[useAutocomplete] Improve TS typing of groupedOptions prop

packages/mui-material/src/useAutocomplete/useAutocomplete.d.ts

@@ -353,14 +353,34 @@ export type AutocompleteGetTagProps = ({ index }: { index: number }) => {
  *
  * - [useAutocomplete API](https://mui.com/base-ui/react-autocomplete/hooks-api/#use-autocomplete)
  */
+export function useAutocomplete<
+  Value,
+  Multiple extends boolean | undefined = false,
+  DisableClearable extends boolean | undefined = false,
+  FreeSolo extends boolean | undefined = false,
+>(
+  props: UseAutocompleteProps<Value, Multiple, DisableClearable, FreeSolo> & {
+    groupBy: (option: Value) => string;
+  },
+): UseAutocompleteReturnValue<Value, Multiple, DisableClearable, FreeSolo, true>
+export function useAutocomplete<
+  Value,
+  Multiple extends boolean | undefined = false,
+  DisableClearable extends boolean | undefined = false,
+  FreeSolo extends boolean | undefined = false,
+>(
+  props: UseAutocompleteProps<Value, Multiple, DisableClearable, FreeSolo> & {
+    groupBy?: undefined;
+  },
+): UseAutocompleteReturnValue<Value, Multiple, DisableClearable, FreeSolo, false>
 export function useAutocomplete<
   Value,
   Multiple extends boolean | undefined = false,
   DisableClearable extends boolean | undefined = false,
   FreeSolo extends boolean | undefined = false,
 >(
   props: UseAutocompleteProps<Value, Multiple, DisableClearable, FreeSolo>,
-): UseAutocompleteReturnValue<Value, Multiple, DisableClearable, FreeSolo>;
+): UseAutocompleteReturnValue<Value, Multiple, DisableClearable, FreeSolo, unknown>;
 
 export interface UseAutocompleteRenderedOption<Value> {
   option: Value;
@@ -372,6 +392,7 @@ export interface UseAutocompleteReturnValue<
   Multiple extends boolean | undefined = false,
   DisableClearable extends boolean | undefined = false,
   FreeSolo extends boolean | undefined = false,
+  HasGroupBy extends boolean | unknown = false,
 > {
   /**
    * Resolver for the root slot's props.
@@ -462,7 +483,11 @@ export interface UseAutocompleteReturnValue<
   /**
    * The options to render. It's either `Value[]` or `AutocompleteGroupedOption<Value>[]` if the groupBy prop is provided.
    */
-  groupedOptions: Value[] | Array<AutocompleteGroupedOption<Value>>;
+  groupedOptions: HasGroupBy extends true
+    ? AutocompleteGroupedOption<Value>[]
+    : HasGroupBy extends false
+      ? Value[]
+      : Value[] | AutocompleteGroupedOption<Value>[];
 }
 
 export default useAutocomplete;

packages/mui-material/src/useAutocomplete/useAutocomplete.spec.ts

@@ -1,5 +1,9 @@
 import { expectType } from '@mui/types';
-import { useAutocomplete, FilterOptionsState } from '@mui/material/useAutocomplete';
+import {
+  useAutocomplete,
+  FilterOptionsState,
+  AutocompleteGroupedOption,
+} from '@mui/material/useAutocomplete';
 
 interface Person {
   id: string;
@@ -181,4 +185,17 @@ function Component() {
     },
     freeSolo: true,
   });
+
+  const ungroupedAutocomplete = useAutocomplete({ options: persons });
+  expectType<Person[], typeof ungroupedAutocomplete.groupedOptions>(
+    ungroupedAutocomplete.groupedOptions,
+  );
+
+  const groupedAutocomplete = useAutocomplete({
+    options: persons,
+    groupBy: ({ id }) => id,
+  });
+  expectType<AutocompleteGroupedOption<Person>[], typeof groupedAutocomplete.groupedOptions>(
+    groupedAutocomplete.groupedOptions,
+  );
 }