narrow return value of useFragment based on returnPartialData option

.changeset/nine-clouds-watch.md

@@ -0,0 +1,5 @@
+---
+'@apollo/client': patch
+---
+
+narrow return value of `useFragment` based on `returnPartialData` option

src/react/hooks/__tests__/useFragment.test.tsx

@@ -1301,4 +1301,39 @@ describe.skip("Type Tests", () => {
       }
     });
   })
+
+  test("`returnPartialData: false` results in `TData`, otherwise `Partial<TData>`", () => {
+    const typedNode = {} as TypedDocumentNode<{ foo: string}>
+    {
+      // default: return type is `Partial<TData>`
+      const result = useFragment({
+        fragment: typedNode,
+        from: { __typename: "Query" }
+      })
+      const test1: Partial<{ foo: string }> | undefined = result.data
+      // @ts-expect-error
+      const test2: { foo: string } | undefined = result.data
+    }
+    {
+      // `returnPartialData: true`: return type is `Partial<TData>`
+      const result = useFragment({
+        fragment: typedNode,
+        from: { __typename: "Query" },
+        returnPartialData: true
+      })
+      const test1: Partial<{ foo: string }> | undefined = result.data
+      // @ts-expect-error
+      const test2: { foo: string } | undefined = result.data
+    }
+    {
+      // `returnPartialData: false`: return type is `TData`
+      const result = useFragment({
+        fragment: typedNode,
+        from: { __typename: "Query" },
+        returnPartialData: false
+      })
+      const test1: Partial<{ foo: string }> | undefined = result.data
+      const test2: { foo: string } | undefined = result.data
+    }
+  })
 })

src/react/hooks/useFragment.ts

@@ -50,7 +50,18 @@ export interface UseFragmentResult<TData> {
   complete: boolean;
   missing?: MissingTree;
 }
-
+export function useFragment_experimental<
+  TData = any,
+  TVars = OperationVariables
+>(
+  options: UseFragmentOptions<TData, TVars> & { returnPartialData: false },
+): UseFragmentResult<TData>
+export function useFragment_experimental<
+  TData = any,
+  TVars = OperationVariables
+>(
+  options: UseFragmentOptions<TData, TVars>,
+): UseFragmentResult<Partial<TData>>
 export function useFragment_experimental<
   TData = any,
   TVars = OperationVariables