fix(core): add hasValue narrowing to ResourceRef (#59708)

alxhub · pkozlowski-opensource · commit 6c92d6534934 · 2025-01-28T09:40:29.000+01:00
`hasValue` attempts to narrow the type of a resource to exclude `undefined`. Because of the way signal types merge in TS, this only works if the type of the resource is the same general type as `hasValue` asserts. For example, if `res` is `WritableResource<string|undefined>` then `.hasValue()` correctly asserts that `res` is `WritableResource<string>` and `.value()` will be narrowed. If `res` is `ResourceRef<string|undefined>` then that narrowing does _not_ work correctly, since `.hasValue()` will assert `res` is `WritableResource<string>` and TS will combine that for a final type of `ResourceRef<string|undefined> & WritableResource<string>`. The final type of `.value()` then will not narrow. This commit fixes the above problem by adding a `.hasValue()` override to `ResourceRef` which asserts the resource is of type `ResourceRef`. Fixes #59707 PR Close #59708
diff --git a/goldens/public-api/core/index.api.md b/goldens/public-api/core/index.api.md
@@ -1634,6 +1634,8 @@ export type ResourceOptions<T, R> = PromiseResourceOptions<T, R> | StreamingReso
 // @public
 export interface ResourceRef<T> extends WritableResource<T> {
     destroy(): void;
+    // (undocumented)
+    hasValue(): this is ResourceRef<Exclude<T, undefined>>;
 }
 
 // @public
diff --git a/packages/core/src/resource/api.ts b/packages/core/src/resource/api.ts
@@ -133,6 +133,8 @@ export interface WritableResource<T> extends Resource<T> {
  * @experimental
  */
 export interface ResourceRef<T> extends WritableResource<T> {
+  hasValue(): this is ResourceRef<Exclude<T, undefined>>;
+
   /**
    * Manually destroy the resource, which cancels pending requests and returns it to `idle` state.
    */
diff --git a/packages/core/src/resource/resource.ts b/packages/core/src/resource/resource.ts
@@ -103,7 +103,7 @@ abstract class BaseWritableResource<T> implements WritableResource<T> {
     () => this.status() === ResourceStatus.Loading || this.status() === ResourceStatus.Reloading,
   );
 
-  hasValue(): this is WritableResource<Exclude<T, undefined>> {
+  hasValue(): this is ResourceRef<Exclude<T, undefined>> {
     return this.value() !== undefined;
   }
 

Original file line number	Diff line number	Diff line change
`@@ -1634,6 +1634,8 @@ export type ResourceOptions<T, R> = PromiseResourceOptions<T, R> \| StreamingReso`
`1634`	`1634`	`// @public`
`1635`	`1635`	`export interface ResourceRef<T> extends WritableResource<T> {`
`1636`	`1636`	`destroy(): void;`
	`1637`	`+ // (undocumented)`
	`1638`	`+ hasValue(): this is ResourceRef<Exclude<T, undefined>>;`
`1637`	`1639`	`}`
`1638`	`1640`
`1639`	`1641`	`// @public`
Original file line number	Diff line number	Diff line change
`@@ -103,7 +103,7 @@ abstract class BaseWritableResource<T> implements WritableResource<T> {`
`103`	`103`	`() => this.status() === ResourceStatus.Loading \|\| this.status() === ResourceStatus.Reloading,`
`104`	`104`	`);`
`105`	`105`
`106`		`- hasValue(): this is WritableResource<Exclude<T, undefined>> {`
	`106`	`+ hasValue(): this is ResourceRef<Exclude<T, undefined>> {`
`107`	`107`	`return this.value() !== undefined;`
`108`	`108`	`}`
`109`	`109`