fix(core): allow explicit read generic with signal input transforms

cexbrayat · alxhub · commit 1ab654cf2815 · 2026-05-01T15:53:56.000-07:00
Using explicit single generic arguments with transforms (for example, input&lt;boolean&gt;(false, {transform: booleanAttribute})) previously failed overload resolution.

Before this fix, type-checking produced:
````
✘ [ERROR] TS2769: No overload matches this call.
  Overload 1 of 5, '(initialValue: boolean, opts?: InputOptionsWithoutTransform&lt;boolean&gt; | undefined): InputSignal&lt;boolean&gt;', gave the following error.
    Type '(value: unknown) =&gt; boolean' is not assignable to type 'undefined'.
  Overload 2 of 5, '(initialValue: undefined, opts: InputOptionsWithoutTransform&lt;boolean&gt;): InputSignal&lt;boolean | undefined&gt;', gave the following error.
    Argument of type 'true' is not assignable to parameter of type 'undefined'. [plugin angular-compiler]
```

This change adds specialized overloads for explicit read generics.
diff --git a/goldens/public-api/core/index.api.md b/goldens/public-api/core/index.api.md
@@ -1025,6 +1025,8 @@ export interface InputFunction {
     <T>(initialValue: undefined, opts: InputOptionsWithoutTransform<T>): InputSignal<T | undefined>;
     <T, TransformT>(initialValue: T, opts: InputOptionsWithTransform<T, TransformT>): InputSignalWithTransform<T, TransformT>;
     <T, TransformT>(initialValue: undefined, opts: InputOptionsWithTransform<T | undefined, TransformT>): InputSignalWithTransform<T | undefined, TransformT>;
+    <T>(initialValue: T, opts: InputOptionsWithTransform<T, unknown>): InputSignalWithTransform<T, T>;
+    <T>(initialValue: undefined, opts: InputOptionsWithTransform<T | undefined, unknown>): InputSignalWithTransform<T | undefined, T | undefined>;
     required: {
         <T>(opts?: InputOptionsWithoutTransform<T>): InputSignal<T>;
         <T, TransformT>(opts: InputOptionsWithTransform<T, TransformT>): InputSignalWithTransform<T, TransformT>;
diff --git a/packages/core/src/authoring/input/input.ts b/packages/core/src/authoring/input/input.ts
@@ -77,6 +77,19 @@ export interface InputFunction {
     initialValue: undefined,
     opts: InputOptionsWithTransform<T | undefined, TransformT>,
   ): InputSignalWithTransform<T | undefined, TransformT>;
+  /**
+   * Declares an input of type `T` with an initial value and a transform function
+   * that accepts values of the same type.
+   */
+  <T>(initialValue: T, opts: InputOptionsWithTransform<T, unknown>): InputSignalWithTransform<T, T>;
+  /**
+   * Declares an input of type `T|undefined` without an initial value and with a transform
+   * function that accepts values of the same type.
+   */
+  <T>(
+    initialValue: undefined,
+    opts: InputOptionsWithTransform<T | undefined, unknown>,
+  ): InputSignalWithTransform<T | undefined, T | undefined>;
 
   /**
    * Initializes a required input.
diff --git a/packages/core/test/authoring/signal_input_signature_test.ts b/packages/core/test/authoring/signal_input_signature_test.ts
@@ -12,7 +12,7 @@
  * the resulting types match our expectations (via comments asserting the `.d.ts`).
  */
 
-import {input} from '../../src/core';
+import {booleanAttribute, input, numberAttribute} from '../../src/core';
 // import preserved to simplify `.d.ts` emit and simplify the `type_tester` logic.
 // tslint:disable-next-line no-duplicate-imports
 import {InputSignal, InputSignalWithTransform} from '../../src/core';
@@ -102,6 +102,19 @@ export class InputSignatureTest {
     transform: (v: string | boolean) => '',
   });
 
+  /** boolean, boolean */
+  explicitReadWithBooleanAttributeTransform = input<boolean>(false, {transform: booleanAttribute});
+  /** number, number */
+  explicitReadWithNumberAttributeTransform = input<number>(0, {transform: numberAttribute});
+  /** boolean | undefined, boolean | undefined */
+  explicitReadWithUndefinedInitialBooleanAttributeTransform = input<boolean>(undefined, {
+    transform: booleanAttribute,
+  });
+  /** number | undefined, number | undefined */
+  explicitReadWithUndefinedInitialNumberAttributeTransform = input<number>(undefined, {
+    transform: numberAttribute,
+  });
+
   /** string, string | boolean */
   requiredWithTransformInferenceNoExplicitGeneric = input.required({
     transform: (v: string | boolean) => '',
