Make getKey and selection props mutually exclusive

change/@fluentui-react-519e3c9c-d7fd-40f6-b9f7-6a2d2e1af28f.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "DetailsList has been modified to warn when \"getKey\" and \"selection\" props are passed simultaneously. The \"getKey\" property is never used if a Selection object is passed. Either the \"getKey\" prop from the Selection object is used, or Selection's default getKey implementation (item) => item.key is used, but never the \"getKey\" prop passed to DetailsList. Making \"getKey\" and \"selection\" mutually exclusive DetailsList properties prevents users from making this mistake.",
+  "packageName": "@fluentui/react",
+  "email": "alexok@microsoft.com",
+  "dependentChangeType": "patch"
+}

packages/react-examples/src/react/DetailsList/DetailsList.Documents.Example.tsx

@@ -167,6 +167,7 @@ export class DetailsListDocumentsExample extends React.Component<{}, IDetailsLis
           selectionDetails: this._getSelectionDetails(),
         });
       },
+      getKey: this._getKey,
     });
 
     this.state = {
@@ -214,7 +215,6 @@ export class DetailsListDocumentsExample extends React.Component<{}, IDetailsLis
               compact={isCompactMode}
               columns={columns}
               selectionMode={SelectionMode.multiple}
-              getKey={this._getKey}
               setKey="multiple"
               layoutMode={DetailsListLayoutMode.justified}
               isHeaderVisible={true}

packages/react/src/components/DetailsList/DetailsList.base.tsx

@@ -9,6 +9,7 @@ import {
   getRTLSafeKeyCode,
   classNamesFunction,
   memoizeFunction,
+  warnMutuallyExclusive,
 } from '../../Utilities';
 import {
   CheckboxVisibility,
@@ -57,6 +58,7 @@ import type { IGroupedList, IGroupDividerProps, IGroupRenderProps, IGroup } from
 import type { IListProps } from '../../List';
 
 const getClassNames = classNamesFunction<IDetailsListStyleProps, IDetailsListStyles>();
+const COMPONENT_NAME = 'DetailsList';
 
 export interface IDetailsListState {
   focusedItemIndex: number;
@@ -801,6 +803,10 @@ export class DetailsListBase extends React.Component<IDetailsListProps, IDetails
       getDerivedStateFromProps: this._getDerivedStateFromProps,
     };
 
+    warnMutuallyExclusive(COMPONENT_NAME, props, {
+      selection: 'getKey',
+    });
+
     this._selection =
       props.selection ||
       new Selection({