fix: react-combobox listbox popup width matches trigger width

change/@fluentui-react-combobox-7bb9e1fd-dd15-4dd6-bdff-951b259e85db.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "fix: set popup Listbox width to trigger width",
+  "packageName": "@fluentui/react-combobox",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}

packages/react-components/react-combobox/src/components/Combobox/__snapshots__/Combobox.test.tsx.snap

@@ -68,7 +68,7 @@ exports[`Combobox renders an open listbox 1`] = `
     <div
       class="fui-Listbox fui-Combobox__listbox"
       role="listbox"
-      style="position: fixed; left: 0px; top: 0px; margin: 0px;"
+      style="position: fixed; left: 0px; top: 0px; margin: 0px; width: 0px;"
     >
       <div
         aria-selected="false"

packages/react-components/react-combobox/src/components/Combobox/useCombobox.tsx

@@ -49,8 +49,17 @@ export const useCombobox_unstable = (props: ComboboxProps, ref: React.Ref<HTMLIn
     excludedPropNames: ['children', 'size'],
   });
 
+  const rootRef = React.useRef<HTMLDivElement>(null);
   const triggerRef = React.useRef<HTMLInputElement>(null);
 
+  // calculate listbox width style based on trigger width
+  const [popupWidth, setPopupWidth] = React.useState<string>();
+  React.useEffect(() => {
+    const width = open ? `${rootRef.current?.clientWidth}px` : undefined;
+    setPopupWidth(width);
+  }, [open]);
+
+  // handle input type-to-select
   const getSearchString = (inputValue: string): string => {
     // if there are commas in the value string, take the text after the last comma
     const searchString = inputValue.split(',').pop();
@@ -150,7 +159,10 @@ export const useCombobox_unstable = (props: ComboboxProps, ref: React.Ref<HTMLIn
     open || hasFocus
       ? resolveShorthand(props.listbox, {
           required: true,
-          defaultProps: { children: props.children },
+          defaultProps: {
+            children: props.children,
+            style: { width: popupWidth },
+          },
         })
       : undefined;
 
@@ -182,6 +194,8 @@ export const useCombobox_unstable = (props: ComboboxProps, ref: React.Ref<HTMLIn
     setOpen,
   };
 
+  state.root.ref = useMergedRefs(state.root.ref, rootRef);
+
   /* handle open/close + focus change when clicking expandIcon */
   const { onMouseDown: onIconMouseDown, onClick: onIconClick } = state.expandIcon || {};
   const onExpandIconMouseDown = useEventCallback(

packages/react-components/react-combobox/src/components/Dropdown/__snapshots__/Dropdown.test.tsx.snap

@@ -68,7 +68,7 @@ exports[`Dropdown renders an open listbox 1`] = `
     <div
       class="fui-Listbox fui-Dropdown__listbox"
       role="listbox"
-      style="position: fixed; left: 0px; top: 0px; margin: 0px;"
+      style="position: fixed; left: 0px; top: 0px; margin: 0px; width: 0px;"
     >
       <div
         aria-selected="false"

packages/react-components/react-combobox/src/components/Dropdown/useDropdown.tsx

@@ -9,6 +9,7 @@ import { Listbox } from '../Listbox/Listbox';
 import type { Slot } from '@fluentui/react-utilities';
 import type { OptionValue } from '../../utils/OptionCollection.types';
 import type { DropdownProps, DropdownState } from './Dropdown.types';
+import { useMergedRefs } from '@fluentui/react-utilities';
 
 /**
  * Create the state required to render Dropdown.
@@ -29,6 +30,14 @@ export const useDropdown_unstable = (props: DropdownProps, ref: React.Ref<HTMLBu
     excludedPropNames: ['children'],
   });
 
+  // set listbox popup width based off the root/trigger width
+  const rootRef = React.useRef<HTMLDivElement>(null);
+  const [popupWidth, setPopupWidth] = React.useState<string>();
+  React.useEffect(() => {
+    const width = open ? `${rootRef.current?.clientWidth}px` : undefined;
+    setPopupWidth(width);
+  }, [open]);
+
   // jump to matching option based on typing
   const searchString = React.useRef('');
   const [setKeyTimeout, clearKeyTimeout] = useTimeout();
@@ -108,7 +117,10 @@ export const useDropdown_unstable = (props: DropdownProps, ref: React.Ref<HTMLBu
     baseState.open || baseState.hasFocus
       ? resolveShorthand(props.listbox, {
           required: true,
-          defaultProps: { children: props.children },
+          defaultProps: {
+            children: props.children,
+            style: { width: popupWidth },
+          },
         })
       : undefined;
 
@@ -141,5 +153,7 @@ export const useDropdown_unstable = (props: DropdownProps, ref: React.Ref<HTMLBu
     ...baseState,
   };
 
+  state.root.ref = useMergedRefs(state.root.ref, rootRef);
+
   return state;
 };