputSignal<T, TransformT>(node: InputSignalNode<T, TransformT>, value: T): void;
 }
 
 // Note: Using an IIFE here to ensure that the spread assignment is not considered
@@ -40,7 +40,7 @@ export const INPUT_SIGNAL_NODE: InputSignalNode<unknown, unknown> = /* @__PURE__
     ...SIGNAL_NODE,
     transformFn: undefined,
 
-    applyValueToInputSignal<ReadT, WriteT>(node: InputSignalNode<ReadT, WriteT>, value: ReadT) {
+    applyValueToInputSignal<T, TransformT>(node: InputSignalNode<T, TransformT>, value: T) {
       signalSetFn(node, value);
     }
   };

packages/core/src/authoring/input/input_type_checking.ts

@@ -8,7 +8,7 @@
 
 import {InputSignalWithTransform} from './input_signal';
 
-/** Retrieves the `WriteT` of an `InputSignal` and `InputSignalWithTransform`. */
+/** Retrieves the write type of an `InputSignal` and `InputSignalWithTransform`. */
 export type ɵUnwrapInputSignalWriteType<Field> =
     Field extends InputSignalWithTransform<any, infer WriteT>? WriteT : never;